This version of the project is now considered obsolete, please select and use a more recent version.

Yocto Project Quick Start

Abstract


1. Welcome!

Welcome to the Yocto Project! The Yocto Project is an open-source collaboration project focused on embedded Linux developers. Among other things, the Yocto Project uses a build system based on the Poky project to construct complete Linux images. The Poky project, in turn, draws from and contributes back to the OpenEmbedded project.

If you don't have a system that runs Linux and you want to give the Yocto Project a test run, you might consider using the Yocto Project Build Appliance. The Build Appliance allows you to build and boot a custom embedded Linux image with the Yocto Project using a non-Linux development system. See the Yocto Project Build Appliance for more information.

On the other hand, if you know all about open-source development, Linux development environments, Git source repositories and the like and you just want some quick information that lets you try out the Yocto Project on your Linux system, skip right to the "Super User" section at the end of this quick start.

For the rest of you, this short document will give you some basic information about the environment and let you experience it in its simplest form. After reading this document, you will have a basic understanding of what the Yocto Project is and how to use some of its core components. This document steps you through a simple example showing you how to build a small image and run it using the Quick EMUlator (QEMU emulator).

For more detailed information on the Yocto Project, you should check out these resources:

Note

Due to production processes, there could be differences between the Yocto Project documentation bundled in a released tarball and the Yocto Project Quick Start on the Yocto Project website. For the latest version of this manual, see the manual on the website.

2. Introducing the Yocto Project Development Environment

The Yocto Project through the OpenEmbedded build system provides an open source development environment targeting the ARM, MIPS, PowerPC and x86 architectures for a variety of platforms including x86-64 and emulated ones. You can use components from the Yocto Project to design, develop, build, debug, simulate, and test the complete software stack using Linux, the X Window System, GNOME Mobile-based application frameworks, and Qt frameworks.

The Yocto Project Development Environment

Here are some highlights for the Yocto Project:

  • Provides a recent Linux kernel along with a set of system commands and libraries suitable for the embedded environment.

  • Makes available system components such as X11, GTK+, Qt, Clutter, and SDL (among others) so you can create a rich user experience on devices that have display hardware. For devices that don't have a display or where you wish to use alternative UI frameworks, these components need not be installed.

  • Creates a focused and stable core compatible with the OpenEmbedded project with which you can easily and reliably build and develop.

  • Fully supports a wide range of hardware and device emulation through the QEMU Emulator.

The Yocto Project can generate images for many kinds of devices. However, the standard example machines target QEMU full-system emulation for x86, x86-64, ARM, MIPS, and PPC-based architectures as well as specific hardware such as the Intel® Desktop Board DH55TC. Because an image developed with the Yocto Project can boot inside a QEMU emulator, the development environment works nicely as a test platform for developing embedded software.

Another important Yocto Project feature is the Sato reference User Interface. This optional GNOME mobile-based UI, which is intended for devices with restricted screen sizes, sits neatly on top of a device using the GNOME Mobile Stack and provides a well-defined user experience. Implemented in its own layer, it makes it clear to developers how they can implement their own user interface on top of a Linux image created with the Yocto Project.

3. What You Need and How You Get It

You need these things to develop in the Yocto Project environment:

  • A host system running a supported Linux distribution (i.e. recent releases of Fedora, openSUSE, CentOS, and Ubuntu). If the host system supports multiple cores and threads, you can configure the Yocto Project build system to decrease the time needed to build images significantly.

  • The right packages.

  • A release of the Yocto Project.

3.1. The Linux Distribution

The Yocto Project team is continually verifying more and more Linux distributions with each release. In general, if you have the current release minus one of the following distributions you should have no problems.

  • Ubuntu

  • Fedora

  • openSUSE

  • CentOS

For a more detailed list of distributions that support the Yocto Project, see the "Supported Linux Distributions" section in the Yocto Project Reference Manual.

Note

For notes about using the Yocto Project on a RHEL 4-based host, see the BuildingOnRHEL4 wiki page.

The OpenEmbedded build system should be able to run on any modern distribution with Python 2.6 or 2.7. Earlier releases of Python are known to not work and the system does not support Python 3 at this time. This document assumes you are running one of the previously noted distributions on your Linux-based host systems.

Note

If you attempt to use a distribution not in the above list, you may or may not have success - you are venturing into untested territory. Refer to OE and Your Distro and Required Software for information for other distributions used with the OpenEmbedded project, which might be a starting point for exploration. If you go down this path, you should expect problems. When you do, please go to Yocto Project Bugzilla and submit a bug. We are interested in hearing about your experience.

3.2. The Packages

Packages and package installation vary depending on your development system and on your intent. For example, if you want to build an image that can run on QEMU in graphical mode (a minimal, basic build requirement), then the number of packages is different than if you want to build an image on a headless system or build out the Yocto Project documentation set. Collectively, the number of required packages is large if you want to be able to cover all cases.

Note

In general, you need to have root access and then install the required packages. Thus, the commands in the following section may or may not work depending on whether or not your Linux distribution has sudo installed.

The next few sections list, by supported Linux Distributions, the required packages needed to build an image that runs on QEMU in graphical mode (e.g. essential plus graphics support).

For lists of required packages for other scenarios, see the "Required Packages for the Host Development System" section in the Yocto Project Reference Manual.

3.2.1. Ubuntu

The essential packages you need for a supported Ubuntu distribution are shown in the following command:

     $ sudo apt-get install gawk wget git-core diffstat unzip texinfo \
     build-essential chrpath libsdl1.2-dev xterm
                

3.2.2. Fedora

The essential packages you need for a supported Fedora distribution are shown in the following command:

     $ sudo yum install gawk make wget tar bzip2 gzip python unzip perl patch \
     diffutils diffstat git cpp gcc gcc-c++ eglibc-devel texinfo chrpath \
     ccache SDL-devel xterm
                

3.2.3. openSUSE

The essential packages you need for a supported openSUSE distribution are shown in the following command:

     $ sudo zypper install python gcc gcc-c++ git chrpath make wget python-xml \
     diffstat texinfo python-curses patch libSDL-devel xterm
                

3.2.4. CentOS

The essential packages you need for a supported CentOS distribution are shown in the following command:

     $ sudo yum -y install gawk make wget tar bzip2 gzip python unzip perl patch \
     diffutils diffstat git cpp gcc gcc-c++ glibc-devel texinfo chrpath SDL-devel xterm
                

Note

Depending on the CentOS version you are using, other requirements and dependencies might exist. For details, you should look at the CentOS sections on the Poky/GettingStarted/Dependencies wiki page.

3.3. Yocto Project Release

You can download the latest Yocto Project release by going to the Yocto Project website clicking "Downloads" in the navigation pane to the left to view all available Yocto Project releases. Be sure to scroll down and look for "Yocto Project" under the "Type" heading in the list. Nightly and developmental builds are also maintained at http://autobuilder.yoctoproject.org/nightly/. However, for this document a released version of Yocto Project is used.

You can also get the Yocto Project files you need by setting up (cloning in Git terms) a local copy of the poky Git repository on your host development system. Doing so allows you to contribute back to the Yocto Project project. For information on how to get set up using this method, see the "Yocto Project Release" item in the Yocto Project Development Manual.

4. A Quick Test Run

Now that you have your system requirements in order, you can give the Yocto Project a try. This section presents some steps that let you do the following:

  • Build an image and run it in the QEMU emulator

  • Use a pre-built image and run it in the QEMU emulator

4.1. Building an Image

In the development environment you will need to build an image whenever you change hardware support, add or change system libraries, or add or change services that have dependencies.

Building an Image

Use the following commands to build your image. The OpenEmbedded build process creates an entire Linux distribution, including the toolchain, from source.

Note

The build process using Sato currently consumes about 50GB of disk space. To allow for variations in the build process and for future package expansion, we recommend having at least 100GB of free disk space.

Note

By default, the build process searches for source code using a pre-determined order through a set of locations. If you encounter problems with the build process finding and downloading source code, see the "How does the OpenEmbedded build system obtain source code and will it work behind my firewall or proxy server?" in the Yocto Project Reference Manual.

     $ wget http://downloads.yoctoproject.org/releases/yocto/yocto-1.4.2/poky-dylan-9.0.2.tar.bz2
     $ tar xjf poky-dylan-9.0.2.tar.bz2
     $ cd poky-dylan-9.0.2
     $ source oe-init-build-env
             

Tip

To help conserve disk space during builds, you can add the following statement to your project's configuration file, which for this example is poky-dylan-9.0.2/build/conf/local.conf. Adding this statement deletes the work directory used for building a package once the package is built.

     INHERIT += "rm_work"
             

  • In the previous example, the first command retrieves the Yocto Project release tarball from the source repositories using the wget command. Alternatively, you can go to the Yocto Project website's "Downloads" page to retrieve the tarball.

  • The second command extracts the files from the tarball and places them into a directory named poky-dylan-9.0.2 in the current directory.

  • The third and fourth commands change the working directory to the Source Directory and run the Yocto Project oe-init-build-env environment setup script. Running this script defines OpenEmbedded build environment settings needed to complete the build. The script also creates the Build Directory, which is build in this case and is located in the Source Directory. After the script runs, your current working directory is set to the Build Directory. Later, when the build completes, the Build Directory contains all the files created during the build.

Take some time to examine your local.conf file in your project's configuration directory, which is found in the Build Directory. The defaults in that file should work fine. However, there are some variables of interest at which you might look.

By default, the target architecture for the build is qemux86, which produces an image that can be used in the QEMU emulator and is targeted at an Intel® 32-bit based architecture. To change this default, edit the value of the MACHINE variable in the configuration file before launching the build.

Another couple of variables of interest are the BB_NUMBER_THREADS and the PARALLEL_MAKE variables. By default, these variables are commented out. However, if you have a multi-core CPU you might want to uncomment the lines and set both variables equal to twice the number of your host's processor cores. Setting these variables can significantly shorten your build time.

Another consideration before you build is the package manager used when creating the image. By default, the OpenEmbedded build system uses the RPM package manager. You can control this configuration by using the PACKAGE_CLASSES variable. For additional package manager selection information, see the "Packaging - package*.bbclass" section in the Yocto Project Reference Manual.

Continue with the following command to build an OS image for the target, which is core-image-sato in this example. For information on the -k option use the bitbake --help command or see the "BitBake" section in the Yocto Project Reference Manual.

     $ bitbake -k core-image-sato
             

Note

BitBake requires Python 2.6 or 2.7. For more information on this requirement, see the FAQ in the Yocto Project Reference Manual.

The final command runs the image:

     $ runqemu qemux86
             

Note

Depending on the number of processors and cores, the amount or RAM, the speed of your Internet connection and other factors, the build process could take several hours the first time you run it. Subsequent builds run much faster since parts of the build are cached.

4.2. Using Pre-Built Binaries and QEMU

If hardware, libraries and services are stable, you can get started by using a pre-built binary of the filesystem image, kernel, and toolchain and run it using the QEMU emulator. This scenario is useful for developing application software.

Using a Pre-Built Image

For this scenario, you need to do several things:

  • Install the appropriate stand-alone toolchain tarball.

  • Download the pre-built image that will boot with QEMU. You need to be sure to get the QEMU image that matches your target machine’s architecture (e.g. x86, ARM, etc.).

  • Download the filesystem image for your target machine's architecture.

  • Set up the environment to emulate the hardware and then start the QEMU emulator.

4.2.1. Installing the Toolchain

You can download a tarball installer, which includes the pre-built toolchain, the runqemu script, and support files from the appropriate directory under http://downloads.yoctoproject.org/releases/yocto/yocto-1.4.2/toolchain/. Toolchains are available for 32-bit and 64-bit development systems from the i686 and x86-64 directories, respectively. Each type of development system supports five target architectures. The names of the tarball installer scripts are such that a string representing the host system appears first in the filename and then is immediately followed by a string representing the target architecture.

     poky-eglibc-<host_system>-<arch>-toolchain-gmae-<release>.sh

     Where:
         <host_system> is a string representing your development system:
                i686 or x86_64.

         <arch> is a string representing the target architecture:
                i586, x86_64, powerpc, mips, or arm.

         <release> is the version of Yocto Project.
            

For example, the following toolchain installer is for a 64-bit development host system and a 32-bit target architecture:

     poky-eglibc-x86_64-i586-toolchain-gmae-1.4.2.sh
            

Toolchains are self-contained and by default are installed into /opt/poky. However, when you run the toolchain installer, you can choose an installation directory.

The following command shows how to run the installer given a toolchain tarball for a 64-bit development host system and a 32-bit target architecture. You must change the permissions on the toolchain installer script so that it is executable.

The example assumes the toolchain installer is located in ~/Downloads/.

Note

If you do not have write permissions for the directory into which you are installing the toolchain, the toolchain installer notifies you and exits. Be sure you have write permissions in the directory and run the installer again.

     $ ~/Downloads/poky-eglibc-x86_64-i586-toolchain-gmae-1.4.2.sh
                

For more information on how to install tarballs, see the "Using a Cross-Toolchain Tarball" and "Using BitBake and the Build Directory" sections in the Yocto Project Application Developer's Guide.

4.2.2. Downloading the Pre-Built Linux Kernel

You can download the pre-built Linux kernel suitable for running in the QEMU emulator from http://downloads.yoctoproject.org/releases/yocto/yocto-1.4.2/machines/qemu. Be sure to use the kernel that matches the architecture you want to simulate. Download areas exist for the five supported machine architectures: qemuarm, qemumips, qemuppc, qemux86, and qemux86-64.

Most kernel files have one of the following forms:

     *zImage-qemu<arch>.bin
     vmlinux-qemu<arch>.bin

     Where:
         <arch> is a string representing the target architecture:
                x86, x86-64, ppc, mips, or arm.
                

You can learn more about downloading a Yocto Project kernel in the "Yocto Project Kernel" bulleted item in the Yocto Project Development Manual.

4.2.3. Downloading the Filesystem

You can also download the filesystem image suitable for your target architecture from http://downloads.yoctoproject.org/releases/yocto/yocto-1.4.2/machines/qemu. Again, be sure to use the filesystem that matches the architecture you want to simulate.

The filesystem image has two tarball forms: ext3 and tar. You must use the ext3 form when booting an image using the QEMU emulator. The tar form can be flattened out in your host development system and used for build purposes with the Yocto Project.

     core-image-<profile>-qemu<arch>.ext3
     core-image-<profile>-qemu<arch>.tar.bz2

     Where:
         <profile> is the filesystem image's profile:
                   lsb, lsb-dev, lsb-sdk, lsb-qt3, minimal, minimal-dev, sato, sato-dev, or sato-sdk.
                   For information on these types of image profiles, see the
                   "Images" chapter
                   in the Yocto Project Reference Manual.

         <arch> is a string representing the target architecture:
                x86, x86-64, ppc, mips, or arm.
                

Note

For the qemu architecture, ext3 and tar files start with the "lib32" string.

4.2.4. Setting Up the Environment and Starting the QEMU Emulator

Before you start the QEMU emulator, you need to set up the emulation environment. The following command form sets up the emulation environment.

     $ source /opt/poky/1.4.2/environment-setup-<arch>-poky-linux-<if>

     Where:
         <arch> is a string representing the target architecture:
                i586, x86_64, ppc603e, mips, or armv5te.

         <if> is a string representing an embedded application binary interface.
              Not all setup scripts include this string.
                

Finally, this command form invokes the QEMU emulator

     $ runqemu <qemuarch> <kernel-image> <filesystem-image>

     Where:
         <qemuarch> is a string representing the target architecture: qemux86, qemux86-64,
                    qemuppc, qemumips, or qemuarm.

         <kernel-image> is the architecture-specific kernel image.

         <filesystem-image> is the .ext3 filesystem image.

                

Continuing with the example, the following two commands setup the emulation environment and launch QEMU. This example assumes the root filesystem (.ext3 file) and the pre-built kernel image file both reside in your home directory. The kernel and filesystem are for a 32-bit target architecture.

     $ cd $HOME
     $ source /opt/poky/1.4.2/environment-setup-i586-poky-linux
     $ runqemu qemux86 bzImage-qemux86.bin \
     core-image-sato-qemux86.ext3
                

The environment in which QEMU launches varies depending on the filesystem image and on the target architecture. For example, if you source the environment for the ARM target architecture and then boot the minimal QEMU image, the emulator comes up in a new shell in command-line mode. However, if you boot the SDK image, QEMU comes up with a GUI.

Note

Booting the PPC image results in QEMU launching in the same shell in command-line mode.

5. Super User

This section [1] gives you a minimal description of how to use the Yocto Project to build images for a BeagleBoard xM starting from scratch. The steps were performed on a 64-bit Ubuntu 10.04 system.

5.1. Getting the Yocto Project

Set up your Source Directory one of two ways:

  • Tarball: Use if you want the latest stable release:

         $ wget http://downloads.yoctoproject.org/releases/yocto/yocto-1.4.2/poky-dylan-9.0.2.tar.bz2
         $ tar xvjf poky-dylan-9.0.2.tar.bz2
                        
  • Git Repository: Use if you want to work with cutting edge development content:

         $ git clone git://git.yoctoproject.org/poky
                        

The remainder of the section assumes the Git repository method.

5.2. Setting Up Your Host

You need some packages for everything to work. Rather than duplicate them here, look at the "The Packages" section earlier in this quick start.

5.3. Initializing the Build Environment

From the parent directory your Source Directory, initialize your environment and provide a meaningful Build Directory name:

     $ source poky/oe-init-build-env mybuilds
            

At this point, the mybuilds directory has been created for you and it is now your current working directory. If you don't provide your own directory name it defaults to build, which is inside the Source Directory.

5.4. Configuring the local.conf File

Initializing the build environment creates a conf/local.conf configuration file in the Build Directory. You need to manually edit this file to specify the machine you are building and to optimize your build time. Here are the minimal changes to make:

     BB_NUMBER_THREADS = "8"
     PARALLEL_MAKE = "-j 8"
     MACHINE ?= "beagleboard"
            

Briefly, set BB_NUMBER_THREADS and PARALLEL_MAKE to twice your host processor's number of cores.

A good deal that goes into a Yocto Project build is simply downloading all of the source tarballs. Maybe you have been working with another build system (OpenEmbedded or Angstrom) for which you have built up a sizable directory of source tarballs. Or, perhaps someone else has such a directory for which you have read access. If so, you can save time by adding statements to your configuration file so that the build process checks local directories first for existing tarballs before checking the Internet. Here is an efficient way to set it up in your local.conf file:

     SOURCE_MIRROR_URL ?= "file:///home/you/your-download-dir/"
     INHERIT += "own-mirrors"
     BB_GENERATE_MIRROR_TARBALLS = "1"
     # BB_NO_NETWORK = "1"
            

You can also use the PREMIRRORS variable. For an example, see the variable's glossary entry in the Yocto Project Reference Manual.

5.5. Building the Image

At this point, you need to select an image to build for the BeagleBoard xM. If this is your first build using the Yocto Project, you should try the smallest and simplest image:

     $ bitbake core-image-minimal
            

Now you just wait for the build to finish.

Here are some variations on the build process that could be helpful:

  • Fetch all the necessary sources without starting the build:

         $ bitbake -c fetchall core-image-minimal
                        

    This variation guarantees that you have all the sources for that BitBake target should you disconnect from the net and want to do the build later offline.

  • Specify to continue the build even if BitBake encounters an error. By default, BitBake aborts the build when it encounters an error. This command keeps a faulty build going:

         $ bitbake -k core-image-minimal
                        

Once you have your image, you can take steps to load and boot it on the target hardware.



[1] Kudos and thanks to Robert P. J. Day of CrashCourse for providing the basis for this "expert" section with information from one of his wiki pages.

Yocto Project Development Manual

Scott Rifenbark

Intel Corporation

Permission is granted to copy, distribute and/or modify this document under the terms of the Creative Commons Attribution-Share Alike 2.0 UK: England & Wales as published by Creative Commons.

Note

Due to production processes, there could be differences between the Yocto Project documentation bundled in the release tarball and the Yocto Project Development Manual on the Yocto Project website. For the latest version of this manual, see the manual on the website.
Revision History
Revision 1.16 October 2011
The initial document released with the Yocto Project 1.1 Release.
Revision 1.2April 2012
Released with the Yocto Project 1.2 Release.
Revision 1.3October 2012
Released with the Yocto Project 1.3 Release.
Revision 1.4April 2013
Released with the Yocto Project 1.4 Release.
Revision 1.4.1June 2013
Released with the Yocto Project 1.4.1 Release.
Revision 1.4.2August 2013
Released with the Yocto Project 1.4.2 Release.

Chapter 1. The Yocto Project Development Manual

1.1. Introduction

Welcome to the Yocto Project Development Manual! This manual provides information on how to use the Yocto Project to develop embedded Linux images and user-space applications that run on targeted devices. The manual provides an overview of image, kernel, and user-space application development using the Yocto Project. Because much of the information in this manual is general, it contains many references to other sources where you can find more detail. For example, you can find detailed information on Git, repositories, and open source in general in many places on the Internet. Another example specific to the Yocto Project is how to quickly set up your host development system and build an image, which you find in the Yocto Project Quick Start.

Note

By default, using the Yocto Project creates a Poky distribution. However, you can create your own distribution by providing key Metadata. A good example is Angstrom, which has had a distribution based on the Yocto Project since its inception. Other examples include commercial distributions like Wind River Linux, Mentor Embedded Linux, and ENEA Linux. See the "Creating Your Own Distribution" section for more information.

The Yocto Project Development Manual does, however, provide guidance and examples on how to change the kernel source code, reconfigure the kernel, and develop an application using the popular Eclipse™ IDE.

1.2. What This Manual Provides

The following list describes what you can get from this guide:

  • Information that lets you get set up to develop using the Yocto Project.

  • Information to help developers who are new to the open source environment and to the distributed revision control system Git, which the Yocto Project uses.

  • An understanding of common end-to-end development models and tasks.

  • Information about common development tasks generally used during image development for embedded devices.

  • Many references to other sources of related information.

1.3. What this Manual Does Not Provide

This manual will not give you the following:

  • Step-by-step instructions if those instructions exist in other Yocto Project documentation. For example, the Yocto Project Application Developer's Guide contains detailed instruction on how to run the Installing the ADT and Toolchains, which is used to set up a cross-development environment.

  • Reference material. This type of material resides in an appropriate reference manual. For example, system variables are documented in the Yocto Project Reference Manual.

  • Detailed public information that is not specific to the Yocto Project. For example, exhaustive information on how to use Git is covered better through the Internet than in this manual.

1.4. Other Information

Because this manual presents overview information for many different topics, you will need to supplement it with other information. The following list presents other sources of information you might find helpful:

  • Yocto Project Website: The home page for the Yocto Project provides lots of information on the project as well as links to software and documentation.

  • Yocto Project Quick Start: This short document lets you get started with the Yocto Project quickly and start building an image.

  • Yocto Project Reference Manual: This manual is a reference guide to the OpenEmbedded build system known as "Poky."

  • Yocto Project Application Developer's Guide: This guide provides information that lets you get going with the Application Development Toolkit (ADT) and stand-alone cross-development toolchains to develop projects using the Yocto Project.

  • Yocto Project Board Support Package (BSP) Developer's Guide: This guide defines the structure for BSP components. Having a commonly understood structure encourages standardization.

  • Yocto Project Linux Kernel Development Manual: This manual describes how to work with Linux Yocto kernels as well as provides a bit of conceptual information on the construction of the Yocto Linux kernel tree.

  • Yocto Project Profiling and Tracing Manual: This manual presents a set of common and generally useful tracing and profiling schemes along with their applications (as appropriate) to each tool.

  • Eclipse IDE Yocto Plug-in: A step-by-step instructional video that demonstrates how an application developer uses Yocto Plug-in features within the Eclipse IDE.

  • FAQ: A list of commonly asked questions and their answers.

  • Release Notes: Features, updates and known issues for the current release of the Yocto Project.

  • Hob: A graphical user interface for BitBake. Hob's primary goal is to enable a user to perform common tasks more easily.

  • Build Appliance: A virtual machine that enables you to build and boot a custom embedded Linux image with the Yocto Project using a non-Linux development system. For more information, see the Build Appliance page.

  • Bugzilla: The bug tracking application the Yocto Project uses. If you find problems with the Yocto Project, you should report them using this application.

  • Yocto Project Mailing Lists: To subscribe to the Yocto Project mailing lists, click on the following URLs and follow the instructions:

  • Internet Relay Chat (IRC): Two IRC channels on freenode are available for Yocto Project and Poky discussions: #yocto and #poky, respectively.

  • OpenEmbedded: The build system used by the Yocto Project. This project is the upstream, generic, embedded distribution from which the Yocto Project derives its build system (Poky) from and to which it contributes.

  • BitBake: The tool used by the OpenEmbedded build system to process project metadata.

  • BitBake User Manual: A comprehensive guide to the BitBake tool. If you want information on BitBake, see the user manual included in the bitbake/doc/manual directory of the Source Directory.

  • Quick EMUlator (QEMU): An open-source machine emulator and virtualizer.

Chapter 2. Getting Started with the Yocto Project

This chapter introduces the Yocto Project and gives you an idea of what you need to get started. You can find enough information to set up your development host and build or use images for hardware supported by the Yocto Project by reading the Yocto Project Quick Start.

The remainder of this chapter summarizes what is in the Yocto Project Quick Start and provides some higher-level concepts you might want to consider.

2.1. Introducing the Yocto Project

The Yocto Project is an open-source collaboration project focused on embedded Linux development. The project currently provides a build system, which is referred to as the OpenEmbedded build system in the Yocto Project documentation. The Yocto Project provides various ancillary tools suitable for the embedded developer and also features the Sato reference User Interface, which is optimized for stylus driven, low-resolution screens.

You can use the OpenEmbedded build system, which uses BitBake to develop complete Linux images and associated user-space applications for architectures based on ARM, MIPS, PowerPC, x86 and x86-64.

Note

By default, using the Yocto Project creates a Poky distribution. However, you can create your own distribution by providing key Metadata. See the "Creating Your Own Distribution" section for more information.

While the Yocto Project does not provide a strict testing framework, it does provide or generate for you artifacts that let you perform target-level and emulated testing and debugging. Additionally, if you are an Eclipse™ IDE user, you can install an Eclipse Yocto Plug-in to allow you to develop within that familiar environment.

2.2. Getting Set Up

Here is what you need to get set up to use the Yocto Project:

  • Host System: You should have a reasonably current Linux-based host system. You will have the best results with a recent release of Fedora, OpenSUSE, Debian, Ubuntu, or CentOS as these releases are frequently tested against the Yocto Project and officially supported. For a list of the distributions under validation and their status, see the "Supported Linux Distributions" section in the Yocto Project Reference Manual and the wiki page at Distribution Support.

    You should also have about 100 gigabytes of free disk space for building images.

  • Packages: The OpenEmbedded build system requires certain packages exist on your development system (e.g. Python 2.6 or 2.7). See "The Packages" section in the Yocto Project Quick Start and the "Required Packages for the Host Development System" section in the Yocto Project Reference Manual for the exact package requirements and the installation commands to install them for the supported distributions.

  • Yocto Project Release: You need a release of the Yocto Project. You set that up with a local Source Directory one of two ways depending on whether you are going to contribute back into the Yocto Project or not.

    Note

    Regardless of the method you use, this manual refers to the resulting local hierarchical set of files as the "Source Directory."

    • Tarball Extraction: If you are not going to contribute back into the Yocto Project, you can simply go to the Yocto Project Website, select the "Downloads" tab, and choose what you want. Once you have the tarball, just extract it into a directory of your choice.

      For example, the following command extracts the Yocto Project 1.4.2 release tarball into the current working directory and sets up the local Source Directory with a top-level folder named poky-dylan-9.0.2:

           $ tar xfj poky-dylan-9.0.2.tar.bz2
                              

      This method does not produce a local Git repository. Instead, you simply end up with a snapshot of the release.

    • Git Repository Method: If you are going to be contributing back into the Yocto Project or you simply want to keep up with the latest developments, you should use Git commands to set up a local Git repository of the upstream poky source repository. Doing so creates a repository with a complete history of changes and allows you to easily submit your changes upstream to the project. Because you clone the repository, you have access to all the Yocto Project development branches and tag names used in the upstream repository.

      Note

      You can view the Yocto Project Source Repositories at http://git.yoctoproject.org/cgit.cgi

      The following transcript shows how to clone the poky Git repository into the current working directory. The command creates the local repository in a directory named poky. For information on Git used within the Yocto Project, see the "Git" section.

           $ git clone git://git.yoctoproject.org/poky
           Cloning into 'poky'...
           remote: Counting objects: 183981, done.
           remote: Compressing objects: 100% (47428/47428), done.
           remote: Total 183981 (delta 132271), reused 183703 (delta 132044)
           Receiving objects: 100% (183981/183981), 89.71 MiB | 2.93 MiB/s, done.
           Resolving deltas: 100% (132271/132271), done.   
                              

      For another example of how to set up your own local Git repositories, see this wiki page, which describes how to create both poky and meta-intel Git repositories.

  • Yocto Project Kernel: If you are going to be making modifications to a supported Yocto Project kernel, you need to establish local copies of the source. You can find Git repositories of supported Yocto Project Kernels organized under "Yocto Linux Kernel" in the Yocto Project Source Repositories at http://git.yoctoproject.org/cgit.cgi.

    This setup can involve creating a bare clone of the Yocto Project kernel and then copying that cloned repository. You can create the bare clone and the copy of the bare clone anywhere you like. For simplicity, it is recommended that you create these structures outside of the Source Directory (usually poky).

    As an example, the following transcript shows how to create the bare clone of the linux-yocto-3.8 kernel and then create a copy of that clone.

    Note

    When you have a local Yocto Project kernel Git repository, you can reference that repository rather than the upstream Git repository as part of the clone command. Doing so can speed up the process.

    In the following example, the bare clone is named linux-yocto-3.8.git, while the copy is named my-linux-yocto-3.8-work:

         $ git clone --bare git://git.yoctoproject.org/linux-yocto-3.8 linux-yocto-3.8.git
         Cloning into bare repository 'linux-yocto-3.8.git'...
         remote: Counting objects: 2847090, done.
         remote: Compressing objects: 100% (454675/454675), done.
         remote: Total 2847090 (delta 2386170), reused 2825793 (delta 2364886)
         Receiving objects: 100% (2847090/2847090), 603.19 MiB | 3.54 MiB/s, done.
         Resolving deltas: 100% (2386170/2386170), done.                

    Now create a clone of the bare clone just created:

         $ git clone linux-yocto-3.8.git my-linux-yocto-3.8-work
         Cloning into 'my-linux-yocto-3.8-work'...
         done.
                    
  • The poky-extras Git Repository: The poky-extras Git repository contains Metadata needed only if you are modifying and building the kernel image. In particular, it contains the kernel BitBake append (.bbappend) files that you edit to point to your locally modified kernel source files and to build the kernel image. Pointing to these local files is much more efficient than requiring a download of the kernel's source files from upstream each time you make changes to the kernel.

    You can find the poky-extras Git Repository in the "Yocto Metadata Layers" area of the Yocto Project Source Repositories at http://git.yoctoproject.org/cgit.cgi. It is good practice to create this Git repository inside the Source Directory.

    Following is an example that creates the poky-extras Git repository inside the Source Directory, which is named poky in this case:

         $ cd ~/poky
         $ git clone git://git.yoctoproject.org/poky-extras poky-extras
         Cloning into 'poky-extras'...
         remote: Counting objects: 690, done.
         remote: Compressing objects: 100% (431/431), done.
         remote: Total 690 (delta 238), reused 690 (delta 238)
         Receiving objects: 100% (690/690), 532.60 KiB, done.
         Resolving deltas: 100% (238/238), done.                
  • Supported Board Support Packages (BSPs): The Yocto Project provides a layer called meta-intel and it is maintained in its own separate Git repository. The meta-intel layer contains many supported BSP Layers.

    Similar considerations exist for setting up the meta-intel layer. You can get set up for BSP development one of two ways: tarball extraction or with a local Git repository. It is a good idea to use the same method that you used to set up the Source Directory. Regardless of the method you use, the Yocto Project uses the following BSP layer naming scheme:

         meta-<BSP_name>
                    

    where <BSP_name> is the recognized BSP name. Here are some examples:

         meta-crownbay
         meta-emenlow
         meta-n450
                    

    See the "BSP Layers" section in the Yocto Project Board Support Package (BSP) Developer's Guide for more information on BSP Layers.

    • Tarball Extraction: You can download any released BSP tarball from the same "Downloads" page of the Yocto Project Website to get the Yocto Project release. Once on the "Download" page, look for "BSP" under the "Type" heading.

      Once you have the tarball, just extract it into a directory of your choice. Again, this method just produces a snapshot of the BSP layer in the form of a hierarchical directory structure.

    • Git Repository Method: If you are working with a local Git repository for your Source Directory, you should also use this method to set up the meta-intel Git repository. You can locate the meta-intel Git repository in the "Yocto Metadata Layers" area of the Yocto Project Source Repositories at http://git.yoctoproject.org/cgit.cgi.

      Typically, you set up the meta-intel Git repository inside the Source Directory. For example, the following transcript shows the steps to clone the meta-intel Git repository inside the local poky Git repository.

           $ cd ~/poky
           $ git clone git://git.yoctoproject.org/meta-intel.git
           Cloning into 'meta-intel'...
           remote: Counting objects: 6264, done.
           remote: Compressing objects: 100% (2135/2135), done.
           remote: Total 6264 (delta 3321), reused 6235 (delta 3293)
           Receiving objects: 100% (6264/6264), 2.17 MiB | 2.63 MiB/s, done.
           Resolving deltas: 100% (3321/3321), done.
                              

      The same wiki page referenced earlier covers how to set up the meta-intel Git repository.

  • Eclipse Yocto Plug-in: If you are developing applications using the Eclipse Integrated Development Environment (IDE), you will need this plug-in. See the "Setting up the Eclipse IDE" section for more information.

2.3. Building Images

The build process creates an entire Linux distribution, including the toolchain, from source. For more information on this topic, see the "Building an Image" section in the Yocto Project Quick Start.

The build process is as follows:

  1. Make sure you have set up the Source Directory described in the previous section.

  2. Initialize the build environment by sourcing a build environment script.

  3. Optionally ensure the conf/local.conf configuration file, which is found in the Build Directory, is set up how you want it. This file defines many aspects of the build environment including the target machine architecture through the MACHINE variable, the development machine's processor use through the BB_NUMBER_THREADS and PARALLEL_MAKE variables, and a centralized tarball download directory through the DL_DIR variable.

  4. Build the image using the bitbake command. If you want information on BitBake, see the user manual included in the bitbake/doc/manual directory of the Source Directory.

  5. Run the image either on the actual hardware or using the QEMU emulator.

2.4. Using Pre-Built Binaries and QEMU

Another option you have to get started is to use pre-built binaries. The Yocto Project provides many types of binaries with each release. See the "Images" chapter in the Yocto Project Reference Manual for descriptions of the types of binaries that ship with a Yocto Project release.

Using a pre-built binary is ideal for developing software applications to run on your target hardware. To do this, you need to be able to access the appropriate cross-toolchain tarball for the architecture on which you are developing. If you are using an SDK type image, the image ships with the complete toolchain native to the architecture. If you are not using an SDK type image, you need to separately download and install the stand-alone Yocto Project cross-toolchain tarball.

Regardless of the type of image you are using, you need to download the pre-built kernel that you will boot in the QEMU emulator and then download and extract the target root filesystem for your target machine’s architecture. You can get architecture-specific binaries and file systems from machines. You can get installation scripts for stand-alone toolchains from toolchains. Once you have all your files, you set up the environment to emulate the hardware by sourcing an environment setup script. Finally, you start the QEMU emulator. You can find details on all these steps in the "Using Pre-Built Binaries and QEMU" section of the Yocto Project Quick Start.

Using QEMU to emulate your hardware can result in speed issues depending on the target and host architecture mix. For example, using the qemux86 image in the emulator on an Intel-based 32-bit (x86) host machine is fast because the target and host architectures match. On the other hand, using the qemuarm image on the same Intel-based host can be slower. But, you still achieve faithful emulation of ARM-specific issues.

To speed things up, the QEMU images support using distcc to call a cross-compiler outside the emulated system. If you used runqemu to start QEMU, and the distccd application is present on the host system, any BitBake cross-compiling toolchain available from the build system is automatically used from within QEMU simply by calling distcc. You can accomplish this by defining the cross-compiler variable (e.g. export CC="distcc"). Alternatively, if you are using a suitable SDK image or the appropriate stand-alone toolchain is present, the toolchain is also automatically used.

Note

Several mechanisms exist that let you connect to the system running on the QEMU emulator:
  • QEMU provides a framebuffer interface that makes standard consoles available.

  • Generally, headless embedded devices have a serial port. If so, you can configure the operating system of the running image to use that port to run a console. The connection uses standard IP networking.

  • SSH servers exist in some QEMU images. The core-image-sato QEMU image has a Dropbear secure shell (SSH) server that runs with the root password disabled. The core-image-basic and core-image-lsb QEMU images have OpenSSH instead of Dropbear. Including these SSH servers allow you to use standard ssh and scp commands. The core-image-minimal QEMU image, however, contains no SSH server.

  • You can use a provided, user-space NFS server to boot the QEMU session using a local copy of the root filesystem on the host. In order to make this connection, you must extract a root filesystem tarball by using the runqemu-extract-sdk command. After running the command, you must then point the runqemu script to the extracted directory instead of a root filesystem image file.

Chapter 3. The Yocto Project Open Source Development Environment

This chapter helps you understand the Yocto Project as an open source development project. In general, working in an open source environment is very different from working in a closed, proprietary environment. Additionally, the Yocto Project uses specific tools and constructs as part of its development environment. This chapter specifically addresses open source philosophy, using the Yocto Project in a team environment, source repositories, Yocto Project terms, licensing, the open source distributed version control system Git, workflows, bug tracking, and how to submit changes.

3.1. Open Source Philosophy

Open source philosophy is characterized by software development directed by peer production and collaboration through an active community of developers. Contrast this to the more standard centralized development models used by commercial software companies where a finite set of developers produces a product for sale using a defined set of procedures that ultimately result in an end product whose architecture and source material are closed to the public.

Open source projects conceptually have differing concurrent agendas, approaches, and production. These facets of the development process can come from anyone in the public (community) that has a stake in the software project. The open source environment contains new copyright, licensing, domain, and consumer issues that differ from the more traditional development environment. In an open source environment, the end product, source material, and documentation are all available to the public at no cost.

A benchmark example of an open source project is the Linux Kernel, which was initially conceived and created by Finnish computer science student Linus Torvalds in 1991. Conversely, a good example of a non-open source project is the Windows® family of operating systems developed by Microsoft® Corporation.

Wikipedia has a good historical description of the Open Source Philosophy here. You can also find helpful information on how to participate in the Linux Community here.

3.2. Using the Yocto Project in a Team Environment

It might not be immediately clear how you can use the Yocto Project in a team environment, or scale it for a large team of developers. One of the strengths of the Yocto Project is that it is extremely flexible. Thus, you can adapt it to many different use cases and scenarios. However, these characteristics can cause a struggle if you are trying to create a working setup that scales across a large team.

To help with these types of situations, this section presents some of the project's most successful experiences, practices, solutions, and available technologies that work well. Keep in mind, the information here is a starting point. You can build off it and customize it to fit any particular working environment and set of practices.

3.2.1. System Configurations

Systems across a large team should meet the needs of two types of developers: those working on the contents of the operating system image itself and those developing applications. Regardless of the type of developer, their workstations must be both reasonably powerful and run Linux.

3.2.1.1. Application Development

For developers who mainly do application level work on top of an existing software stack, here are some practices that work best:

  • Use a pre-built toolchain that contains the software stack itself. Then, develop the application code on top of the stack. This method works well for small numbers of relatively isolated applications.

  • When possible, use the Yocto Project plug-in for the Eclipse™ IDE and other pieces of Application Development Technology (ADT). For more information, see the "Application Development Workflow" section as well as the Yocto Project Application Developer's Guide.

  • Keep your cross-development toolchains updated. You can do this through provisioning either as new toolchain downloads or as updates through a package update mechanism using opkg to provide updates to an existing toolchain. The exact mechanics of how and when to do this are a question for local policy.

  • Use multiple toolchains installed locally into different locations to allow development across versions.

3.2.1.2. Core System Development

For core system development, it is often best to have the build system itself available on the developer workstations so developers can run their own builds and directly rebuild the software stack. You should keep the core system unchanged as much as possible and do your work in layers on top of the core system. Doing so gives you a greater level of portability when upgrading to new versions of the core system or Board Support Packages (BSPs). You can share layers amongst the developers of a particular project and contain the policy configuration that defines the project.

Aside from the previous best practices, there exists a number of tips and tricks that can help speed up core development projects:

  • Use a Shared State Cache (sstate) among groups of developers who are on a fast network. The best way to share sstate is through a Network File System (NFS) share. The first user to build a given component for the first time contributes that object to the sstate, while subsequent builds from other developers then reuse the object rather than rebuild it themselves.

    Although it is possible to use other protocols for the sstate such as HTTP and FTP, you should avoid these. Using HTTP limits the sstate to read-only and FTP provides poor performance.

  • Have autobuilders contribute to the sstate pool similarly to how the developer workstations contribute. For information, see the Autobuilders section.

  • Build stand-alone tarballs that contain "missing" system requirements if for some reason developer workstations do not meet minimum system requirements such as latest Python versions, chrpath, or other tools. You can install and relocate the tarball exactly as you would the usual cross-development toolchain so that all developers can meet minimum version requirements on most distributions.

  • Use a small number of shared, high performance systems for testing purposes (e.g. dual six core Xeons with 24GB RAM and plenty of disk space). Developers can use these systems for wider, more extensive testing while they continue to develop locally using their primary development system.

  • Enable the PR Service when package feeds need to be incremental with continually increasing PR values. Typically, this situation occurs when you use or publish package feeds and use a shared state. You should enable the PR Service for all users who use the shared state pool. For more information on the PR Service, see the "Working With a PR Service".

3.2.2. Source Control Management (SCM)

Keeping your Metadata and any software you are developing under the control of an SCM system that is compatible with the OpenEmbedded build system is advisable. Of the SCMs BitBake supports, the Yocto Project team strongly recommends using Git. Git is a distributed system that is easy to backup (each checkout is a backup in itself), allows you to work remotely, and then connects back to the infrastructure.

Note

For information about BitBake and SCMs, see the BitBake manual located in the bitbake/doc/manual directory of the Source Directory.

It is relatively easy to set up Git services and create infrastructure like http://git.yoctoproject.org, which is based on server software called gitolite with cgit being used to generate the web interface that lets you view the repositories. The gitolite software identifies users using ssh keys and allows branch-based access controls to repositories that you can control as little or as much as necessary.

Note

The setup of these services is beyond the scope of this manual. However, sites such as these exist that describe how to perform setup:

3.2.3. Autobuilders

Autobuilders are often the core of a development project. It is here that changes from individual developers are brought together and centrally tested and subsequent decisions about releases can be made. Autobuilders also allow for "continuous integration" style testing of software components and regression identification and tracking.

See "Welcome to the buildbot for the Yocto Project" for the Yocto Project's reference implementation that uses buildbot. The Yocto Project team has found this implementation works well in this role. A public example of this is the Yocto Project Autobuilders, which we use to test the overall health of the project.

The features of this system are:

  • Highlights when commits break the build.

  • Populates an sstate cache from which developers can pull rather than requiring local builds.

  • Allows commit hook triggers, which trigger builds when commits are made.

  • Allows triggering of automated image booting and testing under the QuickEMUlator (QEMU).

  • Supports incremental build testing and from scratch builds.

  • Shares output that allows developer testing and historical regression investigation.

  • Creates output that can be used for releases.

  • Allows scheduling of builds so that resources can be used efficiently.

3.2.4. Policies and Change Flow

The Yocto Project itself uses a hierarchical structure and a pull model. Scripts exist to create and send pull requests (i.e. create-pull-request and send-pull-request). This model is in line with other open source projects where maintainers are responsible for specific areas of the project and a single maintainer handles the final "top-of-tree" merges.

Note

You can also use a more collective push model. The gitolite software supports both the push and pull models quite easily.

As with any development environment, it is important to document the policy used as well as any main project guidelines so they are understood by everyone. It is also a good idea to have well structured commit messages, which are usually a part of a project's guidelines. Good commit messages are essential when looking back in time and trying to understand why changes were made.

If you discover that changes are needed to the core layer of the project, it is worth sharing those with the community as soon as possible. Chances are if you have discovered the need for changes, someone else in the community needs them also.

3.2.5. Summary

This section summarizes the key recommendations described in the previous sections:

  • Use Git as the source control system.

  • Maintain your Metadata in layers that make sense for your situation. See the "Understanding and Creating Layers" section for more information on layers.

  • Separate the project's Metadata and code by using separate Git repositories. See the "Yocto Project Source Repositories" section for information on these repositories. See the "Getting Set Up" section for information on how to set up various Yocto Project related Git repositories.

  • Set up the directory for the shared state cache (SSTATE_DIR) where it makes sense. For example, set up the sstate cache on a system used by developers in the same organization and share the same source directories on their machines.

  • Set up an Autobuilder and have it populate the sstate cache and source directories.

  • The Yocto Project community encourages you to send patches to the project to fix bugs or add features. If you do submit patches, follow the project commit guidelines for writing good commit messages. See the "How to Submit a Change" section.

  • Send changes to the core sooner than later as others likely run into the same issues. For some guidance on mailing lists to use, see the list in the "How to Submit a Change" section. For a description of the available mailing lists, see "Mailing Lists" section in the Yocto Project Reference Manual.

3.3. Yocto Project Source Repositories

The Yocto Project team maintains complete source repositories for all Yocto Project files at http://git.yoctoproject.org/cgit/cgit.cgi. This web-based source code browser is organized into categories by function such as IDE Plugins, Matchbox, Poky, Yocto Linux Kernel, and so forth. From the interface, you can click on any particular item in the "Name" column and see the URL at the bottom of the page that you need to clone a Git repository for that particular item. Having a local Git repository of the Source Directory (poky) allows you to make changes, contribute to the history, and ultimately enhance the Yocto Project's tools, Board Support Packages, and so forth.

Conversely, if you are a developer that is not interested in contributing back to the Yocto Project, you have the ability to simply download and extract release tarballs and use them within the Yocto Project environment. All that is required is a particular release of the Yocto Project and your application source code.

For any supported release of Yocto Project, you can go to the Yocto Project Website and select the "Downloads" tab and get a tarball of the release. You can also go to this site to download any supported BSP tarballs. Unpacking the tarball gives you a hierarchical Source Directory that lets you develop using the Yocto Project.

Once you are set up through either tarball extraction or a checkout of Git repositories, you are ready to develop.

In summary, here is where you can get the project files needed for development:

  • :SSource Repositories: This area contains IDE Plugins, Matchbox, Poky, Poky Support, Tools, Yocto Linux Kernel, and Yocto Metadata Layers. You can create local copies of Git repositories for each of these areas.

  • :Index of /releases: This area contains index releases such as the Eclipse™ Yocto Plug-in, miscellaneous support, poky, pseudo, installers for cross-development toolchains, and all released versions of Yocto Project in the form of images or tarballs. Downloading and extracting these files does not produce a local copy of the Git repository but rather a snapshot of a particular release or image.

  • "Downloads" page for the Yocto Project Website: Access this page by going to the website and then selecting the "Downloads" tab. This page allows you to download any Yocto Project release or Board Support Package (BSP) in tarball form. The tarballs are similar to those found in the Index of /releases: area.

3.4. Yocto Project Terms

Following is a list of terms and definitions users new to the Yocto Project development environment might find helpful. While some of these terms are universal, the list includes them just in case:

  • Append Files: Files that append build information to a recipe file. Append files are known as BitBake append files and .bbappend files. The OpenEmbedded build system expects every append file to have a corresponding recipe (.bb) file. Furthermore, the append file and corresponding recipe file must use the same root filename. The filenames can differ only in the file type suffix used (e.g. formfactor_0.0.bb and formfactor_0.0.bbappend).

    Information in append files overrides the information in the similarly-named recipe file. For an example of an append file in use, see the "Using .bbappend Files" section.

  • BitBake: The task executor and scheduler used by the OpenEmbedded build system to build images. For more information on BitBake, see the BitBake documentation in the bitbake/doc/manual directory of the Source Directory.

  • Build Directory: This term refers to the area used by the OpenEmbedded build system for builds. The area is created when you source the setup environment script that is found in the Source Directory (i.e. oe-init-build-env). The TOPDIR variable points to the Build Directory.

    You have a lot of flexibility when creating the Build Directory. Following are some examples that show how to create the directory:

    • Create the Build Directory in your current working directory and name it build. This is the default behavior.

           $ source poky-dylan-9.0.2/oe-init-build-env
                                  
    • Provide a directory path and specifically name the build directory. This next example creates a Build Directory named YP-9.0.2 in your home directory within the directory mybuilds. If mybuilds does not exist, the directory is created for you:

           $ source poky-dylan-9.0.2/oe-init-build-env $HOME/mybuilds/YP-9.0.2
                                  
    • Provide an existing directory to use as the Build Directory and use the default build name.

           $ source poky-dylan-9.0.2/oe-init-build-env $HOME/mybuilds/
                                  

  • Build System: In the context of the Yocto Project, this term refers to the OpenEmbedded build system used by the project. This build system is based on the project known as "Poky." For some historical information about Poky, see the Poky term.

  • Classes: Files that provide for logic encapsulation and inheritance so that commonly used patterns can be defined once and then easily used in multiple recipes. Class files end with the .bbclass filename extension.

  • Configuration File: Configuration information in various .conf files provides global definitions of variables. The conf/local.conf configuration file in the Build Directory contains user-defined variables that affect each build. The meta-yocto/conf/distro/poky.conf configuration file defines Yocto "distro" configuration variables used only when building with this policy. Machine configuration files, which are located throughout the Source Directory, define variables for specific hardware and are only used when building for that target (e.g. the machine/beagleboard.conf configuration file defines variables for the Texas Instruments ARM Cortex-A8 development board). Configuration files end with a .conf filename extension.

  • Cross-Development Toolchain: A collection of software development tools and utilities that allow you to develop software for targeted architectures. This toolchain contains cross-compilers, linkers, and debuggers that are specific to an architecture. You can use the OpenEmbedded build system to build a cross-development toolchain installer that, when run, installs the toolchain that contains the development tools you need to cross-compile and test your software. The Yocto Project ships with images that contain installers for toolchains for supported architectures as well. Sometimes this toolchain is referred to as the meta-toolchain.

    Following is a list of toolchain recipes with brief descriptions of each:

    • gcc-cross-initial: The initial compiler needed to bootstrap the toolchain that runs on the host and is used to build software for the target. This tool is a "native" package.

    • gcc-cross-intermediate: The second stage of the bootstrap process that runs on the host and builds software for the target. This tool is a "native" package.

    • gcc-cross: The the final stage of the bootstrap process that results in the cross compiler that runs on the host and builds software for the target. If you are replacing the cross compiler toolchain with a custom version, this is what you must replace. This tool is a "native" package.

    • gcc-runtime: Runtime libraries from the toolchain bootstrapping process. This tool produces a binary for the target.

    • gcc-crosssdk-initial/intermediate: Stage 1 and 2 of the a cross compiler that runs on the host and builds for the SDK. Often the SDK is not the same target as the host. This tool is a "native" binary.

    • gcc-crosssdk: The final stage of the SDK compiler. This tool is a "native" binary. The tool runs on the host and builds for the SDK.

    • gcc-cross-canadian: The compiler that runs on the SDK machine and is included with the SDK that builds software for the target. This tool is a "nativesdk" package.

  • Image: An image is the result produced when BitBake processes a given collection of recipes and related Metadata. Images are the binary output that run on specific hardware or QEMU and for specific use cases. For a list of the supported image types that the Yocto Project provides, see the "Images" chapter in the Yocto Project Reference Manual.

  • Layer: A collection of recipes representing the core, a BSP, or an application stack. For a discussion on BSP Layers, see the "BSP Layers" section in the Yocto Project Board Support Packages (BSP) Developer's Guide.

  • Metadata: The files that BitBake parses when building an image. In general, Metadata includes recipes, classes, and configuration files. In the context of the kernel ("kernel Metadata"), it refers to Metadata in the meta branches of the kernel source Git repositories.

  • OE-Core: A core set of Metadata originating with OpenEmbedded (OE) that is shared between OE and the Yocto Project. This Metadata is found in the meta directory of the Source Directory.

  • Package: In the context of the Yocto Project, this term refers to the packaged output from a baked recipe. A package is generally the compiled binaries produced from the recipe's sources. You "bake" something by running it through BitBake.

    It is worth noting that the term "package" can, in general, have subtle meanings. For example, the packages referred to in the "The Packages" section are compiled binaries that when installed add functionality to your Linux distribution.

    Another point worth noting is that historically within the Yocto Project, recipes were referred to as packages - thus, the existence of several BitBake variables that are seemingly mis-named, (e.g. PR, PRINC, PV, and PE).

  • Poky: The term "poky" can mean several things. In its most general sense, it is an open-source project that was initially developed by OpenedHand. With OpenedHand, poky was developed off of the existing OpenEmbedded build system becoming a build system for embedded images. After Intel Corporation acquired OpenedHand, the project poky became the basis for the Yocto Project's build system. Within the Yocto Project source repositories, poky exists as a separate Git repository that can be cloned to yield a local copy on the host system. Thus, "poky" can refer to the local copy of the Source Directory used to develop within the Yocto Project.

  • Recipe: A set of instructions for building packages. A recipe describes where you get source code and which patches to apply. Recipes describe dependencies for libraries or for other recipes, and they also contain configuration and compilation options. Recipes contain the logical unit of execution, the software/images to build, and use the .bb file extension.

  • Source Directory: This term refers to the directory structure created as a result of either downloading and unpacking a Yocto Project release tarball or creating a local copy of the poky Git repository git://git.yoctoproject.org/poky. Sometimes you might hear the term "poky directory" used to refer to this directory structure.

    Note

    The OpenEmbedded build system does not support file or directory names that contain spaces. Be sure that the Source Directory you use does not contain these types of names.

    The Source Directory contains BitBake, Documentation, Metadata and other files that all support the Yocto Project. Consequently, you must have the Source Directory in place on your development system in order to do any development using the Yocto Project.

    For tarball expansion, the name of the top-level directory of the Source Directory is derived from the Yocto Project release tarball. For example, downloading and unpacking poky-dylan-9.0.2.tar.bz2 results in a Source Directory whose top-level folder is named poky-dylan-9.0.2. If you create a local copy of the Git repository, then you can name the repository anything you like. Throughout much of the documentation, poky is used as the name of the top-level folder of the local copy of the poky Git repository. So, for example, cloning the poky Git repository results in a local Git repository whose top-level folder is also named poky.

    It is important to understand the differences between the Source Directory created by unpacking a released tarball as compared to cloning git://git.yoctoproject.org/poky. When you unpack a tarball, you have an exact copy of the files based on the time of release - a fixed release point. Any changes you make to your local files in the Source Directory are on top of the release. On the other hand, when you clone the poky Git repository, you have an active development repository. In this case, any local changes you make to the Source Directory can be later applied to active development branches of the upstream poky Git repository.

    Finally, if you want to track a set of local changes while starting from the same point as a release tarball, you can create a local Git branch that reflects the exact copy of the files at the time of their release. You do this by using Git tags that are part of the repository.

    For more information on concepts related to Git repositories, branches, and tags, see the "Repositories, Tags, and Branches" section.

  • Tasks: Arbitrary groups of software Recipes. You use tasks to hold recipes that, when built, usually accomplish a single task. For example, a task could contain the recipes for a company’s proprietary or value-add software. Or, the task could contain the recipes that enable graphics. A task is really just another recipe. Because task files are recipes, they end with the .bb filename extension.

  • Upstream: A reference to source code or repositories that are not local to the development system but located in a master area that is controlled by the maintainer of the source code. For example, in order for a developer to work on a particular piece of code, they need to first get a copy of it from an "upstream" source.

3.5. Licensing

Because open source projects are open to the public, they have different licensing structures in place. License evolution for both Open Source and Free Software has an interesting history. If you are interested in this history, you can find basic information here:

In general, the Yocto Project is broadly licensed under the Massachusetts Institute of Technology (MIT) License. MIT licensing permits the reuse of software within proprietary software as long as the license is distributed with that software. MIT is also compatible with the GNU General Public License (GPL). Patches to the Yocto Project follow the upstream licensing scheme. You can find information on the MIT license at here. You can find information on the GNU GPL here.

When you build an image using the Yocto Project, the build process uses a known list of licenses to ensure compliance. You can find this list in the Source Directory at meta/files/common-licenses. Once the build completes, the list of all licenses found and used during that build are kept in the Build Directory at tmp/deploy/licenses.

If a module requires a license that is not in the base list, the build process generates a warning during the build. These tools make it easier for a developer to be certain of the licenses with which their shipped products must comply. However, even with these tools it is still up to the developer to resolve potential licensing issues.

The base list of licenses used by the build process is a combination of the Software Package Data Exchange (SPDX) list and the Open Source Initiative (OSI) projects. SPDX Group is a working group of the Linux Foundation that maintains a specification for a standard format for communicating the components, licenses, and copyrights associated with a software package. OSI is a corporation dedicated to the Open Source Definition and the effort for reviewing and approving licenses that are OSD-conformant.

You can find a list of the combined SPDX and OSI licenses that the Yocto Project uses here.

For information that can help you to maintain compliance with various open source licensing during the lifecycle of a product created using the Yocto Project, see the "Maintaining Open Source License Compliance During Your Product's Lifecycle" section.

3.6. Git

The Yocto Project uses Git, which is a free, open source distributed version control system. Git supports distributed development, non-linear development, and can handle large projects. It is best that you have some fundamental understanding of how Git tracks projects and how to work with Git if you are going to use the Yocto Project for development. This section provides a quick overview of how Git works and provides you with a summary of some essential Git commands.

For more information on Git, see http://git-scm.com/documentation. If you need to download Git, go to http://git-scm.com/download.

3.6.1. Repositories, Tags, and Branches

As mentioned earlier in the section "Yocto Project Source Repositories", the Yocto Project maintains source repositories at http://git.yoctoproject.org/cgit.cgi. If you look at this web-interface of the repositories, each item is a separate Git repository.

Git repositories use branching techniques that track content change (not files) within a project (e.g. a new feature or updated documentation). Creating a tree-like structure based on project divergence allows for excellent historical information over the life of a project. This methodology also allows for an environment from which you can do lots of local experimentation on projects as you develop changes or new features.

A Git repository represents all development efforts for a given project. For example, the Git repository poky contains all changes and developments for Poky over the course of its entire life. That means that all changes that make up all releases are captured. The repository maintains a complete history of changes.

You can create a local copy of any repository by "cloning" it with the Git clone command. When you clone a Git repository, you end up with an identical copy of the repository on your development system. Once you have a local copy of a repository, you can take steps to develop locally. For examples on how to clone Git repositories, see the "Getting Set Up" section.

It is important to understand that Git tracks content change and not files. Git uses "branches" to organize different development efforts. For example, the poky repository has bernard, edison, denzil, danny and master branches among others. You can see all the branches by going to http://git.yoctoproject.org/cgit.cgi/poky/ and clicking on the [...] link beneath the "Branch" heading.

Each of these branches represents a specific area of development. The master branch represents the current or most recent development. All other branches represent off-shoots of the master branch.

When you create a local copy of a Git repository, the copy has the same set of branches as the original. This means you can use Git to create a local working area (also called a branch) that tracks a specific development branch from the source Git repository. in other words, you can define your local Git environment to work on any development branch in the repository. To help illustrate, here is a set of commands that creates a local copy of the poky Git repository and then creates and checks out a local Git branch that tracks the Yocto Project 1.4.2 Release (dylan) development:

     $ cd ~
     $ git clone git://git.yoctoproject.org/poky
     $ cd poky
     $ git checkout -b dylan origin/dylan
            

In this example, the name of the top-level directory of your local Source Directory is poky, and the name of that local working area (local branch) you just created and checked out is dylan. The files in your local repository now reflect the same files that are in the dylan development branch of the Yocto Project's poky upstream repository. It is important to understand that when you create and checkout a local working branch based on a branch name, your local environment matches the "tip" of that development branch at the time you created your local branch, which could be different than the files at the time of a similarly named release. In other words, creating and checking out a local branch based on the dylan branch name is not the same as cloning and checking out the master branch. Keep reading to see how you create a local snapshot of a Yocto Project Release.

Git uses "tags" to mark specific changes in a repository. Typically, a tag is used to mark a special point such as the final change before a project is released. You can see the tags used with the poky Git repository by going to http://git.yoctoproject.org/cgit.cgi/poky/ and clicking on the [...] link beneath the "Tag" heading.

Some key tags are bernard-5.0, denzil-7.0, and dylan-9.0.2. These tags represent Yocto Project releases.

When you create a local copy of the Git repository, you also have access to all the tags. Similar to branches, you can create and checkout a local working Git branch based on a tag name. When you do this, you get a snapshot of the Git repository that reflects the state of the files when the change was made associated with that tag. The most common use is to checkout a working branch that matches a specific Yocto Project release. Here is an example:

     $ cd ~
     $ git clone git://git.yoctoproject.org/poky
     $ cd poky
     $ git checkout -b my-dylan-9.0.2 dylan-9.0.2
            

In this example, the name of the top-level directory of your local Yocto Project Files Git repository is poky. And, the name of the local branch you have created and checked out is my-dylan-9.0.2. The files in your repository now exactly match the Yocto Project 1.4.2 Release tag (dylan-9.0.2). It is important to understand that when you create and checkout a local working branch based on a tag, your environment matches a specific point in time and not the entire development branch.

3.6.2. Basic Commands

Git has an extensive set of commands that lets you manage changes and perform collaboration over the life of a project. Conveniently though, you can manage with a small set of basic operations and workflows once you understand the basic philosophy behind Git. You do not have to be an expert in Git to be functional. A good place to look for instruction on a minimal set of Git commands is here. If you need to download Git, you can do so here.

If you don’t know much about Git, you should educate yourself by visiting the links previously mentioned.

The following list briefly describes some basic Git operations as a way to get started. As with any set of commands, this list (in most cases) simply shows the base command and omits the many arguments they support. See the Git documentation for complete descriptions and strategies on how to use these commands:

  • git init: Initializes an empty Git repository. You cannot use Git commands unless you have a .git repository.

  • git clone: Creates a clone of a repository. During collaboration, this command allows you to create a local repository that is on equal footing with a fellow developer’s repository.

  • git add: Stages updated file contents to the index that Git uses to track changes. You must stage all files that have changed before you can commit them.

  • git commit: Creates a "commit" that documents the changes you made. Commits are used for historical purposes, for determining if a maintainer of a project will allow the change, and for ultimately pushing the change from your local Git repository into the project’s upstream (or master) repository.

  • git status: Reports any modified files that possibly need staged and committed.

  • git checkout <branch-name>: Changes your working branch. This command is analogous to "cd".

  • git checkout –b <working-branch>: Creates a working branch on your local machine where you can isolate work. It is a good idea to use local branches when adding specific features or changes. This way if you do not like what you have done you can easily get rid of the work.

  • git branch: Reports existing local branches and tells you the branch in which you are currently working.

  • git branch -D <branch-name>: Deletes an existing local branch. You need to be in a local branch other than the one you are deleting in order to delete <branch-name>.

  • git pull: Retrieves information from an upstream Git repository and places it in your local Git repository. You use this command to make sure you are synchronized with the repository from which you are basing changes (.e.g. the master branch).

  • git push: Sends all your committed local changes to an upstream Git repository (e.g. a contribution repository). The maintainer of the project draws from these repositories when adding changes to the project’s master repository or other development branch.

  • git merge: Combines or adds changes from one local branch of your repository with another branch. When you create a local Git repository, the default branch is named "master". A typical workflow is to create a temporary branch for isolated work, make and commit your changes, switch to your local master branch, merge the changes from the temporary branch into the local master branch, and then delete the temporary branch.

  • git cherry-pick: Choose and apply specific commits from one branch into another branch. There are times when you might not be able to merge all the changes in one branch with another but need to pick out certain ones.

  • gitk: Provides a GUI view of the branches and changes in your local Git repository. This command is a good way to graphically see where things have diverged in your local repository.

  • git log: Reports a history of your changes to the repository.

  • git diff: Displays line-by-line differences between your local working files and the same files in the upstream Git repository that your branch currently tracks.

3.7. Workflows

This section provides some overview on workflows using Git. In particular, the information covers basic practices that describe roles and actions in a collaborative development environment. Again, if you are familiar with this type of development environment, you might want to just skip this section.

The Yocto Project files are maintained using Git in a "master" branch whose Git history tracks every change and whose structure provides branches for all diverging functionality. Although there is no need to use Git, many open source projects do so. For the Yocto Project, a key individual called the "maintainer" is responsible for the "master" branch of a given Git repository. The "master" branch is the “upstream” repository where the final builds of the project occur. The maintainer is responsible for allowing changes in from other developers and for organizing the underlying branch structure to reflect release strategies and so forth.

Note

For information on finding out who is responsible (maintains) for a particular area of code, see the "How to Submit a Change" section.

The project also has contribution repositories known as "contrib" areas. These areas temporarily hold changes to the project that have been submitted or committed by the Yocto Project development team and by community members that contribute to the project. The maintainer determines if the changes are qualified to be moved from the "contrib" areas into the "master" branch of the Git repository.

Developers (including contributing community members) create and maintain cloned repositories of the upstream "master" branch. These repositories are local to their development platforms and are used to develop changes. When a developer is satisfied with a particular feature or change, they "push" the changes to the appropriate "contrib" repository.

Developers are responsible for keeping their local repository up-to-date with "master". They are also responsible for straightening out any conflicts that might arise within files that are being worked on simultaneously by more than one person. All this work is done locally on the developer’s machines before anything is pushed to a "contrib" area and examined at the maintainer’s level.

A somewhat formal method exists by which developers commit changes and push them into the "contrib" area and subsequently request that the maintainer include them into "master" This process is called “submitting a patch” or "submitting a change." For information on submitting patches and changes, see the "How to Submit a Change" section.

To summarize the environment: we have a single point of entry for changes into the project’s "master" branch of the Git repository, which is controlled by the project’s maintainer. And, we have a set of developers who independently develop, test, and submit changes to "contrib" areas for the maintainer to examine. The maintainer then chooses which changes are going to become a permanent part of the project.

While each development environment is unique, there are some best practices or methods that help development run smoothly. The following list describes some of these practices. For more information about Git workflows, see the workflow topics in the Git Community Book.

  • Make Small Changes: It is best to keep the changes you commit small as compared to bundling many disparate changes into a single commit. This practice not only keeps things manageable but also allows the maintainer to more easily include or refuse changes.

    It is also good practice to leave the repository in a state that allows you to still successfully build your project. In other words, do not commit half of a feature, then add the other half as a separate, later commit. Each commit should take you from one buildable project state to another buildable state.

  • Use Branches Liberally: It is very easy to create, use, and delete local branches in your working Git repository. You can name these branches anything you like. It is helpful to give them names associated with the particular feature or change on which you are working. Once you are done with a feature or change and have merged it into your local master branch, simply discard the temporary branch.

  • Merge Changes: The git merge command allows you to take the changes from one branch and fold them into another branch. This process is especially helpful when more than a single developer might be working on different parts of the same feature. Merging changes also automatically identifies any collisions or "conflicts" that might happen as a result of the same lines of code being altered by two different developers.

  • Manage Branches: Because branches are easy to use, you should use a system where branches indicate varying levels of code readiness. For example, you can have a "work" branch to develop in, a "test" branch where the code or change is tested, a "stage" branch where changes are ready to be committed, and so forth. As your project develops, you can merge code across the branches to reflect ever-increasing stable states of the development.

  • Use Push and Pull: The push-pull workflow is based on the concept of developers "pushing" local commits to a remote repository, which is usually a contribution repository. This workflow is also based on developers "pulling" known states of the project down into their local development repositories. The workflow easily allows you to pull changes submitted by other developers from the upstream repository into your work area ensuring that you have the most recent software on which to develop. The Yocto Project has two scripts named create-pull-request and send-pull-request that ship with the release to facilitate this workflow. You can find these scripts in the scripts folder of the Source Directory. For information on how to use these scripts, see the "Using Scripts to Push a Change Upstream and Request a Pull" section.

  • Patch Workflow: This workflow allows you to notify the maintainer through an email that you have a change (or patch) you would like considered for the "master" branch of the Git repository. To send this type of change, you format the patch and then send the email using the Git commands git format-patch and git send-email. For information on how to use these scripts, see the "How to Submit a Change" section.

3.8. Tracking Bugs

The Yocto Project uses its own implementation of Bugzilla to track bugs. Implementations of Bugzilla work well for group development because they track bugs and code changes, can be used to communicate changes and problems with developers, can be used to submit and review patches, and can be used to manage quality assurance. The home page for the Yocto Project implementation of Bugzilla is http://bugzilla.yoctoproject.org.

Sometimes it is helpful to submit, investigate, or track a bug against the Yocto Project itself such as when discovering an issue with some component of the build system that acts contrary to the documentation or your expectations. Following is the general procedure for submitting a new bug using the Yocto Project Bugzilla. You can find more information on defect management, bug tracking, and feature request processes all accomplished through the Yocto Project Bugzilla on the wiki page here.

  1. Always use the Yocto Project implementation of Bugzilla to submit a bug.

  2. When submitting a new bug, be sure to choose the appropriate Classification, Product, and Component for which the issue was found. Defects for the Yocto Project fall into one of six classifications: Yocto Project Components, Infrastructure, Build System & Metadata, Documentation, QA/Testing, and Runtime. Each of these Classifications break down into multiple Products and, in some cases, multiple Components.

  3. Use the bug form to choose the correct Hardware and Architecture for which the bug applies.

  4. Indicate the Yocto Project version you were using when the issue occurred.

  5. Be sure to indicate the Severity of the bug. Severity communicates how the bug impacted your work.

  6. Provide a brief summary of the issue. Try to limit your summary to just a line or two and be sure to capture the essence of the issue.

  7. Provide a detailed description of the issue. You should provide as much detail as you can about the context, behavior, output, and so forth that surrounds the issue. You can even attach supporting files for output from logs by using the "Add an attachment" button.

  8. Be sure to copy the appropriate people in the "CC List" for the bug. See the "How to Submit a Change" section for information about finding out who is responsible for code.

  9. Submit the bug by clicking the "Submit Bug" button.

3.9. How to Submit a Change

Contributions to the Yocto Project and OpenEmbedded are very welcome. Because the system is extremely configurable and flexible, we recognize that developers will want to extend, configure or optimize it for their specific uses. You should send patches to the appropriate mailing list so that they can be reviewed and merged by the appropriate maintainer.

Before submitting any change, be sure to find out who you should be notifying. Several methods exist through which you find out who you should be copying or notifying:

  • Maintenance File: Examine the maintainers.inc file, which is located in the Source Directory at meta-yocto/conf/distro/include, to see who is responsible for code.

  • Board Support Package (BSP) README Files: For BSP maintainers of supported BSPs, you can examine individual BSP README files. Alternatively, you can examine the MAINTAINERS file, which is found in the meta-intel, for a list of all supported BSP maintainers.

  • Search by File: Using Git, you can enter the following command to bring up a short list of all commits against a specific file:

         git shortlog -- <filename>
                    

    Just provide the name of the file for which you are interested. The information returned is not ordered by history but does include a list of all committers grouped by name. From the list, you can see who is responsible for the bulk of the changes against the file.

For a list of the Yocto Project and related mailing lists, see the "Mailing lists" section in the Yocto Project Reference Manual.

Here is some guidance on which mailing list to use for what type of change:

  • For changes to the core Metadata, send your patch to the openembedded-core mailing list. For example, a change to anything under the meta or scripts directories should be sent to this mailing list.

  • For changes to BitBake (anything under the bitbake directory), send your patch to the bitbake-devel mailing list.

  • For changes to meta-yocto, send your patch to the poky mailing list.

  • For changes to other layers hosted on yoctoproject.org (unless the layer's documentation specifies otherwise), tools, and Yocto Project documentation, use the yocto mailing list.

  • For additional recipes that do not fit into the core Metadata, you should determine which layer the recipe should go into and submit the change in the manner recommended by the documentation (e.g. README) supplied with the layer. If in doubt, please ask on the yocto or openembedded-devel mailing lists.

When you send a patch, be sure to include a "Signed-off-by:" line in the same style as required by the Linux kernel. Adding this line signifies that you, the submitter, have agreed to the Developer's Certificate of Origin 1.1 as follows:

     Developer's Certificate of Origin 1.1

     By making a contribution to this project, I certify that:

     (a) The contribution was created in whole or in part by me and I
         have the right to submit it under the open source license
         indicated in the file; or

     (b) The contribution is based upon previous work that, to the best
         of my knowledge, is covered under an appropriate open source
         license and I have the right under that license to submit that
         work with modifications, whether created in whole or in part
         by me, under the same open source license (unless I am
         permitted to submit under a different license), as indicated
         in the file; or

     (c) The contribution was provided directly to me by some other
         person who certified (a), (b) or (c) and I have not modified
         it.

     (d) I understand and agree that this project and the contribution
         are public and that a record of the contribution (including all
         personal information I submit with it, including my sign-off) is
         maintained indefinitely and may be redistributed consistent with
         this project or the open source license(s) involved.
        

In a collaborative environment, it is necessary to have some sort of standard or method through which you submit changes. Otherwise, things could get quite chaotic. One general practice to follow is to make small, controlled changes. Keeping changes small and isolated aids review, makes merging/rebasing easier and keeps the change history clean when anyone needs to refer to it in future.

When you make a commit, you must follow certain standards established by the OpenEmbedded and Yocto Project development teams. For each commit, you must provide a single-line summary of the change and you should almost always provide a more detailed description of what you did (i.e. the body of the commit message). The only exceptions for not providing a detailed description would be if your change is a simple, self-explanatory change that needs no further description beyond the summary. Here are the guidelines for composing a commit message:

  • Provide a single-line, short summary of the change. This summary is typically viewable in the "shortlist" of changes. Thus, providing something short and descriptive that gives the reader a summary of the change is useful when viewing a list of many commits. This short description should be prefixed by the recipe name (if changing a recipe), or else the short form path to the file being changed.

  • For the body of the commit message, provide detailed information that describes what you changed, why you made the change, and the approach you used. It may also be helpful if you mention how you tested the change. Provide as much detail as you can in the body of the commit message.

  • If the change addresses a specific bug or issue that is associated with a bug-tracking ID, include a reference to that ID in your detailed description. For example, the Yocto Project uses a specific convention for bug references - any commit that addresses a specific bug should include the bug ID in the description (typically at the beginning) as follows:

         Fixes YOCTO #<bug-id>
    
         <detailed description of change>
                    

You can find more guidance on creating well-formed commit messages at this OpenEmbedded wiki page: http://www.openembedded.org/wiki/Commit_Patch_Message_Guidelines.

The next two sections describe general instructions for both pushing changes upstream and for submitting changes as patches.

3.9.1. Using Scripts to Push a Change Upstream and Request a Pull

The basic flow for pushing a change to an upstream "contrib" Git repository is as follows:

  • Make your changes in your local Git repository.

  • Stage your changes by using the git add command on each file you changed.

  • Commit the change by using the git commit command and push it to the "contrib" repository. Be sure to provide a commit message that follows the project’s commit message standards as described earlier.

  • Notify the maintainer that you have pushed a change by making a pull request. The Yocto Project provides two scripts that conveniently let you generate and send pull requests to the Yocto Project. These scripts are create-pull-request and send-pull-request. You can find these scripts in the scripts directory within the Source Directory.

    Using these scripts correctly formats the requests without introducing any whitespace or HTML formatting. The maintainer that receives your patches needs to be able to save and apply them directly from your emails. Using these scripts is the preferred method for sending patches.

    For help on using these scripts, simply provide the -h argument as follows:

         $ ~/poky/scripts/create-pull-request -h
         $ ~/poky/scripts/send-pull-request -h
                        

You can find general Git information on how to push a change upstream in the Git Community Book.

3.9.2. Using Email to Submit a Patch

You can submit patches without using the create-pull-request and send-pull-request scripts described in the previous section. However, keep in mind, the preferred method is to use the scripts.

Depending on the components changed, you need to submit the email to a specific mailing list. For some guidance on which mailing list to use, see the list in the "How to Submit a Change" section. For a description of the available mailing lists, see the "Mailing Lists" section in the Yocto Project Reference Manual.

Here is the general procedure on how to submit a patch through email without using the scripts:

  • Make your changes in your local Git repository.

  • Stage your changes by using the git add command on each file you changed.

  • Commit the change by using the git commit --signoff command. Using the --signoff option identifies you as the person making the change and also satisfies the Developer's Certificate of Origin (DCO) shown earlier.

    When you form a commit, you must follow certain standards established by the Yocto Project development team. See the earlier section "How to Submit a Change" for Yocto Project commit message standards.

  • Format the commit into an email message. To format commits, use the git format-patch command. When you provide the command, you must include a revision list or a number of patches as part of the command. For example, either of these two commands takes your most recent single commit and formats it as an email message in the current directory:

         $ git format-patch -1
                        

    or

         $ git format-patch HEAD~
                        

    After the command is run, the current directory contains a numbered .patch file for the commit.

    If you provide several commits as part of the command, the git format-patch command produces a series of numbered files in the current directory – one for each commit. If you have more than one patch, you should also use the --cover option with the command, which generates a cover letter as the first "patch" in the series. You can then edit the cover letter to provide a description for the series of patches. For information on the git format-patch command, see GIT_FORMAT_PATCH(1) displayed using the man git-format-patch command.

    Note

    If you are or will be a frequent contributor to the Yocto Project or to OpenEmbedded, you might consider requesting a contrib area and the necessary associated rights.
  • Import the files into your mail client by using the git send-email command.

    Note

    In order to use git send-email, you must have the the proper Git packages installed. For Ubuntu and Fedora the package is git-email.

    The git send-email command sends email by using a local or remote Mail Transport Agent (MTA) such as msmtp, sendmail, or through a direct smtp configuration in your Git config file. If you are submitting patches through email only, it is very important that you submit them without any whitespace or HTML formatting that either you or your mailer introduces. The maintainer that receives your patches needs to be able to save and apply them directly from your emails. A good way to verify that what you are sending will be applicable by the maintainer is to do a dry run and send them to yourself and then save and apply them as the maintainer would.

    The git send-email command is the preferred method for sending your patches since there is no risk of compromising whitespace in the body of the message, which can occur when you use your own mail client. The command also has several options that let you specify recipients and perform further editing of the email message. For information on how to use the git send-email command, see GIT-SEND-EMAIL(1) displayed using the man git-send-email command.

Chapter 4. Common Development Models

Many development models exist for which you can use the Yocto Project. This chapter overviews simple methods that use tools provided by the Yocto Project:

  • System Development: System Development covers Board Support Package (BSP) development and kernel modification or configuration. For an example on how to create a BSP, see the "Creating a New BSP Layer Using the yocto-bsp Script" section in the Yocto Project Board Support Package (BSP) Developer's Guide. For more complete information on how to work with the kernel, see the Yocto Project Linux Kernel Development Manual.

  • User Application Development: User Application Development covers development of applications that you intend to run on target hardware. For information on how to set up your host development system for user-space application development, see the Yocto Project Application Developer's Guide. For a simple example of user-space application development using the Eclipse™ IDE, see the "Application Development Workflow" section.

  • Temporary Source Code Modification: Direct modification of temporary source code is a convenient development model to quickly iterate and develop towards a solution. Once you implement the solution, you should of course take steps to get the changes upstream and applied in the affected recipes.

  • Image Development using Hob: You can use the Hob to build custom operating system images within the build environment. Hob provides an efficient interface to the OpenEmbedded build system.

  • Using a Development Shell: You can use a devshell to efficiently debug commands or simply edit packages. Working inside a development shell is a quick way to set up the OpenEmbedded build environment to work on parts of a project.

4.1. System Development Workflow

System development involves modification or creation of an image that you want to run on a specific hardware target. Usually, when you want to create an image that runs on embedded hardware, the image does not require the same number of features that a full-fledged Linux distribution provides. Thus, you can create a much smaller image that is designed to use only the features for your particular hardware.

To help you understand how system development works in the Yocto Project, this section covers two types of image development: BSP creation and kernel modification or configuration.

4.1.1. Developing a Board Support Package (BSP)

A BSP is a package of recipes that, when applied during a build, results in an image that you can run on a particular board. Thus, the package when compiled into the new image, supports the operation of the board.

Note

For a brief list of terms used when describing the development process in the Yocto Project, see the "Yocto Project Terms" section.

The remainder of this section presents the basic steps used to create a BSP using the Yocto Project's BSP Tools. Although not required for BSP creation, the meta-intel repository, which contains many BSPs supported by the Yocto Project, is part of the example.

For an example that shows how to create a new layer using the tools, see the "Creating a New BSP Layer Using the yocto-bsp Script" section in the Yocto Project Board Support Package (BSP) Developer's Guide.

The following illustration and list summarize the BSP creation general workflow.

  1. Set up your host development system to support development using the Yocto Project: See the "The Linux Distribution" and the "The Packages" sections both in the Yocto Project Quick Start for requirements.

  2. Establish a local copy of the project files on your system: You need this Source Directory available on your host system. Having these files on your system gives you access to the build process and to the tools you need. For information on how to set up the Source Directory, see the "Getting Set Up" section.

  3. Establish the meta-intel repository on your system: Having local copies of these supported BSP layers on your system gives you access to layers you might be able to build on or modify to create your BSP. For information on how to get these files, see the "Getting Set Up" section.

  4. Create your own BSP layer using the yocto-bsp script: Layers are ideal for isolating and storing work for a given piece of hardware. A layer is really just a location or area in which you place the recipes and configurations for your BSP. In fact, a BSP is, in itself, a special type of layer. The simplest way to create a new BSP layer that is compliant with the Yocto Project is to use the yocto-bsp script. For information about that script, see the "Creating a New BSP Layer Using the yocto-bsp Script" section in the Yocto Project Board Support (BSP) Developer's Guide.

    Another example that illustrates a layer is an application. Suppose you are creating an application that has library or other dependencies in order for it to compile and run. The layer, in this case, would be where all the recipes that define those dependencies are kept. The key point for a layer is that it is an isolated area that contains all the relevant information for the project that the OpenEmbedded build system knows about. For more information on layers, see the "Understanding and Creating Layers" section. For more information on BSP layers, see the "BSP Layers" section in the Yocto Project Board Support Package (BSP) Developer's Guide.

    Note

    Four BSPs exist that are part of the Yocto Project release: atom-pc, beagleboard, mpc8315e, and routerstationpro. The recipes and configurations for these four BSPs are located and dispersed within the Source Directory. On the other hand, BSP layers for Chief River, Crown Bay, Crystal Forest, Emenlow, Fish River Island 2, Jasper Forest, N450, NUC DC3217IYE, Romley, sys940x, Sugar Bay, and tlk exist in their own separate layers within the larger meta-intel layer.

    When you set up a layer for a new BSP, you should follow a standard layout. This layout is described in the "Example Filesystem Layout" section of the Board Support Package (BSP) Development Guide. In the standard layout, you will notice a suggested structure for recipes and configuration information. You can see the standard layout for a BSP by examining any supported BSP found in the meta-intel layer inside the Source Directory.

  5. Make configuration changes to your new BSP layer: The standard BSP layer structure organizes the files you need to edit in conf and several recipes-* directories within the BSP layer. Configuration changes identify where your new layer is on the local system and identify which kernel you are going to use. When you run the yocto-bsp script, you are able to interactively configure many things for the BSP (e.g. keyboard, touchscreen, and so forth).

  6. Make recipe changes to your new BSP layer: Recipe changes include altering recipes (.bb files), removing recipes you don't use, and adding new recipes or append files (.bbappend) that you need to support your hardware.

  7. Prepare for the build: Once you have made all the changes to your BSP layer, there remains a few things you need to do for the OpenEmbedded build system in order for it to create your image. You need to get the build environment ready by sourcing an environment setup script and you need to be sure two key configuration files are configured appropriately: the conf/local.conf and the conf/bblayers.conf file. You must make the OpenEmbedded build system aware of your new layer. See the "Enabling Your Layer" section for information on how to let the build system know about your new layer.

    The entire process for building an image is overviewed in the section "Building an Image" section of the Yocto Project Quick Start. You might want to reference this information.

  8. Build the image: The OpenEmbedded build system uses the BitBake tool to build images based on the type of image you want to create. You can find more information about BitBake in the user manual, which is found in the bitbake/doc/manual directory of the Source Directory.

    The build process supports several types of images to satisfy different needs. See the "Images" chapter in the Yocto Project Reference Manual for information on supported images.

You can view a video presentation on "Building Custom Embedded Images with Yocto" at Free Electrons. You can also find supplemental information in The Board Support Package (BSP) Development Guide. Finally, there is wiki page write up of the example also located here that you might find helpful.

4.1.2. Modifying the Kernel

Kernel modification involves changing the Yocto Project kernel, which could involve changing configuration options as well as adding new kernel recipes. Configuration changes can be added in the form of configuration fragments, while recipe modification comes through the kernel's recipes-kernel area in a kernel layer you create.

The remainder of this section presents a high-level overview of the Yocto Project kernel architecture and the steps to modify the kernel. You can reference the "Patching the Kernel" section for an example that changes the source code of the kernel. For information on how to configure the kernel, see the "Configuring the Kernel" section. For more information on the kernel and on modifying the kernel, see the Yocto Project Linux Kernel Development Manual.

4.1.2.1. Kernel Overview

Traditionally, when one thinks of a patched kernel, they think of a base kernel source tree and a fixed structure that contains kernel patches. The Yocto Project, however, employs mechanisms that, in a sense, result in a kernel source generator. By the end of this section, this analogy will become clearer.

You can find a web interface to the Yocto Project kernel source repositories at http://git.yoctoproject.org. If you look at the interface, you will see to the left a grouping of Git repositories titled "Yocto Linux Kernel." Within this group, you will find several kernels supported by the Yocto Project:

  • linux-yocto-3.2 - The stable Yocto Project kernel to use with the Yocto Project Release 1.2. This kernel is based on the Linux 3.2 released kernel.

  • linux-yocto-3.4 - The stable Yocto Project kernel to use with the Yocto Project Release 1.3. This kernel is based on the Linux 3.4 released kernel.

  • linux-yocto-3.8 - The stable Yocto Project kernel to use with the Yocto Project Release 1.4. This kernel is based on the Linux 3.8 released kernel.

  • linux-yocto-dev - A development kernel based on the latest upstream release candidate available.

The kernels are maintained using the Git revision control system that structures them using the familiar "tree", "branch", and "leaf" scheme. Branches represent diversions from general code to more specific code, while leaves represent the end-points for a complete and unique kernel whose source files, when gathered from the root of the tree to the leaf, accumulate to create the files necessary for a specific piece of hardware and its features. The following figure displays this concept:

Within the figure, the "Kernel.org Branch Point" represents the point in the tree where a supported base kernel is modified from the Linux kernel. For example, this could be the branch point for the linux-yocto-3.4 kernel. Thus, everything further to the right in the structure is based on the linux-yocto-3.4 kernel. Branch points to right in the figure represent where the linux-yocto-3.4 kernel is modified for specific hardware or types of kernels, such as real-time kernels. Each leaf thus represents the end-point for a kernel designed to run on a specific targeted device.

The overall result is a Git-maintained repository from which all the supported kernel types can be derived for all the supported devices. A big advantage to this scheme is the sharing of common features by keeping them in "larger" branches within the tree. This practice eliminates redundant storage of similar features shared among kernels.

Note

Keep in mind the figure does not take into account all the supported Yocto Project kernel types, but rather shows a single generic kernel just for conceptual purposes. Also keep in mind that this structure represents the Yocto Project source repositories that are either pulled from during the build or established on the host development system prior to the build by either cloning a particular kernel's Git repository or by downloading and unpacking a tarball.

Upstream storage of all the available kernel source code is one thing, while representing and using the code on your host development system is another. Conceptually, you can think of the kernel source repositories as all the source files necessary for all the supported kernels. As a developer, you are just interested in the source files for the kernel on which you are working. And, furthermore, you need them available on your host system.

Kernel source code is available on your host system a couple of different ways. If you are working in the kernel all the time, you probably would want to set up your own local Git repository of the kernel tree. If you just need to make some patches to the kernel, you can access temporary kernel source files that were extracted and used during a build. We will just talk about working with the temporary source code. For more information on how to get kernel source code onto your host system, see the "Yocto Project Kernel" bulleted item earlier in the manual.

What happens during the build? When you build the kernel on your development system, all files needed for the build are taken from the source repositories pointed to by the SRC_URI variable and gathered in a temporary work area where they are subsequently used to create the unique kernel. Thus, in a sense, the process constructs a local source tree specific to your kernel to generate the new kernel image - a source generator if you will.

The following figure shows the temporary file structure created on your host system when the build occurs. This Build Directory contains all the source files used during the build.

Again, for additional information the Yocto Project kernel's architecture and its branching strategy, see the Yocto Project Linux Kernel Development Manual. You can also reference the "Patching the Kernel" section for a detailed example that modifies the kernel.

4.1.2.2. Kernel Modification Workflow

This illustration and the following list summarizes the kernel modification general workflow.

  1. Set up your host development system to support development using the Yocto Project: See "The Linux Distribution" and "The Packages" sections both in the Yocto Project Quick Start for requirements.

  2. Establish a local copy of project files on your system: Having the Source Directory on your system gives you access to the build process and tools you need. For information on how to get these files, see the bulleted item "Yocto Project Release" earlier in this manual.

  3. Establish the temporary kernel source files: Temporary kernel source files are kept in the Build Directory created by the OpenEmbedded build system when you run BitBake. If you have never built the kernel you are interested in, you need to run an initial build to establish local kernel source files.

    If you are building an image for the first time, you need to get the build environment ready by sourcing the environment setup script. You also need to be sure two key configuration files (local.conf and bblayers.conf) are configured appropriately.

    The entire process for building an image is overviewed in the "Building an Image" section of the Yocto Project Quick Start. You might want to reference this information. You can find more information on BitBake in the user manual, which is found in the bitbake/doc/manual directory of the Source Directory.

    The build process supports several types of images to satisfy different needs. See the "Images" chapter in the Yocto Project Reference Manual for information on supported images.

  4. Make changes to the kernel source code if applicable: Modifying the kernel does not always mean directly changing source files. However, if you have to do this, you make the changes to the files in the Build directory.

  5. Make kernel configuration changes if applicable: If your situation calls for changing the kernel's configuration, you can use the yocto-kernel script or menuconfig to enable and disable kernel configurations. Using the script lets you interactively set up kernel configurations. Using menuconfig allows you to interactively develop and test the configuration changes you are making to the kernel. When saved, changes using menuconfig update the kernel's .config file. Try to resist the temptation of directly editing the .config file found in the Build Directory at tmp/sysroots/<machine-name>/kernel. Doing so, can produce unexpected results when the OpenEmbedded build system regenerates the configuration file.

    Once you are satisfied with the configuration changes made using menuconfig, you can directly compare the .config file against a saved original and gather those changes into a config fragment to be referenced from within the kernel's .bbappend file.

  6. Rebuild the kernel image with your changes: Rebuilding the kernel image applies your changes.

4.2. Application Development Workflow

Application development involves creating an application that you want to run on your target hardware, which is running a kernel image created using the OpenEmbedded build system. The Yocto Project provides an Application Development Toolkit (ADT) and stand-alone cross-development toolchains that facilitate quick development and integration of your application into its runtime environment. Using the ADT and toolchains, you can compile and link your application. You can then deploy your application to the actual hardware or to the QEMU emulator for testing. If you are familiar with the popular Eclipse™ IDE, you can use an Eclipse Yocto Plug-in to allow you to develop, deploy, and test your application all from within Eclipse.

While we strongly suggest using the ADT to develop your application, this option might not be best for you. If this is the case, you can still use pieces of the Yocto Project for your development process. However, because the process can vary greatly, this manual does not provide detail on the process.

4.2.1. Workflow Using the ADT and Eclipse

To help you understand how application development works using the ADT, this section provides an overview of the general development process and a detailed example of the process as it is used from within the Eclipse IDE.

The following illustration and list summarize the application development general workflow.

  1. Prepare the host system for the Yocto Project: See "The Linux Distribution" and "The Packages" sections both in the Yocto Project Quick Start for requirements.

  2. Secure the Yocto Project kernel target image: You must have a target kernel image that has been built using the OpenEmbedded build system.

    Depending on whether the Yocto Project has a pre-built image that matches your target architecture and where you are going to run the image while you develop your application (QEMU or real hardware), the area from which you get the image differs.

    • Download the image from machines if your target architecture is supported and you are going to develop and test your application on actual hardware.

    • Download the image from machines/qemu if your target architecture is supported and you are going to develop and test your application using the QEMU emulator.

    • Build your image if you cannot find a pre-built image that matches your target architecture. If your target architecture is similar to a supported architecture, you can modify the kernel image before you build it. See the "Patching the Kernel" section for an example.

    For information on pre-built kernel image naming schemes for images that can run on the QEMU emulator, see the "Downloading the Pre-Built Linux Kernel" section in the Yocto Project Quick Start.

  3. Install the ADT: The ADT provides a target-specific cross-development toolchain, the root filesystem, the QEMU emulator, and other tools that can help you develop your application. While it is possible to get these pieces separately, the ADT Installer provides an easy, inclusive method. You can get these pieces by running an ADT installer script, which is configurable. For information on how to install the ADT, see the "Using the ADT Installer" section in the Yocto Project Application Developer's Guide.

  4. If applicable, secure the target root filesystem and the Cross-development toolchain: If you choose not to install the ADT using the ADT Installer, you need to find and download the appropriate root filesystem and the cross-development toolchain.

    You can find the tarballs for the root filesystem in the same area used for the kernel image. Depending on the type of image you are running, the root filesystem you need differs. For example, if you are developing an application that runs on an image that supports Sato, you need to get a root filesystem that supports Sato.

    You can find the cross-development toolchains at toolchains. Be sure to get the correct toolchain for your development host and your target architecture. See the "Using a Cross-Toolchain Tarball" section in the Yocto Project Application Developer's Guide for information and the "Installing the Toolchain" in the Yocto Project Quick Start for information on finding and installing the correct toolchain based on your host development system and your target architecture.

  5. Create and build your application: At this point, you need to have source files for your application. Once you have the files, you can use the Eclipse IDE to import them and build the project. If you are not using Eclipse, you need to use the cross-development tools you have installed to create the image.

  6. Deploy the image with the application: If you are using the Eclipse IDE, you can deploy your image to the hardware or to QEMU through the project's preferences. If you are not using the Eclipse IDE, then you need to deploy the application to the hardware using other methods. Or, if you are using QEMU, you need to use that tool and load your image in for testing.

  7. Test and debug the application: Once your application is deployed, you need to test it. Within the Eclipse IDE, you can use the debugging environment along with the set of user-space tools installed along with the ADT to debug your application. Of course, the same user-space tools are available separately if you choose not to use the Eclipse IDE.

4.2.2. Working Within Eclipse

The Eclipse IDE is a popular development environment and it fully supports development using the Yocto Project.

Note

This release of the Yocto Project supports both the Juno and Indigo versions of the Eclipse IDE. Thus, the following information provides setup information for both versions.

When you install and configure the Eclipse Yocto Project Plug-in into the Eclipse IDE, you maximize your Yocto Project experience. Installing and configuring the Plug-in results in an environment that has extensions specifically designed to let you more easily develop software. These extensions allow for cross-compilation, deployment, and execution of your output into a QEMU emulation session as well as actual target hardware. You can also perform cross-debugging and profiling. The environment also supports a suite of tools that allows you to perform remote profiling, tracing, collection of power data, collection of latency data, and collection of performance data.

This section describes how to install and configure the Eclipse IDE Yocto Plug-in and how to use it to develop your application.

4.2.2.1. Setting Up the Eclipse IDE

To develop within the Eclipse IDE, you need to do the following:

  1. Install the optimal version of the Eclipse IDE.

  2. Configure the Eclipse IDE.

  3. Install the Eclipse Yocto Plug-in.

  4. Configure the Eclipse Yocto Plug-in.

Note

Do not install Eclipse from your distribution's package repository. Be sure to install Eclipse from the official Eclipse download site as directed in the next section.

4.2.2.1.1. Installing the Eclipse IDE

It is recommended that you have the Juno 4.2 version of the Eclipse IDE installed on your development system. However, if you currently have the Indigo 3.7.2 version installed and you do not want to upgrade the IDE, you can configure Indigo to work with the Yocto Project. See the "Configuring the Eclipse IDE (Indigo)" section.

If you do not have the Juno 4.2 Eclipse IDE installed, you can find the tarball at http://www.eclipse.org/downloads. From that site, choose the Eclipse Classic version particular to your development host. This version contains the Eclipse Platform, the Java Development Tools (JDT), and the Plug-in Development Environment.

Once you have downloaded the tarball, extract it into a clean directory. For example, the following commands unpack and install the downloaded Eclipse IDE tarball into a clean directory using the default name eclipse:

     $ cd ~
     $ tar -xzvf ~/Downloads/eclipse-SDK-4.2-linux-gtk-x86_64.tar.gz
                    

If you have the Indigo 3.7.2 Eclipse IDE already installed and you want to use that version, one issue exists that you need to be aware of regarding the Java Virtual machine’s garbage collection (GC) process. The GC process does not clean up the permanent generation space (PermGen). This space stores metadata descriptions of classes. The default value is set too small and it could trigger an out-of-memory error such as the following:

     Java.lang.OutOfMemoryError: PermGen space
                    

This error causes the application to hang.

To fix this issue, you can use the --vmargs option when you start the Indigo 3.7.2 Eclipse IDE to increase the size of the permanent generation space:

     eclipse --vmargs --XX:PermSize=256M
                    

4.2.2.1.2. Configuring the Eclipse IDE (Juno)

This section presents the steps needed to configure the Juno 4.2 Eclipse IDE. If you are using Indigo 3.7.2, see the "Configuring the Eclipse IDE (Indigo)".

Before installing and configuring the Eclipse Yocto Plug-in, you need to configure the Juno 4.2 Eclipse IDE. Follow these general steps:

  1. Start the Eclipse IDE.

  2. Make sure you are in your Workbench and select "Install New Software" from the "Help" pull-down menu.

  3. Select Juno - http://download.eclipse.org/releases/juno from the "Work with:" pull-down menu.

  4. Expand the box next to "Linux Tools" and select the LTTng - Linux Tracing Toolkit boxes.

  5. Expand the box next to "Mobile and Device Development" and select the following boxes:

    • C/C++ Remote Launch

    • Remote System Explorer End-user Runtime

    • Remote System Explorer User Actions

    • Target Management Terminal

    • TCF Remote System Explorer add-in

    • TCF Target Explorer

  6. Expand the box next to "Programming Languages" and select the Autotools Support for CDT and C/C++ Development Tools boxes.

  7. Complete the installation and restart the Eclipse IDE.

4.2.2.1.3. Configuring the Eclipse IDE (Indigo)

This section presents the steps needed to configure the Indigo 3.7.2 Eclipse IDE. If you are using Juno 4.2, see the "Configuring the Eclipse IDE (Juno)".

Before installing and configuring the Eclipse Yocto Plug-in, you need to configure the Indigo 3.7.2 Eclipse IDE. Follow these general steps:

  1. Start the Eclipse IDE.

  2. Make sure you are in your Workbench and select "Install New Software" from the "Help" pull-down menu.

  3. Select indigo - http://download.eclipse.org/releases/indigo from the "Work with:" pull-down menu.

  4. Expand the box next to "Programming Languages" and select the Autotools Support for CDT (incubation) and C/C++ Development Tools boxes.

  5. Expand the box next to "Linux Tools" and select the LTTng - Linux Tracing Toolkit(incubation) boxes.

  6. Complete the installation and restart the Eclipse IDE.

  7. After the Eclipse IDE restarts and from the Workbench, select "Install New Software" from the "Help" pull-down menu.

  8. Click the "Available Software Sites" link.

  9. Check the box next to http://download.eclipse.org/tm/updates/3.3 and click "OK".

  10. Select http://download.eclipse.org/tm/updates/3.3 from the "Work with:" pull-down menu.

  11. Check the box next to TM and RSE Main Features.

  12. Expand the box next to TM and RSE Optional Add-ons and select every item except RSE Unit Tests and RSE WinCE Services (incubation).

  13. Complete the installation and restart the Eclipse IDE.

  14. If necessary, select "Install New Software" from the "Help" pull-down menu so you can click the "Available Software Sites" link again.

  15. After clicking "Available Software Sites", check the box next to http://download.eclipse.org/tools/cdt/releases/indigo and click "OK".

  16. Select http://download.eclipse.orgtools/cdt/releases/indigo from the "Work with:" pull-down menu.

  17. Check the box next to CDT Main Features.

  18. Expand the box next to "CDT Optional Features" and select C/C++ Remote Launch and Target Communication Framework (incubation).

  19. Complete the installation and restart the Eclipse IDE.

4.2.2.1.4. Installing or Accessing the Eclipse Yocto Plug-in

You can install the Eclipse Yocto Plug-in into the Eclipse IDE one of two ways: use the Yocto Project's Eclipse Update site to install the pre-built plug-in, or build and install the plug-in from the latest source code. If you do not want to permanently install the plug-in but just want to try it out within the Eclipse environment, you can import the plug-in project from the Yocto Project's Source Repositories.

4.2.2.1.4.1. Installing the Pre-built Plug-in from the Yocto Project Eclipse Update Site

To install the Eclipse Yocto Plug-in from the update site, follow these steps:

  1. Start up the Eclipse IDE.

  2. In Eclipse, select "Install New Software" from the "Help" menu.

  3. Click "Add..." in the "Work with:" area.

  4. Enter http://downloads.yoctoproject.org/releases/eclipse-plugin/1.4.2 in the URL field and provide a meaningful name in the "Name" field.

  5. Click "OK" to have the entry added to the "Work with:" drop-down list.

  6. Select the entry for the plug-in from the "Work with:" drop-down list.

  7. Check the box next to Development tools and SDKs for Yocto Linux.

  8. Complete the remaining software installation steps and then restart the Eclipse IDE to finish the installation of the plug-in.

4.2.2.1.4.2. Installing the Plug-in Using the Latest Source Code

To install the Eclipse Yocto Plug-in from the latest source code, follow these steps:

  1. Open a shell and create a Git repository with:

         $ git clone git://git.yoctoproject.org/eclipse-poky yocto-eclipse
                                    

    For this example, the repository is named ~/yocto-eclipse.

  2. Change to the directory where you set up the Git repository:

         $ cd ~/yocto-eclipse
                                    
  3. Be sure you are in the right branch for your Git repository. For this release set the branch to dylan:

         $ git checkout -b dylan origin/dylan
                                    
  4. Change to the scripts directory within the Git repository:

         $ cd scripts
                                    
  5. Set up the local build environment by running the setup script:

         $ ./setup.sh
                                    
  6. When the script finishes execution, it prompts you with instructions on how to run the build.sh script, which is also in the scripts of the Git repository created earlier.

  7. Run the build.sh script as directed. Be sure to provide the name of the Git branch along with the Yocto Project release you are using. Here is an example that uses the dylan branch:

         $ ECLIPSE_HOME=/home/scottrif/yocto-eclipse/scripts/eclipse ./build.sh dylan dylan
                                    

    After running the script, the file org.yocto.sdk-<release>-<date>-archive.zip is in the current directory.

  8. If necessary, start the Eclipse IDE and be sure you are in the Workbench.

  9. Select "Install New Software" from the "Help" pull-down menu.

  10. Click "Add".

  11. Provide anything you want in the "Name" field.

  12. Click "Archive" and browse to the ZIP file you built in step seven. This ZIP file should not be "unzipped", and must be the *archive.zip file created by running the build.sh script.

  13. Click through the "Okay" buttons.

  14. Check the box next to the new entry in the installation window and complete the installation.

  15. Restart the Eclipse IDE if necessary.

At this point you should be able to configure the Eclipse Yocto Plug-in as described in the "Configuring the Eclipse Yocto Plug-in" section.

4.2.2.1.4.3. Importing the Plug-in Project into the Eclipse Environment

Importing the Eclipse Yocto Plug-in project from the Yocto Project source repositories is useful when you want to try out the latest plug-in from the tip of plug-in's development tree. It is important to understand when you import the plug-in you are not installing it into the Eclipse application. Rather, you are importing the project and just using it.

To import the plug-in project, follow these steps:

  1. Open a shell and create a Git repository with:

         $ git clone git://git.yoctoproject.org/eclipse-poky yocto-eclipse
                                    

    For this example, the repository is named ~/yocto-eclipse.

  2. In Eclipse, select "Import" from the "File" menu.

  3. Expand the "General" box and select "existing projects into workspace" and then click "Next".

  4. Select the root directory and browse to ~/yocto-eclipse/plugins.

  5. Three plug-ins exist: org.yocto.bc.ui, org.yocto.sdk.ide, and org.yocto.sdk.remotetools. Select and import all of them.

The left navigation pane in the Eclipse application shows the default projects. Right-click on one of these projects and run it as an Eclipse application to bring up a second instance of Eclipse IDE that has the Yocto Plug-in.

4.2.2.1.5. Configuring the Eclipse Yocto Plug-in

Configuring the Eclipse Yocto Plug-in involves setting the Cross Compiler options and the Target options. The configurations you choose become the default settings for all projects. You do have opportunities to change them later when you configure the project (see the following section).

To start, you need to do the following from within the Eclipse IDE:

  • Choose "Preferences" from the "Windows" menu to display the Preferences Dialog

  • Click "Yocto Project ADT"

4.2.2.1.5.1. Configuring the Cross-Compiler Options

To configure the Cross Compiler Options, you must select the type of toolchain, point to the toolchain, specify the sysroot location, and select the target architecture.

  • Selecting the Toolchain Type: Choose between Standalone pre-built toolchain and Build system derived toolchain for Cross Compiler Options.

    • Standalone Pre-built Toolchain: Select this mode when you are using a stand-alone cross-toolchain. For example, suppose you are an application developer and do not need to build a target image. Instead, you just want to use an architecture-specific toolchain on an existing kernel and target root filesystem.

    • Build System Derived Toolchain: Select this mode if the cross-toolchain has been installed and built as part of the Build Directory. When you select Build system derived toolchain, you are using the toolchain bundled inside the Build Directory.

  • Point to the Toolchain: If you are using a stand-alone pre-built toolchain, you should be pointing to the where it is installed. If you used the ADT Installer script and accepted the default installation directory, the toolchain will be installed in the /opt/poky/1.4.2 directory. Sections "Configuring and Running the ADT Installer Script" and "Using a Cross-Toolchain Tarball" in the Yocto Project Application Developer's Guide describe how to install a stand-alone cross-toolchain.

    If you are using a system-derived toolchain, the path you provide for the Toolchain Root Location field is the Build Directory. See the "Using BitBake and the Build Directory" section in the Yocto Project Application Developer's Guide for information on how to install the toolchain into the Build Directory.

  • Specify the Sysroot Location: This location is where the root filesystem for the target hardware resides. If you used the ADT Installer script and accepted the default installation directory, then the location is /opt/poky/<release>. Additionally, when you use the ADT Installer script, the same location is used for the QEMU user-space tools and the NFS boot process.

    If you used either of the other two methods to install the toolchain or did not accept the ADT Installer script's default installation directory, then the location of the sysroot filesystem depends on where you separately extracted and installed the filesystem.

    For information on how to install the toolchain and on how to extract and install the sysroot filesystem, see the "Installing the ADT and Toolchains" section.

  • Select the Target Architecture: The target architecture is the type of hardware you are going to use or emulate. Use the pull-down Target Architecture menu to make your selection. The pull-down menu should have the supported architectures. If the architecture you need is not listed in the menu, you will need to build the image. See the "Building an Image" section of the Yocto Project Quick Start for more information.

4.2.2.1.5.2. Configuring the Target Options

You can choose to emulate hardware using the QEMU emulator, or you can choose to run your image on actual hardware.

  • QEMU: Select this option if you will be using the QEMU emulator. If you are using the emulator, you also need to locate the kernel and specify any custom options.

    If you selected Build system derived toolchain, the target kernel you built will be located in the Build Directory in tmp/deploy/images directory. If you selected Standalone pre-built toolchain, the pre-built image you downloaded is located in the directory you specified when you downloaded the image.

    Most custom options are for advanced QEMU users to further customize their QEMU instance. These options are specified between paired angled brackets. Some options must be specified outside the brackets. In particular, the options serial, nographic, and kvm must all be outside the brackets. Use the man qemu command to get help on all the options and their use. The following is an example:

        serial ‘<-m 256 -full-screen>’
                                    

    Regardless of the mode, Sysroot is already defined as part of the Cross-Compiler Options configuration in the Sysroot Location: field.

  • External HW: Select this option if you will be using actual hardware.

Click the "OK" to save your plug-in configurations.

4.2.2.2. Creating the Project

You can create two types of projects: Autotools-based, or Makefile-based. This section describes how to create Autotools-based projects from within the Eclipse IDE. For information on creating Makefile-based projects in a terminal window, see the section "Using the Command Line" in the Yocto Project Application Developer's Guide.

To create a project based on a Yocto template and then display the source code, follow these steps:

  1. Select "Project" from the "File -> New" menu.

  2. Double click CC++.

  3. Double click C Project to create the project.

  4. Expand Yocto Project ADT Project.

  5. Select Hello World ANSI C Autotools Project. This is an Autotools-based project based on a Yocto template.

  6. Put a name in the Project name: field. Do not use hyphens as part of the name.

  7. Click "Next".

  8. Add information in the Author and Copyright notice fields.

  9. Be sure the License field is correct.

  10. Click "Finish".

  11. If the "open perspective" prompt appears, click "Yes" so that you in the C/C++ perspective.

  12. The left-hand navigation pane shows your project. You can display your source by double clicking the project's source file.

4.2.2.3. Configuring the Cross-Toolchains

The earlier section, "Configuring the Eclipse Yocto Plug-in", sets up the default project configurations. You can override these settings for a given project by following these steps:

  1. Select "Change Yocto Project Settings" from the "Project" menu. This selection brings up the Yocto Project Settings Dialog and allows you to make changes specific to an individual project.

    By default, the Cross Compiler Options and Target Options for a project are inherited from settings you provide using the Preferences Dialog as described earlier in the "Configuring the Eclipse Yocto Plug-in" section. The Yocto Project Settings Dialog allows you to override those default settings for a given project.

  2. Make your configurations for the project and click "OK". If you are running the Juno version of Eclipse, you can skip down to the next section where you build the project. If you are not working with Juno, you need to reconfigure the project as described in the next step.

  3. Select "Reconfigure Project" from the "Project" menu. This selection reconfigures the project by running autogen.sh in the workspace for your project. The script also runs libtoolize, aclocal, autoconf, autoheader, automake --a, and ./configure. Click on the "Console" tab beneath your source code to see the results of reconfiguring your project.

4.2.2.4. Building the Project

To build the project in Juno, right click on the project in the navigator pane and select "Build Project". If you are not running Juno, select "Build Project" from the "Project" menu. The console should update and you can note the cross-compiler you are using.

4.2.2.5. Starting QEMU in User-Space NFS Mode

To start the QEMU emulator from within Eclipse, follow these steps:

  1. Expose and select "External Tools" from the "Run" menu. Your image should appear as a selectable menu item.

  2. Select your image from the menu to launch the emulator in a new window.

  3. If needed, enter your host root password in the shell window at the prompt. This sets up a Tap 0 connection needed for running in user-space NFS mode.

  4. Wait for QEMU to launch.

  5. Once QEMU launches, you can begin operating within that environment. For example, you could determine the IP Address for the user-space NFS by using the ifconfig command.

4.2.2.6. Deploying and Debugging the Application

Once the QEMU emulator is running the image, you can deploy your application using the Eclipse IDE and use then use the emulator to perform debugging. Follow these steps to deploy the application.

  1. Select "Debug Configurations..." from the "Run" menu.

  2. In the left area, expand C/C++Remote Application.

  3. Locate your project and select it to bring up a new tabbed view in the Debug Configurations Dialog.

  4. Enter the absolute path into which you want to deploy the application. Use the "Remote Absolute File Path for C/C++Application:" field. For example, enter /usr/bin/<programname>.

  5. Click on the "Debugger" tab to see the cross-tool debugger you are using.

  6. Click on the "Main" tab.

  7. Create a new connection to the QEMU instance by clicking on "new".

  8. Select TCF, which means Target Communication Framework.

  9. Click "Next".

  10. Clear out the "host name" field and enter the IP Address determined earlier.

  11. Click "Finish" to close the New Connections Dialog.

  12. Use the drop-down menu now in the "Connection" field and pick the IP Address you entered.

  13. Click "Run" to bring up a login screen and login.

  14. Accept the debug perspective.

4.2.2.7. Running User-Space Tools

As mentioned earlier in the manual, several tools exist that enhance your development experience. These tools are aids in developing and debugging applications and images. You can run these user-space tools from within the Eclipse IDE through the "YoctoTools" menu.

Once you pick a tool, you need to configure it for the remote target. Every tool needs to have the connection configured. You must select an existing TCF-based RSE connection to the remote target. If one does not exist, click "New" to create one.

Here are some specifics about the remote tools:

  • OProfile: Selecting this tool causes the oprofile-server on the remote target to launch on the local host machine. The oprofile-viewer must be installed on the local host machine and the oprofile-server must be installed on the remote target, respectively, in order to use. You must compile and install the oprofile-viewer from the source code on your local host machine. Furthermore, in order to convert the target's sample format data into a form that the host can use, you must have OProfile version 0.9.4 or greater installed on the host.

    You can locate both the viewer and server from http://git.yoctoproject.org/cgit/cgit.cgi/oprofileui/. You can also find more information on setting up and using this tool in the "OProfile" section of the Yocto Project Profiling and Tracing Manual.

    Note

    The oprofile-server is installed by default on the core-image-sato-sdk image.
  • Lttng2.0 ust trace import: Selecting this tool transfers the remote target's Lttng tracing data back to the local host machine and uses the Lttng Eclipse plug-in to graphically display the output. For information on how to use Lttng to trace an application, see http://lttng.org/documentation and the "LTTng (Linux Trace Toolkit, next generation)" section, which is in the Yocto Project Profiling and Tracing Manual.

    Note

    Do not use Lttng-user space (legacy) tool. This tool no longer has any upstream support.

    Before you use the Lttng2.0 ust trace import tool, you need to setup the Lttng Eclipse plug-in and create a Tracing project. Do the following:

    1. Select "Open Perspective" from the "Window" menu and then select "Tracing".

    2. Click "OK" to change the Eclipse perspective into the Tracing perspective.

    3. Create a new Tracing project by selecting "Project" from the "File -> New" menu.

    4. Choose "Tracing Project" from the "Tracing" menu.

    5. Generate your tracing data on the remote target.

    6. Select "Lttng2.0 ust trace import" from the "Yocto Project Tools" menu to start the data import process.

    7. Specify your remote connection name.

    8. For the Ust directory path, specify the location of your remote tracing data. Make sure the location ends with ust (e.g. /usr/mysession/ust).

    9. Click "OK" to complete the import process. The data is now in the local tracing project you created.

    10. Right click on the data and then use the menu to Select "Generic CTF Trace" from the "Trace Type... -> Common Trace Format" menu to map the tracing type.

    11. Right click the mouse and select "Open" to bring up the Eclipse Lttng Trace Viewer so you view the tracing data.

  • PowerTOP: Selecting this tool runs PowerTOP on the remote target machine and displays the results in a new view called PowerTOP.

    The "Time to gather data(sec):" field is the time passed in seconds before data is gathered from the remote target for analysis.

    The "show pids in wakeups list:" field corresponds to the -p argument passed to PowerTOP.

  • LatencyTOP and Perf: LatencyTOP identifies system latency, while Perf monitors the system's performance counter registers. Selecting either of these tools causes an RSE terminal view to appear from which you can run the tools. Both tools refresh the entire screen to display results while they run. For more information on setting up and using perf, see the "perf" section in the Yocto Project Profiling and Tracing Manual. For information on LatencyTOP, see the LatencyTOP website.

4.2.2.8. Customizing an Image Using a BitBake Commander Project and Hob

Within the Eclipse IDE, you can create a Yocto BitBake Commander project, edit the Metadata, and then use Hob to build a customized image all within one IDE.

4.2.2.8.1. Creating the Yocto BitBake Commander Project

To create a Yocto BitBake Commander project, follow these steps:

  1. Select "Other" from the "Window -> Open Perspective" menu and then choose "Bitbake Commander".

  2. Click "OK" to change the perspective to Bitbake Commander.

  3. Select "Project" from the "File -> New" menu to create a new Yocto Bitbake Commander project.

  4. Choose "New Yocto Project" from the "Yocto Project Bitbake Commander" menu and click "Next".

  5. Enter the Project Name and choose the Project Location. The Yocto project's Metadata files will be put under the directory <project_location>/<project_name>. If that directory does not exist, you need to check the "Clone from Yocto Git Repository" box, which would execute a git clone command to get the project's Metadata files.

  6. Select Finish to create the project.

4.2.2.8.2. Editing the Metadata

After you create the Yocto Bitbake Commander project, you can modify the Metadata files by opening them in the project. When editing recipe files (.bb files), you can view BitBake variable values and information by hovering the mouse pointer over the variable name and waiting a few seconds.

To edit the Metadata, follow these steps:

  1. Select your Yocto Bitbake Commander project.

  2. Select "BitBake Recipe" from the "File -> New -> Yocto BitBake Commander" menu to open a new recipe wizard.

  3. Point to your source by filling in the "SRC_URL" field. For example, you can add a recipe to your Source Directory by defining "SRC_URL" as follows:

         ftp://ftp.gnu.org/gnu/m4/m4-1.4.9.tar.gz
                                
  4. Click "Populate" to calculate the archive md5, sha256, license checksum values and to auto-generate the recipe filename.

  5. Fill in the "Description" field.

  6. Be sure values for all required fields exist.

  7. Click "Finish".

4.2.2.8.3. Building and Customizing the Image Using Hob

To build and customize the image using Hob from within the Eclipse IDE, follow these steps:

  1. Select your Yocto Bitbake Commander project.

  2. Select "Launch Hob" from the "Project" menu.

  3. Enter the Build Directory where you want to put your final images.

  4. Click "OK" to launch Hob.

  5. Use Hob to customize and build your own images. For information on Hob, see the Hob Project Page on the Yocto Project website.

4.2.3. Workflow Using Stand-Alone Cross-Development Toolchains

If you want to develop an application without prior installation of the ADT, you still can employ the Cross Development Toolchain, the QEMU emulator, and a number of supported target image files. You just need to follow these general steps:

  1. Install the cross-development toolchain for your target hardware: For information on how to install the toolchain, see the "Using a Cross-Toolchain Tarball" section in the Yocto Project Application Developer's Guide.

  2. Download the Target Image: The Yocto Project supports several target architectures and has many pre-built kernel images and root filesystem images.

    If you are going to develop your application on hardware, go to the machines download area and choose a target machine area from which to download the kernel image and root filesystem. This download area could have several files in it that support development using actual hardware. For example, the area might contain .hddimg files that combine the kernel image with the filesystem, boot loaders, and so forth. Be sure to get the files you need for your particular development process.

    If you are going to develop your application and then run and test it using the QEMU emulator, go to the machines/qemu download area. From this area, go down into the directory for your target architecture (e.g. qemux86_64 for an Intel®-based 64-bit architecture). Download kernel, root filesystem, and any other files you need for your process.

    Note

    In order to use the root filesystem in QEMU, you need to extract it. See the "Extracting the Root Filesystem" section for information on how to extract the root filesystem.
  3. Develop and Test your Application: At this point, you have the tools to develop your application. If you need to separately install and use the QEMU emulator, you can go to QEMU Home Page to download and learn about the emulator.

4.3. Modifying Temporary Source Code

You might find it helpful during development to modify the temporary source code used by recipes to build packages. For example, suppose you are developing a patch and you need to experiment a bit to figure out your solution. After you have initially built the package, you can iteratively tweak the source code, which is located in the Build Directory, and then you can force a re-compile and quickly test your altered code. Once you settle on a solution, you can then preserve your changes in the form of patches. You can accomplish these steps all within either a Quilt or Git workflow.

4.3.1. Finding the Temporary Source Code

During a build, the unpacked temporary source code used by recipes to build packages is available in the Build Directory as defined by the S variable. Below is the default value for the S variable as defined in the meta/conf/bitbake.conf configuration file in the Source Directory:

     S = ${WORKDIR}/${BP}
            

You should be aware that many recipes override the S variable. For example, recipes that fetch their source from Git usually set S to ${WORKDIR}/git.

Note

The BP represents the base recipe name, which consists of the name and version:
     BP = ${BPN}-${PV}
                

The path to the work directory for the recipe (WORKDIR) depends on the recipe name and the architecture of the target device. For example, here is the work directory for recipes and resulting packages that are not device-dependent:

     ${TMPDIR}/work/${PACKAGE_ARCH}-poky-${TARGET_OS}/${PN}-${PV}-${PR}
            

Let's look at an example without variables. Assuming a top-level Source Directory named poky and a default Build Directory of poky/build, the following is the work directory for the acl recipe that creates the acl package:

     ~/poky/build/tmp/work/i586-poky-linux/acl-2.2.51-r3
            

If your resulting package is dependent on the target device, the work directory varies slightly:

     ${TMPDIR}/work/${MACHINE}-poky-${TARGET_OS}/${PN}-${PV}-${PR}
            

Again, assuming top-level Source Directory named poky and a default Build Directory of poky/build, the following are the work and temporary source directories, respectively, for the acl package that is being built for a MIPS-based device:

     ~/poky/build/tmp/work/mips-poky-linux/acl-2.2.51-r2
     ~/poky/build/tmp/work/mips-poky-linux/acl-2.2.51-r2/acl-2.2.51
            

Note

To better understand how the OpenEmbedded build system resolves directories during the build process, see the glossary entries for the WORKDIR, TMPDIR, TOPDIR, PACKAGE_ARCH, TARGET_OS, PN, PV, and PR variables in the Yocto Project Reference Manual.

Now that you know where to locate the directory that has the temporary source code, you can use a Quilt or Git workflow to make your edits, test the changes, and preserve the changes in the form of patches.

4.3.2. Using a Quilt Workflow

Quilt is a powerful tool that allows you to capture source code changes without having a clean source tree. This section outlines the typical workflow you can use to modify temporary source code, test changes, and then preserve the changes in the form of a patch all using Quilt.

Follow these general steps:

  1. Find the Source Code: The temporary source code used by the OpenEmbedded build system is kept in the Build Directory. See the "Finding the Temporary Source Code" section to learn how to locate the directory that has the temporary source code for a particular package.

  2. Change Your Working Directory: You need to be in the directory that has the temporary source code. That directory is defined by the S variable.

  3. Create a New Patch: Before modifying source code, you need to create a new patch. To create a new patch file, use quilt new as below:

         $ quilt new my_changes.patch
                        
  4. Notify Quilt and Add Files: After creating the patch, you need to notify Quilt about the files you plan to edit. You notify Quilt by adding the files to the patch you just created:

         $ quilt add file1.c file2.c file3.c
                        

  5. Edit the Files: Make your changes in the temporary source code to the files you added to the patch.

  6. Test Your Changes: Once you have modified the source code, the easiest way to test your changes is by calling the compile task as shown in the following example:

         $ bitbake -c compile -f <name_of_package>
                        

    The -f or --force option forces the specified task to execute. If you find problems with your code, you can just keep editing and re-testing iteratively until things work as expected.

    Note

    All the modifications you make to the temporary source code disappear once you -c clean or -c cleanall with BitBake for the package. Modifications will also disappear if you use the rm_work feature as described in the "Building an Image" section of the Yocto Project Quick Start.
  7. Generate the Patch: Once your changes work as expected, you need to use Quilt to generate the final patch that contains all your modifications.

         $ quilt refresh
                        

    At this point, the my_changes.patch file has all your edits made to the file1.c, file2.c, and file3.c files.

    You can find the resulting patch file in the patches/ subdirectory of the source (S) directory.

  8. Copy the Patch File: For simplicity, copy the patch file into a directory named files, which you can create in the same directory that holds the recipe (.bb) file or the append (.bbappend) file. Placing the patch here guarantees that the OpenEmbedded build system will find the patch. Next, add the patch into the SRC_URI of the recipe. Here is an example:

         SRC_URI += "file://my_changes.patch"
                        
  9. Increment the Recipe Revision Number: Finally, don't forget to 'bump' the PR value in the recipe since the resulting packages have changed.

4.3.3. Using a Git Workflow

Git is an even more powerful tool that allows you to capture source code changes without having a clean source tree. This section outlines the typical workflow you can use to modify temporary source code, test changes, and then preserve the changes in the form of a patch all using Git. For general information on Git as it is used in the Yocto Project, see the "Git" section.

Note

This workflow uses Git only for its ability to manage local changes to the source code and produce patches independent of any version control system used with the Yocto Project.

Follow these general steps:

  1. Find the Source Code: The temporary source code used by the OpenEmbedded build system is kept in the Build Directory. See the "Finding the Temporary Source Code" section to learn how to locate the directory that has the temporary source code for a particular package.

  2. Change Your Working Directory: You need to be in the directory that has the temporary source code. That directory is defined by the S variable.

  3. If needed, initialize a Git Repository: If the recipe you are working with does not use a Git fetcher, you need to set up a Git repository as follows:

         $ git init
         $ git add *
         $ git commit -m "initial revision"
                        

    The above Git commands initialize a Git repository that is based on the files in your current working directory, stage all the files, and commit the files. At this point, your Git repository is aware of all the source code files. Any edits you now make to files can be committed later and will be tracked by Git.

  4. Edit the Files: Make your changes to the temporary source code.

  5. Test Your Changes: Once you have modified the source code, the easiest way to test your changes is by calling the compile task as shown in the following example:

         $ bitbake -c compile -f <name_of_package>
                        

    The -f or --force option forces the specified task to execute. If you find problems with your code, you can just keep editing and re-testing iteratively until things work as expected.

    Note

    All the modifications you make to the temporary source code disappear once you -c clean, -c cleansstate, or -c cleanall with BitBake for the package. Modifications will also disappear if you use the rm_work feature as described in the "Building an Image" section of the Yocto Project Quick Start.
  6. See the List of Files You Changed: Use the git status command to see what files you have actually edited. The ability to have Git track the files you have changed is an advantage that this workflow has over the Quilt workflow. Here is the Git command to list your changed files:

         $ git status
                        
  7. Stage the Modified Files: Use the git add command to stage the changed files so they can be committed as follows:

         $ git add file1.c file2.c file3.c
                        
  8. Commit the Staged Files and View Your Changes: Use the git commit command to commit the changes to the local repository. Once you have committed the files, you can use the git log command to see your changes:

         $ git commit -m "<commit-summary-message>"
         $ git log
                        

    Note

    The name of the patch file created in the next step is based on your commit-summary-message.
  9. Generate the Patch: Once the changes are committed, use the git format-patch command to generate a patch file:

         $ git format-patch -1
                        

    Specifying "-1" causes Git to generate the patch file for the most recent commit.

    At this point, the patch file has all your edits made to the file1.c, file2.c, and file3.c files. You can find the resulting patch file in the current directory and it is named according to the git commit summary line. The patch file ends with .patch.

  10. Copy the Patch File: For simplicity, copy the patch file into a directory named files, which you can create in the same directory that holds the recipe (.bb) file or the append (.bbappend) file. Placing the patch here guarantees that the OpenEmbedded build system will find the patch. Next, add the patch into the SRC_URI of the recipe. Here is an example:

         SRC_URI += "file://0001-<commit-summary-message>.patch"
                        
  11. Increment the Recipe Revision Number: Finally, don't forget to 'bump' the PR value in the recipe since the resulting packages have changed.

4.4. Image Development Using Hob

The Hob is a graphical user interface for the OpenEmbedded build system, which is based on BitBake. You can use the Hob to build custom operating system images within the Yocto Project build environment. Hob simply provides a friendly interface over the build system used during development. In other words, building images with the Hob lets you take care of common build tasks more easily.

For a better understanding of Hob, see the project page at http://www.yoctoproject.org/tools-resources/projects/hob on the Yocto Project website. If you follow the "Documentation" link from the Hob page, you will find a short introductory training video on Hob. The following lists some features of Hob:

  • You can setup and run Hob using these commands:

         $ source oe-init-build-env
         $ hob
                
  • You can set the MACHINE for which you are building the image.

  • You can modify various policy settings such as the package format with which to build, the parallelism BitBake uses, whether or not to build an external toolchain, and which host to build against.

  • You can manage layers.

  • You can select a base image and then add extra packages for your custom build.

  • You can launch and monitor the build from within Hob.

4.5. Using a Development Shell

When debugging certain commands or even when just editing packages, devshell can be a useful tool. When you invoke devshell, source files are extracted into your working directory and patches are applied. Then, a new terminal is opened and you are placed in the working directory. In the new terminal, all the OpenEmbedded build-related environment variables are still defined so you can use commands such as configure and make. The commands execute just as if the OpenEmbedded build system were executing them. Consequently, working this way can be helpful when debugging a build or preparing software to be used with the OpenEmbedded build system.

Following is an example that uses devshell on a target named matchbox-desktop:

     $ bitbake matchbox-desktop -c devshell
        

This command spawns a terminal with a shell prompt within the OpenEmbedded build environment. The OE_TERMINAL variable controls what type of shell is opened.

For spawned terminals, the following occurs:

  • The PATH variable includes the cross-toolchain.

  • The pkgconfig variables find the correct .pc files.

  • The configure command finds the Yocto Project site files as well as any other necessary files.

Within this environment, you can run configure or compile commands as if they were being run by the OpenEmbedded build system itself. As noted earlier, the working directory also automatically changes to the Source Directory (S).

When you are finished, you just exit the shell or close the terminal window.

Note

It is worth remembering that when using devshell you need to use the full compiler name such as arm-poky-linux-gnueabi-gcc instead of just using gcc. The same applies to other applications such as binutils, libtool and so forth. BitBake sets up environment variables such as CC to assist applications, such as make to find the correct tools.

It is also worth noting that devshell still works over X11 forwarding and similar situations.

Chapter 5. Common Tasks

5.1. Understanding and Creating Layers
5.1.1. Layers
5.1.2. Creating Your Own Layer
5.1.3. Enabling Your Layer
5.1.4. Using .bbappend Files
5.1.5. Prioritizing Your Layer
5.1.6. Managing Layers
5.1.7. Creating a General Layer Using the yocto-layer Script
5.2. Customizing Images
5.2.1. Customizing Images Using Custom .bb Files
5.2.2. Customizing Images Using Custom Package Groups
5.2.3. Customizing Images Using Custom IMAGE_FEATURES and EXTRA_IMAGE_FEATURES
5.2.4. Customizing Images Using local.conf
5.3. Writing a Recipe to Add a Package to Your Image
5.3.1. Single .c File Package (Hello World!)
5.3.2. Autotooled Package
5.3.3. Makefile-Based Package
5.3.4. Splitting an Application into Multiple Packages
5.3.5. Post-Installation Scripts
5.4. Adding a New Machine
5.4.1. Adding the Machine Configuration File
5.4.2. Adding a Kernel for the Machine
5.4.3. Adding a Formfactor Configuration File
5.5. Working With Libraries
5.5.1. Including Static Library Files
5.5.2. Combining Multiple Versions of Library Files into One Image
5.5.3. Installing Multiple Versions of the Same Library
5.6. Configuring the Kernel
5.6.1. Using  menuconfig
5.6.2. Creating Configuration Fragments
5.6.3. Fine-Tuning the Kernel Configuration File
5.7. Patching the Kernel
5.7.1. Create a Layer for your Changes
5.7.2. Finding the Kernel Source Code
5.7.3. Creating the Patch
5.7.4. Set Up Your Layer for the Build
5.7.5. Set Up for the Build
5.7.6. Build the Modified QEMU Kernel Image
5.7.7. Boot the Image and Verify Your Changes
5.8. Creating Your Own Distribution
5.9. Building a Tiny System
5.9.1. Overview
5.9.2. Goals and Guiding Principles
5.9.3. Understand What Gives Your Image Size
5.9.4. Trim the Root Filesystem
5.9.5. Trim the Kernel
5.9.6. Look for Other Ways to Minimize Size
5.9.7. Iterate on the Process
5.10. Working with Packages
5.10.1. Incrementing a Package Revision Number
5.10.2. Handling a Package Name Alias
5.10.3. Handling Optional Module Packaging
5.10.4. Setting Up Runtime Package Management
5.10.5. Testing Packages With ptest
5.11. Building Software from an External Source
5.12. Selecting an Initialization Manager
5.12.1. Using systemd Exclusively
5.12.2. Using systemd for the Main Image and Using SysVinit for the Rescue Image
5.13. Excluding Recipes From the Build
5.14. Using an External SCM
5.15. Creating a Read-Only Root Filesystem
5.15.1. Creating the Root Filesystem
5.15.2. Post-Installation Scripts
5.15.3. Areas With Write Access
5.16. Debugging With the GNU Project Debugger (GDB) Remotely
5.16.1. Set Up the Cross-Development Debugging Environment
5.16.2. Launch Gdbserver on the Target
5.16.3. Launch GDB on the Host Computer
5.16.4. Connect to the Remote GDB Server
5.16.5. Use the Debugger
5.17. Profiling with OProfile
5.17.1. Profiling on the Target
5.17.2. Using OProfileUI
5.18. Maintaining Open Source License Compliance During Your Product's Lifecycle
5.18.1. Providing the Source Code
5.18.2. Providing License Text
5.18.3. Providing Compilation Scripts and Source Code Modifications

This chapter describes fundamental procedures such as creating layers, adding new software packages, extending or customizing images, porting work to new hardware (adding a new machine), and so forth. You will find the procedures documented here occur often in the develop cycle using the Yocto Project.

5.1. Understanding and Creating Layers

The OpenEmbedded build system supports organizing Metadata into multiple layers. Layers allow you to isolate different types of customizations from each other. You might find it tempting to keep everything in one layer when working on a single project. However, the more modular you organize your Metadata, the easier it is to cope with future changes.

To illustrate how layers are used to keep things modular, consider machine customizations. These types of customizations typically reside in a special layer, rather than a general layer, called a Board Specific Package (BSP) Layer. Furthermore, the machine customizations should be isolated from recipes and Metadata that support a new GUI environment, for example. This situation gives you a couple of layers: one for the machine configurations, and one for the GUI environment. It is important to understand, however, that the BSP layer can still make machine-specific additions to recipes within the GUI environment layer without polluting the GUI layer itself with those machine-specific changes. You can accomplish this through a recipe that is a BitBake append (.bbappend) file, which is described later in this section.

5.1.1. Layers

The Source Directory contains both general layers and BSP layers right out of the box. You can easily identify layers that ship with a Yocto Project release in the Source Directory by their folder names. Folders that are layers begin with the string meta.

Note

It is not a requirement that a layer begins with the string meta.

For example, when you set up the Source Directory structure, you will see several layers: meta, meta-hob, meta-skeleton, meta-yocto, and meta-yocto-bsp. Each of these folders is a layer.

Furthermore, if you set up a local copy of the meta-intel Git repository and then explore the folder of that general layer, you will discover many BSP layers inside. For more information on BSP layers, see the "BSP Layers" section in the Yocto Project Board Support Package (BSP) Developer's Guide.

5.1.2. Creating Your Own Layer

It is very easy to create your own layers to use with the OpenEmbedded build system. The Yocto Project ships with scripts that speed up creating general layers and BSP layers. This section describes the steps you perform by hand to create a layer so that you can better understand them. For information about the layer-creation scripts, see the "Creating a New BSP Layer Using the yocto-bsp Script" section in the Yocto Project Board Support Package (BSP) Developer's Guide and the "Creating a General Layer Using the yocto-layer Script" section further down in this manual.

Follow these general steps to create your layer:

  1. Check Existing Layers: Before creating a new layer, you should be sure someone has not already created a layer containing the Metadata you need. You can see the OpenEmbedded Metadata Index for a list of layers from the OpenEmbedded community that can be used in the Yocto Project.

  2. Create a Directory: Create the directory for your layer. While not strictly required, prepend the name of the folder with the string meta-. For example:

         meta-mylayer
         meta-GUI_xyz
         meta-mymachine
                            

  3. Create a Layer Configuration File: Inside your new layer folder, you need to create a conf/layer.conf file. It is easiest to take an existing layer configuration file and copy that to your layer's conf directory and then modify the file as needed.

    The meta-yocto-bsp/conf/layer.conf file demonstrates the required syntax:

         # We have a conf and classes directory, add to BBPATH
         BBPATH .= ":${LAYERDIR}"
    
         # We have recipes-* directories, add to BBFILES
         BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
                     ${LAYERDIR}/recipes-*/*/*.bbappend"
    
         BBFILE_COLLECTIONS += "yoctobsp"
         BBFILE_PATTERN_yoctobsp = "^${LAYERDIR}/"
         BBFILE_PRIORITY_yoctobsp = "5"
                            

    Here is an explanation of the example:

    • The configuration and classes directory is appended to BBPATH.

      Note

      All non-distro layers, which include all BSP layers, are expected to append the layer directory to the BBPATH. On the other hand, distro layers, such as meta-yocto, can choose to enforce their own precedence over BBPATH. For an example of that syntax, see the layer.conf file for the meta-yocto layer.
    • The recipes for the layers are appended to BBFILES.

    • The BBFILE_COLLECTIONS variable is then appended with the layer name.

    • The BBFILE_PATTERN variable is set to a regular expression and is used to match files from BBFILES into a particular layer. In this case, LAYERDIR is used to make BBFILE_PATTERN match within the layer's path.

    • The BBFILE_PRIORITY variable then assigns a priority to the layer. Applying priorities is useful in situations where the same package might appear in multiple layers and allows you to choose what layer should take precedence.

    Note the use of the LAYERDIR variable, which expands to the directory of the current layer.

    Through the use of the BBPATH variable, BitBake locates .bbclass files, configuration files, and files that are included with include and require statements. For these cases, BitBake uses the first file that matches the name found in BBPATH. This is similar to the way the PATH variable is used for binaries. We recommend, therefore, that you use unique .bbclass and configuration filenames in your custom layer.

  4. Add Content: Depending on the type of layer, add the content. If the layer adds support for a machine, add the machine configuration in a conf/machine/ file within the layer. If the layer adds distro policy, add the distro configuration in a conf/distro/ file with the layer. If the layer introduces new recipes, put the recipes you need in recipes-* subdirectories within the layer.

    Note

    In order to be compliant with the Yocto Project, a layer must contain a README file.

To create layers that are easier to maintain, you should consider the following:

  • Avoid "overlaying" entire recipes from other layers in your configuration. In other words, do not copy an entire recipe into your layer and then modify it. Use .bbappend files to override the parts of the recipe you need to modify.

  • Avoid duplicating include files. Use .bbappend files for each recipe that uses an include file. Or, if you are introducing a new recipe that requires the included file, use the path relative to the original layer directory to refer to the file. For example, use require recipes-core/somepackage/somefile.inc instead of require somefile.inc. If you're finding you have to overlay the include file, it could indicate a deficiency in the include file in the layer to which it originally belongs. If this is the case, you need to address that deficiency instead of overlaying the include file. For example, consider how Qt 4 database support plug-ins are configured. The Source Directory does not have MySQL or PostgreSQL, however OpenEmbedded's layer meta-oe does. Consequently, meta-oe uses .bbappend files to modify the QT_SQL_DRIVER_FLAGS variable to enable the appropriate plugins. This variable was added to the qt4.inc include file in the Source Directory specifically to allow the meta-oe layer to be able to control which plugins are built.

We also recommend the following:

  • Store custom layers in a Git repository that uses the meta-<layer_name> format.

  • Clone the repository alongside other meta directories in the Source Directory.

Following these recommendations keeps your Source Directory and its configuration entirely inside the Yocto Project's core base.

5.1.3. Enabling Your Layer

Before the OpenEmbedded build system can use your new layer, you need to enable it. To enable your layer, simply add your layer's path to the BBLAYERS variable in your conf/bblayers.conf file, which is found in the Build Directory. The following example shows how to enable a layer named meta-mylayer:

     LCONF_VERSION = "6"

     BBPATH = "${TOPDIR}"
     BBFILES ?= ""

     BBLAYERS ?= " \
       $HOME/poky/meta \
       $HOME/poky/meta-yocto \
       $HOME/poky/meta-yocto-bsp \
       $HOME/poky/meta-mylayer \
       "

     BBLAYERS_NON_REMOVABLE ?= " \
       $HOME/poky/meta \
       $HOME/poky/meta-yocto \
       "
                

BitBake parses each conf/layer.conf file as specified in the BBLAYERS variable within the conf/bblayers.conf file. During the processing of each conf/layer.conf file, BitBake adds the recipes, classes and configurations contained within the particular layer to the source directory.

5.1.4. Using .bbappend Files

Recipes used to append Metadata to other recipes are called BitBake append files. BitBake append files use the .bbappend file type suffix, while the corresponding recipes to which Metadata is being appended use the .bb file type suffix.

A .bbappend file allows your layer to make additions or changes to the content of another layer's recipe without having to copy the other recipe into your layer. Your .bbappend file resides in your layer, while the main .bb recipe file to which you are appending Metadata resides in a different layer.

Append files must have the same root names as their corresponding recipes. For example, the append file someapp_1.4.2.bbappend must apply to someapp_1.4.2.bb. This means the original recipe and append file names are version number-specific. If the corresponding recipe is renamed to update to a newer version, the corresponding .bbappend file must be renamed as well. During the build process, BitBake displays an error on starting if it detects a .bbappend file that does not have a corresponding recipe with a matching name. See the BB_DANGLINGAPPENDS_WARNONLY variable for information on how to handle this error.

Being able to append information to an existing recipe not only avoids duplication, but also automatically applies recipe changes in a different layer to your layer. If you were copying recipes, you would have to manually merge changes as they occur.

As an example, consider the main formfactor recipe and a corresponding formfactor append file both from the Source Directory. Here is the main formfactor recipe, which is named formfactor_0.0.bb and located in the "meta" layer at meta/recipes-bsp/formfactor:

     DESCRIPTION = "Device formfactor information"
     SECTION = "base"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COREBASE}/LICENSE;md5=3f40d7994397109285ec7b81fdeb3b58 \
                         file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
     PR = "r21"

     SRC_URI = "file://config file://machconfig"
     S = "${WORKDIR}"

     PACKAGE_ARCH = "${MACHINE_ARCH}"
     INHIBIT_DEFAULT_DEPS = "1"

     do_install() {
     	# Only install file if it has a contents
             install -d ${D}${sysconfdir}/formfactor/
             install -m 0644 ${S}/config ${D}${sysconfdir}/formfactor/
     	if [ -s "${S}/machconfig" ]; then
     	        install -m 0644 ${S}/machconfig ${D}${sysconfdir}/formfactor/
     	fi
     }          

In the main recipe, note the SRC_URI variable, which tells the OpenEmbedded build system where to find files during the build.

Following is the append file, which is named formfactor_0.0.bbappend and is from the Crown Bay BSP Layer named meta-intel/meta-crownbay. The file is in recipes-bsp/formfactor:

     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

     PRINC := "${@int(PRINC) + 2}"
                

By default, the build system uses the FILESPATH variable to locate files. This append file extends the locations by setting the FILESEXTRAPATHS variable. Setting this variable in the .bbappend file is the most reliable and recommended method for adding directories to the search path used by the build system to find files.

The statement in this example extends the directories to include ${THISDIR}/${PN}, which resolves to a directory named formfactor in the same directory in which the append file resides (i.e. meta-intel/meta-crownbay/recipes-bsp/formfactor/formfactor. This implies that you must have the supporting directory structure set up that will contain any files or patches you will be including from the layer.

Using the immediate expansion assignment operator := is important because of the reference to THISDIR. The trailing colon character is important as it ensures that items in the list remain colon-separated.

Note

BitBake automatically defines the THISDIR variable. You should never set this variable yourself. Using _prepend ensures your path will be searched prior to other paths in the final list.

Also, not all append files add extra files. Many append files simply exist to add build options (e.g. systemd). For these cases, it is not necessary to use the "_prepend" part of the statement.

5.1.5. Prioritizing Your Layer

Each layer is assigned a priority value. Priority values control which layer takes precedence if there are recipe files with the same name in multiple layers. For these cases, the recipe file from the layer with a higher priority number takes precedence. Priority values also affect the order in which multiple .bbappend files for the same recipe are applied. You can either specify the priority manually, or allow the build system to calculate it based on the layer's dependencies.

To specify the layer's priority manually, use the BBFILE_PRIORITY variable. For example:

     BBFILE_PRIORITY_mylayer = "1"
                

Note

It is possible for a recipe with a lower version number PV in a layer that has a higher priority to take precedence.

Also, the layer priority does not currently affect the precedence order of .conf or .bbclass files. Future versions of BitBake might address this.

5.1.6. Managing Layers

You can use the BitBake layer management tool to provide a view into the structure of recipes across a multi-layer project. Being able to generate output that reports on configured layers with their paths and priorities and on .bbappend files and their applicable recipes can help to reveal potential problems.

Use the following form when running the layer management tool.

     $ bitbake-layers <command> [arguments]
                

The following list describes the available commands:

  • help: Displays general help or help on a specified command.

  • show-layers: Shows the current configured layers.

  • show-recipes: Lists available recipes and the layers that provide them.

  • show-overlayed: Lists overlayed recipes. A recipe is overlayed when a recipe with the same name exists in another layer that has a higher layer priority.

  • show-appends: Lists .bbappend files and the recipe files to which they apply.

  • show-cross-depends: Lists dependency relationships between recipes that cross layer boundaries.

  • flatten: Flattens the layer configuration into a separate output directory. Flattening your layer configuration builds a "flattened" directory that contains the contents of all layers, with any overlayed recipes removed and any .bbappend files appended to the corresponding recipes. You might have to perform some manual cleanup of the flattened layer as follows:

    • Non-recipe files (such as patches) are overwritten. The flatten command shows a warning for these files.

    • Anything beyond the normal layer setup has been added to the layer.conf file. Only the lowest priority layer's layer.conf is used.

    • Overridden and appended items from .bbappend files need to be cleaned up. The contents of each .bbappend end up in the flattened recipe. However, if there are appended or changed variable values, you need to tidy these up yourself. Consider the following example. Here, the bitbake-layers command adds the line #### bbappended ... so that you know where the following lines originate:

           ...
           DESCRIPTION = "A useful utility"
           ...
           EXTRA_OECONF = "--enable-something"
           ...
      
           #### bbappended from meta-anotherlayer ####
      
           DESCRIPTION = "Customized utility"
           EXTRA_OECONF += "--enable-somethingelse"
                                      

      Ideally, you would tidy up these utilities as follows:

           ...
           DESCRIPTION = "Customized utility"
           ...
           EXTRA_OECONF = "--enable-something --enable-somethingelse"
           ...
                                      

5.1.7. Creating a General Layer Using the yocto-layer Script

The yocto-layer script simplifies creating a new general layer.

Note

For information on BSP layers, see the "BSP Layers" section in the Yocto Project Board Specific (BSP) Developer's Guide.

The default mode of the script's operation is to prompt you for information needed to generate the layer:

  • The layer priority

  • Whether or not to create a sample recipe.

  • Whether or not to create a sample append file.

Use the yocto-layer create sub-command to create a new general layer. In its simplest form, you can create a layer as follows:

     $ yocto-layer create mylayer
                

The previous example creates a layer named meta-mylayer in the current directory.

As the yocto-layer create command runs, default values for the prompts appear in brackets. Pressing enter without supplying anything for the prompts or pressing enter and providing an invalid response causes the script to accept the default value. Once the script completes, the new layer is created in the current working directory. The script names the layer by prepending meta- to the name you provide.

Minimally, the script creates the following within the layer:

  • The conf directory: This directory contains the layers .conf. The root name for the file is the same as the root name your provided for the layer.

  • The COPYING.MIT: The copyright and use notice for the software.

  • The README file: A file describing the contents of your new layer.

If you choose to generate a sample recipe file, the script prompts you for the name for the recipe and then creates it in <layer>/recipes-example/example/. in a directory named recipes-example. The script creates a .bb file and a directory, which contains a sample helloworld.c source file and along with a sample patch file. If you do not provide a recipe name, the script uses "example".

If you choose to generate a sample append file, the script prompts you for the name for the file and then creates it in <layer>/recipes-example-bbappend/example-bbappend/. The script creates a .bbappend file and a directory, which contains a sample patch file. If you do not provide a recipe name, the script uses "example". The script also prompts you for the version of the append file. The version should match the recipe to which the append file is associated.

The easiest way to see how the yocto-layer script works is to experiment with the script. You can also read the usage information by entering the following:

     $ yocto-layer help
                

Once you create your general layer, you must add it to your bblayers.conf file. Here is an example:

     BBLAYERS = ?" \
        /usr/local/src/yocto/meta \
        /usr/local/src/yocto/meta-yocto \
        /usr/local/src/yocto/meta-yocto-bsp \
        /usr/local/src/yocto/meta-mylayer \
        "

     BBLAYERS_NON_REMOVABLE ?= " \
        /usr/local/src/yocto/meta \
        /usr/local/src/yocto/meta-yocto \
        "
                

Adding the layer to this file enables the build system to locate the layer during the build.

5.2. Customizing Images

You can customize images to satisfy particular requirements. This section describes several methods and provides guidelines for each.

5.2.1. Customizing Images Using Custom .bb Files

One way to get additional software into an image is to create a custom image. The following example shows the form for the two lines you need:

     IMAGE_INSTALL = "packagegroup-core-x11-base package1 package2"

     inherit core-image
                

By creating a custom image, a developer has total control over the contents of the image. It is important to use the correct names of packages in the IMAGE_INSTALL variable. You must use the OpenEmbedded notation and not the Debian notation for the names (e.g. eglibc-dev instead of libc6-dev).

The other method for creating a custom image is to base it on an existing image. For example, if you want to create an image based on core-image-sato but add the additional package strace to the image, copy the meta/recipes-sato/images/core-image-sato.bb to a new .bb and add the following line to the end of the copy:

     IMAGE_INSTALL += "strace"
                

5.2.2. Customizing Images Using Custom Package Groups

For complex custom images, the best approach is to create a custom package group recipe that is used to build the image or images. A good example of a package group recipe is meta/recipes-core/packagegroups/packagegroup-core-boot.bb. The PACKAGES variable lists the package group packages you wish to produce. inherit packagegroup sets appropriate default values and automatically adds -dev and -dbg complementary packages for every package specified in PACKAGES. Note that the inherit line should be towards the top of the recipe, certainly before you set PACKAGES. For each package you specify in PACKAGES, you can use RDEPENDS and RRECOMMENDS entries to provide a list of packages the parent task package should contain. Following is an example:

     DESCRIPTION = "My Custom Package Groups"

     inherit packagegroup

     PACKAGES = "\
         packagegroup-custom-apps \
         packagegroup-custom-tools \
         "

     RDEPENDS_packagegroup-custom-apps = "\
         dropbear \
         portmap \
         psplash"

     RDEPENDS_packagegroup-custom-tools = "\
         oprofile \
         oprofileui-server \
         lttng-control \
         lttng-viewer"

     RRECOMMENDS_packagegroup-custom-tools = "\
         kernel-module-oprofile"
                

In the previous example, two package group packages are created with their dependencies and their recommended package dependencies listed: packagegroup-custom-apps, and packagegroup-custom-tools. To build an image using these package group packages, you need to add packagegroup-custom-apps and/or packagegroup-custom-tools to IMAGE_INSTALL. For other forms of image dependencies see the other areas of this section.

5.2.3. Customizing Images Using Custom IMAGE_FEATURES and EXTRA_IMAGE_FEATURES

You might want to customize your image by enabling or disabling high-level image features by using the IMAGE_FEATURES and EXTRA_IMAGE_FEATURES variables. Although the functions for both variables are nearly equivalent, best practices dictate using IMAGE_FEATURES from within a recipe and using EXTRA_IMAGE_FEATURES from within your local.conf file, which is found in the Build Directory.

To understand how these features work, the best reference is meta/classes/core-image.bbclass. In summary, the file looks at the contents of the IMAGE_FEATURES variable and then maps those contents into a set of package groups. Based on this information, the build system automatically adds the appropriate packages to the IMAGE_INSTALL variable. Effectively, you are enabling extra features by extending the class or creating a custom class for use with specialized image .bb files.

Use the EXTRA_IMAGE_FEATURES variable from within your local configuration file. Using a separate area from which to enable features with this variable helps you avoid overwriting the features in the image recipe that are enabled with IMAGE_FEATURES. The value of EXTRA_IMAGE_FEATURES is added to IMAGE_FEATURES within meta/conf/bitbake.conf.

To illustrate how you can use these variables to modify your image, consider an example that selects the SSH server. The Yocto Project ships with two SSH servers you can use with your images: Dropbear and OpenSSH. Dropbear is a minimal SSH server appropriate for resource-constrained environments, while OpenSSH is a well-known standard SSH server implementation. By default, the core-image-sato image is configured to use Dropbear. The core-image-basic and core-image-lsb images both include OpenSSH. The core-image-minimal image does not contain an SSH server.

You can customize your image and change these defaults. Edit the IMAGE_FEATURES variable in your recipe or use the EXTRA_IMAGE_FEATURES in your local.conf file so that it configures the image you are working with to include ssh-server-dropbear or ssh-server-openssh.

Note

See the "Images" section in the Yocto Project Reference Manual for a complete list of image features that ship with the Yocto Project.

5.2.4. Customizing Images Using local.conf

It is possible to customize image contents by using variables from your local configuration in your conf/local.conf file. Because it is limited to local use, this method generally only allows you to add packages and is not as flexible as creating your own customized image. When you add packages using local variables this way, you need to realize that these variable changes affect all images at the same time and might not be what you require.

The simplest way to add extra packages to all images is by using the IMAGE_INSTALL variable with the _append operator:

     IMAGE_INSTALL_append = " strace"
                

Use of the syntax is important. Specifically, the space between the quote and the package name, which is strace in this example. This space is required since the _append operator does not add the space.

Furthermore, you must use _append instead of the += operator if you want to avoid ordering issues. The reason for this is because doing so unconditionally appends to the variable and avoids ordering problems due to the variable being set in image recipes and .bbclass files with operators like ?=. Using _append ensures the operation takes affect.

As shown in its simplest use, IMAGE_INSTALL_append affects all images. It is possible to extend the syntax so that the variable applies to a specific image only. Here is an example:

     IMAGE_INSTALL_append_pn-core-image-minimal = " strace"
                

This example adds strace to core-image-minimal only.

You can add packages using a similar approach through the CORE_IMAGE_EXTRA_INSTALL variable. If you use this variable, only core-image-* images are affected.

5.3. Writing a Recipe to Add a Package to Your Image

Recipes add packages to your image. Writing a recipe means creating a .bb file that sets some variables. For information on variables that are useful for recipes and for information about recipe naming issues, see the "Required" section of the Yocto Project Reference Manual.

Before writing a recipe from scratch, it is often useful to check whether someone else has written one already. OpenEmbedded is a good place to look as it has a wider scope and range of packages. Because the Yocto Project aims to be compatible with OpenEmbedded, most recipes you find there should work for you.

For new packages, the simplest way to add a recipe is to base it on a similar pre-existing recipe. The sections that follow provide some examples that show how to add standard types of packages.

Note

When writing shell functions, you need to be aware of BitBake's curly brace parsing. If a recipe uses a closing curly brace within the function and the character has no leading spaces, BitBake produces a parsing error. If you use a pair of curly brace in a shell function, the closing curly brace must not be located at the start of the line without leading spaces.

Here is an example that causes BitBake to produce a parsing error:

     fakeroot create_shar() {
         cat << "EOF" > ${SDK_DEPLOY}/${TOOLCHAIN_OUTPUTNAME}.sh
     usage()
     {
       echo "test"
       ###### The following "}" at the start of the line causes a parsing error ######
     }
     EOF
     }
            

Writing the recipe this way avoids the error:

     fakeroot create_shar() {
         cat << "EOF" > ${SDK_DEPLOY}/${TOOLCHAIN_OUTPUTNAME}.sh
     usage()
     {
       echo "test"
       ######The following "}" with a leading space at the start of the line avoids the error ######
      }
     EOF
     }
            

5.3.1. Single .c File Package (Hello World!)

Building an application from a single file that is stored locally (e.g. under files/) requires a recipe that has the file listed in the SRC_URI variable. Additionally, you need to manually write the do_compile and do_install tasks. The S variable defines the directory containing the source code, which is set to WORKDIR in this case - the directory BitBake uses for the build.

     DESCRIPTION = "Simple helloworld application"
     SECTION = "examples"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"
     PR = "r0"

     SRC_URI = "file://helloworld.c"

     S = "${WORKDIR}"

     do_compile() {
     	${CC} helloworld.c -o helloworld
     }

     do_install() {
     	install -d ${D}${bindir}
     	install -m 0755 helloworld ${D}${bindir}
     }
                

By default, the helloworld, helloworld-dbg, and helloworld-dev packages are built. For information on how to customize the packaging process, see the "Splitting an Application into Multiple Packages" section.

5.3.2. Autotooled Package

Applications that use Autotools such as autoconf and automake require a recipe that has a source archive listed in SRC_URI and also inherits Autotools, which instructs BitBake to use the autotools.bbclass file, which contains the definitions of all the steps needed to build an Autotool-based application. The result of the build is automatically packaged. And, if the application uses NLS for localization, packages with local information are generated (one package per language). Following is one example: (hello_2.3.bb)

     DESCRIPTION = "GNU Helloworld application"
     SECTION = "examples"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe"
     PR = "r0"

     SRC_URI = "${GNU_MIRROR}/hello/hello-${PV}.tar.gz"

     inherit autotools gettext
                 

The variable LIC_FILES_CHKSUM is used to track source license changes as described in the "Tracking License Changes" section. You can quickly create Autotool-based recipes in a manner similar to the previous example.

5.3.3. Makefile-Based Package

Applications that use GNU make also require a recipe that has the source archive listed in SRC_URI. You do not need to add a do_compile step since by default BitBake starts the make command to compile the application. If you need additional make options, you should store them in the EXTRA_OEMAKE variable. BitBake passes these options into the make GNU invocation. Note that a do_install task is still required. Otherwise, BitBake runs an empty do_install task by default.

Some applications might require extra parameters to be passed to the compiler. For example, the application might need an additional header path. You can accomplish this by adding to the CFLAGS variable. The following example shows this:

     CFLAGS_prepend = "-I ${S}/include "
                

In the following example, mtd-utils is a makefile-based package:

     DESCRIPTION = "Tools for managing memory technology devices."
     SECTION = "base"
     DEPENDS = "zlib lzo e2fsprogs util-linux"
     HOMEPAGE = "http://www.linux-mtd.infradead.org/"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=0636e73ff0215e8d672dc4c32c317bb3 \
                    file://include/common.h;beginline=1;endline=17;md5=ba05b07912a44ea2bf81ce409380049c"

     SRC_URI = "git://git.infradead.org/mtd-utils.git;protocol=git;tag=995cfe51b0a3cf32f381c140bf72b21bf91cef1b \
	     	file://add-exclusion-to-mkfs-jffs2-git-2.patch"

     S = "${WORKDIR}/git/"

     PR = "r1"

     EXTRA_OEMAKE = "'CC=${CC}' 'RANLIB=${RANLIB}' 'AR=${AR}' \
        'CFLAGS=${CFLAGS} -I${S}/include -DWITHOUT_XATTR' 'BUILDDIR=${S}'"

     do_install () {
	     oe_runmake install DESTDIR=${D} SBINDIR=${sbindir} MANDIR=${mandir} \
            INCLUDEDIR=${includedir}
	     install -d ${D}${includedir}/mtd/
	     for f in ${S}/include/mtd/*.h; do
	     	install -m 0644 $f ${D}${includedir}/mtd/
	     done
     }

     PARALLEL_MAKE = ""

     BBCLASSEXTEND = "native"
                

If your sources are available as a tarball instead of a Git repository, you will need to provide the URL to the tarball as well as an md5 or sha256 sum of the download. Here is an example:

     SRC_URI="ftp://ftp.infradead.org/pub/mtd-utils/mtd-utils-1.4.9.tar.bz2"
     SRC_URI[md5sum]="82b8e714b90674896570968f70ca778b"
                

You can generate the md5 or sha256 sums by using the md5sum or sha256sum commands with the target file as the only argument. Here is an example:

     $ md5sum mtd-utils-1.4.9.tar.bz2
     82b8e714b90674896570968f70ca778b mtd-utils-1.4.9.tar.bz2
                

5.3.4. Splitting an Application into Multiple Packages

You can use the variables PACKAGES and FILES to split an application into multiple packages.

Following is an example that uses the libXpm recipe. By default, this recipe generates a single package that contains the library along with a few binaries. You can modify the recipe to split the binaries into separate packages:

     require xorg-lib-common.inc

     DESCRIPTION = "X11 Pixmap library"
     LICENSE = "X-BSD"
     LIC_FILES_CHKSUM = "file://COPYING;md5=3e07763d16963c3af12db271a31abaa5"
     DEPENDS += "libxext libsm libxt"
     PR = "r3"
     PE = "1"

     XORG_PN = "libXpm"

     PACKAGES =+ "sxpm cxpm"
     FILES_cxpm = "${bindir}/cxpm"
     FILES_sxpm = "${bindir}/sxpm"
                

In the previous example, we want to ship the sxpm and cxpm binaries in separate packages. Since bindir would be packaged into the main PN package by default, we prepend the PACKAGES variable so additional package names are added to the start of list. This results in the extra FILES_* variables then containing information that define which files and directories go into which packages. Files included by earlier packages are skipped by latter packages. Thus, the main PN package does not include the above listed files.

5.3.5. Post-Installation Scripts

To add a post-installation script to a package, add a pkg_postinst_PACKAGENAME() function to the .bb file and use PACKAGENAME as the name of the package you want to attach to the postinst script. Normally, PN can be used, which automatically expands to PACKAGENAME. A post-installation function has the following structure:

     pkg_postinst_PACKAGENAME () {
     #!/bin/sh -e
     # Commands to carry out
     }
                

The script defined in the post-installation function is called when the root filesystem is created. If the script succeeds, the package is marked as installed. If the script fails, the package is marked as unpacked and the script is executed when the image boots again.

Sometimes it is necessary for the execution of a post-installation script to be delayed until the first boot. For example, the script might need to be executed on the device itself. To delay script execution until boot time, use the following structure in the post-installation script:

     pkg_postinst_PACKAGENAME () {
     #!/bin/sh -e
     if [ x"$D" = "x" ]; then
          # Actions to carry out on the device go here
     else
          exit 1
     fi
     }
                

The previous example delays execution until the image boots again because the D variable points to the directory containing the image when the root filesystem is created at build time but is unset when executed on the first boot.

5.4. Adding a New Machine

Adding a new machine to the Yocto Project is a straightforward process. This section provides information that gives you an idea of the changes you must make. The information covers adding machines similar to those the Yocto Project already supports. Although well within the capabilities of the Yocto Project, adding a totally new architecture might require changes to gcc/eglibc and to the site information, which is beyond the scope of this manual.

For a complete example that shows how to add a new machine, see the "Creating a New BSP Layer Using the yocto-bsp Script" in the Yocto Project Board Support Package (BSP) Developer's Guide.

5.4.1. Adding the Machine Configuration File

To add a machine configuration, you need to add a .conf file with details of the device being added to the conf/machine/ file. The name of the file determines the name the OpenEmbedded build system uses to reference the new machine.

The most important variables to set in this file are as follows:

You might also need these variables:

You can find full details on these variables in the reference section. You can leverage many existing machine .conf files from meta/conf/machine/.

5.4.2. Adding a Kernel for the Machine

The OpenEmbedded build system needs to be able to build a kernel for the machine. You need to either create a new kernel recipe for this machine, or extend an existing recipe. You can find several kernel examples in the Source Directory at meta/recipes-kernel/linux that you can use as references.

If you are creating a new recipe, normal recipe-writing rules apply for setting up a SRC_URI. Thus, you need to specify any necessary patches and set S to point at the source code. You need to create a configure task that configures the unpacked kernel with a defconfig. You can do this by using a make defconfig command or, more commonly, by copying in a suitable defconfig file and and then running make oldconfig. By making use of inherit kernel and potentially some of the linux-*.inc files, most other functionality is centralized and the the defaults of the class normally work well.

If you are extending an existing kernel, it is usually a matter of adding a suitable defconfig file. The file needs to be added into a location similar to defconfig files used for other machines in a given kernel. A possible way to do this is by listing the file in the SRC_URI and adding the machine to the expression in COMPATIBLE_MACHINE:

     COMPATIBLE_MACHINE = '(qemux86|qemumips)'
                

5.4.3. Adding a Formfactor Configuration File

A formfactor configuration file provides information about the target hardware for which the image is being built and information that the build system cannot obtain from other sources such as the kernel. Some examples of information contained in a formfactor configuration file include framebuffer orientation, whether or not the system has a keyboard, the positioning of the keyboard in relation to the screen, and the screen resolution.

The build system uses reasonable defaults in most cases. However, if customization is necessary, you need to create a machconfig file in the meta/recipes-bsp/formfactor/files directory. This directory contains directories for specific machines such as qemuarm and qemux86. For information about the settings available and the defaults, see the meta/recipes-bsp/formfactor/files/config file found in the same area.

Following is an example for qemuarm:

     HAVE_TOUCHSCREEN=1
     HAVE_KEYBOARD=1

     DISPLAY_CAN_ROTATE=0
     DISPLAY_ORIENTATION=0
     #DISPLAY_WIDTH_PIXELS=640
     #DISPLAY_HEIGHT_PIXELS=480
     #DISPLAY_BPP=16
     DISPLAY_DPI=150
     DISPLAY_SUBPIXEL_ORDER=vrgb
                

5.5. Working With Libraries

Libraries are an integral part of your system. This section describes some common practices you might find helpful when working with libraries to build your system:

5.5.1. Including Static Library Files

If you are building a library and the library offers static linking, you can control which static library files (*.a files) get included in the built library.

The PACKAGES and FILES_* variables in the meta/conf/bitbake.conf configuration file define how files installed by the do_install task are packaged. By default, the PACKAGES variable contains ${PN}-staticdev, which includes all static library files.

Note

Some previously released versions of the Yocto Project defined the static library files through ${PN}-dev.

Following, is part of the BitBake configuration file. You can see where the static library files are defined:

     PACKAGES = "${PN}-dbg ${PN} ${PN}-doc ${PN}-dev ${PN}-staticdev ${PN}-locale"
     PACKAGES_DYNAMIC = "${PN}-locale-*"
     FILES = ""

     FILES_${PN} = "${bindir}/* ${sbindir}/* ${libexecdir}/* ${libdir}/lib*${SOLIBS} \
                 ${sysconfdir} ${sharedstatedir} ${localstatedir} \
                 ${base_bindir}/* ${base_sbindir}/* \
                 ${base_libdir}/*${SOLIBS} \
                 ${datadir}/${BPN} ${libdir}/${BPN}/* \
                 ${datadir}/pixmaps ${datadir}/applications \
                 ${datadir}/idl ${datadir}/omf ${datadir}/sounds \
                 ${libdir}/bonobo/servers"

     FILES_${PN}-doc = "${docdir} ${mandir} ${infodir} ${datadir}/gtk-doc \
                 ${datadir}/gnome/help"
     SECTION_${PN}-doc = "doc"

     FILES_${PN}-dev = "${includedir} ${libdir}/lib*${SOLIBSDEV} ${libdir}/*.la \
                     ${libdir}/*.o ${libdir}/pkgconfig ${datadir}/pkgconfig \
                     ${datadir}/aclocal ${base_libdir}/*.o"
     SECTION_${PN}-dev = "devel"
     ALLOW_EMPTY_${PN}-dev = "1"
     RDEPENDS_${PN}-dev = "${PN} (= ${EXTENDPKGV})"

     FILES_${PN}-staticdev = "${libdir}/*.a ${base_libdir}/*.a"
     SECTION_${PN}-staticdev = "devel"
     RDEPENDS_${PN}-staticdev = "${PN}-dev (= ${EXTENDPKGV})"
                

5.5.2. Combining Multiple Versions of Library Files into One Image

The build system offers the ability to build libraries with different target optimizations or architecture formats and combine these together into one system image. You can link different binaries in the image against the different libraries as needed for specific use cases. This feature is called "Multilib."

An example would be where you have most of a system compiled in 32-bit mode using 32-bit libraries, but you have something large, like a database engine, that needs to be a 64-bit application and uses 64-bit libraries. Multilib allows you to get the best of both 32-bit and 64-bit libraries.

While the Multilib feature is most commonly used for 32 and 64-bit differences, the approach the build system uses facilitates different target optimizations. You could compile some binaries to use one set of libraries and other binaries to use other different sets of libraries. The libraries could differ in architecture, compiler options, or other optimizations.

This section overviews the Multilib process only. For more details on how to implement Multilib, see the Multilib wiki page.

Aside from this wiki page, several examples exist in the meta-skeleton layer found in the Source Directory:

  • conf/multilib-example.conf configuration file

  • conf/multilib-example2.conf configuration file

  • recipes-multilib/images/core-image-multilib-example.bb recipe

5.5.2.1. Preparing to Use Multilib

User-specific requirements drive the Multilib feature. Consequently, there is no one "out-of-the-box" configuration that likely exists to meet your needs.

In order to enable Multilib, you first need to ensure your recipe is extended to support multiple libraries. Many standard recipes are already extended and support multiple libraries. You can check in the meta/conf/multilib.conf configuration file in the Source Directory to see how this is done using the BBCLASSEXTEND variable. Eventually, all recipes will be covered and this list will be unneeded.

For the most part, the Multilib class extension works automatically to extend the package name from ${PN} to ${MLPREFIX}${PN}, where MLPREFIX is the particular multilib (e.g. "lib32-" or "lib64-"). Standard variables such as DEPENDS, RDEPENDS, RPROVIDES, RRECOMMENDS, PACKAGES, and PACKAGES_DYNAMIC are automatically extended by the system. If you are extending any manual code in the recipe, you can use the ${MLPREFIX} variable to ensure those names are extended correctly. This automatic extension code resides in multilib.bbclass.

5.5.2.2. Using Multilib

After you have set up the recipes, you need to define the actual combination of multiple libraries you want to build. You accomplish this through your local.conf configuration file in the Build Directory. An example configuration would be as follows:

     MACHINE = "qemux86-64"
     require conf/multilib.conf
     MULTILIBS = "multilib:lib32"
     DEFAULTTUNE_virtclass-multilib-lib32 = "x86"
     IMAGE_INSTALL = "lib32-connman"
                    

This example enables an additional library named lib32 alongside the normal target packages. When combining these "lib32" alternatives, the example uses "x86" for tuning. For information on this particular tuning, see meta/conf/machine/include/ia32/arch-ia32.inc.

The example then includes lib32-connman in all the images, which illustrates one method of including a multiple library dependency. You can use a normal image build to include this dependency, for example:

     $ bitbake core-image-sato
                    

You can also build Multilib packages specifically with a command like this:

     $  bitbake lib32-connman
                    

5.5.2.3. Additional Implementation Details

Different packaging systems have different levels of native Multilib support. For the RPM Package Management System, the following implementation details exist:

  • A unique architecture is defined for the Multilib packages, along with creating a unique deploy folder under tmp/deploy/rpm in the Build Directory. For example, consider lib32 in a qemux86-64 image. The possible architectures in the system are "all", "qemux86_64", "lib32_qemux86_64", and "lib32_x86".

  • The ${MLPREFIX} variable is stripped from ${PN} during RPM packaging. The naming for a normal RPM package and a Multilib RPM package in a qemux86-64 system resolves to something similar to bash-4.1-r2.x86_64.rpm and bash-4.1.r2.lib32_x86.rpm, respectively.

  • When installing a Multilib image, the RPM backend first installs the base image and then installs the Multilib libraries.

  • The build system relies on RPM to resolve the identical files in the two (or more) Multilib packages.

For the IPK Package Management System, the following implementation details exist:

  • The ${MLPREFIX} is not stripped from ${PN} during IPK packaging. The naming for a normal RPM package and a Multilib IPK package in a qemux86-64 system resolves to something like bash_4.1-r2.x86_64.ipk and lib32-bash_4.1-rw_x86.ipk, respectively.

  • The IPK deploy folder is not modified with ${MLPREFIX} because packages with and without the Multilib feature can exist in the same folder due to the ${PN} differences.

  • IPK defines a sanity check for Multilib installation using certain rules for file comparison, overridden, etc.

5.5.3. Installing Multiple Versions of the Same Library

Situations can exist where you need to install and use multiple versions of the same library on the same system at the same time. These situations almost always exist when a library API changes and you have multiple pieces of software that depend on the separate versions of the library. To accommodate these situations, you can install multiple versions of the same library in parallel on the same system.

The process is straight forward as long as the libraries use proper versioning. With properly versioned libraries, all you need to do to individually specify the libraries is create separate, appropriately named recipes where the PN part of the name includes a portion that differentiates each library version (e.g.the major part of the version number). Thus, instead of having a single recipe that loads one version of a library (e.g. clutter), you provide multiple recipes that result in different versions of the libraries you want. As an example, the following two recipes would allow the two separate versions of the clutter library to co-exist on the same system:

     clutter-1.6_1.6.20.bb
     clutter-1.8_1.8.4.bb
                

Additionally, if you have other recipes that depend on a given library, you need to use the DEPENDS variable to create the dependency. Continuing with the same example, if you want to have a recipe depend on the 1.8 version of the clutter library, use the following in your recipe:

     DEPENDS = "clutter-1.8"
                

5.6. Configuring the Kernel

Configuring the Yocto Project kernel consists of making sure the .config file has all the right information in it for the image you are building. You can use the menuconfig tool and configuration fragments to make sure your .config file is just how you need it. This section describes how to use menuconfig, create and use configuration fragments, and how to interactively tweak your .config file to create the leanest kernel configuration file possible.

For more information on kernel configuration, see the "Changing the Configuration" section in the Yocto Project Linux Kernel Development Manual.

5.6.1. Using  menuconfig

The easiest way to define kernel configurations is to set them through the menuconfig tool. This tool provides an interactive method with which to set kernel configurations. For general information on menuconfig, see http://en.wikipedia.org/wiki/Menuconfig.

To use the menuconfig tool in the Yocto Project development environment, you must build the tool using BitBake. Thus, the environment must be set up using the oe-init-build-env script found in the Build Directory. The following commands build and invoke menuconfig assuming the Source Directory top-level folder is ~/poky:

     $ cd ~/poky
     $ source oe-init-build-env
     $ bitbake linux-yocto -c menuconfig
                

Once menuconfig comes up, its standard interface allows you to interactively examine and configure all the kernel configuration parameters. After making your changes, simply exit the tool and save your changes to create an updated version of the .config configuration file.

Consider an example that configures the linux-yocto-3.4 kernel. The OpenEmbedded build system recognizes this kernel as linux-yocto. Thus, the following commands from the shell in which you previously sourced the environment initialization script cleans the shared state cache and the WORKDIR directory and then builds and launches menuconfig:

     $ bitbake linux-yocto -c menuconfig
                

Once menuconfig launches, use the interface to navigate through the selections to find the configuration settings in which you are interested. For example, consider the CONFIG_SMP configuration setting. You can find it at Processor Type and Features under the configuration selection Symmetric Multi-processing Support. After highlighting the selection, use the arrow keys to select or deselect the setting. When you are finished with all your selections, exit out and save them.

Saving the selections updates the .config configuration file. This is the file that the OpenEmbedded build system uses to configure the kernel during the build. You can find and examine this file in the Build Directory in tmp/work/. The actual .config is located in the area where the specific kernel is built. For example, if you were building a Linux Yocto kernel based on the Linux 3.4 kernel and you were building a QEMU image targeted for x86 architecture, the .config file would be located here:

     ~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-3.4.11+git1+84f...
        ...656ed30-r1/linux-qemux86-standard-build
                

Note

The previous example directory is artificially split and many of the characters in the actual filename are omitted in order to make it more readable. Also, depending on the kernel you are using, the exact pathname for linux-yocto-3.4... might differ.

Within the .config file, you can see the kernel settings. For example, the following entry shows that symmetric multi-processor support is not set:

     # CONFIG_SMP is not set
                

A good method to isolate changed configurations is to use a combination of the menuconfig tool and simple shell commands. Before changing configurations with menuconfig, copy the existing .config and rename it to something else, use menuconfig to make as many changes an you want and save them, then compare the renamed configuration file against the newly created file. You can use the resulting differences as your base to create configuration fragments to permanently save in your kernel layer.

Note

Be sure to make a copy of the .config and don't just rename it. The build system needs an existing .config from which to work.

5.6.2. Creating Configuration Fragments

Configuration fragments are simply kernel options that appear in a file placed where the OpenEmbedded build system can find and apply them. Syntactically, the configuration statement is identical to what would appear in the .config file, which is in the Build Directory in tmp/work/<arch>-poky-linux/linux-yocto-<release-specific-string>/linux-<arch>-<build-type>.

It is simple to create a configuration fragment. For example, issuing the following from the shell creates a configuration fragment file named my_smp.cfg that enables multi-processor support within the kernel:

     $ echo "CONFIG_SMP=y" >> my_smp.cfg
                

Note

All configuration files must use the .cfg extension in order for the OpenEmbedded build system to recognize them as a configuration fragment.

Where do you put your configuration files? You can place these configuration files in the same area pointed to by SRC_URI. The OpenEmbedded build system will pick up the configuration and add it to the kernel's configuration. For example, suppose you had a set of configuration options in a file called myconfig.cfg. If you put that file inside a directory named /linux-yocto that resides in the same directory as the kernel's append file and then add a SRC_URI statement such as the following to the kernel's append file, those configuration options will be picked up and applied when the kernel is built.

     SRC_URI += "file://myconfig.cfg"
                

As mentioned earlier, you can group related configurations into multiple files and name them all in the SRC_URI statement as well. For example, you could group separate configurations specifically for Ethernet and graphics into their own files and add those by using a SRC_URI statement like the following in your append file:

     SRC_URI += "file://myconfig.cfg \
            file://eth.cfg \
            file://gfx.cfg"
                

5.6.3. Fine-Tuning the Kernel Configuration File

You can make sure the .config file is as lean or efficient as possible by reading the output of the kernel configuration fragment audit, noting any issues, making changes to correct the issues, and then repeating.

As part of the kernel build process, the kernel_configcheck task runs. This task validates the kernel configuration by checking the final .config file against the input files. During the check, the task produces warning messages for the following issues:

  • Requested options that did not make the final .config file.

  • Configuration items that appear twice in the same configuration fragment.

  • Configuration items tagged as "required" were overridden.

  • A board overrides a non-board specific option.

  • Listed options not valid for the kernel being processed. In other words, the option does not appear anywhere.

Note

The kernel_configcheck task can also optionally report if an option is overridden during processing.

For each output warning, a message points to the file that contains a list of the options and a pointer to the config fragment that defines them. Collectively, the files are the key to streamlining the configuration.

To streamline the configuration, do the following:

  1. Start with a full configuration that you know works - it builds and boots successfully. This configuration file will be your baseline.

  2. Separately run the configme and kernel_configcheck tasks.

  3. Take the resulting list of files from the kernel_configcheck task warnings and do the following:

    • Drop values that are redefined in the fragment but do not change the final .config file.

    • Analyze and potentially drop values from the .config file that override required configurations.

    • Analyze and potentially remove non-board specific options.

    • Remove repeated and invalid options.

  4. After you have worked through the output of the kernel configuration audit, you can re-run the configme and kernel_configcheck tasks to see the results of your changes. If you have more issues, you can deal with them as described in the previous step.

Iteratively working through steps two through four eventually yields a minimal, streamlined configuration file. Once you have the best .config, you can build the Linux Yocto kernel.

5.7. Patching the Kernel

Patching the kernel involves changing or adding configurations to an existing kernel, changing or adding recipes to the kernel that are needed to support specific hardware features, or even altering the source code itself.

Note

You can use the yocto-kernel script found in the Source Directory under scripts to manage kernel patches and configuration. See the "Managing kernel Patches and Config Items with yocto-kernel" section in the Yocto Project Board Support Packages (BSP) Developer's Guide for more information.

This example creates a simple patch by adding some QEMU emulator console output at boot time through printk statements in the kernel's calibrate.c source code file. Applying the patch and booting the modified image causes the added messages to appear on the emulator's console.

The example assumes a clean build exists for the qemux86 machine in a Source Directory named poky. Furthermore, the Build Directory is build and is located in poky and the kernel is based on the Linux 3.4 kernel. For general information on how to configure the most efficient build, see the "Building an Image" section in the Yocto Project Quick Start.

Also, for more information on patching the kernel, see the "Applying Patches" section in the Yocto Project Linux Kernel Development Manual.

5.7.1. Create a Layer for your Changes

The first step is to create a layer so you can isolate your changes:

     $cd ~/poky
     $mkdir meta-mylayer
                

Creating a directory that follows the Yocto Project layer naming conventions sets up the layer for your changes. The layer is where you place your configuration files, append files, and patch files. To learn more about creating a layer and filling it with the files you need, see the "Understanding and Creating Layers" section.

5.7.2. Finding the Kernel Source Code

Each time you build a kernel image, the kernel source code is fetched and unpacked into the following directory:

     ${S}/linux
                

See the "Finding the Temporary Source Code" section and the S variable for more information about where source is kept during a build.

For this example, we are going to patch the init/calibrate.c file by adding some simple console printk statements that we can see when we boot the image using QEMU.

5.7.3. Creating the Patch

Two methods exist by which you can create the patch: Git workflow and Quilt workflow. For kernel patches, the Git workflow is more appropriate. This section assumes the Git workflow and shows the steps specific to this example.

  1. Change the working directory: Change to where the kernel source code is before making your edits to the calibrate.c file:

         $ cd ~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-${PV}-${PR}/linux
                            

    Because you are working in an established Git repository, you must be in this directory in order to commit your changes and create the patch file.

    Note

    The PV and PR variables represent the version and revision for the linux-yocto recipe. The PV variable includes the Git meta and machine hashes, which make the directory name longer than you might expect.
  2. Edit the source file: Edit the init/calibrate.c file to have the following changes:

         void __cpuinit calibrate_delay(void)
         {
             unsigned long lpj;
             static bool printed;
             int this_cpu = smp_processor_id();
    
             printk("*************************************\n");
             printk("*                                   *\n");
             printk("*        HELLO YOCTO KERNEL         *\n");
             printk("*                                   *\n");
             printk("*************************************\n");
    
         	if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
                   .
                   .
                   .
                            
  3. Stage and commit your changes: These Git commands display the modified file, stage it, and then commit the file:

         $ git status
         $ git add init/calibrate.c
         $ git commit -m "calibrate: Add printk example"
                            
  4. Generate the patch file: This Git command creates the a patch file named 0001-calibrate-Add-printk-example.patch in the current directory.

         $ git format-patch -1
                            

5.7.4. Set Up Your Layer for the Build

These steps get your layer set up for the build:

  1. Create additional structure: Create the additional layer structure:

         $ cd ~/poky/meta-mylayer
         $ mkdir conf
         $ mkdir recipes-kernel
         $ mkdir recipes-kernel/linux
         $ mkdir recipes-kernel/linux/linux-yocto
                             

    The conf directory holds your configuration files, while the recipes-kernel directory holds your append file and your patch file.

  2. Create the layer configuration file: Move to the meta-mylayer/conf directory and create the layer.conf file as follows:

         # We have a conf and classes directory, add to BBPATH
         BBPATH .= ":${LAYERDIR}"
    
         # We have recipes-* directories, add to BBFILES
         BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
                     ${LAYERDIR}/recipes-*/*/*.bbappend"
    
         BBFILE_COLLECTIONS += "mylayer"
         BBFILE_PATTERN_mylayer = "^${LAYERDIR}/"
         BBFILE_PRIORITY_mylayer = "5"
                             

    Notice mylayer as part of the last three statements.

  3. Create the kernel recipe append file: Move to the meta-mylayer/recipes-kernel/linux directory and create the linux-yocto_3.4.bbappend file as follows:

         FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
    
         SRC_URI += "file://0001-calibrate-Add-printk-example.patch"
    
         PRINC := "${@int(PRINC) + 1}"
                            

    The FILESEXTRAPATHS and SRC_URI statements enable the OpenEmbedded build system to find the patch file. For more information on using append files, see the "Using .bbappend Files" section.

  4. Put the patch file in your layer: Move the 0001-calibrate-Add-printk-example.patch file to the meta-mylayer/recipes-kernel/linux/linux-yocto directory.

5.7.5. Set Up for the Build

Do the following to make sure the build parameters are set up for the example. Once you set up these build parameters, they do not have to change unless you change the target architecture of the machine you are building:

  • Build for the correct target architecture: Your selected MACHINE definition within the local.conf file in the Build Directory specifies the target architecture used when building the Linux kernel. By default, MACHINE is set to qemux86, which specifies a 32-bit Intel® Architecture target machine suitable for the QEMU emulator.

  • Identify your meta-mylayer layer: The BBLAYERS variable in the bblayers.conf file found in the poky/build/conf directory needs to have the path to your local meta-mylayer layer. By default, the BBLAYERS variable contains paths to meta, meta-yocto, and meta-yocto-bsp in the poky Git repository. Add the path to your meta-mylayer location:

         BBLAYERS ?= " \
           $HOME/poky/meta \
           $HOME/poky/meta-yocto \
           $HOME/poky/meta-yocto-bsp \
           $HOME/poky/meta-mylayer \
           "
    
         BBLAYERS_NON_REMOVABLE ?= " \
           $HOME/poky/meta \
           $HOME/poky/meta-yocto \
           "
                            

5.7.6. Build the Modified QEMU Kernel Image

The following steps build your modified kernel image:

  1. Be sure your build environment is initialized: Your environment should be set up since you previously sourced the oe-init-build-env script. If it is not, source the script again from poky.

         $ cd ~/poky
         $ source oe-init-build-env
                            

  2. Clean up: Be sure to clean the shared state out by running the cleansstate BitBake task as follows from your Build Directory:

         $ bitbake -c cleansstate linux-yocto
                            

    Note

    Never remove any files by hand from the tmp/deploy directory inside the Build Directory. Always use the various BitBake clean tasks to clear out previous build artifacts.
  3. Build the image: Next, build the kernel image using this command:

         $ bitbake -k linux-yocto
                            

5.7.7. Boot the Image and Verify Your Changes

These steps boot the image and allow you to see the changes

  1. Boot the image: Boot the modified image in the QEMU emulator using this command:

         $ runqemu qemux86
                            
  2. Verify the changes: Log into the machine using root with no password and then use the following shell command to scroll through the console's boot output.

         # dmesg | less
                            

    You should see the results of your printk statements as part of the output.

5.8. Creating Your Own Distribution

When you build an image using the Yocto Project and do not alter any distribution Metadata, you are creating a Poky distribution. If you wish to gain more control over package alternative selections, compile-time options, and other low-level configurations, you can create your own distribution.

To create your own distribution, the basic steps consist of creating your own distribution layer, creating your own distribution configuration file, and then adding any needed code and Metadata to the layer. The following steps provide some more detail:

  • Create a layer for your new distro: Create your distribution layer so that you can keep your Metadata and code for the distribution separate. It is strongly recommended that you create and use your own layer for configuration and code. Using your own layer as compared to just placing configurations in a local.conf configuration file makes it easier to reproduce the same build configuration when using multiple build machines. See the "Creating a General Layer Using the yocto-layer Script" section for information on how to quickly set up a layer.

  • Create the distribution configuration file: The distribution configuration file needs to be created in the conf/distro directory of your layer. You need to name it using your distribution name (e.g. mydistro.conf).

    You can split out parts of your configuration file into include files and then "require" them from within your distribution configuration file. Be sure to place the include files in the conf/distro/include directory of your layer. A common example usage of include files would be to separate out the selection of desired version and revisions for individual recipes.

    Your configuration file needs to set the following required variables:

         DISTRO_NAME [required]
         DISTRO_VERSION [required]
                        

    These following variables are optional and you typically set them from the distribution configuration file:

         DISTRO_FEATURES [optional]
         DISTRO_EXTRA_RDEPENDS [optional]
         DISTRO_EXTRA_RRECOMMENDS [optional]
         TCLIBC [optional]
                        

    Tip

    If you want to base your distribution configuration file on the very basic configuration from OE-Core, you can use conf/distro/defaultsetup.conf as a reference and just include variables that differ as compared to defaultsetup.conf. Alternatively, you can create a distribution configuration file from scratch using the defaultsetup.conf file or configuration files from other distributions such as Poky or Angstrom as references.
  • Provide miscellaneous variables: Be sure to define any other variables for which you want to create a default or enforce as part of the distribution configuration. You can include nearly any variable from the local.conf file. The variables you use are not limited to the list in the previous bulleted item.

  • Point to Your distribution configuration file: In your local.conf file in the Build Directory, set your DISTRO variable to point to your distribution's configuration file. For example, if your distribution's configuration file is named mydistro.conf, then you point to it as follows:

         DISTRO = "mydistro"
                        
  • Add more to the layer if necessary: Use your layer to hold other information needed for the distribution:

    • Add recipes for installing distro-specific configuration files that are not already installed by another recipe. If you have distro-specific configuration files that are included by an existing recipe, you should add a .bbappend for those. For general information on how to add recipes to your layer, see the "Creating Your Own Layer" section.

    • Add any image recipes that are specific to your distribution.

    • Add a psplash append file for a branded splash screen. For information on append files, see the "Using .bbappend Files" section.

    • Add any other append files to make custom changes that are specific to individual recipes.

5.9. Building a Tiny System

Very small distributions have some significant advantages such as requiring less on-die or in-package memory (cheaper), better performance through efficient cache usage, lower power requirements due to less memory, faster boot times, and reduced development overhead. Some real-world examples where a very small distribution gives you distinct advantages are digital cameras, medical devices, and small headless systems.

This section presents information that shows you how you can trim your distribution to even smaller sizes than the poky-tiny distribution, which is around 5 Mbytes, that can be built out-of-the-box using the Yocto Project.

5.9.1. Overview

The following list presents the overall steps you need to consider and perform to create distributions with smaller root filesystems, faster boot times, maintain your critical functionality, and avoid initial RAM disks:

  • Determine your goals and guiding principles.

  • Understand what gives your image size.

  • Reduce the size of the root filesystem.

  • Reduce the size of the kernel.

  • Look for other ways to minimize size.

  • Iterate on the process.

5.9.2. Goals and Guiding Principles

Before you can reach your destination, you need to know where you are going. Here is an example list that you can use as a guide when creating very small distributions:

  • Determine how much space you need (e.g. a kernel that is 1 Mbyte or less and a root filesystem that is 3 Mbytes or less).

  • Find the areas that are currently taking 90% of the space and concentrate on reducing those areas.

  • Do not create any difficult "hacks" to achieve your goals.

  • Leverage the device-specific options.

  • Work in a separate layer so that you keep changes isolated. For information on how to create layers, see the "Understanding and Creating Layers" section.

5.9.3. Understand What Gives Your Image Size

It is easiest to have something to start with when creating your own distribution. You can use the Yocto Project out-of-the-box to create the poky-tiny distribution. Ultimately, you will want to make changes in your own distribution that are likely modeled after poky-tiny.

Note

To use poky-tiny in your build, set the DISTRO variable in your local.conf file to "poky-tiny" as described in the "Creating Your Own Distribution" section.

Understanding some memory concepts will help you reduce the system size. Memory consists of static, dynamic, and temporary memory. Static memory is the TEXT (code), DATA (initialized data in the code), and BSS (uninitialized data) sections. Dynamic memory contains memory that is allocated at runtime, stacks, hash tables, and so forth. Temporary memory is recovered after the boot process. This memory consists of memory used for decompressing the kernel and for the __init__ functions.

To help you see where you currently are with kernel and root filesystem sizes, you can use two tools found in the Source Directory in the scripts directory:

  • ksize.py: Reports component sizes for the kernel build objects.

  • dirsize.py: Reports component sizes for the root filesystem.

This next tool and command helps you organize configuration fragments and view file dependencies in a human-readable form:

  • merge_config.sh: Helps you manage configuration files and fragments within the kernel. With this tool, you can merge individual configuration fragments together. The tool allows you to make overrides and warns you of any missing configuration options. The tool is ideal for allowing you to iterate on configurations, create minimal configurations, and create configuration files for different machines without having to duplicate your process.

    The merge_config.sh script is part of the Linux Yocto kernel Git repository in the scripts/kconfig directory.

    For more information on configuration fragments, see the "Generating Configuration Files" section of the Yocto Project Linux Kernel Development Manual and the "Creating Configuration Fragments" section, which is in this manual.

  • bitbake -u depexp -g <bitbake_target>: Using the BitBake command with these options brings up a Dependency Explorer from which you can view file dependencies. Understanding these dependencies allows you to make informed decisions when cutting out various pieces of the kernel and root filesystem.

5.9.4. Trim the Root Filesystem

The root filesystem is made up of packages for booting, libraries, and applications. To change things, you can configure how the packaging happens, which changes the way you build them. You can also tweak the filesystem itself or select a different filesystem.

First, find out what is hogging your root filesystem by running the dirsize.py script from your root directory:

     $ cd <root-directory-of-image>
     $ dirsize.py 100000 > dirsize-100k.log
     $ cat dirsize-100k.log
                

You can apply a filter to the script to ignore files under a certain size. This example filters out anything below 100 Kbytes. The sizes reported by the tool are uncompressed and thus, will be smaller by a relatively constant factor in a compressed root filesystem. When you examine your log file, you can focus on areas of the root filesystem that take up large amounts of memory.

You need to be sure that what you eliminate does not cripple the functionality you need. One way to see how packages relate to each other is by using the Dependency Explorer UI with the BitBake command:

     $ cd <image-directory>
     $ bitbake -u depexp -g <image>
                

Use the interface to select potential packages you wish to eliminate and see their dependency relationships.

When deciding how to reduce the size, get rid of packages that result in minimal impact on the feature set. For example, you might not need a VGA display. Or, you might be able to get by with devtmpfs and mdev instead of udev.

Use the local.conf file to make changes. For example, to eliminate udev and glib, set the following in the local configuration file:

     VIRTUAL-RUNTIME_dev_manager = ""
                

Finally, you should consider exactly the type of root filesystem you need to meet your needs while also reducing its size. For example, consider cramfs, squashfs, ubifs, ext2, or an initramfs using initramfs. Be aware that ext3 requires a 1 Mbyte journal. If you are okay with running read-only you do not need this journal.

Note

After each round of elimination, you need to rebuild your system and then use the tools to see the effects of your reductions.

5.9.5. Trim the Kernel

The kernel is built by including policies for hardware-independent aspects. What subsystems do you enable? For what architecture are you building? Which drivers do you build by default.

Note

You can modify the kernel source if you want to help with boot time.

Run the ksize.py script from the top-level Linux build directory to get an idea of what is making up the kernel:

     $ cd <top-level-linux-build-directory>
     $ ksize.py > ksize.log
     $ cat ksize.log
                

When you examine the log, you will see how much space is taken up with the built-in .o files for drivers, networking, core kernel files, filesystem, sound, and so forth. The sizes reported by the tool are uncompressed and thus, will be smaller by a relatively constant factor in a compressed kernel image. Look to reduce the areas that are large and taking up around the "90% rule."

To examine, or drill down, into any particular area, use the -d option with the script:

     $ ksize.py -d > ksize.log
                

Using this option breaks out the individual file information for each area of the kernel (e.g. drivers, networking, and so forth).

Use your log file to see what you can eliminate from the kernel based on features you can let go. For example, if you are not going to need sound, you do not need any drivers that support sound.

After figuring out what to eliminate, you need to reconfigure the kernel to reflect those changes during the next build. You could run menuconfig and make all your changes at once. However, that makes it difficult to see the effects of your individual eliminations and also makes it difficult to replicate the changes for perhaps another target device. A better method is to start with no configurations using allnoconfig, create configuration fragments for individual changes, and then manage the fragments into a single configuration file using merge_config.sh. The tool makes it easy for you to iterate using the configuration change and build cycle.

Each time you make configuration changes, you need to rebuild the kernel and check to see what impact your changes had on the overall size.

5.9.6. Look for Other Ways to Minimize Size

Depending on your particular circumstances, other areas that you can trim likely exist. The key to finding these areas is through tools and methods described here combined with experimentation and iteration. Here are a couple of areas to experiment with:

  • eglibc: In general, follow this process:

    1. Remove eglibc features from DISTRO_FEATURES that you think you do not need.

    2. Build your distribution.

    3. If the build fails due to missing symbols in a package, determine if you can reconfigure the package to not need those features. For example, change the configuration to not support wide character support as is done for ncurses. Or, if support for those characters is needed, determine what eglibc features provide the support and restore the configuration.

    4. Rebuild and repeat the process.

  • busybox: For BusyBox, use a process similar as described for eglibc. A difference is you will need to boot the resulting system to see if you are able to do everything you expect from the running system. You need to be sure to integrate configuration fragments into Busybox because BusyBox handles its own core features and then allows you to add configuration fragments on top.

5.9.7. Iterate on the Process

If you have not reached your goals on system size, you need to iterate on the process. The process is the same. Use the tools and see just what is taking up 90% of the root filesystem and the kernel. Decide what you can eliminate without limiting your device beyond what you need.

Depending on your system, a good place to look might be Busybox, which provides a stripped down version of Unix tools in a single, executable file. You might be able to drop virtual terminal services or perhaps ipv6.

5.10. Working with Packages

This section describes a few tasks that involve packages:

  • Incrementing a package revision number

  • Handling a package name alias

  • Handling optional module packaging

  • Setting up Runtime Package Management

  • Setting up and running package test (ptest)

5.10.1. Incrementing a Package Revision Number

If a committed change results in changing the package output, then the value of the PR variable needs to be increased (or "bumped"). Increasing PR occurs one of two ways:

  • Automatically using a Package Revision Service (PR Service).

  • Manually incrementing the PR variable.

Given that one of the challenges any build system and its users face is how to maintain a package feed that is compatible with existing package manager applications such as RPM, APT, and OPKG, using an automated system is much preferred over a manual system. In either system, the main requirement is that version numbering increases in a linear fashion and that a number of version components exist that support that linear progression.

The following two sections provide information on the PR Service and on manual PR bumping.

5.10.1.1. Working With a PR Service

As mentioned, attempting to maintain revision numbers in the Metadata is error prone, inaccurate and causes problems for people submitting recipes. Conversely, the PR Service automatically generates increasing numbers, particularly the revision field, which removes the human element.

Note

For additional information on using a PR Service, you can see the PR Service wiki page.

The Yocto Project uses variables in order of decreasing priority to facilitate revision numbering (i.e. PE, PV, and PR for epoch, version and revision, respectively). The values are highly dependent on the policies and procedures of a given distribution and package feed.

Because the OpenEmbedded build system uses "signatures", which are unique to a given build, the build system knows when to rebuild packages. All the inputs into a given task are represented by a signature, which can trigger a rebuild when different. Thus, the build system itself does not rely on the PR numbers to trigger a rebuild. The signatures, however, can be used to generate PR values.

The PR Service works with both OEBasic and OEBasicHash generators. The value of PR bumps when the checksum changes and the different generator mechanisms change signatures under different circumstances.

As implemented, the build system includes values from the PR Service into the PR field as an addition using the form ".x" so r0 becomes r0.1, r0.2 and so forth. This scheme allows existing PR values to be used for whatever reasons, which include manual PR bumps should it be necessary.

By default, the PR Service is not enabled or running. Thus, the packages generated are just "self consistent". The build system adds and removes packages and there are no guarantees about upgrade paths but images will be consistent and correct with the latest changes.

The simplest form for a PR Service is for it to exist for a single host development system that builds the package feed (building system). For this scenario, you can enable the PR Service by adding the following to your local.conf file in the Build Directory:

     PRSERV_HOST = "localhost:0"
                    

Once the service is started, packages will automatically get increasing PR values and BitBake will take care of starting and stopping the server.

If you have a more complex setup where multiple host development systems work against a common, shared package feed, you have a single PR Service running and it is connected to each building system. For this scenario, you need to start the PR Service using the bitbake-prserv command:

     bitbake-prserv ‐‐host <ip> ‐‐port <port> ‐‐start
                    

In addition to hand-starting the service, you need to update the local.conf file of each building system as described earlier so each system points to the server and port.

It is also recommended you use Build History, which adds some sanity checks to package versions, in conjunction with the server that is running the PR Service. To enable build history, add the following to each building system's local.conf file:

     # It is recommended to activate "buildhistory" for testing the PR service
     INHERIT += "buildhistory"
     BUILDHISTORY_COMMIT = "1"
                    

For information on Build History, see the "Maintaining Build Output Quality" section in the Yocto Project Reference Manual.

Note

The OpenEmbedded build system does not maintain PR information as part of the shared state (sstate) packages. If you maintain an sstate feed, its expected that either all your building systems that contribute to the sstate feed use a shared PR Service, or you do not run a PR Service on any of your building systems. Having some systems use a PR Service while others do not leads to obvious problems.

For more information on shared state, see the "Shared State Cache" section in the Yocto Project Reference Manual.

5.10.1.2. Manually Bumping PR

The alternative to setting up a PR Service is to manually bump the PR variable.

If a committed change results in changing the package output, then the value of the PR variable needs to be increased (or "bumped") as part of that commit. For new recipes you should add the PR variable and set its initial value equal to "r0", which is the default. Even though the default value is "r0", the practice of adding it to a new recipe makes it harder to forget to bump the variable when you make changes to the recipe in future.

If you are sharing a common .inc file with multiple recipes, you can also use the INC_PR variable to ensure that the recipes sharing the .inc file are rebuilt when the .inc file itself is changed. The .inc file must set INC_PR (initially to "r0"), and all recipes referring to it should set PR to "$(INC_PR).0" initially, incrementing the last number when the recipe is changed. If the .inc file is changed then its INC_PR should be incremented.

When upgrading the version of a package, assuming the PV changes, the PR variable should be reset to "r0" (or "$(INC_PR).0" if you are using INC_PR).

Usually, version increases occur only to packages. However, if for some reason PV changes but does not increase, you can increase the PE variable (Package Epoch). The PE variable defaults to "0".

Version numbering strives to follow the Debian Version Field Policy Guidelines. These guidelines define how versions are compared and what "increasing" a version means.

5.10.2. Handling a Package Name Alias

Sometimes a package name you are using might exist under an alias or as a similarly named package in a different distribution. The OpenEmbedded build system implements a distro_check task that automatically connects to major distributions and checks for these situations. If the package exists under a different name in a different distribution, you get a distro_check mismatch. You can resolve this problem by defining a per-distro recipe name alias using the DISTRO_PN_ALIAS variable.

Following is an example that shows how you specify the DISTRO_PN_ALIAS variable:

     DISTRO_PN_ALIAS_pn-PACKAGENAME = "distro1=package_name_alias1 \
                                       distro2=package_name_alias2 \
                                       distro3=package_name_alias3 \
                                       ..."
                

If you have more than one distribution alias, separate them with a space. Note that the build system currently automatically checks the Fedora, OpenSUSE, Debian, Ubuntu, and Mandriva distributions for source package recipes without having to specify them using the DISTRO_PN_ALIAS variable. For example, the following command generates a report that lists the Linux distributions that include the sources for each of the recipes.

     $ bitbake world -f -c distro_check
                

The results are stored in the build/tmp/log/distro_check-${DATETIME}.results file found in the Source Directory.

5.10.3. Handling Optional Module Packaging

Many pieces of software split functionality into optional modules (or plugins) and the plugins that are built might depend on configuration options. To avoid having to duplicate the logic that determines what modules are available in your recipe or to avoid having to package each module by hand, the OpenEmbedded build system provides functionality to handle module packaging dynamically.

To handle optional module packaging, you need to do two things:

  • Ensure the module packaging is actually done

  • Ensure that any dependencies on optional modules from other recipes are satisfied by your recipe

5.10.3.1. Making Sure the Packaging is Done

To ensure the module packaging actually gets done, you use the do_split_packages function within the populate_packages Python function in your recipe. The do_split_packages function searches for a pattern of files or directories under a specified path and creates a package for each one it finds by appending to the PACKAGES variable and setting the appropriate values for FILES_packagename, RDEPENDS_packagename, DESCRIPTION_packagename, and so forth. Here is an example from the lighttpd recipe:

     python populate_packages_prepend () {
         lighttpd_libdir = d.expand('${libdir}')
         do_split_packages(d, lighttpd_libdir, '^mod_(.*)\.so$',
                          'lighttpd-module-%s', 'Lighttpd module for %s',
                           extra_depends='')
     }
                    

The previous example specifies a number of things in the call to do_split_packages.

  • A directory within the files installed by your recipe through do_install in which to search.

  • A regular expression to match module files in that directory. In the example, note the parentheses () that mark the part of the expression from which the module name should be derived.

  • A pattern to use for the package names.

  • A description for each package.

  • An empty string for extra_depends, which disables the default dependency on the main lighttpd package. Thus, if a file in ${libdir} called mod_alias.so is found, a package called lighttpd-module-alias is created for it and the DESCRIPTION is set to "Lighttpd module for alias".

Often, packaging modules is as simple as the previous example. However, more advanced options exist that you can use within do_split_packages to modify its behavior. And, if you need to, you can add more logic by specifying a hook function that is called for each package. It is also perfectly acceptable to call do_split_packages multiple times if you have more than one set of modules to package.

For more examples that show how to use do_split_packages, see the connman.inc file in the meta/recipes-connectivity/connman/ directory of the poky source repository. You can also find examples in meta/classes/kernel.bbclass.

Following is a reference that shows do_split_packages mandatory and optional arguments:

     Mandatory arguments

     root
        The path in which to search
     file_regex
        Regular expression to match searched files.
        Use parentheses () to mark the part of this
        expression that should be used to derive the
        module name (to be substituted where %s is
        used in other function arguments as noted below)
     output_pattern
        Pattern to use for the package names. Must
        include %s.
     description
        Description to set for each package. Must
        include %s.

     Optional arguments

     postinst
        Postinstall script to use for all packages
        (as a string)
     recursive
        True to perform a recursive search - default
        False
     hook
        A hook function to be called for every match.
        The function will be called with the following
        arguments (in the order listed):

        f
           Full path to the file/directory match
        pkg
           The package name
        file_regex
           As above
        output_pattern
           As above
        modulename
           The module name derived using file_regex

     extra_depends
        Extra runtime dependencies (RDEPENDS) to be
        set for all packages. The default value of None
        causes a dependency on the main package
        (${PN}) - if you do not want this, pass empty
        string '' for this parameter.
     aux_files_pattern
        Extra item(s) to be added to FILES for each
        package. Can be a single string item or a list
        of strings for multiple items. Must include %s.
     postrm
        postrm script to use for all packages (as a
        string)
     allow_dirs
        True to allow directories to be matched -
        default False
     prepend
        If True, prepend created packages to PACKAGES
        instead of the default False which appends them
     match_path
        match file_regex on the whole relative path to
        the root rather than just the file name
     aux_files_pattern_verbatim
        Extra item(s) to be added to FILES for each
        package, using the actual derived module name
        rather than converting it to something legal
        for a package name. Can be a single string item
        or a list of strings for multiple items. Must
        include %s.
     allow_links
        True to allow symlinks to be matched - default
        False
                     

5.10.3.2. Satisfying Dependencies

The second part for handling optional module packaging is to ensure that any dependencies on optional modules from other recipes are satisfied by your recipe. You can be sure these dependencies are satisfied by using the PACKAGES_DYNAMIC variable. Here is an example that continues with the lighttpd recipe shown earlier:

     PACKAGES_DYNAMIC = "lighttpd-module-.*"
                    

The name specified in the regular expression can of course be anything. In this example, it is lighttpd-module- and is specified as the prefix to ensure that any RDEPENDS and RRECOMMENDS on a package name starting with the prefix are satisfied during build time. If you are using do_split_packages as described in the previous section, the value you put in PACKAGES_DYNAMIC should correspond to the name pattern specified in the call to do_split_packages.

5.10.4. Setting Up Runtime Package Management

For RPM, IPK, and DEB package formats, it is possible to set up a repository that is a host-based package feed from which you can install packages on the target system during runtime. Doing so is optional and depends on the following:

  • You take specific steps to set up the feed.

  • When you build your image, you select to use the appropriate package manager by setting the PACKAGE_CLASSES variable.

  • You have a web server, such as Apache 2, installed and configured on the development host.

  • You have createrepo installed on the development host.

  • You enable package management on the target by listing "package-management" in the IMAGE_FEATURES variable.

Following are the steps to set up the optional repository. This examples assumes you are using RPM and the Apache 2 server:

  1. Add the directory to your Apache configuration, which you can find at /etc/httpd/conf/httpd.conf. Use commands similar to these on the development system. These example commands assume a top-level Source Directory named poky in your home directory:

         <VirtualHost *:80>
           ....
             Alias /rpm ~/poky/build/tmp/deploy/rpm
             <Directory "~/poky/build/tmp/deploy/rpm">
               Options +Indexes
             </Directory>
         </VirtualHost>
                            

  2. Reload the Apache configuration as follows. For all commands, be sure you have root privileges.

    If your development system is using Fedora or CentOS, use the following:

         service httpd reload
                            

    For Ubuntu, use the following:

         /etc/init.d/apache2 reload
                            

    For OpenSUSE, use the following:

         /etc/init.d/apache2 reload
                            

  3. Change your working directory to tmp/deploy/rpm in the Build Directory.

  4. Create the repository data on the host using this command:

         createrepo .
                            

    Note

    If you're updating, add ‐‐update to save some time.

  5. If you are using Security-Enhanced Linux (SELinux), you need to label the files as being accessible through Apache. Use the following command from the development host:

         chcon -R -h -t httpd_sys_content_t .
                            

  6. On the target machine, add the repository to Smart. For somealias, provide a local alias for the repository:

         smart channel ‐‐add <somealias> type=rpm-md baseurl=http://server.name/rpm
                            

  7. Also from the target machine, fetch the repository information using this command:

         smart update
                            

After taking these steps and making sure that the other requirements mentioned at the beginning of the section are met, reboot the target device to take advantage of runtime package installations.

If your packages are IPK, you can install packages onto an existing running system by first sharing the tmp/deploy/ipk/ directory through a web server and then by changing /etc/opkg/base-feeds.conf to point at the shared server. Following is an example:

     $ src/gz all http://www.mysite.com/somedir/deploy/ipk/all
     $ src/gz armv7a http://www.mysite.com/somedir/deploy/ipk/armv7a
     $ src/gz beagleboard http://www.mysite.com/somedir/deploy/ipk/beagleboard
                

5.10.5. Testing Packages With ptest

A Package Test (ptest) runs tests against packages built by the OpenEmbedded build system on the target machine. A ptest contains at least two items: the actual test, and a shell script (run-ptest) that starts the test. The shell script that starts the test must not contain the actual test, the script only starts it. On the other hand, the test can be anything from a simple shell script that runs a binary and checks the output to an elaborate system of test binaries and data files.

The test generates output in the format used by Automake:

     <result>: <testname>
                

where the result can be PASS, FAIL, or SKIP, and the testname can be any identifying string.

Note

With this release of the Yocto Project, three recipes exist that are "ptest-enabled": bash, glib-2.0, and dbus. These three recipes are Autotool-enabled.

5.10.5.1. Adding ptest to Your Build

To add package testing to your build, add the DISTRO_FEATURES and EXTRA_IMAGE_FEATURES variables to your local.conf file, which is found in the Build Directory:

     DISTRO_FEATURES_append = " ptest"
     EXTRA_IMAGE_FEATURES += "ptest-pkgs"
                    

Once your build is complete, the ptest files are installed into the /usr/lib/<package>/ptest directory within the image, where <package> is the name of the package.

5.10.5.2. Running ptest

The ptest-runner package installs a shell script that loops through all installed ptest test suites and runs them in sequence. Consequently, you might want to add this package to your image.

5.10.5.3. Getting Your Package Ready

In order to enable a recipe to run installed ptests on target hardware, you need to prepare the recipes that build the packages you want to test. Here is what you have to do for each recipe:

  • Be sure the recipe inherits ptest: Include the following line in each recipe:

         inherit ptest
                                

  • Create run-ptest: This script starts your test. Locate the script where you will refer to it using SRC_URI. Here is an example that starts a test for dbus:

         #!/bin/sh
         cd test
         make -k runtest-TESTS
                                

  • Ensure dependencies are met: If the test adds build or runtime dependencies that normally do not exist for the package (such as requiring "make" to run the test suite), use the DEPENDS and RDEPENDS variables in your recipe in order for the package to meet the dependencies. Here is an example where the package has a runtime dependency on "make":

         RDEPENDS_${PN}-ptest += "make"
                                

  • Add a function to build the test suite: Not many packages support cross-compilation of their test suites. Consequently, you usually need to add a cross-compilation function to the package.

    Many packages based on Automake compile and run the test suite by using a single command such as make check. However, the native make check builds and runs on the same computer, while cross-compiling requires that the package is built on the host but executed on the target. The built version of Automake that ships with the Yocto Project includes a patch that separates building and execution. Consequently, packages that use the unaltered, patched version of make check automatically cross-compiles.

    However, you still must add a do_compile_ptest function to build the test suite. Add a function similar to the following to your recipe:

         do_compile_ptest() {
            oe_runmake buildtest-TESTS
         }
                                

  • Ensure special configurations are set: If the package requires special configurations prior to compiling the test code, you must insert a do_configure_ptest function into the recipe.

  • Install the test suite: The ptest.bbclass class automatically copies the file run-ptest to the target and then runs make install-ptest to run the tests. If this is not enough, you need to create a do_install_ptest function and make sure it gets called after the "make install-ptest" completes.

5.11. Building Software from an External Source

By default, the OpenEmbedded build system does its work from within the Build Directory. The build process involves fetching the source files, unpacking them, and then patching them if necessary before the build takes place.

Situations exist where you might want to build software from source files that are external to and thus outside of the Source Directory. For example, suppose you have a project that includes a new BSP with a heavily customized kernel, a very minimal image, and some new user-space recipes. And, you want to minimize exposing the build system to the development team so that they can focus on their project and maintain everyone's workflow as much as possible. In this case, you want a kernel source directory on the development machine where the development occurs. You want the recipe's SRC_URI variable to point to the external directory and use it as is, not copy it.

To build from software that comes from an external source, all you need to do is change your recipe so that it inherits the externalsrc.bbclass class and then sets the S variable to point to your external source code. Here are the statements to put in your recipe:

     inherit externalsrc
     S = "/some/path/to/your/package/source"
            

It is important to know that the externalsrc.bbclass assumes that the source directory S and the Build Directory B are different even though these directories are the same by default. This assumption is important because it supports building different variants of the recipe by using the BBCLASSEXTEND variable. You could allow the Build Directory to be the same as the source directory but you would not be able to build more than one variant of the recipe. Consequently, if you are building multiple variants of the recipe, you need to establish a Build Directory that is different than the Source Directory.

5.12. Selecting an Initialization Manager

By default, the Yocto Project uses SysVinit as the initialization manager. However, support also exists for systemd, which is a full replacement for init with parallel starting of services, reduced shell overhead and other features that are used by many distributions.

If you want to use SysVinit, you do not have to do anything. But, if you want to use systemd, you must take some steps as described in the following sections.

Note

It is recommended that you create your own distribution configuration file to hold these settings instead of using your local.conf file. For information on creating your own distribution, see the "Creating Your Own Distribution" section.

5.12.1. Using systemd Exclusively

Set the following variables in your distribution configuration file as follows:

     DISTRO_FEATURES_append = " systemd"
     VIRTUAL-RUNTIME_init_manager = "systemd"
                

You can also prevent the sysvinit distribution feature from being automatically enabled as follows:

     DISTRO_FEATURES_BACKFILL_CONSIDERED = "sysvinit"
                

Doing so removes any redundant sysvinit scripts.

5.12.2. Using systemd for the Main Image and Using SysVinit for the Rescue Image

Set the following variables in your distribution configuration file as follows:

     DISTRO_FEATURES_append = " systemd"
     VIRTUAL-RUNTIME_init_manager = "systemd"
                

Doing so causes your main image to use the packagegroup-core-boot.bb recipe and systemd. The rescue/minimal image cannot use this package group. However, it can install sysvinit and the appropriate packages will have support for both systemd and sysvinit.

5.13. Excluding Recipes From the Build

You might find that there are groups of recipes or append files that you want to filter out of the build process. Usually, this is not necessary. However, on rare occasions where you might want to use a layer but exclude parts that are causing problems, such as introducing a different version of a recipe, you can use BBMASK to exclude the recipe.

It is possible to filter or mask out .bb and .bbappend files. You can do this by providing an expression with the BBMASK variable. Here is an example:

     BBMASK = "/meta-mymachine/recipes-maybe/"
            

Here, all .bb and .bbappend files in the directory that match the expression are ignored during the build process.

Note

The value you provide is passed to Python's regular expression compiler. The expression is compared against the full paths to the files. For complete syntax information, see Python's documentation at http://docs.python.org/release/2.3/lib/re-syntax.html.

5.14. Using an External SCM

If you're working on a recipe that pulls from an external Source Code Manager (SCM), it is possible to have the OpenEmbedded build system notice new recipe changes added to the SCM and then build the resulting package that depends on the new recipes by using the latest versions. This only works for SCMs from which it is possible to get a sensible revision number for changes. Currently, you can do this with Apache Subversion (SVN), Git, and Bazaar (BZR) repositories.

To enable this behavior, simply add the following to the local.conf configuration file found in the Build Directory:

     SRCREV_pn-<PN> = "${AUTOREV}"
            

where PN is the name of the recipe for which you want to enable automatic source revision updating.

5.15. Creating a Read-Only Root Filesystem

Suppose, for security reasons, you need to disable your target device's root filesystem's write permissions (i.e. you need a read-only root filesystem). Or, perhaps you are running the device's operating system from a read-only storage device. For either case, you can customize your image for that behavior.

Note

Supporting a read-only root filesystem requires that the system and applications do not try to write to the root filesystem. You must configure all parts of the target system to write elsewhere, or to gracefully fail in the event of failing to write to the root filesystem.

5.15.1. Creating the Root Filesystem

To create the read-only root filesystem, simply add the read-only-rootfs feature to your image. Using either of the following statements in your image recipe or from within the local.conf file found in the Build Directory causes the build system to create a read-only root filesystem:

     IMAGE_FEATURES = "read-only-rootfs"
                

or

     EXTRA_IMAGE_FEATURES = "read-only-rootfs"
                

For more information on how to use these variables, see the "Customizing Images Using Custom IMAGE_FEATURES and EXTRA_IMAGE_FEATURES" section. For information on the variables, see IMAGE_FEATURES and EXTRA_IMAGE_FEATURES.

5.15.2. Post-Installation Scripts

It is very important that you make sure all post-Installation (pkg_postinst) scripts for packages that are installed into the image can be run at the time when the root filesystem is created during the build on the host system. These scripts cannot attempt to run during first-boot on the target device. With the read-only-rootfs feature enabled, the build system checks during root filesystem creation to make sure all post-installation scripts succeed. If any of these scripts still need to be run after the root filesystem is created, the build immediately fails. These checks during build time ensure that the build fails rather than the target device fails later during its initial boot operation.

Most of the common post-installation scripts generated by the build system for the out-of-the-box Yocto Project are engineered so that they can run during root filesystem creation (e.g. post-installation scripts for caching fonts). However, if you create and add custom scripts, you need to be sure they can be run during file system creation.

Here are some common problems that prevent post-installation scripts from running during root filesystem creation:

  • Not using $D in front of absolute paths: The build system defines $D at root filesystem creation time, and it is blank when run on the target device. This implies two purposes for $D: ensuring paths are valid in both the host and target environments, and checking to determine which environment is being used as a method for taking appropriate actions.

  • Attempting to run processes that are specific to or dependent on the target architecture: You can work around these attempts by using native tools to accomplish the same tasks, or by alternatively running the processes under QEMU, which has the qemu_run_binary function. For more information, see the meta/classes/qemu.bbclass class in the Source Directory.

5.15.3. Areas With Write Access

With the read-only-rootfs feature enabled, any attempt by the target to write to the root filesystem at runtime fails. Consequently, you must make sure that you configure processes and applications that attempt these types of writes do so to directories with write access (e.g. /tmp or /var/run).

5.16. Debugging With the GNU Project Debugger (GDB) Remotely

GDB allows you to examine running programs, which in turn helps you to understand and fix problems. It also allows you to perform post-mortem style analysis of program crashes. GDB is available as a package within the Yocto Project and is installed in SDK images by default. See the "Images" chapter in the Yocto Project Reference Manual for a description of these images. You can find information on GDB at http://sourceware.org/gdb/.

Tip

For best results, install -dbg packages for the applications you are going to debug. Doing so makes extra debug symbols available that give you more meaningful output.

Sometimes, due to memory or disk space constraints, it is not possible to use GDB directly on the remote target to debug applications. These constraints arise because GDB needs to load the debugging information and the binaries of the process being debugged. Additionally, GDB needs to perform many computations to locate information such as function names, variable names and values, stack traces and so forth - even before starting the debugging process. These extra computations place more load on the target system and can alter the characteristics of the program being debugged.

To help get past the previously mentioned constraints, you can use Gdbserver. Gdbserver runs on the remote target and does not load any debugging information from the debugged process. Instead, a GDB instance processes the debugging information that is run on a remote computer - the host GDB. The host GDB then sends control commands to Gdbserver to make it stop or start the debugged program, as well as read or write memory regions of that debugged program. All the debugging information loaded and processed as well as all the heavy debugging is done by the host GDB. Offloading these processes gives the Gdbserver running on the target a chance to remain small and fast.

Because the host GDB is responsible for loading the debugging information and for doing the necessary processing to make actual debugging happen, the user has to make sure the host can access the unstripped binaries complete with their debugging information and also be sure the target is compiled with no optimizations. The host GDB must also have local access to all the libraries used by the debugged program. Because Gdbserver does not need any local debugging information, the binaries on the remote target can remain stripped. However, the binaries must also be compiled without optimization so they match the host's binaries.

To remain consistent with GDB documentation and terminology, the binary being debugged on the remote target machine is referred to as the "inferior" binary. For documentation on GDB see the GDB site.

The remainder of this section describes the steps you need to take to debug using the GNU project debugger.

5.16.1. Set Up the Cross-Development Debugging Environment

Before you can initiate a remote debugging session, you need to be sure you have set up the cross-development environment, toolchain, and sysroot. The "Preparing for Application Development" chapter of the Yocto Project Application Developer's Guide describes this process. Be sure you have read that chapter and have set up your environment.

5.16.2. Launch Gdbserver on the Target

Make sure Gdbserver is installed on the target. If it is not, install the package gdbserver, which needs the libthread-db1 package.

Here is an example that when entered from the host connects to the target and launches Gdbserver in order to "debug" a binary named helloworld:

     $ gdbserver localhost:2345 /usr/bin/helloworld
                

Gdbserver should now be listening on port 2345 for debugging commands coming from a remote GDB process that is running on the host computer. Communication between Gdbserver and the host GDB are done using TCP. To use other communication protocols, please refer to the Gdbserver documentation.

5.16.3. Launch GDB on the Host Computer

Running GDB on the host computer takes a number of stages, which this section describes.

5.16.3.1. Build the Cross-GDB Package

A suitable GDB cross-binary is required that runs on your host computer but also knows about the the ABI of the remote target. You can get this binary from the Cross-Development Toolchain. Here is an example where the toolchain has been installed in the default directory /opt/poky/1.4.2:

     /opt/poky/1.4/sysroots/i686-pokysdk-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gdb
                    

where arm is the target architecture and linux-gnueabi is the target ABI.

Alternatively, you can use BitBake to build the gdb-cross binary. Here is an example:

     $ bitbake gdb-cross
                    

Once the binary is built, you can find it here:

     tmp/sysroots/<host-arch>/usr/bin/<target-platform>/<target-abi>-gdb
                    

5.16.3.2. Create the GDB Initialization File and Point to Your Root Filesystem

Aside from the GDB cross-binary, you also need a GDB initialization file in the same top directory in which your binary resides. When you start GDB on your host development system, GDB finds this initialization file and executes all the commands within. For information on the .gdbinit, see "Debugging with GDB", which is maintained by sourceware.org.

You need to add a statement in the .gdbinit file that points to your root filesystem. Here is an example that points to the root filesystem for an ARM-based target device:

     set sysroot /home/jzhang/sysroot_arm
                    

5.16.3.3. Launch the Host GDB

Before launching the host GDB, you need to be sure you have sourced the cross-debugging environment script, which if you installed the root filesystem in the default location is at /opt/poky/1.4.2 and begins with the string "environment-setup". For more information, see the "Setting Up the Cross-Development Environment" section in the Yocto Project Application Developer's Guide.

Finally, switch to the directory where the binary resides and run the cross-gdb binary. Provide the binary file you are going to debug. For example, the following command continues with the example used in the previous section by loading the helloworld binary as well as the debugging information:

     $ arm-poky-linux-gnuabi-gdb helloworld
                    

The commands in your .gdbinit execute and the GDB prompt appears.

5.16.4. Connect to the Remote GDB Server

From the target, you need to connect to the remote GDB server that is running on the host. You need to specify the remote host and port. Here is the command continuing with the example:

     target remote 192.168.7.2:2345
                

5.16.5. Use the Debugger

You can now proceed with debugging as normal - as if you were debugging on the local machine. For example, to instruct GDB to break in the "main" function and then continue with execution of the inferior binary use the following commands from within GDB:

     (gdb) break main
     (gdb) continue
                

For more information about using GDB, see the project's online documentation at http://sourceware.org/gdb/download/onlinedocs/.

5.17. Profiling with OProfile

OProfile is a statistical profiler well suited for finding performance bottlenecks in both user-space software and in the kernel. This profiler provides answers to questions like "Which functions does my application spend the most time in when doing X?" Because the OpenEmbedded build system is well integrated with OProfile, it makes profiling applications on target hardware straightforward.

Note

For more information on how to set up and run OProfile, see the "OProfile" section in the Yocto Project Profiling and Tracing Manual.

To use OProfile, you need an image that has OProfile installed. The easiest way to do this is with tools-profile in the IMAGE_FEATURES variable. You also need debugging symbols to be available on the system where the analysis takes place. You can gain access to the symbols by using dbg-pkgs in the IMAGE_FEATURES variable or by installing the appropriate -dbg packages.

For successful call graph analysis, the binaries must preserve the frame pointer register and should also be compiled with the -fno-omit-framepointer flag. You can achieve this by setting the SELECTED_OPTIMIZATION variable with the following options:

     -fexpensive-optimizations
     -fno-omit-framepointer
     -frename-registers
     -O2
            

You can also achieve it by setting the DEBUG_BUILD variable to "1" in the local.conf configuration file. If you use the DEBUG_BUILD variable, you also add extra debugging information that can make the debug packages large.

5.17.1. Profiling on the Target

Using OProfile you can perform all the profiling work on the target device. A simple OProfile session might look like the following:

     # opcontrol --reset
     # opcontrol --start --separate=lib --no-vmlinux -c 5
              .
              .
        [do whatever is being profiled]
              .
              .
     # opcontrol --stop
     $ opreport -cl
                

In this example, the reset command clears any previously profiled data. The next command starts OProfile. The options used when starting the profiler separate dynamic library data within applications, disable kernel profiling, and enable callgraphing up to five levels deep.

Note

To profile the kernel, you would specify the --vmlinux=/path/to/vmlinux option. The vmlinux file is usually in the source directory in the /boot/ directory and must match the running kernel.

After you perform your profiling tasks, the next command stops the profiler. After that, you can view results with the opreport command with options to see the separate library symbols and callgraph information.

Callgraphing logs information about time spent in functions and about a function's calling function (parent) and called functions (children). The higher the callgraphing depth, the more accurate the results. However, higher depths also increase the logging overhead. Consequently, you should take care when setting the callgraphing depth.

Note

On ARM, binaries need to have the frame pointer enabled for callgraphing to work. To accomplish this use the -fno-omit-framepointer option with gcc.

For more information on using OProfile, see the OProfile online documentation at http://oprofile.sourceforge.net/docs/.

5.17.2. Using OProfileUI

A graphical user interface for OProfile is also available. You can download and build this interface from the Yocto Project at http://git.yoctoproject.org/cgit.cgi/oprofileui/. If the "tools-profile" image feature is selected, all necessary binaries are installed onto the target device for OProfileUI interaction. For a list of image features that ship with the Yocto Project, see the "Images" section in the Yocto Project Reference Manual.

Even though the source directory usually includes all needed patches on the target device, you might find you need other OProfile patches for recent OProfileUI features. If so, see the OProfileUI README for the most recent information.

5.17.2.1. Online Mode

Using OProfile in online mode assumes a working network connection with the target hardware. With this connection, you just need to run "oprofile-server" on the device. By default, OProfile listens on port 4224.

Note

You can change the port using the --port command-line option.

The client program is called oprofile-viewer and its UI is relatively straightforward. You access key functionality through the buttons on the toolbar, which are duplicated in the menus. Here are the buttons:

  • Connect: Connects to the remote host. You can also supply the IP address or hostname.

  • Disconnect: Disconnects from the target.

  • Start: Starts profiling on the device.

  • Stop: Stops profiling on the device and downloads the data to the local host. Stopping the profiler generates the profile and displays it in the viewer.

  • Download: Downloads the data from the target and generates the profile, which appears in the viewer.

  • Reset: Resets the sample data on the device. Resetting the data removes sample information collected from previous sampling runs. Be sure you reset the data if you do not want to include old sample information.

  • Save: Saves the data downloaded from the target to another directory for later examination.

  • Open: Loads previously saved data.

The client downloads the complete 'profile archive' from the target to the host for processing. This archive is a directory that contains the sample data, the object files, and the debug information for the object files. The archive is then converted using the oparchconv script, which is included in this distribution. The script uses opimport to convert the archive from the target to something that can be processed on the host.

Downloaded archives reside in the Build Directory in /tmp and are cleared up when they are no longer in use.

If you wish to perform kernel profiling, you need to be sure a vmlinux file that matches the running kernel is available. In the source directory, that file is usually located in /boot/vmlinux-KERNELVERSION, where KERNEL-version is the version of the kernel. The OpenEmbedded build system generates separate vmlinux packages for each kernel it builds. Thus, it should just be a question of making sure a matching package is installed (e.g. opkg install kernel-vmlinux). The files are automatically installed into development and profiling images alongside OProfile. A configuration option exists within the OProfileUI settings page that you can use to enter the location of the vmlinux file.

Waiting for debug symbols to transfer from the device can be slow, and it is not always necessary to actually have them on the device for OProfile use. All that is needed is a copy of the filesystem with the debug symbols present on the viewer system. The "Launch GDB on the Host Computer" section covers how to create such a directory with the Source Directory and how to use the OProfileUI Settings Dialog to specify the location. If you specify the directory, it will be used when the file checksums match those on the system you are profiling.

5.17.2.2. Offline Mode

If network access to the target is unavailable, you can generate an archive for processing in oprofile-viewer as follows:

     # opcontrol --reset
     # opcontrol --start --separate=lib --no-vmlinux -c 5
            .
            .
     [do whatever is being profiled]
            .
            .
     # opcontrol --stop
     # oparchive -o my_archive
                    

In the above example, my_archive is the name of the archive directory where you would like the profile archive to be kept. After the directory is created, you can copy it to another host and load it using oprofile-viewer open functionality. If necessary, the archive is converted.

5.18. Maintaining Open Source License Compliance During Your Product's Lifecycle

One of the concerns for a development organization using open source software is how to maintain compliance with various open source licensing during the lifecycle of the product. While this section does not provide legal advice or comprehensively cover all scenarios, it does present methods that you can use to assist you in meeting the compliance requirements during a software release.

With hundreds of different open source licenses that the Yocto Project tracks, it is difficult to know the requirements of each and every license. However, we can begin to cover the requirements of the major FLOSS licenses, by assuming that there are three main areas of concern:

  • Source code must be provided.

  • License text for the software must be provided.

  • Compilation scripts and modifications to the source code must be provided.

There are other requirements beyond the scope of these three and the methods described in this section (e.g. the mechanism through which source code is distributed).

As different organizations have different methods of complying with open source licensing, this section is not meant to imply that there is only one single way to meet your compliance obligations, but rather to describe one method of achieving compliance. The remainder of this section describes methods supported to meet the previously mentioned three requirements. Once you take steps to meet these requirements, and prior to releasing images, sources, and the build system, you should audit all artifacts to ensure completeness.

Note

The Yocto Project generates a license manifest during image creation that is located in ${DEPLOY_DIR}/licenses/<image_name-datestamp> to assist with any audits.

5.18.1. Providing the Source Code

Compliance activities should begin before you generate the final image. The first thing you should look at is the requirement that tops the list for most compliance groups - providing the source. The Yocto Project has a few ways of meeting this requirement.

One of the easiest ways to meet this requirement is to provide the entire DL_DIR used by the build. This method, however, has a few issues. The most obvious is the size of the directory since it includes all sources used in the build and not just the source used in the released image. It will include toolchain source, and other artifacts, which you would not generally release. However, the more serious issue for most companies is accidental release of proprietary software. The Yocto Project provides an archiver class to help avoid some of these concerns. See the "Archiving Sources - archive*.bbclass" section in the Yocto Project Reference Manual for information on this class.

Before you employ DL_DIR or the archiver class, you need to decide how you choose to provide source. The source archiver class can generate tarballs and SRPMs and can create them with various levels of compliance in mind. One way of doing this (but certainly not the only way) is to release just the original source as a tarball. You can do this by adding the following to the local.conf file found in the Build Directory:

     ARCHIVER_MODE ?= "original"
     ARCHIVER_CLASS = "${@'archive-${ARCHIVER_MODE}-source' if
     ARCHIVER_MODE != 'none' else ''}"
     INHERIT += "${ARCHIVER_CLASS}"
     SOURCE_ARCHIVE_PACKAGE_TYPE = "tar"
                

During the creation of your image, the source from all recipes that deploy packages to the image is placed within subdirectories of DEPLOY_DIR/sources based on the LICENSE for each recipe. Releasing the entire directory enables you to comply with requirements concerning providing the unmodified source. It is important to note that the size of the directory can get large.

A way to help mitigate the size issue is to only release tarballs for licenses that require the release of source. Let's assume you are only concerned with GPL code as identified with the following:

     $ cd poky/build/tmp/deploy/sources
     $ mkdir ~/gpl_source_release
     $ for dir in */*GPL*; do cp -r $dir ~/gpl_source_release; done
                

At this point, you could create a tarball from the gpl_source_release directory and provide that to the end user. This method would be a step toward achieving compliance with section 3a of GPLv2 and with section 6 of GPLv3.

5.18.2. Providing License Text

One requirement that is often overlooked is inclusion of license text. This requirement also needs to be dealt with prior to generating the final image. Some licenses require the license text to accompany the binary. You can achieve this by adding the following to your local.conf file:

     COPY_LIC_MANIFEST = "1"
     COPY_LIC_DIRS = "1"
                

Adding these statements to the configuration file ensures that the licenses collected during package generation are included on your image. As the source archiver has already archived the original unmodified source that contains the license files, you would have already met the requirements for inclusion of the license information with source as defined by the GPL and other open source licenses.

5.18.3. Providing Compilation Scripts and Source Code Modifications

At this point, we have addressed all we need to address prior to generating the image. The next two requirements are addressed during the final packaging of the release.

By releasing the version of the OpenEmbedded build system and the layers used during the build, you will be providing both compilation scripts and the source code modifications in one step.

If the deployment team has a BSP layer and a distro layer, and those those layers are used to patch, compile, package, or modify (in any way) any open source software included in your released images, you may be required to to release those layers under section 3 of GPLv2 or section 1 of GPLv3. One way of doing that is with a clean checkout of the version of the Yocto Project and layers used during your build. Here is an example:

     # We built using the dylan branch of the poky repo
     $ git clone -b dylan git://git.yoctoproject.org/poky
     $ cd poky
     # We built using the release_branch for our layers
     $ git clone -b release_branch git://git.mycompany.com/meta-my-bsp-layer
     $ git clone -b release_branch git://git.mycompany.com/meta-my-software-layer
     # clean up the .git repos
     $ find . -name ".git" -type d -exec rm -rf {} \;
                

One thing a development organization might want to consider for end-user convenience is to modify meta-yocto/conf/bblayers.conf.sample to ensure that when the end user utilizes the released build system to build an image, the development organization's layers are included in the bblayers.conf file automatically:

     # LAYER_CONF_VERSION is increased each time build/conf/bblayers.conf
     # changes incompatibly
     LCONF_VERSION = "6"

     BBPATH = "${TOPDIR}"
     BBFILES ?= ""

     BBLAYERS ?= " \
       ##COREBASE##/meta \
       ##COREBASE##/meta-yocto \
       ##COREBASE##/meta-yocto-bsp \
       ##COREBASE##/meta-mylayer \
       "

     BBLAYERS_NON_REMOVABLE ?= " \
       ##COREBASE##/meta \
       ##COREBASE##/meta-yocto \
       "
                

Creating and providing an archive of the Metadata layers (recipes, configuration files, and so forth) enables you to meet your requirements to include the scripts to control compilation as well as any modifications to the original source.

Yocto Project Application Developer's Guide

Jessica Zhang

Intel Corporation

Permission is granted to copy, distribute and/or modify this document under the terms of the Creative Commons Attribution-Share Alike 2.0 UK: England & Wales as published by Creative Commons.

Note

Due to production processes, there could be differences between the Yocto Project documentation bundled in the release tarball and the Yocto Project Application Developer's Guide on the Yocto Project website. For the latest version of this manual, see the manual on the website.
Revision History
Revision 1.06 April 2011
Released with the Yocto Project 1.0 Release.
Revision 1.0.123 May 2011
Released with the Yocto Project 1.0.1 Release.
Revision 1.16 October 2011
Released with the Yocto Project 1.1 Release.
Revision 1.2April 2012
Released with the Yocto Project 1.2 Release.
Revision 1.3October 2012
Released with the Yocto Project 1.3 Release.
Revision 1.4April 2013
Released with the Yocto Project 1.4 Release.
Revision 1.4.1June 2013
Released with the Yocto Project 1.4.1 Release.
Revision 1.4.2August 2013
Released with the Yocto Project 1.4.2 Release.

Chapter 1. Introduction

Welcome to the Yocto Project Application Developer's Guide. This manual provides information that lets you begin developing applications using the Yocto Project.

The Yocto Project provides an application development environment based on an Application Development Toolkit (ADT) and the availability of stand-alone cross-development toolchains and other tools. This manual describes the ADT and how you can configure and install it, how to access and use the cross-development toolchains, how to customize the development packages installation, how to use command line development for both Autotools-based and Makefile-based projects, and an introduction to the Eclipse™ IDE Yocto Plug-in.

Note

The ADT is distribution-neutral and does not require the Yocto Project reference distribution, which is called Poky. This manual, however, uses examples that use the Poky distribution.

1.1. The Application Development Toolkit (ADT)

Part of the Yocto Project development solution is an Application Development Toolkit (ADT). The ADT provides you with a custom-built, cross-development platform suited for developing a user-targeted product application.

Fundamentally, the ADT consists of the following:

  • An architecture-specific cross-toolchain and matching sysroot both built by the OpenEmbedded build system. The toolchain and sysroot are based on a Metadata configuration and extensions, which allows you to cross-develop on the host machine for the target hardware.

  • The Eclipse IDE Yocto Plug-in.

  • The Quick EMUlator (QEMU), which lets you simulate target hardware.

  • Various user-space tools that greatly enhance your application development experience.

1.1.1. The Cross-Development Toolchain

The Cross-Development Toolchain consists of a cross-compiler, cross-linker, and cross-debugger that are used to develop user-space applications for targeted hardware. This toolchain is created either by running the ADT Installer script, a toolchain installer script, or through a Build Directory that is based on your Metadata configuration or extension for your targeted device. The cross-toolchain works with a matching target sysroot.

1.1.2. Sysroot

The matching target sysroot contains needed headers and libraries for generating binaries that run on the target architecture. The sysroot is based on the target root filesystem image that is built by the OpenEmbedded build system and uses the same Metadata configuration used to build the cross-toolchain.

1.1.3. Eclipse Yocto Plug-in

The Eclipse IDE is a popular development environment and it fully supports development using the Yocto Project. When you install and configure the Eclipse Yocto Project Plug-in into the Eclipse IDE, you maximize your Yocto Project experience. Installing and configuring the Plug-in results in an environment that has extensions specifically designed to let you more easily develop software. These extensions allow for cross-compilation, deployment, and execution of your output into a QEMU emulation session. You can also perform cross-debugging and profiling. The environment also supports a suite of tools that allows you to perform remote profiling, tracing, collection of power data, collection of latency data, and collection of performance data.

For information about the application development workflow that uses the Eclipse IDE and for a detailed example of how to install and configure the Eclipse Yocto Project Plug-in, see the "Working Within Eclipse" section of the Yocto Project Development Manual.

1.1.4. The QEMU Emulator

The QEMU emulator allows you to simulate your hardware while running your application or image. QEMU is made available a number of ways:

  • If you use the ADT Installer script to install ADT, you can specify whether or not to install QEMU.

  • If you have downloaded a Yocto Project release and unpacked it to create a Source Directory and you have sourced the environment setup script, QEMU is installed and automatically available.

  • If you have installed the cross-toolchain tarball and you have sourced the toolchain's setup environment script, QEMU is also installed and automatically available.

1.1.5. User-Space Tools

User-space tools are included as part of the distribution. You will find these tools helpful during development. The tools include LatencyTOP, PowerTOP, OProfile, Perf, SystemTap, and Lttng-ust. These tools are common development tools for the Linux platform.

  • LatencyTOP: LatencyTOP focuses on latency that causes skips in audio, stutters in your desktop experience, or situations that overload your server even when you have plenty of CPU power left. You can find out more about LatencyTOP at https://latencytop.org/.

  • PowerTOP: Helps you determine what software is using the most power. You can find out more about PowerTOP at https://01.org/powertop/.

  • OProfile: A system-wide profiler for Linux systems that is capable of profiling all running code at low overhead. You can find out more about OProfile at http://oprofile.sourceforge.net/about/. For examples on how to setup and use this tool, see the "OProfile" section in the Yocto Project Profiling and Tracing Manual.

  • Perf: Performance counters for Linux used to keep track of certain types of hardware and software events. For more information on these types of counters see https://perf.wiki.kernel.org/ and click on “Perf tools.” For examples on how to setup and use this tool, see the "perf" section in the Yocto Project Profiling and Tracing Manual.

  • SystemTap: A free software infrastructure that simplifies information gathering about a running Linux system. This information helps you diagnose performance or functional problems. SystemTap is not available as a user-space tool through the Eclipse IDE Yocto Plug-in. See http://sourceware.org/systemtap for more information on SystemTap. For examples on how to setup and use this tool, see the "SystemTap" section in the Yocto Project Profiling and Tracing Manual.

  • Lttng-ust: A User-space Tracer designed to provide detailed information on user-space activity. See http://lttng.org/ust for more information on Lttng-ust.

Chapter 2. Preparing for Application Development

In order to develop applications, you need set up your host development system. Several ways exist that allow you to install cross-development tools, QEMU, the Eclipse Yocto Plug-in, and other tools. This chapter describes how to prepare for application development.

2.1. Installing the ADT and Toolchains

The following list describes installation methods that set up varying degrees of tool availability on your system. Regardless of the installation method you choose, you must source the cross-toolchain environment setup script before you use a toolchain. See the "Setting Up the Cross-Development Environment" section for more information.

Note

Avoid mixing installation methods when installing toolchains for different architectures. For example, avoid using the ADT Installer to install some toolchains and then hand-installing cross-development toolchains by running the toolchain installer for different architectures. Mixing installation methods can result in situations where the ADT Installer becomes unreliable and might not install the toolchain.

If you must mix installation methods, you might avoid problems by deleting /var/lib/opkg, thus purging the opkg package metadata

  • Use the ADT installer script: This method is the recommended way to install the ADT because it automates much of the process for you. For example, you can configure the installation to install the QEMU emulator and the user-space NFS, specify which root filesystem profiles to download, and define the target sysroot location.

  • Use an existing toolchain: Using this method, you select and download an architecture-specific toolchain installer and then run the script to hand-install the toolchain. If you use this method, you just get the cross-toolchain and QEMU - you do not get any of the other mentioned benefits had you run the ADT Installer script.

  • Use the toolchain from within the Build Directory: If you already have a Build Directory, you can build the cross-toolchain within the directory. However, like the previous method mentioned, you only get the cross-toolchain and QEMU - you do not get any of the other benefits without taking separate steps.

2.1.1. Using the ADT Installer

To run the ADT Installer, you need to get the ADT Installer tarball, be sure you have the necessary host development packages that support the ADT Installer, and then run the ADT Installer Script.

For a list of the host packages needed to support ADT installation and use, see the "ADT Installer Extras" lists in the "Required Packages for the Host Development System" section of the Yocto Project Reference Manual.

2.1.1.1. Getting the ADT Installer Tarball

The ADT Installer is contained in the ADT Installer tarball. You can download the tarball into any directory from the Index of Releases, specifically at http://downloads.yoctoproject.org/releases/yocto/yocto-1.4.2/adt-installer. Or, you can use BitBake to generate the tarball inside the existing Build Directory.

If you use BitBake to generate the ADT Installer tarball, you must source the environment setup script (oe-init-build-env) located in the Source Directory before running the BitBake command that creates the tarball.

The following example commands download the Poky tarball, set up the Source Directory, set up the environment while also creating the default Build Directory, and run the BitBake command that results in the tarball ~/yocto-project/build/tmp/deploy/sdk/adt_installer.tar.bz2:

     $ cd ~
     $ mkdir yocto-project
     $ cd yocto-project
     $ wget http://downloads.yoctoproject.org/releases/yocto/yocto-1.4.2/poky-dylan-9.0.2.tar.bz2
     $ tar xjf poky-dylan-9.0.2.tar.bz2
     $ source poky-dylan-9.0.2/oe-init-build-env
     $ bitbake adt-installer
                

2.1.1.2. Configuring and Running the ADT Installer Script

Before running the ADT Installer script, you need to unpack the tarball. You can unpack the tarball in any directory you wish. For example, this command copies the ADT Installer tarball from where it was built into the home directory and then unpacks the tarball into a top-level directory named adt-installer:

     $ cd ~
     $ cp ~/poky/build/tmp/deploy/sdk/adt_installer.tar.bz2 $HOME
     $ tar -xjf adt_installer.tar.bz2
                

Unpacking it creates the directory adt-installer, which contains the ADT Installer script (adt_installer) and its configuration file (adt_installer.conf).

Before you run the script, however, you should examine the ADT Installer configuration file and be sure you are going to get what you want. Your configurations determine which kernel and filesystem image are downloaded.

The following list describes the configurations you can define for the ADT Installer. For configuration values and restrictions, see the comments in the adt-installer.conf file:

  • YOCTOADT_REPO: This area includes the IPKG-based packages and the root filesystem upon which the installation is based. If you want to set up your own IPKG repository pointed to by YOCTOADT_REPO, you need to be sure that the directory structure follows the same layout as the reference directory set up at http://adtrepo.yoctoproject.org. Also, your repository needs to be accessible through HTTP.

  • YOCTOADT_TARGETS: The machine target architectures for which you want to set up cross-development environments.

  • YOCTOADT_QEMU: Indicates whether or not to install the emulator QEMU.

  • YOCTOADT_NFS_UTIL: Indicates whether or not to install user-mode NFS. If you plan to use the Eclipse IDE Yocto plug-in against QEMU, you should install NFS.

    Note

    To boot QEMU images using our userspace NFS server, you need to be running portmap or rpcbind. If you are running rpcbind, you will also need to add the -i option when rpcbind starts up. Please make sure you understand the security implications of doing this. You might also have to modify your firewall settings to allow NFS booting to work.
  • YOCTOADT_ROOTFS_<arch>: The root filesystem images you want to download from the YOCTOADT_IPKG_REPO repository.

  • YOCTOADT_TARGET_SYSROOT_IMAGE_<arch>: The particular root filesystem used to extract and create the target sysroot. The value of this variable must have been specified with YOCTOADT_ROOTFS_<arch>. For example, if you downloaded both minimal and sato-sdk images by setting YOCTOADT_ROOTFS_<arch> to "minimal sato-sdk", then YOCTOADT_ROOTFS_<arch> must be set to either minimal or sato-sdk.

  • YOCTOADT_TARGET_SYSROOT_LOC_<arch>: The location on the development host where the target sysroot is created.

After you have configured the adt_installer.conf file, run the installer using the following command. Be sure that you are not trying to use cross-compilation tools. When you run the installer, the environment must use a host gcc:

     $ cd ~/adt-installer
     $ ./adt_installer
                

Once the installer begins to run, you are asked to enter the location for cross-toolchain installation. The default location is /opt/poky/<release>. After either accepting the default location or selecting your own location, you are prompted to run the installation script interactively or in silent mode. If you want to closely monitor the installation, choose “I” for interactive mode rather than “S” for silent mode. Follow the prompts from the script to complete the installation.

Once the installation completes, the ADT, which includes the cross-toolchain, is installed in the selected installation directory. You will notice environment setup files for the cross-toolchain in the installation directory, and image tarballs in the adt-installer directory according to your installer configurations, and the target sysroot located according to the YOCTOADT_TARGET_SYSROOT_LOC_<arch> variable also in your configuration file.

2.1.2. Using a Cross-Toolchain Tarball

If you want to simply install the cross-toolchain by hand, you can do so by running the toolchain installer. If you use this method to install the cross-toolchain and you might still need to install the target sysroot by installing and extracting it separately. For information on how to install the sysroot, see the "Extracting the Root Filesystem" section.

Follow these steps:

  1. Go to http://downloads.yoctoproject.org/releases/yocto/yocto-1.4.2/toolchain/ and find the folder that matches your host development system (i.e. i686 for 32-bit machines or x86-64 for 64-bit machines).

  2. Go into that folder and download the toolchain installer whose name includes the appropriate target architecture. For example, if your host development system is an Intel-based 64-bit system and you are going to use your cross-toolchain for an Intel-based 32-bit target, go into the x86_64 folder and download the following installer:

         poky-eglibc-x86_64-i586-toolchain-gmae-1.4.2.sh
                        

    Note

    As an alternative to steps one and two, you can build the toolchain installer if you have a Build Directory. If you need GMAE, you should use the bitbake meta-toolchain-gmae command. Running the resulting installation script will support such development. If you are not concerned with GMAE, you can generate the toolchain installer using bitbake meta-toolchain. Either of these methods requires you to still install the target sysroot by installing and extracting it separately. For information on how to install the sysroot, see the "Extracting the Root Filesystem" section.

    A final method of building the toolchain installer exists that has significant advantages over the previous two methods. This method results in a toolchain installer that contains the sysroot that matches your target root filesystem. To build this installer, use the bitbake image -c populate_sdk command.

    Remember, before using any bitbake command, you must source the poky-dylan-9.0.2/oe-init-build-env script located in the Source Directory and you must make sure your conf/local.conf variables are correct. In particular, you need to be sure the MACHINE variable matches the architecture for which you are building and that the SDKMACHINE variable is correctly set if you are building a toolchain for an architecture that differs from your current development host machine.

    When the BitBake command completes, the toolchain installer will be in tmp/deploy/sdk in the Build Directory.

  3. Once you have the installer, run it to install the toolchain. You must change the permissions on the toolchain installer script so that it is executable.

    The following command shows how to run the installer given a toolchain tarball for a 64-bit development host system and a 32-bit target architecture. The example assumes the toolchain installer is located in ~/Downloads/.

         $ ~/Downloads/poky-eglibc-x86_64-i586-toolchain-gmae-1.4.2.sh
                        

    Note

    If you do not have write permissions for the directory into which you are installing the toolchain, the toolchain installer notifies you and exits. Be sure you have write permissions in the directory and run the installer again.

    Once the tarball is expanded, the cross-toolchain is installed. You will notice environment setup files for the cross-toolchain in the directory.

2.1.3. Using BitBake and the Build Directory

A final way of making the cross-toolchain available is to use BitBake to generate the toolchain within an existing Build Directory. This method does not install the toolchain into the default /opt directory. As with the previous method, if you need to install the target sysroot, you must do that separately as well.

Follow these steps to generate the toolchain into the Build Directory:

  1. Source the environment setup script oe-init-build-env located in the Source Directory.

  2. At this point, you should be sure that the MACHINE variable in the local.conf file found in the conf directory of the Build Directory is set for the target architecture. Comments within the local.conf file list the values you can use for the MACHINE variable.

    Note

    You can populate the Build Directory with the cross-toolchains for more than a single architecture. You just need to edit the MACHINE variable in the local.conf file and re-run the BitBake command.
  3. Run bitbake meta-ide-support to complete the cross-toolchain generation.

    Note

    If you change out of your working directory after you source the environment setup script and before you run the BitBake command, the command might not work. Be sure to run the BitBake command immediately after checking or editing the local.conf but without changing out of your working directory.

    Once the BitBake command finishes, the cross-toolchain is generated and populated within the Build Directory. You will notice environment setup files for the cross-toolchain in the Build Directory in the tmp directory. Setup script filenames contain the strings environment-setup.

    Be aware that when you use this method to install the toolchain you still need to separately extract and install the sysroot filesystem. For information on how to do this, see the "Extracting the Root Filesystem" section.

2.2. Setting Up the Cross-Development Environment

Before you can develop using the cross-toolchain, you need to set up the cross-development environment by sourcing the toolchain's environment setup script. If you used the ADT Installer or hand-installed cross-toolchain, then you can find this script in the directory you chose for installation. The default installation directory is the /opt/poky/1.4.2 directory. If you installed the toolchain in the Build Directory, you can find the environment setup script for the toolchain in the Build Directory's tmp directory.

Be sure to run the environment setup script that matches the architecture for which you are developing. Environment setup scripts begin with the string "environment-setup" and include as part of their name the architecture. For example, the toolchain environment setup script for a 64-bit IA-based architecture installed in the default installation directory would be the following:

     /opt/poky/1.4.2/environment-setup-x86_64-poky-linux
        

2.3. Securing Kernel and Filesystem Images

You will need to have a kernel and filesystem image to boot using your hardware or the QEMU emulator. Furthermore, if you plan on booting your image using NFS or you want to use the root filesystem as the target sysroot, you need to extract the root filesystem.

2.3.1. Getting the Images

To get the kernel and filesystem images, you either have to build them or download pre-built versions. You can find examples for both these situations in the "A Quick Test Run" section of the Yocto Project Quick Start.

The Yocto Project ships basic kernel and filesystem images for several architectures (x86, x86-64, mips, powerpc, and arm) that you can use unaltered in the QEMU emulator. These kernel images reside in the release area - http://downloads.yoctoproject.org/releases/yocto/yocto-1.4.2/machines and are ideal for experimentation using Yocto Project. For information on the image types you can build using the OpenEmbedded build system, see the "Images" chapter in the Yocto Project Reference Manual.

If you are planning on developing against your image and you are not building or using one of the Yocto Project development images (e.g. core-image-*-dev), you must be sure to include the development packages as part of your image recipe.

Furthermore, if you plan on remotely deploying and debugging your application from within the Eclipse IDE, you must have an image that contains the Yocto Target Communication Framework (TCF) agent (tcf-agent). By default, the Yocto Project provides only one type pre-built image that contains the tcf-agent. And, those images are SDK (e.g.core-image-sato-sdk).

If you want to use a different image type that contains the tcf-agent, you can do so one of two ways:

  • Modify the conf/local.conf configuration in the Build Directory and then rebuild the image. With this method, you need to modify the EXTRA_IMAGE_FEATURES variable to have the value of "tools-debug" before rebuilding the image. Once the image is rebuilt, the tcf-agent will be included in the image and is launched automatically after the boot.

  • Manually build the tcf-agent. To build the agent, follow these steps:

    1. Be sure the ADT is installed as described in the "Installing the ADT and Toolchains" section.

    2. Set up the cross-development environment as described in the "Setting Up the Cross-Development Environment" section.

    3. Get the tcf-agent source code using the following commands:

           $ git clone http://git.eclipse.org/gitroot/tcf/org.eclipse.tcf.agent.git
           $ cd agent
                                  
    4. Modify the Makefile.inc file for the cross-compilation environment by setting the OPSYS and MACHINE variables according to your target.

    5. Use the cross-development tools to build the tcf-agent. Before you "Make" the file, be sure your cross-tools are set up first. See the "Makefile-Based Projects" section for information on how to make sure the cross-tools are set up correctly.

      If the build is successful, the tcf-agent output will be obj/$(OPSYS)/$(MACHINE)/Debug/agent.

    6. Deploy the agent into the image's root filesystem.

2.3.2. Extracting the Root Filesystem

You must extract the root filesystem if you want to boot the image using NFS or you want to use the root filesystem as the target sysroot. For example, the Eclipse IDE environment with the Eclipse Yocto Plug-in installed allows you to use QEMU to boot under NFS. Another example is if you want to develop your target application using the root filesystem as the target sysroot.

To extract the root filesystem, first source the cross-development environment setup script and then use the runqemu-extract-sdk command on the filesystem image. For example, the following commands set up the environment and then extract the root filesystem from a previously built filesystem image tarball named core-image-sato-sdk-qemux86-2011091411831.rootfs.tar.bz2. The example extracts the root filesystem into the $HOME/qemux86-sato directory:

     $ source $HOME/toolchain_dir/environment-setup-i586-poky-linux
     $ runqemu-extract-sdk \
        ~Downloads/core-image-sato-sdk-qemux86-2011091411831.rootfs.tar.bz2 \
        $HOME/qemux86-sato
            

In this case, you could now point to the target sysroot at $HOME/qemux86-sato.

Chapter 3. Optionally Customizing the Development Packages Installation

Because the Yocto Project is suited for embedded Linux development, it is likely that you will need to customize your development packages installation. For example, if you are developing a minimal image, then you might not need certain packages (e.g. graphics support packages). Thus, you would like to be able to remove those packages from your target sysroot.

3.1. Package Management Systems

The OpenEmbedded build system supports the generation of sysroot files using three different Package Management Systems (PMS):

  • OPKG: A less well known PMS whose use originated in the OpenEmbedded and OpenWrt embedded Linux projects. This PMS works with files packaged in an .ipk format. See http://en.wikipedia.org/wiki/Opkg for more information about OPKG.

  • RPM: A more widely known PMS intended for GNU/Linux distributions. This PMS works with files packaged in an .rms format. The build system currently installs through this PMS by default. See http://en.wikipedia.org/wiki/RPM_Package_Manager for more information about RPM.

  • Debian: The PMS for Debian-based systems is built on many PMS tools. The lower-level PMS tool dpkg forms the base of the Debian PMS. For information on dpkg see http://en.wikipedia.org/wiki/Dpkg.

3.2. Configuring the PMS

Whichever PMS you are using, you need to be sure that the PACKAGE_CLASSES variable in the conf/local.conf file is set to reflect that system. The first value you choose for the variable specifies the package file format for the root filesystem at sysroot. Additional values specify additional formats for convenience or testing. See the configuration file for details.

Note

For build performance information related to the PMS, see the "Packaging - package*.bbclass" section in the Yocto Project Reference Manual.

As an example, consider a scenario where you are using OPKG and you want to add the libglade package to the target sysroot.

First, you should generate the ipk file for the libglade package and add it into a working opkg repository. Use these commands:

     $ bitbake libglade
     $ bitbake package-index
        

Next, source the environment setup script found in the Source Directory. Follow that by setting up the installation destination to point to your sysroot as <sysroot_dir>. Finally, have an OPKG configuration file <conf_file> that corresponds to the opkg repository you have just created. The following command forms should now work:

     $ opkg-cl –f <conf_file> -o <sysroot_dir> update
     $ opkg-cl –f <cconf_file> -o <sysroot_dir> \
        --force-overwrite install libglade
     $ opkg-cl –f <cconf_file> -o <sysroot_dir> \
        --force-overwrite install libglade-dbg
     $ opkg-cl –f <conf_file> -o <sysroot_dir> \
        --force-overwrite install libglade-dev
        

Chapter 4. Using the Command Line

Recall that earlier the manual discussed how to use an existing toolchain tarball that had been installed into the default installation directory, /opt/poky, which is outside of the Build Directory (see the section "Using a Cross-Toolchain Tarball)". And, that sourcing your architecture-specific environment setup script initializes a suitable cross-toolchain development environment. During the setup, locations for the compiler, QEMU scripts, QEMU binary, a special version of pkgconfig and other useful utilities are added to the PATH variable. Variables to assist pkgconfig and autotools are also defined so that, for example, configure.sh can find pre-generated test results for tests that need target hardware on which to run. These conditions allow you to easily use the toolchain outside of the OpenEmbedded build environment on both autotools-based projects and Makefile-based projects.

4.1. Autotools-Based Projects

Once you have a suitable cross-toolchain installed, it is very easy to develop a project outside of the OpenEmbedded build system. This section presents a simple "Helloworld" example that shows how to set up, compile, and run the project.

4.1.1. Creating and Running a Project Based on GNU Autotools

Follow these steps to create a simple autotools-based project:

  1. Create your directory: Create a clean directory for your project and then make that directory your working location:

         $ mkdir $HOME/helloworld
         $ cd $HOME/helloworld
                        
  2. Populate the directory: Create hello.c, Makefile.am, and configure.in files as follows:

    • For hello.c, include these lines:

           #include <stdio.h>
      
           main()
              {
                 printf("Hello World!\n");
              }
                                  
    • For Makefile.am, include these lines:

           bin_PROGRAMS = hello
           hello_SOURCES = hello.c
                                  
    • For configure.in, include these lines:

           AC_INIT(hello.c)
           AM_INIT_AUTOMAKE(hello,0.1)
           AC_PROG_CC
           AC_PROG_INSTALL
           AC_OUTPUT(Makefile)
                                  
  3. Source the cross-toolchain environment setup file: Installation of the cross-toolchain creates a cross-toolchain environment setup script in the directory that the ADT was installed. Before you can use the tools to develop your project, you must source this setup script. The script begins with the string "environment-setup" and contains the machine architecture, which is followed by the string "poky-linux". Here is an example that sources a script from the default ADT installation directory that uses the 32-bit Intel x86 Architecture and using the dylan Yocto Project release:

         $ source /opt/poky/1.4.2/environment-setup-i586-poky-linux
                        
  4. Generate the local aclocal.m4 files and create the configure script: The following GNU Autotools generate the local aclocal.m4 files and create the configure script:

         $ aclocal
         $ autoconf
                        
  5. Generate files needed by GNU coding standards: GNU coding standards require certain files in order for the project to be compliant. This command creates those files:

         $ touch NEWS README AUTHORS ChangeLog
                        
  6. Generate the configure file: This command generates the configure:

         $ automake -a
                        
  7. Cross-compile the project: This command compiles the project using the cross-compiler:

         $ ./configure ${CONFIGURE_FLAGS}
                        
  8. Make and install the project: These two commands generate and install the project into the destination directory:

         $ make
         $ make install DESTDIR=./tmp
                        
  9. Verify the installation: This command is a simple way to verify the installation of your project. Running the command prints the architecture on which the binary file can run. This architecture should be the same architecture that the installed cross-toolchain supports.

         $ file ./tmp/usr/local/bin/hello
                        
  10. Execute your project: To execute the project in the shell, simply enter the name. You could also copy the binary to the actual target hardware and run the project there as well:

         $ ./hello
                        

    As expected, the project displays the "Hello World!" message.

4.1.2. Passing Host Options

For an Autotools-based project, you can use the cross-toolchain by just passing the appropriate host option to configure.sh. The host option you use is derived from the name of the environment setup script found in the directory in which you installed the cross-toolchain. For example, the host option for an ARM-based target that uses the GNU EABI is armv5te-poky-linux-gnueabi. You will notice that the name of the script is environment-setup-armv5te-poky-linux-gnueabi. Thus, the following command works:

     $ ./configure --host=armv5te-poky-linux-gnueabi \
        --with-libtool-sysroot=<sysroot-dir>
            

This single command updates your project and rebuilds it using the appropriate cross-toolchain tools.

Note

If configure script results in problems recognizing the --with-libtool-sysroot=<sysroot-dir> option, regenerate the script to enable the support by doing the following and then re-running the script:
     $ libtoolize --automake
     $ aclocal -I ${OECORE_NATIVE_SYSROOT}/usr/share/aclocal \
        [-I <dir_containing_your_project-specific_m4_macros>]
     $ autoconf
     $ autoheader
     $ automake -a
                

4.2. Makefile-Based Projects

For a Makefile-based project, you use the cross-toolchain by making sure the tools are used. You can do this as follows:

     CC=arm-poky-linux-gnueabi-gcc
     LD=arm-poky-linux-gnueabi-ld
     CFLAGS=”${CFLAGS} --sysroot=<sysroot-dir>”
     CXXFLAGS=”${CXXFLAGS} --sysroot=<sysroot-dir>”
        

Yocto Project Board Support Package Developer's Guide

Tom Zanussi

Intel Corporation

Richard Purdie

Linux Foundation

Permission is granted to copy, distribute and/or modify this document under the terms of the Creative Commons Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales as published by Creative Commons.

Note

Due to production processes, there could be differences between the Yocto Project documentation bundled in the release tarball and the Yocto Project Board Support Package (BSP) Developer's Guide on the Yocto Project website. For the latest version of this manual, see the manual on the website.
Revision History
Revision 0.924 November 2010
The initial document draft released with the Yocto Project 0.9 Release.
Revision 1.06 April 2011
Released with the Yocto Project 1.0 Release.
Revision 1.0.123 May 2011
Released with the Yocto Project 1.0.1 Release.
Revision 1.16 October 2011
Released with the Yocto Project 1.1 Release.
Revision 1.2April 2012
Released with the Yocto Project 1.2 Release.
Revision 1.3October 2012
Released with the Yocto Project 1.3 Release.
Revision 1.4April 2013
Released with the Yocto Project 1.4 Release.
Revision 1.4.1June 2013
Released with the Yocto Project 1.4.1 Release.
Revision 1.4.2August 2013
Released with the Yocto Project 1.4.2 Release.

Chapter 1. Board Support Packages (BSP) - Developer's Guide

A Board Support Package (BSP) is a collection of information that defines how to support a particular hardware device, set of devices, or hardware platform. The BSP includes information about the hardware features present on the device and kernel configuration information along with any additional hardware drivers required. The BSP also lists any additional software components required in addition to a generic Linux software stack for both essential and optional platform features.

This guide presents information about BSP Layers, defines a structure for components so that BSPs follow a commonly understood layout, discusses how to customize a recipe for a BSP, addresses BSP licensing, and provides information that shows you how to create and manage a BSP Layer using two Yocto Project BSP Tools.

1.1. BSP Layers

The BSP consists of a file structure inside a base directory. Collectively, you can think of the base directory and the file structure as a BSP Layer. BSP Layers use the following naming convention:

     meta-<bsp_name>
                

"bsp_name" is a placeholder for the machine or platform name.

The layer's base directory (meta-<bsp_name>) is the root of the BSP Layer. This root is what you add to the BBLAYERS variable in the conf/bblayers.conf file found in the Build Directory. Adding the root allows the OpenEmbedded build system to recognize the BSP definition and from it build an image. Here is an example:

     BBLAYERS = ?" \
       /usr/local/src/yocto/meta \
       /usr/local/src/yocto/meta-yocto \
       /usr/local/src/yocto/meta-yocto-bsp \
       /usr/local/src/yocto/meta-mylayer \
       "

     BBLAYERS_NON_REMOVABLE ?= " \
       /usr/local/src/yocto/meta \
       /usr/local/src/yocto/meta-yocto \
       "
                

Some BSPs require additional layers on top of the BSP's root layer in order to be functional. For these cases, you also need to add those layers to the BBLAYERS variable in order to build the BSP. You must also specify in the "Dependencies" section of the BSP's README file any requirements for additional layers and, preferably, any build instructions that might be contained elsewhere in the README file.

Some layers function as a layer to hold other BSP layers. An example of this type of layer is the meta-intel layer. The meta-intel layer contains over 10 individual BSP layers.

For more detailed information on layers, see the "Understanding and Creating Layers" section of the Yocto Project Development Manual.

1.2. Example Filesystem Layout

Providing a common form allows end-users to understand and become familiar with the layout. A common format also encourages standardization of software support of hardware.

The proposed form does have elements that are specific to the OpenEmbedded build system. It is intended that this information can be used by other build systems besides the OpenEmbedded build system and that it will be simple to extract information and convert it to other formats if required. The OpenEmbedded build system, through its standard layers mechanism, can directly accept the format described as a layer. The BSP captures all the hardware-specific details in one place in a standard format, which is useful for any person wishing to use the hardware platform regardless of the build system they are using.

The BSP specification does not include a build system or other tools - it is concerned with the hardware-specific components only. At the end-distribution point, you can ship the BSP combined with a build system and other tools. However, it is important to maintain the distinction that these are separate components that happen to be combined in certain end products.

Before looking at the common form for the file structure inside a BSP Layer, you should be aware that some requirements do exist in order for a BSP to be considered compliant with the Yocto Project. For that list of requirements, see the "Released BSP Requirements" section.

Below is the common form for the file structure inside a BSP Layer. While you can use this basic form for the standard, realize that the actual structures for specific BSPs could differ.

     meta-<bsp_name>/
     meta-<bsp_name>/<bsp_license_file>
     meta-<bsp_name>/README
     meta-<bsp_name>/README.sources
     meta-<bsp_name>/binary/<bootable_images>
     meta-<bsp_name>/conf/layer.conf
     meta-<bsp_name>/conf/machine/*.conf
     meta-<bsp_name>/recipes-bsp/*
     meta-<bsp_name>/recipes-core/*
     meta-<bsp_name>/recipes-graphics/*
     meta-<bsp_name>/recipes-kernel/linux/linux-yocto_<kernel_rev>.bbappend
                

Below is an example of the Crown Bay BSP:

     meta-crownbay/COPYING.MIT
     meta-crownbay/README
     meta-crownbay/README.sources
     meta-crownbay/binary/
     meta-crownbay/conf/
     meta-crownbay/conf/layer.conf
     meta-crownbay/conf/machine/
     meta-crownbay/conf/machine/crownbay.conf
     meta-crownbay/conf/machine/crownbay-noemgd.conf
     meta-crownbay/recipes-bsp/
     meta-crownbay/recipes-bsp/formfactor/
     meta-crownbay/recipes-bsp/formfactor/formfactor_0.0.bbappend
     meta-crownbay/recipes-bsp/formfactor/formfactor/
     meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay/
     meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay/machconfig
     meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay-noemgd/
     meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay-noemgd/machconfig
     meta-crownbay/recipes-graphics/
     meta-crownbay/recipes-graphics/xorg-xserver/
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config_0.1.bbappend
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay/
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay/xorg.conf
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay-noemgd/
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay-noemgd/xorg.conf
     meta-crownbay/recipes-kernel/
     meta-crownbay/recipes-kernel/linux/
     meta-crownbay/recipes-kernel/linux/linux-yocto_3.2.bbappend
     meta-crownbay/recipes-kernel/linux/linux-yocto_3.4.bbappend
     meta-crownbay/recipes-kernel/linux/linux-yocto_3.8.bbappend
     meta-crownbay/recipes-kernel/linux/linux-yocto-dev.bbappend
     meta-crownbay/recipes-kernel/linux/linux-yocto-rt_3.2.bbappend
     meta-crownbay/recipes-kernel/linux/linux-yocto-rt_3.4.bbappend
     meta-crownbay/recipes-kernel/linux/linux-yocto-rt_3.8.bbappend
                

The following sections describe each part of the proposed BSP format.

1.2.1. License Files

You can find these files in the BSP Layer at:

     meta-<bsp_name>/<bsp_license_file>
                

These optional files satisfy licensing requirements for the BSP. The type or types of files here can vary depending on the licensing requirements. For example, in the Crown Bay BSP all licensing requirements are handled with the COPYING.MIT file.

Licensing files can be MIT, BSD, GPLv*, and so forth. These files are recommended for the BSP but are optional and totally up to the BSP developer.

1.2.2. README File

You can find this file in the BSP Layer at:

     meta-<bsp_name>/README
                

This file provides information on how to boot the live images that are optionally included in the binary/ directory. The README file also provides special information needed for building the image.

At a minimum, the README file must contain a list of dependencies, such as the names of any other layers on which the BSP depends and the name of the BSP maintainer with his or her contact information.

1.2.3. README.sources File

You can find this file in the BSP Layer at:

     meta-<bsp_name>/README.sources
                

This file provides information on where to locate the BSP source files. For example, information provides where to find the sources that comprise the images shipped with the BSP. Information is also included to help you find the Metadata used to generate the images that ship with the BSP.

1.2.4. Pre-built User Binaries

You can find these files in the BSP Layer at:

     meta-<bsp_name>/binary/<bootable_images>
                

This optional area contains useful pre-built kernels and user-space filesystem images appropriate to the target system. This directory typically contains graphical (e.g. Sato) and minimal live images when the BSP tarball has been created and made available in the Yocto Project website. You can use these kernels and images to get a system running and quickly get started on development tasks.

The exact types of binaries present are highly hardware-dependent. However, a README file should be present in the BSP Layer that explains how to use the kernels and images with the target hardware. If pre-built binaries are present, source code to meet licensing requirements must also exist in some form.

1.2.5. Layer Configuration File

You can find this file in the BSP Layer at:

     meta-<bsp_name>/conf/layer.conf
                

The conf/layer.conf file identifies the file structure as a layer, identifies the contents of the layer, and contains information about how the build system should use it. Generally, a standard boilerplate file such as the following works. In the following example, you would replace "bsp" and "_bsp" with the actual name of the BSP (i.e. <bsp_name> from the example template).

     # We have a conf and classes directory, add to BBPATH
     BBPATH .= ":${LAYERDIR}"

     # We have recipes-* directories, add to BBFILES
     BBFILES += "${LAYERDIR}/recipes-*/*.bb \
                 ${LAYERDIR}/recipes-*/*.bbappend"

     BBFILE_COLLECTIONS += "bsp"
     BBFILE_PATTERN_bsp = "^${LAYERDIR}/"
     BBFILE_PRIORITY_bsp = "6"
                

To illustrate the string substitutions, here are the last three statements from the Crown Bay conf/layer.conf file:

     BBFILE_COLLECTIONS += "crownbay"
     BBFILE_PATTERN_crownbay = "^${LAYERDIR}/"
     BBFILE_PRIORITY_crownbay = "6"
                

This file simply makes BitBake aware of the recipes and configuration directories. The file must exist so that the OpenEmbedded build system can recognize the BSP.

1.2.6. Hardware Configuration Options

You can find these files in the BSP Layer at:

     meta-<bsp_name>/conf/machine/*.conf
                

The machine files bind together all the information contained elsewhere in the BSP into a format that the build system can understand. If the BSP supports multiple machines, multiple machine configuration files can be present. These filenames correspond to the values to which users have set the MACHINE variable.

These files define things such as the kernel package to use (PREFERRED_PROVIDER of virtual/kernel), the hardware drivers to include in different types of images, any special software components that are needed, any bootloader information, and also any special image format requirements.

Each BSP Layer requires at least one machine file. However, you can supply more than one file. For example, in the Crown Bay BSP shown earlier in this section, the conf/machine directory contains two configuration files: crownbay.conf and crownbay-noemgd.conf. The crownbay.conf file is used for the Crown Bay BSP that supports the Intel® Embedded Media and Graphics Driver (Intel® EMGD), while the crownbay-noemgd file is used for the Crown Bay BSP that supports Video Electronics Standards Association (VESA) graphics only.

This crownbay.conf file could also include a hardware "tuning" file that is commonly used to define the package architecture and specify optimization flags, which are carefully chosen to give best performance on a given processor.

Tuning files are found in the meta/conf/machine/include directory within the Source Directory. Tuning files can also reside in the BSP Layer itself. For example, the ia32-base.inc file resides in the meta-intel BSP Layer in conf/machine/include.

To use an include file, you simply include them in the machine configuration file. For example, the Crown Bay BSP crownbay.conf has the following statements:

     require conf/machine/include/tune-atom.inc
     require conf/machine/include/ia32-base.inc
                

1.2.7. Miscellaneous Recipe Files

You can find these files in the BSP Layer at:

     meta-<bsp_name>/recipes-bsp/*
                

This optional directory contains miscellaneous recipe files for the BSP. Most notably would be the formfactor files. For example, in the Crown Bay BSP there is the formfactor_0.0.bbappend file, which is an append file used to augment the recipe that starts the build. Furthermore, there are machine-specific settings used during the build that are defined by the machconfig files. In the Crown Bay example, two machconfig files exist: one that supports the Intel® Embedded Media and Graphics Driver (Intel® EMGD) and one that does not:

     meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay/machconfig
     meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay-noemgd/machconfig
     meta-crownbay/recipes-bsp/formfactor/formfactor_0.0.bbappend
                

Note

If a BSP does not have a formfactor entry, defaults are established according to the formfactor configuration file that is installed by the main formfactor recipe meta/recipes-bsp/formfactor/formfactor_0.0.bb, which is found in the Source Directory.

1.2.8. Display Support Files

You can find these files in the BSP Layer at:

     meta-<bsp_name>/recipes-graphics/*
                

This optional directory contains recipes for the BSP if it has special requirements for graphics support. All files that are needed for the BSP to support a display are kept here. For example, the Crown Bay BSP contains two versions of the xorg.conf file. The version in crownbay builds a BSP that supports the Intel® Embedded Media Graphics Driver (EMGD), while the version in crownbay-noemgd builds a BSP that supports Video Electronics Standards Association (VESA) graphics only:

     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config_0.1.bbappend
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay/xorg.conf
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay-noemgd/xorg.conf
                

1.2.9. Linux Kernel Configuration

You can find these files in the BSP Layer at:

     meta-<bsp_name>/recipes-kernel/linux/linux-yocto_*.bbappend
                

These files append your specific changes to the main kernel recipe you are using.

For your BSP, you typically want to use an existing Yocto Project kernel recipe found in the Source Directory at meta/recipes-kernel/linux. You can append your specific changes to the kernel recipe by using a similarly named append file, which is located in the BSP Layer (e.g. the meta-<bsp_name>/recipes-kernel/linux directory).

Suppose you are using the linux-yocto_3.4.bb recipe to build the kernel. In other words, you have selected the kernel in your <bsp_name>.conf file by adding these types of statements:

     PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
     PREFERRED_VERSION_linux-yocto = "3.4%"
                

Note

When the preferred provider is assumed by default, the PREFERRED_PROVIDER statement does not appear in the <bsp_name>.conf file.

You would use the linux-yocto_3.4.bbappend file to append specific BSP settings to the kernel, thus configuring the kernel for your particular BSP.

As an example, look at the existing Crown Bay BSP. The append file used is:

     meta-crownbay/recipes-kernel/linux/linux-yocto_3.4.bbappend
                

The following listing shows the file. Be aware that the actual commit ID strings in this example listing might be different than the actual strings in the file from the meta-intel Git source repository.

     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

     COMPATIBLE_MACHINE_crownbay = "crownbay"
     KMACHINE_crownbay  = "crownbay"
     KBRANCH_crownbay  = "standard/crownbay"

     COMPATIBLE_MACHINE_crownbay-noemgd = "crownbay-noemgd"
     KMACHINE_crownbay-noemgd  = "crownbay"
     KBRANCH_crownbay-noemgd  = "standard/crownbay"

     SRCREV_machine_pn-linux-yocto_crownbay ?= "449f7f520350700858f21a5554b81cc8ad23267d"
     SRCREV_meta_pn-linux-yocto_crownbay ?= "9e3bdb7344054264b750e53fbbb6394cc1c942ac"
     SRCREV_emgd_pn-linux-yocto_crownbay ?= "86643bdd8cbad616a161ab91f51108cf0da827bc"

     SRCREV_machine_pn-linux-yocto_crownbay-noemgd ?= "449f7f520350700858f21a5554b81cc8ad23267d"
     SRCREV_meta_pn-linux-yocto_crownbay-noemgd ?= "9e3bdb7344054264b750e53fbbb6394cc1c942ac"

     KSRC_linux_yocto_3_4 ?= "git.yoctoproject.org/linux-yocto-3.4.git"
     SRC_URI_crownbay = "git://git.yoctoproject.org/linux-yocto-3.4.git;protocol=git;nocheckout=1;branch=${KBRANCH},meta,emgd-1.14;name=machine,meta,emgd"
     SRC_URI_crownbay-noemgd = "git://git.yoctoproject.org/linux-yocto-3.4.git;protocol=git;nocheckout=1;branch=${KBRANCH},meta;name=machine,meta"
                

This append file contains statements used to support the Crown Bay BSP for both Intel® EMGD and the VESA graphics. The build process, in this case, recognizes and uses only the statements that apply to the defined machine name - crownbay in this case. So, the applicable statements in the linux-yocto_3.4.bbappend file are follows:

     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

     COMPATIBLE_MACHINE_crownbay = "crownbay"
     KMACHINE_crownbay  = "crownbay"
     KBRANCH_crownbay  = "standard/crownbay"

     SRCREV_machine_pn-linux-yocto_crownbay ?= "449f7f520350700858f21a5554b81cc8ad23267d"
     SRCREV_meta_pn-linux-yocto_crownbay ?= "9e3bdb7344054264b750e53fbbb6394cc1c942ac"
     SRCREV_emgd_pn-linux-yocto_crownbay ?= "86643bdd8cbad616a161ab91f51108cf0da827bc"
                

The append file defines crownbay as the COMPATIBLE_MACHINE and uses the KMACHINE variable to ensure the machine name used by the OpenEmbedded build system maps to the machine name used by the Linux Yocto kernel. The file also uses the optional KBRANCH variable to ensure the build process uses the standard/default/crownbay kernel branch. Finally, the append file points to specific commits in the Source Directory Git repository and the meta Git repository branches to identify the exact kernel needed to build the Crown Bay BSP.

Note

For crownbay, a specific commit is also needed to point to the branch that supports EMGD graphics. At a minimum, every BSP points to the machine and meta commits.

One thing missing in this particular BSP, which you will typically need when developing a BSP, is the kernel configuration file (.config) for your BSP. When developing a BSP, you probably have a kernel configuration file or a set of kernel configuration files that, when taken together, define the kernel configuration for your BSP. You can accomplish this definition by putting the configurations in a file or a set of files inside a directory located at the same level as your kernel's append file and having the same name as the kernel's main recipe file. With all these conditions met, simply reference those files in a SRC_URI statement in the append file.

For example, suppose you had a some configuration options in a file called network_configs.cfg. You can place that file inside a directory named /linux-yocto and then add a SRC_URI statement such as the following to the append file. When the OpenEmbedded build system builds the kernel, the configuration options are picked up and applied.

     SRC_URI += "file://network_configs.cfg"
                

To group related configurations into multiple files, you perform a similar procedure. Here is an example that groups separate configurations specifically for Ethernet and graphics into their own files and adds the configurations by using a SRC_URI statement like the following in your append file:

     SRC_URI += "file://myconfig.cfg \
            file://eth.cfg \
            file://gfx.cfg"
                

The FILESEXTRAPATHS variable is in boilerplate form in the previous example in order to make it easy to do that. This variable must be in your layer or BitBake will not find the patches or configurations even if you have them in your SRC_URI. The FILESEXTRAPATHS variable enables the build process to find those configuration files.

Note

Other methods exist to accomplish grouping and defining configuration options. For example, if you are working with a local clone of the kernel repository, you could checkout the kernel's meta branch, make your changes, and then push the changes to the local bare clone of the kernel. The result is that you directly add configuration options to the meta branch for your BSP. The configuration options will likely end up in that location anyway if the BSP gets added to the Yocto Project.

In general, however, the Yocto Project maintainers take care of moving the SRC_URI-specified configuration options to the kernel's meta branch. Not only is it easier for BSP developers to not have to worry about putting those configurations in the branch, but having the maintainers do it allows them to apply 'global' knowledge about the kinds of common configuration options multiple BSPs in the tree are typically using. This allows for promotion of common configurations into common features.

1.3. Requirements and Recommendations for Released BSPs

Certain requirements exist for a released BSP to be considered compliant with the Yocto Project. Additionally, recommendations also exist. This section describes the requirements and recommendations for released BSPs.

1.3.1. Released BSP Requirements

Before looking at BSP requirements, you should consider the following:

  • The requirements here assume the BSP layer is a well-formed, "legal" layer that can be added to the Yocto Project. For guidelines on creating a layer that meets these base requirements, see the "BSP Layers" and the "Understanding and Creating Layers" in the Yocto Project Development Manual.

  • The requirements in this section apply regardless of how you ultimately package a BSP. You should consult the packaging and distribution guidelines for your specific release process. For an example of packaging and distribution requirements, see the "Third Party BSP Release Process" wiki page.

  • The requirements for the BSP as it is made available to a developer are completely independent of the released form of the BSP. For example, the BSP Metadata can be contained within a Git repository and could have a directory structure completely different from what appears in the officially released BSP layer.

  • It is not required that specific packages or package modifications exist in the BSP layer, beyond the requirements for general compliance with the Yocto Project. For example, no requirement exists dictating that a specific kernel or kernel version be used in a given BSP.

Following are the requirements for a released BSP that conforms to the Yocto Project:

  • Layer Name: The BSP must have a layer name that follows the Yocto Project standards. For information on BSP layer names, see the "BSP Layers" section.

  • File System Layout: When possible, use the same directory names in your BSP layer as listed in the recipes.txt file. In particular, you should place recipes (.bb files) and recipe modifications (.bbappend files) into recipes-* subdirectories by functional area as outlined in recipes.txt. If you cannot find a category in recipes.txt to fit a particular recipe, you can make up your own recipe-* subdirectory. You can find recipes.txt in the meta directory of the Source Directory, or in the OpenEmbedded Core Layer (openembedded-core) found at http://git.openembedded.org/openembedded-core/tree/meta.

    Within any particular recipes-* category, the layout should match what is found in the OpenEmbedded Core Git repository (openembedded-core) or the Source Directory (poky). In other words, make sure you place related files in appropriately related recipes-* subdirectories specific to the recipe's function, or within a subdirectory containing a set of closely-related recipes. The recipes themselves should follow the general guidelines for recipes used in the Yocto Project found in the "Yocto Recipe and Patch Style Guide".

  • License File: You must include a license file in the meta-<bsp_name> directory. This license covers the BSP Metadata as a whole. You must specify which license to use since there is no default license if one is not specified. See the COPYING.MIT file for the Fish River Island 2 BSP in the meta-fri2 BSP layer as an example.

  • README File: You must include a README file in the meta-<bsp_name> directory. See the README file for the Fish River Island 2 BSP in the meta-fri2 BSP layer as an example.

    At a minimum, the README file should contain the following:

    • A brief description about the hardware the BSP targets.

    • A list of all the dependencies on which a BSP layer depends. These dependencies are typically a list of required layers needed to build the BSP. However, the dependencies should also contain information regarding any other dependencies the BSP might have.

    • Any required special licensing information. For example, this information includes information on special variables needed to satisfy a EULA, or instructions on information needed to build or distribute binaries built from the BSP Metadata.

    • The name and contact information for the BSP layer maintainer. This is the person to whom patches and questions should be sent. For information on how to find the right person, see the "How to Submit a Change" section in the Yocto Project Development Manual.

    • Instructions on how to build the BSP using the BSP layer.

    • Instructions on how to boot the BSP build from the BSP layer.

    • Instructions on how to boot the binary images contained in the /binary directory, if present.

    • Information on any known bugs or issues that users should know about when either building or booting the BSP binaries.

  • README.sources File: You must include a README.sources in the meta-<bsp_name> directory. This file specifies exactly where you can find the sources used to generate the binary images contained in the /binary directory, if present. See the README.sources file for the Fish River Island 2 BSP in the meta-fri2 BSP layer as an example.

  • Layer Configuration File: You must include a conf/layer.conf in the meta-<bsp_name> directory. This file identifies the meta-<bsp_name> BSP layer as a layer to the build system.

  • Machine Configuration File: You must include a conf/machine/<bsp_name>.conf in the meta-<bsp_name> directory. This configuration file defines a machine target that can be built using the BSP layer. Multiple machine configuration files define variations of machine configurations that are supported by the BSP. If a BSP supports multiple machine variations, you need to adequately describe each variation in the BSP README file. Do not use multiple machine configuration files to describe disparate hardware. If you do have very different targets, you should create separate BSP layers for each target.

    Note

    It is completely possible for a developer to structure the working repository as a conglomeration of unrelated BSP files, and to possibly generate BSPs targeted for release from that directory using scripts or some other mechanism. Such considerations are outside the scope of this document.

1.3.2. Released BSP Recommendations

Following are recommendations for a released BSP that conforms to the Yocto Project:

  • Bootable Images: BSP releases can contain one or more bootable images. Including bootable images allows users to easily try out the BSP on their own hardware.

    In some cases, it might not be convenient to include a bootable image. In this case, you might want to make two versions of the BSP available: one that contains binary images, and one that does not. The version that does not contain bootable images avoids unnecessary download times for users not interested in the images.

    If you need to distribute a BSP and include bootable images or build kernel and filesystems meant to allow users to boot the BSP for evaluation purposes, you should put the images and artifacts within a binary/ subdirectory located in the meta-<bsp_name> directory.

    Note

    If you do include a bootable image as part of the BSP and the image was built by software covered by the GPL or other open source licenses, it is your responsibility to understand and meet all licensing requirements, which could include distribution of source files.
  • Use a Yocto Linux Kernel: Kernel recipes in the BSP should be based on a Yocto Linux kernel. Basing your recipes on these kernels reduces the costs for maintaining the BSP and increases its scalability. See the Yocto Linux Kernel category in the Source Repositories for these kernels.

1.4. Customizing a Recipe for a BSP

If you plan on customizing a recipe for a particular BSP, you need to do the following:

  • Create a .bbappend file for the modified recipe. For information on using append files, see the "Using .bbappend Files" section in the Yocto Project Development Manual.

  • Ensure your directory structure in the BSP layer that supports your machine is such that it can be found by the build system. See the example later in this section for more information.

  • Put the append file in a directory whose name matches the machine's name and is located in an appropriate sub-directory inside the BSP layer (i.e. recipes-bsp, recipes-graphics, recipes-core, and so forth).

  • Place the BSP-specific files in the directory named for your machine inside the BSP layer.

Following is a specific example to help you better understand the process. Consider an example that customizes a recipe by adding a BSP-specific configuration file named interfaces to the init-ifupdown_1.0.bb recipe for machine "xyz". Do the following:

  1. Edit the init-ifupdown_1.0.bbappend file so that it contains the following:

         FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
         PRINC := "${@int(PRINC) + 2}"
                           

    The append file needs to be in the meta-xyz/recipes-core/init-ifupdown directory.

  2. Create and place the new interfaces configuration file in the BSP's layer here:

         meta-xyz/recipes-core/init-ifupdown/files/xyz/interfaces
                           

    The FILESEXTRAPATHS variable in the append files extends the search path the build system uses to find files during the build. Consequently, for this example you need to have the files directory in the same location as your append file.

1.5. BSP Licensing Considerations

In some cases, a BSP contains separately licensed Intellectual Property (IP) for a component or components. For these cases, you are required to accept the terms of a commercial or other type of license that requires some kind of explicit End User License Agreement (EULA). Once the license is accepted, the OpenEmbedded build system can then build and include the corresponding component in the final BSP image. If the BSP is available as a pre-built image, you can download the image after agreeing to the license or EULA.

You could find that some separately licensed components that are essential for normal operation of the system might not have an unencumbered (or free) substitute. Without these essential components, the system would be non-functional. Then again, you might find that other licensed components that are simply 'good-to-have' or purely elective do have an unencumbered, free replacement component that you can use rather than agreeing to the separately licensed component. Even for components essential to the system, you might find an unencumbered component that is not identical but will work as a less-capable version of the licensed version in the BSP recipe.

For cases where you can substitute a free component and still maintain the system's functionality, the "Downloads" page from the Yocto Project website's makes available de-featured BSPs that are completely free of any IP encumbrances. For these cases, you can use the substitution directly and without any further licensing requirements. If present, these fully de-featured BSPs are named appropriately different as compared to the names of the respective encumbered BSPs. If available, these substitutions are your simplest and most preferred options. Use of these substitutions of course assumes the resulting functionality meets system requirements.

If however, a non-encumbered version is unavailable or it provides unsuitable functionality or quality, you can use an encumbered version.

A couple different methods exist within the OpenEmbedded build system to satisfy the licensing requirements for an encumbered BSP. The following list describes them in order of preference:

  1. Use the LICENSE_FLAGS variable to define the recipes that have commercial or other types of specially-licensed packages: For each of those recipes, you can specify a matching license string in a local.conf variable named LICENSE_FLAGS_WHITELIST. Specifying the matching license string signifies that you agree to the license. Thus, the build system can build the corresponding recipe and include the component in the image. See the "Enabling Commercially Licensed Recipes" section in the Yocto Project Reference Manual for details on how to use these variables.

    If you build as you normally would, without specifying any recipes in the LICENSE_FLAGS_WHITELIST, the build stops and provides you with the list of recipes that you have tried to include in the image that need entries in the LICENSE_FLAGS_WHITELIST. Once you enter the appropriate license flags into the whitelist, restart the build to continue where it left off. During the build, the prompt will not appear again since you have satisfied the requirement.

    Once the appropriate license flags are on the white list in the LICENSE_FLAGS_WHITELIST variable, you can build the encumbered image with no change at all to the normal build process.

  2. Get a pre-built version of the BSP: You can get this type of BSP by visiting the "Downloads" page of the Yocto Project website. You can download BSP tarballs that contain proprietary components after agreeing to the licensing requirements of each of the individually encumbered packages as part of the download process. Obtaining the BSP this way allows you to access an encumbered image immediately after agreeing to the click-through license agreements presented by the website. Note that if you want to build the image yourself using the recipes contained within the BSP tarball, you will still need to create an appropriate LICENSE_FLAGS_WHITELIST to match the encumbered recipes in the BSP.

Note

Pre-compiled images are bundled with a time-limited kernel that runs for a predetermined amount of time (10 days) before it forces the system to reboot. This limitation is meant to discourage direct redistribution of the image. You must eventually rebuild the image if you want to remove this restriction.

1.6. Using the Yocto Project's BSP Tools

The Yocto Project includes a couple of tools that enable you to create a BSP layer from scratch and do basic configuration and maintenance of the kernel without ever looking at a Metadata file. These tools are yocto-bsp and yocto-kernel, respectively.

The following sections describe the common location and help features as well as provide details for the yocto-bsp and yocto-kernel tools.

1.6.1. Common Features

Designed to have a command interface somewhat like Git, each tool is structured as a set of sub-commands under a top-level command. The top-level command (yocto-bsp or yocto-kernel) itself does nothing but invoke or provide help on the sub-commands it supports.

Both tools reside in the scripts/ subdirectory of the Source Directory. Consequently, to use the scripts, you must source the environment just as you would when invoking a build:

     $ source oe-init-build-env [build_dir]
                    

The most immediately useful function is to get help on both tools. The built-in help system makes it easy to drill down at any time and view the syntax required for any specific command. Simply enter the name of the command with the help switch:

     $ yocto-bsp help
     Usage:

      Create a customized Yocto BSP layer.

      usage: yocto-bsp [--version] [--help] COMMAND [ARGS]

      Current 'yocto-bsp' commands are:
         create            Create a new Yocto BSP
         list              List available values for options and BSP properties

      See 'yocto-bsp help COMMAND' for more information on a specific command.


     Options:
       --version    show program's version number and exit
       -h, --help   show this help message and exit
       -D, --debug  output debug information
                    

Similarly, entering just the name of a sub-command shows the detailed usage for that sub-command:

     $ yocto-bsp create

     Usage:

      Create a new Yocto BSP

      usage: yocto-bsp create <bsp-name> <karch> [-o <DIRNAME> | --outdir <DIRNAME>]
             [-i <JSON PROPERTY FILE> | --infile <JSON PROPERTY_FILE>]

      This command creates a Yocto BSP based on the specified parameters.
      The new BSP will be a new Yocto BSP layer contained by default within
      the top-level directory specified as 'meta-bsp-name'.  The -o option
      can be used to place the BSP layer in a directory with a different
      name and location.

      ...
                    

For any sub-command, you can use the word "help" option just before the sub-command to get more extensive documentation:

     $ yocto-bsp help create

     NAME
         yocto-bsp create - Create a new Yocto BSP

     SYNOPSIS
         yocto-bsp create <bsp-name> <karch> [-o <DIRNAME> | --outdir <DIRNAME>]
             [-i <JSON PROPERTY FILE> | --infile <JSON PROPERTY_FILE>]

     DESCRIPTION
         This command creates a Yocto BSP based on the specified
         parameters.  The new BSP will be a new Yocto BSP layer contained
         by default within the top-level directory specified as
         'meta-bsp-name'.  The -o option can be used to place the BSP layer
         in a directory with a different name and location.

         The value of the 'karch' parameter determines the set of files
         that will be generated for the BSP, along with the specific set of
         'properties' that will be used to fill out the BSP-specific
         portions of the BSP.  The possible values for the 'karch' parameter
         can be listed via 'yocto-bsp list karch'.

         ...
                    

Now that you know where these two commands reside and how to access information on them, you should find it relatively straightforward to discover the commands necessary to create a BSP and perform basic kernel maintenance on that BSP using the tools.

Note

You can also use the yocto-layer tool to create a "generic" layer. For information on this tool, see the "Creating a General Layer Using the yocto-layer Script" section in the Yocto Project Development Guide.

The next sections provide a concrete starting point to expand on a few points that might not be immediately obvious or that could use further explanation.

1.6.2. Creating a new BSP Layer Using the yocto-bsp Script

The yocto-bsp script creates a new BSP layer for any architecture supported by the Yocto Project, as well as QEMU versions of the same. The default mode of the script's operation is to prompt you for information needed to generate the BSP layer.

For the current set of BSPs, the script prompts you for various important parameters such as:

  • The kernel to use

  • The branch of that kernel to use (or re-use)

  • Whether or not to use X, and if so, which drivers to use

  • Whether to turn on SMP

  • Whether the BSP has a keyboard

  • Whether the BSP has a touchscreen

  • Remaining configurable items associated with the BSP

You use the yocto-bsp create sub-command to create a new BSP layer. This command requires you to specify a particular kernel architecture (karch) on which to base the BSP. Assuming you have sourced the environment, you can use the yocto-bsp list karch sub-command to list the architectures available for BSP creation as follows:

     $ yocto-bsp list karch
     Architectures available:
         qemu
         x86_64
         i386
         powerpc
         arm
         mips
                    

The remainder of this section presents an example that uses myarm as the machine name and qemu as the machine architecture. Of the available architectures, qemu is the only architecture that causes the script to prompt you further for an actual architecture. In every other way, this architecture is representative of how creating a BSP for an actual machine would work. The reason the example uses this architecture is because it is an emulated architecture and can easily be followed without requiring actual hardware.

As the yocto-bsp create command runs, default values for the prompts appear in brackets. Pressing enter without supplying anything on the command line or pressing enter and providing an invalid response causes the script to accept the default value. Once the script completes, the new meta-myarm BSP layer is created in the current working directory. This example assumes you have sourced the oe-init-build-env and are currently in the top-level folder of the Source Directory.

Following is the complete example:

     $ yocto-bsp create myarm qemu
     Which qemu architecture would you like to use? [default: i386]
	     1) i386    (32-bit)
	     2) x86_64  (64-bit)
	     3) ARM     (32-bit)
	     4) PowerPC (32-bit)
	     5) MIPS    (32-bit)
     3
     Would you like to use the default (3.8) kernel? (y/n) [default: y]
     Do you need a new machine branch for this BSP (the alternative is to re-use an existing branch)? [y/n] [default: y]
     Getting branches from remote repo git://git.yoctoproject.org/linux-yocto-3.8.git...
     Please choose a machine branch to base your new BSP branch on: [default: standard/base]
             1) standard/arm-versatile-926ejs
             2) standard/base
             3) standard/beagleboard
             4) standard/ck
             5) standard/crownbay
             6) standard/edf
             7) standard/emenlow
             8) standard/fri2
             9) standard/fsl-mpc8315e-rdb
             10) standard/mti-malta32
             11) standard/mti-malta64
             12) standard/qemuppc
             13) standard/routerstationpro
             14) standard/sys940x
     1
     Would you like SMP support? (y/n) [default: y]
     Does your BSP have a touchscreen? (y/n) [default: n]
     Does your BSP have a keyboard? (y/n) [default: y]

     New qemu BSP created in meta-myarm
                    

Let's take a closer look at the example now:

  1. For the QEMU architecture, the script first prompts you for which emulated architecture to use. In the example, we use the ARM architecture.

  2. The script then prompts you for the kernel. The default 3.8 kernel is acceptable. So, the example accepts the default. If you enter 'n', the script prompts you to further enter the kernel you do want to use (e.g. 3.2, 3.2_preempt-rt, and so forth.).

  3. Next, the script asks whether you would like to have a new branch created especially for your BSP in the local Linux Yocto Kernel Git repository . If not, then the script re-uses an existing branch.

    In this example, the default (or "yes") is accepted. Thus, a new branch is created for the BSP rather than using a common, shared branch. The new branch is the branch committed to for any patches you might later add. The reason a new branch is the default is that typically new BSPs do require BSP-specific patches. The tool thus assumes that most of time a new branch is required.

  4. Regardless of which choice you make in the previous step, you are now given the opportunity to select a particular machine branch on which to base your new BSP-specific machine branch (or to re-use if you had elected to not create a new branch). Because this example is generating an ARM-based BSP, the example uses #1 at the prompt, which selects the ARM-versatile branch.

  5. The remainder of the prompts are routine. Defaults are accepted for each.

  6. By default, the script creates the new BSP Layer in the current working directory of the Source Directory, which is poky in this case.

Once the BSP Layer is created, you must add it to your bblayers.conf file. Here is an example:

     BBLAYERS = ?" \
        /usr/local/src/yocto/meta \
        /usr/local/src/yocto/meta-yocto \
        /usr/local/src/yocto/meta-yocto-bsp \
        /usr/local/src/yocto/meta-myarm \
        "

     BBLAYERS_NON_REMOVABLE ?= " \
        /usr/local/src/yocto/meta \
        /usr/local/src/yocto/meta-yocto \
        "
                    

Adding the layer to this file allows the build system to build the BSP and the yocto-kernel tool to be able to find the layer and other Metadata it needs on which to operate.

1.6.3. Managing Kernel Patches and Config Items with yocto-kernel

Assuming you have created a BSP Layer using yocto-bsp and you added it to your BBLAYERS variable in the bblayers.conf file, you can now use the yocto-kernel script to add patches and configuration items to the BSP's kernel.

The yocto-kernel script allows you to add, remove, and list patches and kernel config settings to a BSP's kernel .bbappend file. All you need to do is use the appropriate sub-command. Recall that the easiest way to see exactly what sub-commands are available is to use the yocto-kernel built-in help as follows:

     $ yocto-kernel
     Usage:

      Modify and list Yocto BSP kernel config items and patches.

      usage: yocto-kernel [--version] [--help] COMMAND [ARGS]

      Current 'yocto-kernel' commands are:
        config list       List the modifiable set of bare kernel config options for a BSP
        config add        Add or modify bare kernel config options for a BSP
        config rm         Remove bare kernel config options from a BSP
        patch list        List the patches associated with a BSP
        patch add         Patch the Yocto kernel for a BSP
        patch rm          Remove patches from a BSP
        feature list      List the features used by a BSP
        feature add       Have a BSP use a feature
        feature rm        Have a BSP stop using a feature
        features list     List the features available to BSPs
        feature describe  Describe a particular feature
        feature create    Create a new BSP-local feature
        feature destroy   Remove a BSP-local feature

      See 'yocto-kernel help COMMAND' for more information on a specific command.



     Options:
       --version    show program's version number and exit
       -h, --help   show this help message and exit
       -D, --debug  output debug information
                    

The yocto-kernel patch add sub-command allows you to add a patch to a BSP. The following example adds two patches to the myarm BSP:

     $ yocto-kernel patch add myarm ~/test.patch
     Added patches:
             test.patch

     $ yocto-kernel patch add myarm ~/yocto-testmod.patch
     Added patches:
             yocto-testmod.patch
                    

Note

Although the previous example adds patches one at a time, it is possible to add multiple patches at the same time.

You can verify patches have been added by using the yocto-kernel patch list sub-command. Here is an example:

     $ yocto-kernel patch list myarm
     The current set of machine-specific patches for myarm is:
             1) test.patch
             2) yocto-testmod.patch
                    

You can also use the yocto-kernel script to remove a patch using the yocto-kernel patch rm sub-command. Here is an example:

     $ yocto-kernel patch rm myarm
     Specify the patches to remove:
             1) test.patch
             2) yocto-testmod.patch
     1
     Removed patches:
             test.patch
                    

Again, using the yocto-kernel patch list sub-command, you can verify that the patch was in fact removed:

     $ yocto-kernel patch list myarm
     The current set of machine-specific patches for myarm is:
             1) yocto-testmod.patch
                    

In a completely similar way, you can use the yocto-kernel config add sub-command to add one or more kernel config item settings to a BSP. The following commands add a couple of config items to the myarm BSP:

     $ yocto-kernel config add myarm CONFIG_MISC_DEVICES=y
     Added items:
             CONFIG_MISC_DEVICES=y

     $ yocto-kernel config add myarm CONFIG_YOCTO_TESTMOD=y
     Added items:
             CONFIG_YOCTO_TESTMOD=y
                    

Note

Although the previous example adds config items one at a time, it is possible to add multiple config items at the same time.

You can list the config items now associated with the BSP. Doing so shows you the config items you added as well as others associated with the BSP:

     $ yocto-kernel config list myarm
     The current set of machine-specific kernel config items for myarm is:
             1) CONFIG_MISC_DEVICES=y
             2) CONFIG_YOCTO_TESTMOD=y
                    

Finally, you can remove one or more config items using the yocto-kernel config rm sub-command in a manner completely analogous to yocto-kernel patch rm.

Yocto Project Linux Kernel Development Manual

Darren Hart

Intel Corporation

Permission is granted to copy, distribute and/or modify this document under the terms of the Creative Commons Attribution-Share Alike 2.0 UK: England & Wales as published by Creative Commons.

Note

Due to production processes, there could be differences between the Yocto Project documentation bundled in the release tarball and the Yocto Project Linux Kernel Development Manual on the Yocto Project website. For the latest version of this manual, see the manual on the website.
Revision History
Revision 1.4April 2013
Released with the Yocto Project 1.4 Release.
Revision 1.4.1June 2013
Released with the Yocto Project 1.4.1 Release.
Revision 1.4.2August 2013
Released with the Yocto Project 1.4.2 Release.

Chapter 1. Introduction

1.1. Overview

Regardless of how you intend to make use of the Yocto Project, chances are you will work with the Linux kernel. This manual provides background information on the Yocto Linux kernel Metadata, describes common tasks you can perform using the kernel tools, and shows you how to use the kernel Metadata needed to work with the kernel inside the Yocto Project.

Each Yocto Project release has a set of linux-yocto recipes, whose Git repositories you can view in the Yocto Source Repositories under the "Yocto Linux Kernel" heading. New recipes for the release track the latest upstream developments and introduce newly supported platforms. Previous recipes in the release are refreshed and supported for at least one additional release. As they align, these previous releases are updated to include the latest from the Long Term Support Initiative (LTSI) project. Also included is a linux-yocto development recipe (linux-yocto-dev.bb) should you want to work with the very latest in upstream Linux kernel development and kernel Metadata development.

The Yocto Project also provides a powerful set of kernel tools for managing Linux kernel sources and configuration data. You can use these tools to make a single configuration change, apply multiple patches, or work with your own kernel sources.

In particular, the kernel tools allow you to generate configuration fragments that specify only what you must, and nothing more. Configuration fragments only need to contain the highest level visible CONFIG options as presented by the Linux kernel menuconfig system. Contrast this against a complete Linux kernel .config, which includes all the automatically selected CONFIG options. This efficiency reduces your maintenance effort and allows you to further separate your configuration in ways that make sense for your project. A common split separates policy and hardware. For example, all your kernels might support the proc and sys filesystems, but only specific boards require sound, USB, or specific drivers. Specifying these configurations individually allows you to aggregate them together as needed, but maintains them in only one place. Similar logic applies to separating source changes.

If you do not maintain your own kernel sources and need to make only minimal changes to the sources, the released recipes provide a vetted base upon which to layer your changes. Doing so allows you to benefit from the continual kernel integration and testing performed during development of the Yocto Project.

If, instead, you have a very specific Linux kernel source tree and are unable to align with one of the official linux-yocto recipes, an alternative exists by which you can use the Yocto Project Linux kernel tools with your own kernel sources.

1.2. Other Resources

The sections that follow provide instructions for completing specific Linux kernel development tasks. These instructions assume you are comfortable working with BitBake recipes and basic open-source development tools. Understanding these concepts will facilitate the process of working with the kernel recipes. If you find you need some additional background, please be sure to review and understand the following documentation:

Finally, while this document focuses on the manual creation of recipes, patches, and configuration files, the Yocto Project Board Support Package (BSP) tools are available to automate this process with existing content and work well to create the initial framework and boilerplate code. For details on these tools, see the "Using the Yocto Project's BSP Tools" section in the Yocto Project Board Support Package (BSP) Developer's Guide.

Chapter 2. Common Tasks

This chapter presents several common tasks you perform when you work with the Yocto Project Linux kernel. These tasks include preparing a layer, modifying an existing recipe, iterative development, working with your own sources, and incorporating out-of-tree modules.

Note

The examples presented in this chapter work with the Yocto Project 1.2.2 Release and forward.

2.1. Creating and Preparing a Layer

If you are going to be modifying kernel recipes, it is recommended that you create and prepare your own layer in which to do your work. Your layer contains its own BitBake append files (.bbappend) and provides a convenient mechanism to create your own recipe files (.bb). For details on how to create and work with layers, see the following sections in the Yocto Project Development Manual:

2.2. Modifying an Existing Recipe

In many cases, you can customize an existing linux-yocto recipe to meet the needs of your project. Each release of the Yocto Project provides a few Linux kernel recipes from which you can choose. These are located in the Source Directory in meta/recipes-kernel/linux.

Modifying an existing recipe can consist of the following:

  • Creating the append file

  • Applying patches

  • Changing the configuration

Before modifying an existing recipe, be sure that you have created a minimal, custom layer from which you can work. See the "Creating and Preparing a Layer" section for some general resources. You can also see the "Set Up Your Layer for the Build" section of the Yocto Project Development Manual for a detailed example.

2.2.1. Creating the Append File

You create this file in your custom layer. You also name it accordingly based on the linux-yocto recipe you are using. For example, if you are modifying the meta/recipes-kernel/linux/linux-yocto_3.4.bb recipe, the append file will typical be located as follows within your custom layer:

     <your-layer>/recipes-kernel/linux/linux-yocto_3.4.bbappend
                

The append file should initially contain the following text:

     FILESEXTRAPATHS := "${THISDIR}/${PN}"
                

The path ${THISDIR}/${PN} expands to "linux-yocto" in the current directory for this example. If you add any new files that modify the kernel recipe and you have extended FILESPATH as described above, you must place the files in your layer in the following area:

     <your-layer>/recipes-kernel/linux/linux-yocto/
                

Note

If you are working on a new machine Board Support Package (BSP), be sure to refer to the Yocto Project Board Support Package (BSP) Developer's Guide.

2.2.2. Applying Patches

If you have a single patch or a small series of patches that you want to apply to the Linux kernel source, you can do so just as you would with any other recipe. You first copy the patches to the path added to FILESEXTRAPATHS in your .bbappend file as described in the previous section, and then reference them in SRC_URI statements.

For example, you can apply a three-patch series by adding the following lines to your linux-yocto .bbappend file in your layer:

     SRC_URI += "file://0001-first-change.patch"
     SRC_URI += "file://0002-first-change.patch"
     SRC_URI += "file://0003-first-change.patch"
                

The next time you run BitBake to build the Linux kernel, BitBake detects the change in the recipe and fetches and applies the patches before building the kernel.

For a detailed example showing how to patch the kernel, see the "Patching the Kernel" section in the Yocto Project Development Manual.

2.2.3. Changing the Configuration

You can make wholesale or incremental changes to the Linux kernel .config file by including a defconfig or by specifying configuration fragments in the SRC_URI.

If you have a complete Linux kernel .config file you want to use, copy it to a directory named files, which must be in your layer's recipes-kernel/linux directory, and name the file "defconfig". Then, add the following lines to your linux-yocto .bbappend file in your layer:

     FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
     SRC_URI += "file://defconfig"
                

The SRC_URI tells the build system how to search for the file, while the FILESEXTRAPATHS extends the FILESPATH variable (search directories) to include the files directory you created for the configuration changes.

Generally speaking, the preferred approach is to determine the incremental change you want to make and add that as a configuration fragment. For example, if you want to add support for a basic serial console, create a file named 8250.cfg in the files directory with the following content (without indentation):

     CONFIG_SERIAL_8250=y
     CONFIG_SERIAL_8250_CONSOLE=y
     CONFIG_SERIAL_8250_PCI=y
     CONFIG_SERIAL_8250_NR_UARTS=4
     CONFIG_SERIAL_8250_RUNTIME_UARTS=4
     CONFIG_SERIAL_CORE=y
     CONFIG_SERIAL_CORE_CONSOLE=y
                

Next, include this configuration fragment and extend the FILESPATH variable in your .bbappend file:

     FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
     SRC_URI += "file://8250.cfg"
                

The next time you run BitBake to build the Linux kernel, BitBake detects the change in the recipe and fetches and applies the new configuration before building the kernel.

For a detailed example showing how to configure the kernel, see the "Configuring the Kernel" section in the Yocto Project Development Manual.

2.3. Using an Iterative Development Process

If you do not have existing patches or configuration files, you can iteratively generate them from within the BitBake build environment as described within this section. During an iterative workflow, running a previously completed BitBake task causes BitBake to invalidate the tasks that follow the completed task in the build sequence. Invalidated tasks rebuild the next time you run the build using BitBake.

As you read this section, be sure to substitute the name of your Linux kernel recipe for the term "linux-yocto".

2.3.1. "-dirty" String

If kernel images are being built with "-dirty" on the end of the version string, this simply means that modifications in the source directory have not been committed.

     $ git status
                

You can use the above Git command to report modified, removed, or added files. You should commit those changes to the tree regardless of whether they will be saved, exported, or used. Once you commit the changes, you need to rebuild the kernel.

To force a pickup and commit of all such pending changes, enter the following:

     $ git add .
     $ git commit -s -a -m "getting rid of -dirty"
                

Next, rebuild the kernel.

2.3.2. Generating Configuration Files

You can manipulate the .config file used to build a linux-yocto recipe with the menuconfig command as follows:

     $ bitbake linux-yocto -c menuconfig
                

This command starts the Linux kernel configuration tool, which allows you to prepare a new .config file for the build. When you exit the tool, be sure to save your changes at the prompt.

The resulting .config file is located in ${WORKDIR} under the linux-${MACHINE}-${KTYPE}-build directory. You can use the entire .config file as the defconfig file as described in the "Changing the Configuration" section.

A better method is to create a configuration fragment using the differences between two configuration files: one previously created and saved, and one freshly created using the menuconfig tool.

To create a configuration fragment using this method, follow these steps:

  1. Complete a build at least through the kernel configuration task as follows:

         $ bitbake linux-yocto -c kernel_configme -f
                            
  2. Copy and rename the resulting .config file (e.g. config.orig).

  3. Run the menuconfig command:

         $ bitbake linux-yocto -c menuconfig
                            
  4. Prepare a configuration fragment based on the differences between the two files.

Ultimately, the configuration fragment file needs to be a list of Linux kernel CONFIG_ assignments. It cannot be in diff format. Here is an example of a command that creates your configuration fragment file. Regardless of the exact command you use, plan on reviewing the output as you can usually remove some of the defaults:

     $ diff -Nurp config.orig .config | sed -n "s/^\+//p" > frag.cfg
                

See the "Changing the Configuration" section for information on how to use the output as a configuration fragment.

Note

You can also use this method to create configuration fragments for a BSP. See the "BSP Descriptions" section for more information.

The kernel tools also provide configuration validation. You can use these tools to produce warnings for when a requested configuration does not appear in the final .config file or when you override a policy configuration in a hardware configuration fragment. Here is an example with some sample output of the command that runs these tools:

     $ bitbake linux-yocto -c kernel_configcheck -f

     ...

     NOTE: validating kernel configuration
     This BSP sets 3 invalid/obsolete kernel options.
     These config options are not offered anywhere within this kernel.
     The full list can be found in your kernel src dir at:
     meta/cfg/standard/mybsp/invalid.cfg

     This BSP sets 21 kernel options that are possibly non-hardware related.
     The full list can be found in your kernel src dir at:
     meta/cfg/standard/mybsp/specified_non_hdw.cfg

     WARNING: There were 2 hardware options requested that do not
              have a corresponding value present in the final ".config" file.
              This probably means you are not't getting the config you wanted.
              The full list can be found in your kernel src dir at:
              meta/cfg/standard/mybsp/mismatch.cfg
                

The output describes the various problems that you can encounter along with where to find the offending configuration items. You can use the information in the logs to adjust your configuration files and then repeat the kernel_configme and kernel_configcheck commands until they produce no warnings.

For more information on how to use the menuconfig tool, see the "Using menuconfig" section in the Yocto Project Development Manual.

2.3.3. Modifying Source Code

You can experiment with source code changes and create a simple patch without leaving the BitBake environment. To get started, be sure to complete a build at least through the kernel configuration task:

     $ bitbake linux-yocto -c kernel_configme -f
                

Taking this step ensures you have the sources prepared and the configuration completed. You can find the sources in the ${WORKDIR}/linux directory.

You can edit the sources as you would any other Linux source tree. However, keep in mind that you will lose changes if you trigger the fetch task for the recipe. You can avoid triggering this task by not issuing BitBake's cleanall, cleansstate, or forced fetch commands. Also, do not modify the recipe itself while working with temporary changes or BitBake might run the fetch command depending on the changes to the recipe.

To test your temporary changes, instruct BitBake to run the compile again. The -f option forces the command to run even though BitBake might think it has already done so:

     $ bitbake linux-yocto -c compile -f
                

If the compile fails, you can update the sources and repeat the compile. Once compilation is successful, you can inspect and test the resulting build (i.e. kernel, modules, and so forth) from the Build Directory:

     ${WORKDIR}/linux-${MACHINE}-${KTYPE}-build
                

Alternatively, you can run the deploy command to place the kernel image in the tmp/deploy/images directory:

	$ bitbake linux-yocto -c deploy
                

And, of course, you can perform the remaining installation and packaging steps by issuing:

	$ bitbake linux-yocto
                

For rapid iterative development, the edit-compile-repeat loop described in this section is preferable to rebuilding the entire recipe because the installation and packaging tasks are very time consuming.

Once you are satisfied with your source code modifications, you can make them permanent by generating patches and applying them to the SRC_URI statement as described in section "Applying Patches" section. If you are not familiar with generating patches, refer to the "Creating the Patch" section in the Yocto Project Development Manual.

2.4. Working With Your Own Sources

If you cannot work with one of the Linux kernel versions supported by existing linux-yocto recipes, you can still make use of the Yocto Project Linux kernel tooling by working with your own sources. When you use your own sources, you will not be able to leverage the existing kernel Metadata and stabilization work of the linux-yocto sources. However, you will be able to manage your own Metadata in the same format as the linux-yocto sources. Maintaining format compatibility facilitates converging with linux-yocto on a future, mutually-supported kernel version.

To help you use your own sources, the Yocto Project provides a linux-yocto custom recipe (linux-yocto-custom.bb) that uses kernel.org sources and the Yocto Project Linux kernel tools for managing kernel Metadata. You can find this recipe in the poky Git repository of the Yocto Project Source Repository at:

     poky/meta-skeleton/recipes-kernel/linux/linux-yocto-custom.bb
            

Here are some basic steps you can use to work with your own sources:

  1. Copy the linux-yocto-custom.bb recipe to your layer and give it a meaningful name. The name should include the version of the Linux kernel you are using (e.g. linux-yocto-myproject_3.5.bb, where "3.5" is the base version of the Linux kernel with which you would be working).

  2. In the same directory inside your layer, create a matching directory to store your patches and configuration files (e.g. linux-yocto-myproject).

  3. Edit the following variables in your recipe as appropriate for your project:

    • SRC_URI: The SRC_URI should be a Git repository that uses one of the supported Git fetcher protocols (i.e. file, git, http, and so forth). The skeleton recipe provides an example SRC_URI as a syntax reference.

    • LINUX_VERSION: The Linux kernel version you are using (e.g. "3.4").

    • LINUX_VERSION_EXTENSION: The Linux kernel CONFIG_LOCALVERSION that is compiled into the resulting kernel and visible through the uname command.

    • SRCREV: The commit ID from which you want to build.

    • PR: Treat this variable the same as you would in any other recipe. Increment the variable to indicate to the OpenEmbedded build system that the recipe has changed.

    • PV: The default PV assignment is typically adequate. It combines the LINUX_VERSION with the Source Control Manager (SCM) revision as derived from the SRCPV variable. The combined results are a string with the following form:

           3.4.11+git1+68a635bf8dfb64b02263c1ac80c948647cc76d5f_1+218bd8d2022b9852c60d32f0d770931e3cf343e2
                                  

      While lengthy, the extra verbosity in PV helps ensure you are using the exact sources from which you intend to build.

    • COMPATIBLE_MACHINE: A list of the machines supported by your new recipe. This variable in the example recipe is set by default to a regular expression that matches only the empty string, "(^$)". This default setting triggers an explicit build failure. You must change it to match a list of the machines that your new recipe supports. For example, to support the qemux86 and qemux86-64 machines, use the following form:

           COMPATIBLE_MACHINE = "qemux86|qemux86-64"
                                  
  4. Provide further customizations to your recipe as needed just as you would customize an existing linux-yocto recipe. See the "Modifying an Existing Recipe" section for information.

2.5. Incorporating Out-of-Tree Modules

While it is always preferable to work with sources integrated into the Linux kernel sources, if you need an external kernel module, the hello-mod.bb recipe is available as a template from which you can create your own out-of-tree Linux kernel module recipe.

This template recipe is located in the poky Git repository of the Yocto Project Source Repository at:

     poky/meta-skeleton/recipes-kernel/hello-mod/hello-mod_0.1.bb
            

To get started, copy this recipe to your layer and give it a meaningful name (e.g. mymodule_1.0.bb). In the same directory, create a directory named files where you can store any source files, patches, or other files necessary for building the module that do not come with the sources. Finally, update the recipe as appropriate for the module. Typically you will need to set the following variables:

Depending on the build system used by the module sources, you might need to make some adjustments. For example, a typical module Makefile looks much like the one provided with the hello-mod template:

     obj-m := hello.o

     SRC := $(shell pwd)

     all:
         $(MAKE) -C $(KERNEL_SRC) M=$(SRC)

     modules_install:
         $(MAKE) -C $(KERNEL_SRC) M=$(SRC) modules_install
     ...
            

The important point to note here is the KERNEL_SRC variable. The class module.bbclass sets this variable, as well as the KERNEL_PATH variable to ${STAGING_KERNEL_DIR} with the necessary Linux kernel build information to build modules. If your module Makefile uses a different variable, you might want to override the do_compile() step, or create a patch to the Makefile to work with the more typical KERNEL_SRC or KERNEL_PATH variables.

After you have prepared your recipe, you will likely want to include the module in your images. To do this, see the documentation for the following variables in the Yocto Project Reference Manual and set one of them as appropriate in your machine configuration file:

modules are often not required for boot and can be excluded from certain build configurations. The following allows for the most flexibility:

     MACHINE_EXTRA_RRECOMMENDS += "kernel-module-mymodule"
            

Where the value is derived by appending the module filename without the .ko extension to the string "kernel-module-".

Because the variable is RRECOMMENDS and not a RDEPENDS variable, the build will not fail if this module is not available to include in the image.

2.6. Inspecting Changes and Commits

A common question when working with a kernel is: "What changes have been applied to this tree?" Rather than using "grep" across directories to see what has changed, you can use Git to inspect or search the kernel tree. Using Git is an efficient way to see what has changed in the tree.

2.6.1. What Changed in a Kernel?

Following are a few examples that show how to use Git commands to examine changes. These examples are by no means the only way to see changes.

Note

In the following examples, unless you provide a commit range, kernel.org history is blended with Yocto Project kernel changes. You can form ranges by using branch names from the kernel tree as the upper and lower commit markers with the Git commands. You can see the branch names through the web interface to the Yocto Project source repositories at http://git.yoctoproject.org/cgit.cgi.

To see a full range of the changes, use the git whatchanged command and specify a commit range for the branch (<commit>..<commit>).

Here is an example that looks at what has changed in the emenlow branch of the linux-yocto-3.4 kernel. The lower commit range is the commit associated with the standard/base branch, while the upper commit range is the commit associated with the standard/emenlow branch.

     $ git whatchanged origin/standard/base..origin/standard/emenlow
                

To see short, one line summaries of changes use the git log command:

     $ git log --oneline origin/standard/base..origin/standard/emenlow
                

Use this command to see code differences for the changes:

     $ git diff origin/standard/base..origin/standard/emenlow
                

Use this command to see the commit log messages and the text differences:

     $ git show origin/standard/base..origin/standard/emenlow
                

Use this command to create individual patches for each change. Here is an example that that creates patch files for each commit and places them in your Documents directory:

     $ git format-patch -o $HOME/Documents origin/standard/base..origin/standard/emenlow
                

2.6.2. Showing a Particular Feature or Branch Change

Tags in the Yocto Project kernel tree divide changes for significant features or branches. The git show <tag> command shows changes based on a tag. Here is an example that shows systemtap changes:

     $ git show systemtap
                

You can use the git branch --contains <tag> command to show the branches that contain a particular feature. This command shows the branches that contain the systemtap feature:

     $ git branch --contains systemtap
                

Chapter 3. Working with Advanced Metadata

3.1. Overview

In addition to supporting configuration fragments and patches, the Yocto Project kernel tools also support rich Metadata that you can use to define complex policies and Board Support Package (BSP) support. The purpose of the Metadata and the tools that manage it, known as the kern-tools (kern-tools-native_git.bb), is to help you manage the complexity of the configuration and sources used to support multiple BSPs and Linux kernel types.

3.2. Using Kernel Metadata in a Recipe

The kernel sources in the Yocto Project contain kernel Metadata, which is located in the meta branches of the kernel source Git repositories. This Metadata defines Board Support Packages (BSPs) that correspond to definitions in linux-yocto recipes for the same BSPs. A BSP consists of an aggregation of kernel policy and hardware-specific feature enablements. The BSP can be influenced from within the linux-yocto recipe.

Note

Linux kernel source that contains kernel Metadata is said to be "linux-yocto style" kernel source. A Linux kernel recipe that inherits from the linux-yocto.inc include file is said to be a "linux-yocto style" recipe.

Every linux-yocto style recipe must define the KMACHINE variable. This variable is typically set to the same value as the MACHINE variable, which is used by BitBake (e.g. "routerstationpro" or "fri2"). Multiple BSPs can reuse the same KMACHINE name if they are built using the same BSP description. The "fri2" and "fri2-noemgd" BSP combination in the meta-intel layer is a good example of two BSPs using the same KMACHINE value (i.e. "fri2"). See the BSP Descriptions section for more information.

The linux-yocto style recipes can optionally define the following variables:

     KBRANCH
     KERNEL_FEATURES
     KBRANCH_DEFAULT
     LINUX_KERNEL_TYPE
        

KBRANCH_DEFAULT defines the Linux kernel source repository's default branch to use to build the Linux kernel. The value is used as the default for KBRANCH, which can define an alternate branch typically with a machine override as follows:

     KBRANCH_fri2 = "standard/fri2"
        

Unless you specify otherwise, KBRANCH_DEFAULT initializes to "master".

LINUX_KERNEL_TYPE defines the kernel type to be used in assembling the configuration. If you do not specify a LINUX_KERNEL_TYPE, it defaults to "standard". Together with KMACHINE, LINUX_KERNEL_TYPE defines the search arguments used by the kernel tools to find the appropriate description within the kernel Metadata with which to build out the sources and configuration. The linux-yocto recipes define "standard", "tiny", and "preempt-rt" kernel types. See the Kernel Types section for more information on kernel types.

During the build, the kern-tools search for the BSP description file that most closely matches the KMACHINE and LINUX_KERNEL_TYPE variables passed in from the recipe. The tools use the first BSP description it finds that match both variables. If the tools cannot find a match, they issue a warning such as the following:

     WARNING: Can't find any BSP hardware or required configuration fragments.
     WARNING: Looked at meta/cfg/broken/fri2-broken/hdw_frags.txt and
              meta/cfg/broken/fri2-broken/required_frags.txt in directory:
              meta/cfg/broken/fri2-broken
        

In this example, KMACHINE was set to "fri2-broken" and LINUX_KERNEL_TYPE was set to "broken".

The tools first search for the KMACHINE and then for the LINUX_KERNEL_TYPE. If the tools cannot find a partial match, they will use the sources from the KBRANCH and any configuration specified in the SRC_URI.

You can use the KERNEL_FEATURES variable to include features (configuration fragments, patches, or both) that are not already included by the KMACHINE and LINUX_KERNEL_TYPE variable combination. For example, to include a feature specified as "features/netfilter.scc", specify:

     KERNEL_FEATURES += "features/netfilter.scc"
        

To include a feature called "cfg/sound.scc" just for the qemux86 machine, specify:

     KERNEL_FEATURES_append_qemux86 = "cfg/sound.scc"
        

The value of the entries in KERNEL_FEATURES are dependent on their location within the kernel Metadata itself. The examples here are taken from the linux-yocto-3.4 repository where "features" and "cfg" are subdirectories within the meta/cfg/kernel-cache directory. For more information, see the "Kernel Metadata Syntax" section.

Note

The processing of the these variables has evolved some between the 0.9 and 1.3 releases of the Yocto Project and associated kern-tools sources. The descriptions in this section are accurate for 1.3 and later releases of the Yocto Project.

3.3. Kernel Metadata Location

Kernel Metadata can be defined in either the kernel recipe (recipe-space) or in the kernel tree (in-tree). Where you choose to define the Metadata depends on what you want to do and how you intend to work. Regardless of where you define the kernel Metadata, the syntax used applies equally.

If you are unfamiliar with the Linux kernel and only wish to apply a configuration and possibly a couple of patches provided to you by others, the recipe-space method is recommended. This method is also a good approach if you are working with Linux kernel sources you do not control or if you just do not want to maintain a Linux kernel Git repository on your own. For partial information on how you can define kernel Metadata in the recipe-space, see the "Modifying an Existing Recipe" section.

Conversely, if you are actively developing a kernel and are already maintaining a Linux kernel Git repository of your own, you might find it more convenient to work with the kernel Metadata in the same repository as the Linux kernel sources. This method can make iterative development of the Linux kernel more efficient outside of the BitBake environment.

3.3.1. Recipe-Space Metadata

When stored in recipe-space, the kernel Metadata files reside in a directory hierarchy below FILESEXTRAPATHS. For a linux-yocto recipe or for a Linux kernel recipe derived by copying and modifying oe-core/meta-skeleton/recipes-kernel/linux/linux-yocto-custom.bb to a recipe in your layer, FILESEXTRAPATHS is typically set to ${THISDIR}/${PN}. See the "Modifying an Existing Recipe" section for more information.

Here is an example that shows a trivial tree of kernel Metadata stored in recipe-space within a BSP layer:

     meta-my_bsp_layer/
     `-- recipes-kernel
         `-- linux
             `-- linux-yocto
                 |-- bsp-standard.scc
                 |-- bsp.cfg
                 `-- standard.cfg
            

When the Metadata is stored in recipe-space, you must take steps to ensure BitBake has the necessary information to decide what files to fetch and when they need to be fetched again. It is only necessary to specify the .scc files on the SRC_URI. BitBake parses them and fetches any files referenced in the .scc files by the include, patch, or kconf commands. Because of this, it is necessary to bump the recipe PR value when changing the content of files not explicitly listed in the SRC_URI.

3.3.2. In-Tree Metadata

When stored in-tree, the kernel Metadata files reside in the meta directory of the Linux kernel sources. The meta directory can be present in the same repository branch as the sources, such as "master", or meta can be its own orphan branch.

Note

An orphan branch in Git is a branch with unique history and content to the other branches in the repository. Orphan branches are useful to track Metadata changes independently from the sources of the Linux kernel, while still keeping them together in the same repository.

For the purposes of this document, we will discuss all in-tree Metadata as residing below the meta/cfg/kernel-cache directory.

Following is an example that shows how a trivial tree of Metadata is stored in a custom Linux kernel Git repository:

     meta/
     `-- cfg
         `-- kernel-cache
             |-- bsp-standard.scc
             |-- bsp.cfg
             `-- standard.cfg
            

To use a branch different from where the sources reside, specify the branch in the KMETA variable in your Linux kernel recipe. Here is an example:

     KMETA = "meta"
            

To use the same branch as the sources, set KMETA to an empty string:

     KMETA = ""
            

If you are working with your own sources and want to create an orphan meta branch, use these commands from within your Linux kernel Git repository:

     $ git checkout --orphan meta
     $ git rm -rf .
     $ git commit --allow-empty -m "Create orphan meta branch"
            

3.4. Kernel Metadata Syntax

The kernel Metadata consists of three primary types of files: scc [2] description files, configuration fragments, and patches. The scc files define variables and include or otherwise reference any of the three file types. The description files are used to aggregate all types of kernel Metadata into what ultimately describes the sources and the configuration required to build a Linux kernel tailored to a specific machine.

The scc description files are used to define two fundamental types of kernel Metadata:

  • Features

  • Board Support Packages (BSPs)

Features aggregate sources in the form of patches and configuration fragments into a modular reusable unit. You can use features to implement conceptually separate kernel Metadata descriptions such as pure configuration fragments, simple patches, complex features, and kernel types. Kernel types define general kernel features and policy to be reused in the BSPs.

BSPs define hardware-specific features and aggregate them with kernel types to form the final description of what will be assembled and built.

While the kernel Metadata syntax does not enforce any logical separation of configuration fragments, patches, features or kernel types, best practices dictate a logical separation of these types of Metadata. The following Metadata file hierarchy is recommended:

     <base>/
        bsp/
        cfg/
        features/
        ktypes/
        patches/
        

The bsp directory contains the BSP descriptions. The remaining directories all contain "features". Separating bsp from the rest of the structure aids conceptualizing intended usage.

Use these guidelines to help place your scc description files within the structure:

  • If your file contains only configuration fragments, place the file in the cfg directory.

  • If your file contains only source-code fixes, place the file in the patches directory.

  • If your file encapsulates a major feature, often combining sources and configurations, place the file in features directory.

  • If your file aggregates non-hardware configuration and patches in order to define a base kernel policy or major kernel type to be reused across multiple BSPs, place the file in ktypes directory.

These distinctions can easily become blurred - especially as out-of-tree features slowly merge upstream over time. Also, remember that how the description files are placed is a purely logical organization and has no impact on the functionality of the kernel Metadata. There is no impact because all of cfg, features, patches, and ktypes, contain "features" as far as the kernel tools are concerned.

Paths used in kernel Metadata files are relative to <base>, which is either FILESEXTRAPATHS if you are creating Metadata in recipe-space, or meta/cfg/kernel-cache/ if you are creating Metadata in-tree.

3.4.1. Configuration

The simplest unit of kernel Metadata is the configuration-only feature. This feature consists of one or more Linux kernel configuration parameters in a configuration fragment file (.cfg) and an .scc file that describes the fragment.

The Symmetric Multi-Processing (SMP) fragment included in the linux-yocto-3.4 Git repository consists of the following two files:

     cfg/smp.scc:
        define KFEATURE_DESCRIPTION "Enable SMP"
        kconf hardware smp.cfg

     cfg/smp.cfg:
        CONFIG_SMP=y
        CONFIG_SCHED_SMT=y
            

You can find information on configuration fragment files in the "Creating Configuration Fragments" section of the Yocto Project Development Manual and in the "Generating Configuration Files" section earlier in this manual.

KFEATURE_DESCRIPTION provides a short description of the fragment. Higher level kernel tools use this description.

The kconf command is used to include the actual configuration fragment in an .scc file, and the "hardware" keyword identifies the fragment as being hardware enabling, as opposed to general policy, which would use the "non-hardware" keyword. The distinction is made for the benefit of the configuration validation tools, which warn you if a hardware fragment overrides a policy set by a non-hardware fragment.

Note

The description file can include multiple kconf statements, one per fragment.

As described in the "Generating Configuration Files" section, you can use the following BitBake command to audit your configuration:

     $ bitbake linux-yocto -c kernel_configcheck -f
            

3.4.2. Patches

Patch descriptions are very similar to configuration fragment descriptions, which are described in the previous section. However, instead of a .cfg file, these descriptions work with source patches.

A typical patch includes a description file and the patch itself:

     patches/mypatch.scc:
        patch mypatch.patch

     patches/mypatch.patch:
        <typical-patch>
            

You can create the typical .patch file using diff -Nurp or git format-patch.

The description file can include multiple patch statements, one per patch.

3.4.3. Features

Features are complex kernel Metadata types that consist of configuration fragments (kconf), patches (patch), and possibly other feature description files (include).

Here is an example that shows a feature description file:

     features/myfeature.scc
        define KFEATURE_DESCRIPTION "Enable myfeature"

        patch 0001-myfeature-core.patch
        patch 0002-myfeature-interface.patch

        include cfg/myfeature_dependency.scc
        kconf non-hardware myfeature.cfg
            

This example shows how the patch and kconf commands are used as well as how an additional feature description file is included.

Typically, features are less granular than configuration fragments and are more likely than configuration fragments and patches to be the types of things you want to specify in the KERNEL_FEATURES variable of the Linux kernel recipe. See the "Using Kernel Metadata in a Recipe" section earlier in the manual.

3.4.4. Kernel Types

A kernel type defines a high-level kernel policy by aggregating non-hardware configuration fragments with patches you want to use when building a Linux kernels of a specific type. Syntactically, kernel types are no different than features as described in the "Features" section. The LINUX_KERNEL_TYPE variable in the kernel recipe selects the kernel type. See the "Using Kernel Metadata in a Recipe" section for more information.

As an example, the linux-yocto-3.4 tree defines three kernel types: "standard", "tiny", and "preempt-rt":

  • "standard": Includes the generic Linux kernel policy of the Yocto Project linux-yocto kernel recipes. This policy includes, among other things, which file systems, networking options, core kernel features, and debugging and tracing options are supported.

  • "preempt-rt": Applies the PREEMPT_RT patches and the configuration options required to build a real-time Linux kernel. This kernel type inherits from the "standard" kernel type.

  • "tiny": Defines a bare minimum configuration meant to serve as a base for very small Linux kernels. The "tiny" kernel type is independent from the "standard" configuration. Although the "tiny" kernel type does not currently include any source changes, it might in the future.

The "standard" kernel type is defined by standard.scc:

     # Include this kernel type fragment to get the standard features and
     # configuration values.

     # Include all standard features
     include standard-nocfg.scc

     kconf non-hardware standard.cfg

     # individual cfg block section
     include cfg/fs/devtmpfs.scc
     include cfg/fs/debugfs.scc
     include cfg/fs/btrfs.scc
     include cfg/fs/ext2.scc
     include cfg/fs/ext3.scc
     include cfg/fs/ext4.scc

     include cfg/net/ipv6.scc
     include cfg/net/ip_nf.scc
     include cfg/net/ip6_nf.scc
     include cfg/net/bridge.scc
            

As with any .scc file, a kernel type definition can aggregate other .scc files with include commands. These definitions can also directly pull in configuration fragments and patches with the kconf and patch commands, respectively.

Note

It is not strictly necessary to create a kernel type .scc file. The Board Support Package (BSP) file can implicitly define the kernel type using a define KTYPE myktype line. See the "BSP Descriptions" section for more information.

3.4.5. BSP Descriptions

BSP descriptions combine kernel types with hardware-specific features. The hardware-specific portion is typically defined independently, and then aggregated with each supported kernel type. Consider this simple BSP description that supports the "mybsp" machine:

     mybsp.scc:
        define KMACHINE mybsp
        define KTYPE standard
        define KARCH i386

        kconf mybsp.cfg
            

Every BSP description should define the KMACHINE, KTYPE, and KARCH variables. These variables allow the OpenEmbedded build system to identify the description as meeting the criteria set by the recipe being built. This simple example supports the "mybsp" machine for the "standard" kernel and the "i386" architecture.

Be aware that a hard link between the KTYPE variable and a kernel type description file does not exist. Thus, if you do not have kernel types defined in your kernel Metadata, you only need to ensure that the kernel recipe's LINUX_KERNEL_TYPE variable and the KTYPE variable in the BSP description file match.

Note

Future versions of the tooling make the specification of KTYPE in the BSP optional.

If you did want to separate your kernel policy from your hardware configuration, you could do so by specifying a kernel type, such as "standard" and including that description file in the BSP description file. See the "Kernel Types" section for more information.

You might also have multiple hardware configurations that you aggregate into a single hardware description file that you could include in the BSP description file, rather than referencing a single .cfg file. Consider the following:

     mybsp.scc:
        define KMACHINE mybsp
        define KTYPE standard
        define KARCH i386

        include standard.scc
        include mybsp-hw.scc
            

In the above example, standard.scc aggregates all the configuration fragments, patches, and features that make up your standard kernel policy whereas mybsp-hw.scc aggregates all those necessary to support the hardware available on the "mybsp" machine. For information on how to break a complete .config file into the various configuration fragments, see the "Generating Configuration Files" section.

Many real-world examples are more complex. Like any other .scc file, BSP descriptions can aggregate features. Consider the Fish River Island 2 (fri2) BSP definition from the linux-yocto-3.4 Git repository:

     fri2.scc:
        kconf hardware fri2.cfg

        include cfg/x86.scc
        include features/eg20t/eg20t.scc
        include cfg/dmaengine.scc
        include features/ericsson-3g/f5521gw.scc
        include features/power/intel.scc
        include cfg/efi.scc
        include features/usb/ehci-hcd.scc
        include features/usb/ohci-hcd.scc
        include features/iwlwifi/iwlwifi.scc
            

The fri2.scc description file includes a hardware configuration fragment (fri2.cfg) specific to the Fish River Island 2 BSP as well as several more general configuration fragments and features enabling hardware found on the machine. This description file is then included in each of the three "fri2" description files for the supported kernel types (i.e. "standard", "preempt-rt", and "tiny"). Consider the "fri2" description for the "standard" kernel type:

     fri2-standard.scc:
        define KMACHINE fri2
        define KTYPE standard
        define KARCH i386

        include ktypes/standard/standard.scc
        branch fri2

        git merge emgd-1.14

        include fri2.scc

        # Extra fri2 configs above the minimal defined in fri2.scc
        include cfg/efi-ext.scc
        include features/drm-emgd/drm-emgd.scc
        include cfg/vesafb.scc

        # default policy for standard kernels
        include cfg/usb-mass-storage.scc
            

The include command midway through the file includes the fri2.scc description that defines all hardware enablements for the BSP that is common to all kernel types. Using this command significantly reduces duplication.

This "fri2" standard description introduces a few more variables and commands that are worth further discussion. Notice the branch fri2 command, which creates a machine-specific branch into which source changes are applied. With this branch set up, the git merge command uses Git to merge in a feature branch named "emgd-1.14". You could also handle this with the patch command. However, for commonly used features such as this, feature branches are a convenient mechanism. See the "Feature Branches" section for more information.

Now consider the "fri2" description for the "tiny" kernel type:

     fri2-tiny.scc:
        define KMACHINE fri2
        define KTYPE tiny
        define KARCH i386

        include ktypes/tiny/tiny.scc
        branch fri2

        include fri2.scc
            

As you might expect, the "tiny" description includes quite a bit less. In fact, it includes only the minimal policy defined by the "tiny" kernel type and the hardware-specific configuration required for booting the machine along with the most basic functionality of the system as defined in the base "fri2" description file.

Notice again the three critical variables: KMACHINE, KTYPE, and KARCH. Of these variables, only the KTYPE has changed. It is now set to "tiny".

3.5. Organizing Your Source

Many recipes based on the linux-yocto-custom.bb recipe use Linux kernel sources that have only a single branch - "master". This type of repository structure is fine for linear development supporting a single machine and architecture. However, if you work with multiple boards and architectures, a kernel source repository with multiple branches is more efficient. For example, suppose you need a series of patches for one board to boot. Sometimes, these patches are works-in-progress or fundamentally wrong, yet they are still necessary for specific boards. In these situations, you most likely do not want to include these patches in every kernel you build (i.e. have the patches as part of the lone "master" branch). It is situations like these that give rise to multiple branches used within a Linux kernel sources Git repository.

Repository organization strategies exist that maximize source reuse, remove redundancy, and logically order your changes. This section presents strategies for the following cases:

  • Encapsulating patches in a feature description and only including the patches in the BSP descriptions of the applicable boards.

  • Creating a machine branch in your kernel source repository and applying the patches on that branch only.

  • Creating a feature branch in your kernel source repository and merging that branch into your BSP when needed.

The approach you take is entirely up to you and depends on what works best for your development model.

3.5.1. Encapsulating Patches

if you are reusing patches from an external tree and are not working on the patches, you might find the encapsulated feature to be appropriate. Given this scenario, you do not need to create any branches in the source repository. Rather, you just take the static patches you need and encapsulate them within a feature description. Once you have the feature description, you simply include that into the BSP description as described in the "BSP Descriptions" section.

You can find information on how to create patches and BSP descriptions in the "Patches" and "BSP Descriptions" sections.

3.5.2. Machine Branches

When you have multiple machines and architectures to support, or you are actively working on board support, it is more efficient to create branches in the repository based on individual machines. Having machine branches allows common source to remain in the "master" branch with any features specific to a machine stored in the appropriate machine branch. This organization method frees you from continually reintegrating your patches into a feature.

Once you have a new branch, you can set up your kernel Metadata to use the branch a couple different ways. In the recipe, you can specify the new branch as the KBRANCH to use for the board as follows:

     KBRANCH = "mynewbranch"
            

Another method is to use the branch command in the BSP description:

     mybsp.scc:
        define KMACHINE mybsp
        define KTYPE standard
        define KARCH i386
        include standard.scc

        branch mynewbranch

        include mybsp-hw.scc
            

If you find yourself with numerous branches, you might consider using a hierarchical branching system similar to what the linux-yocto Linux kernel repositories use:

     <common>/<kernel_type>/<machine>
            

If you had two kernel types, "standard" and "small" for instance, and three machines, the branches in your Git repository might look like this:

     common/base
     common/standard/base
     common/standard/machine_a
     common/standard/machine_b
     common/standard/machine_c
     common/small/base
     common/small/machine_a
            

This organization can help clarify the branch relationships. In this case, common/standard/machine_a includes everything in common/base and common/standard/base. The "standard" and "small" branches add sources specific to those kernel types that for whatever reason are not appropriate for the other branches.

Note

The "base" branches are an artifact of the way Git manages its data internally on the filesystem: Git will not allow you to use common/standard and common/standard/machine_a because it would have to create a file and a directory named "standard".

3.5.3. Feature Branches

When you are actively developing new features, it can be more efficient to work with that feature as a branch, rather than as a set of patches that have to be regularly updated. The Yocto Project Linux kernel tools provide for this with the git merge command.

To merge a feature branch into a BSP, insert the git merge command after any branch commands:

     mybsp.scc:
        define KMACHINE mybsp
        define KTYPE standard
        define KARCH i386
        include standard.scc

        branch mynewbranch
        git merge myfeature

        include mybsp-hw.scc
            

3.6. SCC Description File Reference

This section provides a brief reference for the commands you can use within an SCC description file (.scc):

  • branch [ref]: Creates a new branch relative to the current branch (typically ${KTYPE}) using the currently checked-out branch, or "ref" if specified.

  • define: Defines variables, such as KMACHINE, KTYPE, KARCH, and KFEATURE_DESCRIPTION.

  • include SCC_FILE: Includes an SCC file in the current file. The file is parsed as if you had inserted it inline.

  • kconf [hardware|non-hardware] CFG_FILE: Queues a configuration fragment for merging into the final Linux .config file.

  • git merge GIT_BRANCH: Merges the feature branch into the current branch.

  • patch PATCH_FILE: Applies the patch to the current Git branch.



[2] scc stands for Series Configuration Control, but the naming has less significance in the current implementation of the tooling than it had in the past. Consider scc files to be description files.

Appendix A. Advanced Kernel Concepts

A.1. Yocto Project Kernel Development and Maintenance

Kernels available through the Yocto Project, like other kernels, are based off the Linux kernel releases from http://www.kernel.org. At the beginning of a major development cycle, the Yocto Project team chooses its kernel based on factors such as release timing, the anticipated release timing of final upstream kernel.org versions, and Yocto Project feature requirements. Typically, the kernel chosen is in the final stages of development by the community. In other words, the kernel is in the release candidate or "rc" phase and not yet a final release. But, by being in the final stages of external development, the team knows that the kernel.org final release will clearly be within the early stages of the Yocto Project development window.

This balance allows the team to deliver the most up-to-date kernel possible, while still ensuring that the team has a stable official release for the baseline Linux kernel version.

The ultimate source for kernels available through the Yocto Project are released kernels from kernel.org. In addition to a foundational kernel from kernel.org, the kernels available contain a mix of important new mainline developments, non-mainline developments (when there is no alternative), Board Support Package (BSP) developments, and custom features. These additions result in a commercially released Yocto Project Linux kernel that caters to specific embedded designer needs for targeted hardware.

Once a kernel is officially released, the Yocto Project team goes into their next development cycle, or upward revision (uprev) cycle, while still continuing maintenance on the released kernel. It is important to note that the most sustainable and stable way to include feature development upstream is through a kernel uprev process. Back-porting hundreds of individual fixes and minor features from various kernel versions is not sustainable and can easily compromise quality.

During the uprev cycle, the Yocto Project team uses an ongoing analysis of kernel development, BSP support, and release timing to select the best possible kernel.org version. The team continually monitors community kernel development to look for significant features of interest. The team does consider back-porting large features if they have a significant advantage. User or community demand can also trigger a back-port or creation of new functionality in the Yocto Project baseline kernel during the uprev cycle.

Generally speaking, every new kernel both adds features and introduces new bugs. These consequences are the basic properties of upstream kernel development and are managed by the Yocto Project team's kernel strategy. It is the Yocto Project team's policy to not back-port minor features to the released kernel. They only consider back-porting significant technological jumps - and, that is done after a complete gap analysis. The reason for this policy is that back-porting any small to medium sized change from an evolving kernel can easily create mismatches, incompatibilities and very subtle errors.

These policies result in both a stable and a cutting edge kernel that mixes forward ports of existing features and significant and critical new functionality. Forward porting functionality in the kernels available through the Yocto Project kernel can be thought of as a "micro uprev." The many “micro uprevs” produce a kernel version with a mix of important new mainline, non-mainline, BSP developments and feature integrations. This kernel gives insight into new features and allows focused amounts of testing to be done on the kernel, which prevents surprises when selecting the next major uprev. The quality of these cutting edge kernels is evolving and the kernels are used in leading edge feature and BSP development.

A.2. Kernel Architecture

This section describes the architecture of the kernels available through the Yocto Project and provides information on the mechanisms used to achieve that architecture.

A.2.1. Overview

As mentioned earlier, a key goal of the Yocto Project is to present the developer with a kernel that has a clear and continuous history that is visible to the user. The architecture and mechanisms used achieve that goal in a manner similar to the upstream kernel.org.

You can think of a Yocto Project kernel as consisting of a baseline Linux kernel with added features logically structured on top of the baseline. The features are tagged and organized by way of a branching strategy implemented by the source code manager (SCM) Git. For information on Git as applied to the Yocto Project, see the "Git" section in the Yocto Project Development Manual.

The result is that the user has the ability to see the added features and the commits that make up those features. In addition to being able to see added features, the user can also view the history of what made up the baseline kernel.

The following illustration shows the conceptual Yocto Project kernel.

In the illustration, the "Kernel.org Branch Point" marks the specific spot (or release) from which the Yocto Project kernel is created. From this point "up" in the tree, features and differences are organized and tagged.

The "Yocto Project Baseline Kernel" contains functionality that is common to every kernel type and BSP that is organized further up the tree. Placing these common features in the tree this way means features do not have to be duplicated along individual branches of the structure.

From the Yocto Project Baseline Kernel, branch points represent specific functionality for individual BSPs as well as real-time kernels. The illustration represents this through three BSP-specific branches and a real-time kernel branch. Each branch represents some unique functionality for the BSP or a real-time kernel.

In this example structure, the real-time kernel branch has common features for all real-time kernels and contains more branches for individual BSP-specific real-time kernels. The illustration shows three branches as an example. Each branch points the way to specific, unique features for a respective real-time kernel as they apply to a given BSP.

The resulting tree structure presents a clear path of markers (or branches) to the developer that, for all practical purposes, is the kernel needed for any given set of requirements.

A.2.2. Branching Strategy and Workflow

The Yocto Project team creates kernel branches at points where functionality is no longer shared and thus, needs to be isolated. For example, board-specific incompatibilities would require different functionality and would require a branch to separate the features. Likewise, for specific kernel features, the same branching strategy is used.

This branching strategy results in a tree that has features organized to be specific for particular functionality, single kernel types, or a subset of kernel types. This strategy also results in not having to store the same feature twice internally in the tree. Rather, the kernel team stores the unique differences required to apply the feature onto the kernel type in question.

Note

The Yocto Project team strives to place features in the tree such that they can be shared by all boards and kernel types where possible. However, during development cycles or when large features are merged, the team cannot always follow this practice. In those cases, the team uses isolated branches to merge features.

BSP-specific code additions are handled in a similar manner to kernel-specific additions. Some BSPs only make sense given certain kernel types. So, for these types, the team creates branches off the end of that kernel type for all of the BSPs that are supported on that kernel type. From the perspective of the tools that create the BSP branch, the BSP is really no different than a feature. Consequently, the same branching strategy applies to BSPs as it does to features. So again, rather than store the BSP twice, the team only stores the unique differences for the BSP across the supported multiple kernels.

While this strategy can result in a tree with a significant number of branches, it is important to realize that from the developer's point of view, there is a linear path that travels from the baseline kernel.org, through a select group of features and ends with their BSP-specific commits. In other words, the divisions of the kernel are transparent and are not relevant to the developer on a day-to-day basis. From the developer's perspective, this path is the "master" branch. The developer does not need to be aware of the existence of any other branches at all. Of course, there is value in the existence of these branches in the tree, should a person decide to explore them. For example, a comparison between two BSPs at either the commit level or at the line-by-line code diff level is now a trivial operation.

Working with the kernel as a structured tree follows recognized community best practices. In particular, the kernel as shipped with the product, should be considered an "upstream source" and viewed as a series of historical and documented modifications (commits). These modifications represent the development and stabilization done by the Yocto Project kernel development team.

Because commits only change at significant release points in the product life cycle, developers can work on a branch created from the last relevant commit in the shipped Yocto Project kernel. As mentioned previously, the structure is transparent to the developer because the kernel tree is left in this state after cloning and building the kernel.

A.2.3. Source Code Manager - Git

The Source Code Manager (SCM) is Git. This SCM is the obvious mechanism for meeting the previously mentioned goals. Not only is it the SCM for kernel.org but, Git continues to grow in popularity and supports many different work flows, front-ends and management techniques.

You can find documentation on Git at http://git-scm.com/documentation. You can also get an introduction to Git as it applies to the Yocto Project in the "Git" section in the Yocto Project Development Manual. These referenced sections overview Git and describe a minimal set of commands that allows you to be functional using Git.

Note

You can use as much, or as little, of what Git has to offer to accomplish what you need for your project. You do not have to be a "Git Master" in order to use it with the Yocto Project.

Appendix B. Kernel Maintenance

B.1. Tree Construction

This section describes construction of the Yocto Project kernel source repositories as accomplished by the Yocto Project team to create kernel repositories. These kernel repositories are found under the heading "Yocto Linux Kernel" at http://git.yoctoproject.org/cgit.cgi and can be shipped as part of a Yocto Project release. The team creates these repositories by compiling and executing the set of feature descriptions for every BSP and feature in the product. Those feature descriptions list all necessary patches, configuration, branching, tagging and feature divisions found in a kernel. Thus, the Yocto Project kernel repository (or tree) is built.

The existence of this tree allows you to access and clone a particular Yocto Project kernel repository and use it to build images based on their configurations and features.

You can find the files used to describe all the valid features and BSPs in the Yocto Project kernel in any clone of the Yocto Project kernel source repository Git tree. For example, the following command clones the Yocto Project baseline kernel that branched off of linux.org version 3.4:

     $ git clone git://git.yoctoproject.org/linux-yocto-3.4
            

For another example of how to set up a local Git repository of the Yocto Project kernel files, see the "Yocto Project Kernel" bulleted item in the Yocto Project Development Manual.

Once you have cloned the kernel Git repository on your local machine, you can switch to the meta branch within the repository. Here is an example that assumes the local Git repository for the kernel is in a top-level directory named linux-yocto-3.4:

     $ cd ~/linux-yocto-3.4
     $ git checkout -b meta origin/meta
            

Once you have checked out and switched to the meta branch, you can see a snapshot of all the kernel configuration and feature descriptions that are used to build that particular kernel repository. These descriptions are in the form of .scc files.

You should realize, however, that browsing your local kernel repository for feature descriptions and patches is not an effective way to determine what is in a particular kernel branch. Instead, you should use Git directly to discover the changes in a branch. Using Git is an efficient and flexible way to inspect changes to the kernel.

Note

Ground up reconstruction of the complete kernel tree is an action only taken by the Yocto Project team during an active development cycle. When you create a clone of the kernel Git repository, you are simply making it efficiently available for building and development.

The following steps describe what happens when the Yocto Project Team constructs the Yocto Project kernel source Git repository (or tree) found at http://git.yoctoproject.org/cgit.cgi given the introduction of a new top-level kernel feature or BSP. These are the actions that effectively create the tree that includes the new feature, patch or BSP:

  1. A top-level kernel feature is passed to the kernel build subsystem. Normally, this feature is a BSP for a particular kernel type.

  2. The file that describes the top-level feature is located by searching these system directories:

    • The in-tree kernel-cache directories, which are located in meta/cfg/kernel-cache

    • Areas pointed to by SRC_URI statements found in recipes

    For a typical build, the target of the search is a feature description in an .scc file whose name follows this format:

         <bsp_name>-<kernel_type>.scc
                        

  3. Once located, the feature description is either compiled into a simple script of actions, or into an existing equivalent script that is already part of the shipped kernel.

  4. Extra features are appended to the top-level feature description. These features can come from the KERNEL_FEATURES variable in recipes.

  5. Each extra feature is located, compiled and appended to the script as described in step three.

  6. The script is executed to produce a series of meta-* directories. These directories are descriptions of all the branches, tags, patches and configurations that need to be applied to the base Git repository to completely create the source (build) branch for the new BSP or feature.

  7. The base repository is cloned, and the actions listed in the meta-* directories are applied to the tree.

  8. The Git repository is left with the desired branch checked out and any required branching, patching and tagging has been performed.

The kernel tree is now ready for developer consumption to be locally cloned, configured, and built into a Yocto Project kernel specific to some target hardware.

Note

The generated meta-* directories add to the kernel as shipped with the Yocto Project release. Any add-ons and configuration data are applied to the end of an existing branch. The full repository generation that is found in the official Yocto Project kernel repositories at http://git.yoctoproject.org/cgit.cgi is the combination of all supported boards and configurations.

The technique the Yocto Project team uses is flexible and allows for seamless blending of an immutable history with additional patches specific to a deployment. Any additions to the kernel become an integrated part of the branches.

B.2. Build Strategy

Once a local Git repository of the Yocto Project kernel exists on a development system, you can consider the compilation phase of kernel development - building a kernel image. Some prerequisites exist that are validated by the build process before compilation starts:

  • The SRC_URI points to the kernel Git repository.

  • A BSP build branch exists. This branch has the following form:

         <kernel_type>/<bsp_name>
                    

The OpenEmbedded build system makes sure these conditions exist before attempting compilation. Other means, however, do exist, such as as bootstrapping a BSP.

Before building a kernel, the build process verifies the tree and configures the kernel by processing all of the configuration "fragments" specified by feature descriptions in the .scc files. As the features are compiled, associated kernel configuration fragments are noted and recorded in the meta-* series of directories in their compilation order. The fragments are migrated, pre-processed and passed to the Linux Kernel Configuration subsystem (lkc) as raw input in the form of a .config file. The lkc uses its own internal dependency constraints to do the final processing of that information and generates the final .config file that is used during compilation.

Using the board's architecture and other relevant values from the board's template, kernel compilation is started and a kernel image is produced.

The other thing that you notice once you configure a kernel is that the build process generates a build tree that is separate from your kernel's local Git source repository tree. This build tree has a name that uses the following form, where ${MACHINE} is the metadata name of the machine (BSP) and "kernel_type" is one of the Yocto Project supported kernel types (e.g. "standard"):

     linux-${MACHINE}-<kernel_type>-build
        

The existing support in the kernel.org tree achieves this default functionality.

This behavior means that all the generated files for a particular machine or BSP are now in the build tree directory. The files include the final .config file, all the .o files, the .a files, and so forth. Since each machine or BSP has its own separate Build Directory in its own separate branch of the Git repository, you can easily switch between different builds.

Appendix C. Kernel Development FAQ

C.1.

How do I use my own Linux kernel .config file?

Refer to the "Changing the Configuration" section for information.

C.2.

How do I create configuration fragments?

Refer to the "Generating Configuration Files" section for information.

C.3.

How do I use my own Linux kernel sources?

Refer to the "Working With Your Own Sources" section for information.

C.4.

How do I install/not-install the kernel image on the rootfs?

The kernel image (e.g. vmlinuz) is provided by the kernel-image package. Image recipes depend on kernel-base. To specify whether or not the kernel image is installed in the generated root filesystem, override RDEPENDS_kernel-base to include or not include "kernel-image".

See the "Using .bbappend Files" section in the Yocto Project Development Manual for information on how to use an append file to override metadata.

C.5.

How do I install a specific kernel module?

Linux kernel modules are packaged individually. To ensure a specific kernel module is included in an image, include it in the appropriate machine RRECOMMENDS variable.

These other variables are useful for installing specific modules:

     MACHINE_ESSENTIAL_EXTRA_RDEPENDS
     MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS
     MACHINE_EXTRA_RDEPENDS
     MACHINE_EXTRA_RRECOMMENDS
                

For example, set the following in the qemux86.conf file to include the ab123 kernel modules with images built for the qemux86 machine:

     MACHINE_EXTRA_RRECOMMENDS += "kernel-module-ab123"
                

For more information, see the "Incorporating Out-of-Tree Modules" section.

C.6.

How do I change the Linux kernel command line?

The Linux kernel command line is typically specified in the machine config using the APPEND variable. For example, you can add some helpful debug information doing the following:

     APPEND += "printk.time=y initcall_debug debug"
                

Yocto Project Profiling and Tracing Manual

Tom Zanussi

Intel Corporation

Permission is granted to copy, distribute and/or modify this document under the terms of the Creative Commons Attribution-Share Alike 2.0 UK: England & Wales as published by Creative Commons.

Note

Due to production processes, there could be differences between the Yocto Project documentation bundled in the release tarball and the Yocto Project Tracing and Profiling Manual on the Yocto Project website. For the latest version of this manual, see the manual on the website.
Revision History
Revision 1.4April 2013
Released with the Yocto Project 1.4 Release.
Revision 1.4.1June 2013
Released with the Yocto Project 1.4.1 Release.
Revision 1.4.2August 2013
Released with the Yocto Project 1.4.2 Release.

Chapter 1. Yocto Project Tracing and Profiling Manual

1.1. Introduction

Yocto bundles a number of tracing and profiling tools - this 'HOWTO' describes their basic usage and shows by example how to make use of them to examine application and system behavior.

The tools presented are for the most part completely open-ended and have quite good and/or extensive documentation of their own which can be used to solve just about any problem you might come across in Linux. Each section that describes a particular tool has links to that tool's documentation and website.

The purpose of this 'HOWTO' is to present a set of common and generally useful tracing and profiling idioms along with their application (as appropriate) to each tool, in the context of a general-purpose 'drill-down' methodology that can be applied to solving a large number (90%?) of problems. For help with more advanced usages and problems, please see the documentation and/or websites listed for each tool.

The final section of this 'HOWTO' is a collection of real-world examples which we'll be continually adding to as we solve more problems using the tools - feel free to add your own examples to the list!

1.2. General Setup

Most of the tools are available only in 'sdk' images or in images built after adding 'tools-profile' to your local.conf. So, in order to be able to access all of the tools described here, please first build and boot an 'sdk' image e.g.

     $ bitbake core-image-sato-sdk
            

or alternatively by adding 'tools-profile' to the EXTRA_IMAGE_FEATURES line in your local.conf:

      EXTRA_IMAGE_FEATURES = "debug-tweaks tools-profile"
            

If you use the 'tools-profile' method, you don't need to build an sdk image - the tracing and profiling tools will be included in non-sdk images as well e.g.:

     $ bitbake core-image-sato
            

Note

By default, the Yocto build system strips symbols from the binaries it packages, which makes it difficult to use some of the tools.

You can prevent that by putting the following in your local.conf when you build the image:

     INHIBIT_PACKAGE_STRIP = "1"
            

The above setting will noticeably increase the size of your image.

If you've already build a stripped image, you can generate debug packages (xxx-dbg) which you can manually install as needed.

To generate debug info for packages, you can add dbg-pkgs to EXTRA_IMAGE_FEATURES in local.conf. For example:

     EXTRA_IMAGE_FEATURES = "debug-tweaks tools-profile dbg-pkgs"
            

Additionally, in order to generate the right type of debuginfo, we also need to add the following to local.conf:

     PACKAGE_DEBUG_SPLIT_STYLE = 'debug-file-directory'
            

Chapter 2. Overall Architecture of the Linux Tracing and Profiling Tools

2.1. Architecture of the Tracing and Profiling Tools

It may seem surprising to see a section covering an 'overall architecture' for what seems to be a random collection of tracing tools that together make up the Linux tracing and profiling space. The fact is, however, that in recent years this seemingly disparate set of tools has started to converge on a 'core' set of underlying mechanisms:

  • static tracepoints
  • dynamic tracepoints
    • kprobes
    • uprobes
  • the perf_events subsystem
  • debugfs

Tying it Together: Rather than enumerating here how each tool makes use of these common mechanisms, textboxes like this will make note of the specific usages in each tool as they come up in the course of the text.

Chapter 3. Basic Usage (with examples) for each of the Yocto Tracing Tools

This chapter presents basic usage examples for each of the tracing tools.

3.1. perf

The 'perf' tool is the profiling and tracing tool that comes bundled with the Linux kernel.

Don't let the fact that it's part of the kernel fool you into thinking that it's only for tracing and profiling the kernel - you can indeed use it to trace and profile just the kernel , but you can also use it to profile specific applications separately (with or without kernel context), and you can also use it to trace and profile the kernel and all applications on the system simultaneously to gain a system-wide view of what's going on.

In many ways, it aims to be a superset of all the tracing and profiling tools available in Linux today, including all the other tools covered in this HOWTO. The past couple of years have seen perf subsume a lot of the functionality of those other tools, and at the same time those other tools have removed large portions of their previous functionality and replaced it with calls to the equivalent functionality now implemented by the perf subsystem. Extrapolation suggests that at some point those other tools will simply become completely redundant and go away; until then, we'll cover those other tools in these pages and in many cases show how the same things can be accomplished in perf and the other tools when it seems useful to do so.

The coverage below details some of the most common ways you'll likely want to apply the tool; full documentation can be found either within the tool itself or in the man pages at perf(1).

3.1.1. Setup

For this section, we'll assume you've already performed the basic setup outlined in the General Setup section.

In particular, you'll get the most mileage out of perf if you profile an image built with INHIBIT_PACKAGE_STRIP = "1" in your local.conf.

perf runs on the target system for the most part. You can archive profile data and copy it to the host for analysis, but for the rest of this document we assume you've ssh'ed to the host and will be running the perf commands on the target.

3.1.2. Basic Usage

The perf tool is pretty much self-documenting. To remind yourself of the available commands, simply type 'perf', which will show you basic usage along with the available perf subcommands:

     root@crownbay:~# perf

     usage: perf [--version] [--help] COMMAND [ARGS]

     The most commonly used perf commands are:
       annotate        Read perf.data (created by perf record) and display annotated code
       archive         Create archive with object files with build-ids found in perf.data file
       bench           General framework for benchmark suites
       buildid-cache   Manage build-id cache.
       buildid-list    List the buildids in a perf.data file
       diff            Read two perf.data files and display the differential profile
       evlist          List the event names in a perf.data file
       inject          Filter to augment the events stream with additional information
       kmem            Tool to trace/measure kernel memory(slab) properties
       kvm             Tool to trace/measure kvm guest os
       list            List all symbolic event types
       lock            Analyze lock events
       probe           Define new dynamic tracepoints
       record          Run a command and record its profile into perf.data
       report          Read perf.data (created by perf record) and display the profile
       sched           Tool to trace/measure scheduler properties (latencies)
       script          Read perf.data (created by perf record) and display trace output
       stat            Run a command and gather performance counter statistics
       test            Runs sanity tests.
       timechart       Tool to visualize total system behavior during a workload
       top             System profiling tool.

     See 'perf help COMMAND' for more information on a specific command.
            

3.1.2.1. Using perf to do Basic Profiling

As a simple test case, we'll profile the 'wget' of a fairly large file, which is a minimally interesting case because it has both file and network I/O aspects, and at least in the case of standard Yocto images, it's implemented as part of busybox, so the methods we use to analyze it can be used in a very similar way to the whole host of supported busybox applets in Yocto.

     root@crownbay:~# rm linux-2.6.19.2.tar.bz2; \
     wget http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2
                

The quickest and easiest way to get some basic overall data about what's going on for a particular workload it to profile it using 'perf stat'. 'perf stat' basically profiles using a few default counters and displays the summed counts at the end of the run:

     root@crownbay:~# perf stat wget http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2
     Connecting to downloads.yoctoproject.org (140.211.169.59:80)
     linux-2.6.19.2.tar.b 100% |***************************************************| 41727k  0:00:00 ETA

     Performance counter stats for 'wget http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2':

           4597.223902 task-clock                #    0.077 CPUs utilized
                 23568 context-switches          #    0.005 M/sec
                    68 CPU-migrations            #    0.015 K/sec
                   241 page-faults               #    0.052 K/sec
            3045817293 cycles                    #    0.663 GHz
       <not supported> stalled-cycles-frontend
       <not supported> stalled-cycles-backend
             858909167 instructions              #    0.28  insns per cycle
             165441165 branches                  #   35.987 M/sec
              19550329 branch-misses             #   11.82% of all branches

          59.836627620 seconds time elapsed
                

Many times such a simple-minded test doesn't yield much of interest, but sometimes it does (see Real-world Yocto bug (slow loop-mounted write speed)).

Also, note that 'perf stat' isn't restricted to a fixed set of counters - basically any event listed in the output of 'perf list' can be tallied by 'perf stat'. For example, suppose we wanted to see a summary of all the events related to kernel memory allocation/freeing along with cache hits and misses:

     root@crownbay:~# perf stat -e kmem:* -e cache-references -e cache-misses wget http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2
     Connecting to downloads.yoctoproject.org (140.211.169.59:80)
     linux-2.6.19.2.tar.b 100% |***************************************************| 41727k  0:00:00 ETA

     Performance counter stats for 'wget http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2':

                  5566 kmem:kmalloc
                125517 kmem:kmem_cache_alloc
                     0 kmem:kmalloc_node
                     0 kmem:kmem_cache_alloc_node
                 34401 kmem:kfree
                 69920 kmem:kmem_cache_free
                   133 kmem:mm_page_free
                    41 kmem:mm_page_free_batched
                 11502 kmem:mm_page_alloc
                 11375 kmem:mm_page_alloc_zone_locked
                     0 kmem:mm_page_pcpu_drain
                     0 kmem:mm_page_alloc_extfrag
              66848602 cache-references
               2917740 cache-misses              #    4.365 % of all cache refs

          44.831023415 seconds time elapsed
                

So 'perf stat' gives us a nice easy way to get a quick overview of what might be happening for a set of events, but normally we'd need a little more detail in order to understand what's going on in a way that we can act on in a useful way.

To dive down into a next level of detail, we can use 'perf record'/'perf report' which will collect profiling data and present it to use using an interactive text-based UI (or simply as text if we specify --stdio to 'perf report').

As our first attempt at profiling this workload, we'll simply run 'perf record', handing it the workload we want to profile (everything after 'perf record' and any perf options we hand it - here none - will be executedin a new shell). perf collects samples until the process exits and records them in a file named 'perf.data' in the current working directory.

     root@crownbay:~# perf record wget http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2

     Connecting to downloads.yoctoproject.org (140.211.169.59:80)
     linux-2.6.19.2.tar.b 100% |************************************************| 41727k  0:00:00 ETA
     [ perf record: Woken up 1 times to write data ]
     [ perf record: Captured and wrote 0.176 MB perf.data (~7700 samples) ]
            

To see the results in a 'text-based UI' (tui), simply run 'perf report', which will read the perf.data file in the current working directory and display the results in an interactive UI:

     root@crownbay:~# perf report
                

The above screenshot displays a 'flat' profile, one entry for each 'bucket' corresponding to the functions that were profiled during the profiling run, ordered from the most popular to the least (perf has options to sort in various orders and keys as well as display entries only above a certain threshold and so on - see the perf documentation for details). Note that this includes both userspace functions (entries containing a [.]) and kernel functions accounted to the process (entries containing a [k]). (perf has command-line modifiers that can be used to restrict the profiling to kernel or userspace, among others).

Notice also that the above report shows an entry for 'busybox', which is the executable that implements 'wget' in Yocto, but that instead of a useful function name in that entry, it displays an not-so-friendly hex value instead. The steps below will show how to fix that problem.

Before we do that, however, let's try running a different profile, one which shows something a little more interesting. The only difference between the new profile and the previous one is that we'll add the -g option, which will record not just the address of a sampled function, but the entire callchain to the sampled function as well:

     root@crownbay:~# perf record -g wget http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2
     Connecting to downloads.yoctoproject.org (140.211.169.59:80)
     linux-2.6.19.2.tar.b 100% |************************************************| 41727k  0:00:00 ETA
     [ perf record: Woken up 3 times to write data ]
     [ perf record: Captured and wrote 0.652 MB perf.data (~28476 samples) ]


     root@crownbay:~# perf report
                

Using the callgraph view, we can actually see not only which functions took the most time, but we can also see a summary of how those functions were called and learn something about how the program interacts with the kernel in the process.

Notice that each entry in the above screenshot now contains a '+' on the left-hand side. This means that we can expand the entry and drill down into the callchains that feed into that entry. Pressing 'enter' on any one of them will expand the callchain (you can also press 'E' to expand them all at the same time or 'C' to collapse them all).

In the screenshot above, we've toggled the __copy_to_user_ll() entry and several subnodes all the way down. This lets us see which callchains contributed to the profiled __copy_to_user_ll() function which contributed 1.77% to the total profile.

As a bit of background explanation for these callchains, think about what happens at a high level when you run wget to get a file out on the network. Basically what happens is that the data comes into the kernel via the network connection (socket) and is passed to the userspace program 'wget' (which is actually a part of busybox, but that's not important for now), which takes the buffers the kernel passes to it and writes it to a disk file to save it.

The part of this process that we're looking at in the above call stacks is the part where the kernel passes the data it's read from the socket down to wget i.e. a copy-to-user.

Notice also that here there's also a case where the a hex value is displayed in the callstack, here in the expanded sys_clock_gettime() function. Later we'll see it resolve to a userspace function call in busybox.

The above screenshot shows the other half of the journey for the data - from the wget program's userspace buffers to disk. To get the buffers to disk, the wget program issues a write(2), which does a copy-from-user to the kernel, which then takes care via some circuitous path (probably also present somewhere in the profile data), to get it safely to disk.

Now that we've seen the basic layout of the profile data and the basics of how to extract useful information out of it, let's get back to the task at hand and see if we can get some basic idea about where the time is spent in the program we're profiling, wget. Remember that wget is actually implemented as an applet in busybox, so while the process name is 'wget', the executable we're actually interested in is busybox. So let's expand the first entry containing busybox:

Again, before we expanded we saw that the function was labeled with a hex value instead of a symbol as with most of the kernel entries. Expanding the busybox entry doesn't make it any better.

The problem is that perf can't find the symbol information for the busybox binary, which is actually stripped out by the Yocto build system.

One way around that is to put the following in your local.conf when you build the image:

     INHIBIT_PACKAGE_STRIP = "1"
                

However, we already have an image with the binaries stripped, so what can we do to get perf to resolve the symbols? Basically we need to install the debuginfo for the busybox package.

To generate the debug info for the packages in the image, we can to add dbg-pkgs to EXTRA_IMAGE_FEATURES in local.conf. For example:

     EXTRA_IMAGE_FEATURES = "debug-tweaks tools-profile dbg-pkgs"
                

Additionally, in order to generate the type of debuginfo that perf understands, we also need to add the following to local.conf:

     PACKAGE_DEBUG_SPLIT_STYLE = 'debug-file-directory'
                

Once we've done that, we can install the debuginfo for busybox. The debug packages once built can be found in build/tmp/deploy/rpm/* on the host system. Find the busybox-dbg-...rpm file and copy it to the target. For example:

     [trz@empanada core2]$ scp /home/trz/yocto/crownbay-tracing-dbg/build/tmp/deploy/rpm/core2/busybox-dbg-1.20.2-r2.core2.rpm root@192.168.1.31:
     root@192.168.1.31's password:
     busybox-dbg-1.20.2-r2.core2.rpm                     100% 1826KB   1.8MB/s   00:01
                

Now install the debug rpm on the target:

     root@crownbay:~# rpm -i busybox-dbg-1.20.2-r2.core2.rpm
                

Now that the debuginfo is installed, we see that the busybox entries now display their functions symbolically:

If we expand one of the entries and press 'enter' on a leaf node, we're presented with a menu of actions we can take to get more information related to that entry:

One of these actions allows us to show a view that displays a busybox-centric view of the profiled functions (in this case we've also expanded all the nodes using the 'E' key):

Finally, we can see that now that the busybox debuginfo is installed, the previously unresolved symbol in the sys_clock_gettime() entry mentioned previously is now resolved, and shows that the sys_clock_gettime system call that was the source of 6.75% of the copy-to-user overhead was initiated by the handle_input() busybox function:

At the lowest level of detail, we can dive down to the assembly level and see which instructions caused the most overhead in a function. Pressing 'enter' on the 'udhcpc_main' function, we're again presented with a menu:

Selecting 'Annotate udhcpc_main', we get a detailed listing of percentages by instruction for the udhcpc_main function. From the display, we can see that over 50% of the time spent in this function is taken up by a couple tests and the move of a constant (1) to a register:

As a segue into tracing, let's try another profile using a different counter, something other than the default 'cycles'.

The tracing and profiling infrastructure in Linux has become unified in a way that allows us to use the same tool with a completely different set of counters, not just the standard hardware counters that traditionally tools have had to restrict themselves to (of course the traditional tools can also make use of the expanded possibilities now available to them, and in some cases have, as mentioned previously).

We can get a list of the available events that can be used to profile a workload via 'perf list':

     root@crownbay:~# perf list

     List of pre-defined events (to be used in -e):
      cpu-cycles OR cycles                               [Hardware event]
      stalled-cycles-frontend OR idle-cycles-frontend    [Hardware event]
      stalled-cycles-backend OR idle-cycles-backend      [Hardware event]
      instructions                                       [Hardware event]
      cache-references                                   [Hardware event]
      cache-misses                                       [Hardware event]
      branch-instructions OR branches                    [Hardware event]
      branch-misses                                      [Hardware event]
      bus-cycles                                         [Hardware event]
      ref-cycles                                         [Hardware event]

      cpu-clock                                          [Software event]
      task-clock                                         [Software event]
      page-faults OR faults                              [Software event]
      minor-faults                                       [Software event]
      major-faults                                       [Software event]
      context-switches OR cs                             [Software event]
      cpu-migrations OR migrations                       [Software event]
      alignment-faults                                   [Software event]
      emulation-faults                                   [Software event]

      L1-dcache-loads                                    [Hardware cache event]
      L1-dcache-load-misses                              [Hardware cache event]
      L1-dcache-prefetch-misses                          [Hardware cache event]
      L1-icache-loads                                    [Hardware cache event]
      L1-icache-load-misses                              [Hardware cache event]
      .
      .
      .
      rNNN                                               [Raw hardware event descriptor]
      cpu/t1=v1[,t2=v2,t3 ...]/modifier                  [Raw hardware event descriptor]
       (see 'perf list --help' on how to encode it)

      mem:<addr>[:access]                                [Hardware breakpoint]

      sunrpc:rpc_call_status                             [Tracepoint event]
      sunrpc:rpc_bind_status                             [Tracepoint event]
      sunrpc:rpc_connect_status                          [Tracepoint event]
      sunrpc:rpc_task_begin                              [Tracepoint event]
      skb:kfree_skb                                      [Tracepoint event]
      skb:consume_skb                                    [Tracepoint event]
      skb:skb_copy_datagram_iovec                        [Tracepoint event]
      net:net_dev_xmit                                   [Tracepoint event]
      net:net_dev_queue                                  [Tracepoint event]
      net:netif_receive_skb                              [Tracepoint event]
      net:netif_rx                                       [Tracepoint event]
      napi:napi_poll                                     [Tracepoint event]
      sock:sock_rcvqueue_full                            [Tracepoint event]
      sock:sock_exceed_buf_limit                         [Tracepoint event]
      udp:udp_fail_queue_rcv_skb                         [Tracepoint event]
      hda:hda_send_cmd                                   [Tracepoint event]
      hda:hda_get_response                               [Tracepoint event]
      hda:hda_bus_reset                                  [Tracepoint event]
      scsi:scsi_dispatch_cmd_start                       [Tracepoint event]
      scsi:scsi_dispatch_cmd_error                       [Tracepoint event]
      scsi:scsi_eh_wakeup                                [Tracepoint event]
      drm:drm_vblank_event                               [Tracepoint event]
      drm:drm_vblank_event_queued                        [Tracepoint event]
      drm:drm_vblank_event_delivered                     [Tracepoint event]
      random:mix_pool_bytes                              [Tracepoint event]
      random:mix_pool_bytes_nolock                       [Tracepoint event]
      random:credit_entropy_bits                         [Tracepoint event]
      gpio:gpio_direction                                [Tracepoint event]
      gpio:gpio_value                                    [Tracepoint event]
      block:block_rq_abort                               [Tracepoint event]
      block:block_rq_requeue                             [Tracepoint event]
      block:block_rq_issue                               [Tracepoint event]
      block:block_bio_bounce                             [Tracepoint event]
      block:block_bio_complete                           [Tracepoint event]
      block:block_bio_backmerge                          [Tracepoint event]
      .
      .
      writeback:writeback_wake_thread                    [Tracepoint event]
      writeback:writeback_wake_forker_thread             [Tracepoint event]
      writeback:writeback_bdi_register                   [Tracepoint event]
      .
      .
      writeback:writeback_single_inode_requeue           [Tracepoint event]
      writeback:writeback_single_inode                   [Tracepoint event]
      kmem:kmalloc                                       [Tracepoint event]
      kmem:kmem_cache_alloc                              [Tracepoint event]
      kmem:mm_page_alloc                                 [Tracepoint event]
      kmem:mm_page_alloc_zone_locked                     [Tracepoint event]
      kmem:mm_page_pcpu_drain                            [Tracepoint event]
      kmem:mm_page_alloc_extfrag                         [Tracepoint event]
      vmscan:mm_vmscan_kswapd_sleep                      [Tracepoint event]
      vmscan:mm_vmscan_kswapd_wake                       [Tracepoint event]
      vmscan:mm_vmscan_wakeup_kswapd                     [Tracepoint event]
      vmscan:mm_vmscan_direct_reclaim_begin              [Tracepoint event]
      .
      .
      module:module_get                                  [Tracepoint event]
      module:module_put                                  [Tracepoint event]
      module:module_request                              [Tracepoint event]
      sched:sched_kthread_stop                           [Tracepoint event]
      sched:sched_wakeup                                 [Tracepoint event]
      sched:sched_wakeup_new                             [Tracepoint event]
      sched:sched_process_fork                           [Tracepoint event]
      sched:sched_process_exec                           [Tracepoint event]
      sched:sched_stat_runtime                           [Tracepoint event]
      rcu:rcu_utilization                                [Tracepoint event]
      workqueue:workqueue_queue_work                     [Tracepoint event]
      workqueue:workqueue_execute_end                    [Tracepoint event]
      signal:signal_generate                             [Tracepoint event]
      signal:signal_deliver                              [Tracepoint event]
      timer:timer_init                                   [Tracepoint event]
      timer:timer_start                                  [Tracepoint event]
      timer:hrtimer_cancel                               [Tracepoint event]
      timer:itimer_state                                 [Tracepoint event]
      timer:itimer_expire                                [Tracepoint event]
      irq:irq_handler_entry                              [Tracepoint event]
      irq:irq_handler_exit                               [Tracepoint event]
      irq:softirq_entry                                  [Tracepoint event]
      irq:softirq_exit                                   [Tracepoint event]
      irq:softirq_raise                                  [Tracepoint event]
      printk:console                                     [Tracepoint event]
      task:task_newtask                                  [Tracepoint event]
      task:task_rename                                   [Tracepoint event]
      syscalls:sys_enter_socketcall                      [Tracepoint event]
      syscalls:sys_exit_socketcall                       [Tracepoint event]
      .
      .
      .
      syscalls:sys_enter_unshare                         [Tracepoint event]
      syscalls:sys_exit_unshare                          [Tracepoint event]
      raw_syscalls:sys_enter                             [Tracepoint event]
      raw_syscalls:sys_exit                              [Tracepoint event]
                

Tying it Together: These are exactly the same set of events defined by the trace event subsystem and exposed by ftrace/tracecmd/kernelshark as files in /sys/kernel/debug/tracing/events, by SystemTap as kernel.trace("tracepoint_name") and (partially) accessed by LTTng.

Only a subset of these would be of interest to us when looking at this workload, so let's choose the most likely subsystems (identified by the string before the colon in the Tracepoint events) and do a 'perf stat' run using only those wildcarded subsystems:

     root@crownbay:~# perf stat -e skb:* -e net:* -e napi:* -e sched:* -e workqueue:* -e irq:* -e syscalls:* wget http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2
     Performance counter stats for 'wget http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2':

                 23323 skb:kfree_skb
                     0 skb:consume_skb
                 49897 skb:skb_copy_datagram_iovec
                  6217 net:net_dev_xmit
                  6217 net:net_dev_queue
                  7962 net:netif_receive_skb
                     2 net:netif_rx
                  8340 napi:napi_poll
                     0 sched:sched_kthread_stop
                     0 sched:sched_kthread_stop_ret
                  3749 sched:sched_wakeup
                     0 sched:sched_wakeup_new
                     0 sched:sched_switch
                    29 sched:sched_migrate_task
                     0 sched:sched_process_free
                     1 sched:sched_process_exit
                     0 sched:sched_wait_task
                     0 sched:sched_process_wait
                     0 sched:sched_process_fork
                     1 sched:sched_process_exec
                     0 sched:sched_stat_wait
         2106519415641 sched:sched_stat_sleep
                     0 sched:sched_stat_iowait
             147453613 sched:sched_stat_blocked
           12903026955 sched:sched_stat_runtime
                     0 sched:sched_pi_setprio
                  3574 workqueue:workqueue_queue_work
                  3574 workqueue:workqueue_activate_work
                     0 workqueue:workqueue_execute_start
                     0 workqueue:workqueue_execute_end
                 16631 irq:irq_handler_entry
                 16631 irq:irq_handler_exit
                 28521 irq:softirq_entry
                 28521 irq:softirq_exit
                 28728 irq:softirq_raise
                     1 syscalls:sys_enter_sendmmsg
                     1 syscalls:sys_exit_sendmmsg
                     0 syscalls:sys_enter_recvmmsg
                     0 syscalls:sys_exit_recvmmsg
                    14 syscalls:sys_enter_socketcall
                    14 syscalls:sys_exit_socketcall
                       .
                       .
                       .
                 16965 syscalls:sys_enter_read
                 16965 syscalls:sys_exit_read
                 12854 syscalls:sys_enter_write
                 12854 syscalls:sys_exit_write
                       .
                       .
                       .

          58.029710972 seconds time elapsed
                

Let's pick one of these tracepoints and tell perf to do a profile using it as the sampling event:

     root@crownbay:~# perf record -g -e sched:sched_wakeup wget http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2
                

The screenshot above shows the results of running a profile using sched:sched_switch tracepoint, which shows the relative costs of various paths to sched_wakeup (note that sched_wakeup is the name of the tracepoint - it's actually defined just inside ttwu_do_wakeup(), which accounts for the function name actually displayed in the profile:

     /*
      * Mark the task runnable and perform wakeup-preemption.
      */
     static void
     ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
     {
          trace_sched_wakeup(p, true);
          .
          .
          .
     }
                

A couple of the more interesting callchains are expanded and displayed above, basically some network receive paths that presumably end up waking up wget (busybox) when network data is ready.

Note that because tracepoints are normally used for tracing, the default sampling period for tracepoints is 1 i.e. for tracepoints perf will sample on every event occurrence (this can be changed using the -c option). This is in contrast to hardware counters such as for example the default 'cycles' hardware counter used for normal profiling, where sampling periods are much higher (in the thousands) because profiling should have as low an overhead as possible and sampling on every cycle would be prohibitively expensive.

3.1.2.2. Using perf to do Basic Tracing

Profiling is a great tool for solving many problems or for getting a high-level view of what's going on with a workload or across the system. It is however by definition an approximation, as suggested by the most prominent word associated with it, 'sampling'. On the one hand, it allows a representative picture of what's going on in the system to be cheaply taken, but on the other hand, that cheapness limits its utility when that data suggests a need to 'dive down' more deeply to discover what's really going on. In such cases, the only way to see what's really going on is to be able to look at (or summarize more intelligently) the individual steps that go into the higher-level behavior exposed by the coarse-grained profiling data.

As a concrete example, we can trace all the events we think might be applicable to our workload:

     root@crownbay:~# perf record -g -e skb:* -e net:* -e napi:* -e sched:sched_switch -e sched:sched_wakeup -e irq:*
      -e syscalls:sys_enter_read -e syscalls:sys_exit_read -e syscalls:sys_enter_write -e syscalls:sys_exit_write
      wget http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2
                

We can look at the raw trace output using 'perf script' with no arguments:

     root@crownbay:~# perf script

           perf  1262 [000] 11624.857082: sys_exit_read: 0x0
           perf  1262 [000] 11624.857193: sched_wakeup: comm=migration/0 pid=6 prio=0 success=1 target_cpu=000
           wget  1262 [001] 11624.858021: softirq_raise: vec=1 [action=TIMER]
           wget  1262 [001] 11624.858074: softirq_entry: vec=1 [action=TIMER]
           wget  1262 [001] 11624.858081: softirq_exit: vec=1 [action=TIMER]
           wget  1262 [001] 11624.858166: sys_enter_read: fd: 0x0003, buf: 0xbf82c940, count: 0x0200
           wget  1262 [001] 11624.858177: sys_exit_read: 0x200
           wget  1262 [001] 11624.858878: kfree_skb: skbaddr=0xeb248d80 protocol=0 location=0xc15a5308
           wget  1262 [001] 11624.858945: kfree_skb: skbaddr=0xeb248000 protocol=0 location=0xc15a5308
           wget  1262 [001] 11624.859020: softirq_raise: vec=1 [action=TIMER]
           wget  1262 [001] 11624.859076: softirq_entry: vec=1 [action=TIMER]
           wget  1262 [001] 11624.859083: softirq_exit: vec=1 [action=TIMER]
           wget  1262 [001] 11624.859167: sys_enter_read: fd: 0x0003, buf: 0xb7720000, count: 0x0400
           wget  1262 [001] 11624.859192: sys_exit_read: 0x1d7
           wget  1262 [001] 11624.859228: sys_enter_read: fd: 0x0003, buf: 0xb7720000, count: 0x0400
           wget  1262 [001] 11624.859233: sys_exit_read: 0x0
           wget  1262 [001] 11624.859573: sys_enter_read: fd: 0x0003, buf: 0xbf82c580, count: 0x0200
           wget  1262 [001] 11624.859584: sys_exit_read: 0x200
           wget  1262 [001] 11624.859864: sys_enter_read: fd: 0x0003, buf: 0xb7720000, count: 0x0400
           wget  1262 [001] 11624.859888: sys_exit_read: 0x400
           wget  1262 [001] 11624.859935: sys_enter_read: fd: 0x0003, buf: 0xb7720000, count: 0x0400
           wget  1262 [001] 11624.859944: sys_exit_read: 0x400
                

This gives us a detailed timestamped sequence of events that occurred within the workload with respect to those events.

In many ways, profiling can be viewed as a subset of tracing - theoretically, if you have a set of trace events that's sufficient to capture all the important aspects of a workload, you can derive any of the results or views that a profiling run can.

Another aspect of traditional profiling is that while powerful in many ways, it's limited by the granularity of the underlying data. Profiling tools offer various ways of sorting and presenting the sample data, which make it much more useful and amenable to user experimentation, but in the end it can't be used in an open-ended way to extract data that just isn't present as a consequence of the fact that conceptually, most of it has been thrown away.

Full-blown detailed tracing data does however offer the opportunity to manipulate and present the information collected during a tracing run in an infinite variety of ways.

Another way to look at it is that there are only so many ways that the 'primitive' counters can be used on their own to generate interesting output; to get anything more complicated than simple counts requires some amount of additional logic, which is typically very specific to the problem at hand. For example, if we wanted to make use of a 'counter' that maps to the value of the time difference between when a process was scheduled to run on a processor and the time it actually ran, we wouldn't expect such a counter to exist on its own, but we could derive one called say 'wakeup_latency' and use it to extract a useful view of that metric from trace data. Likewise, we really can't figure out from standard profiling tools how much data every process on the system reads and writes, along with how many of those reads and writes fail completely. If we have sufficient trace data, however, we could with the right tools easily extract and present that information, but we'd need something other than pre-canned profiling tools to do that.

Luckily, there is general-purpose way to handle such needs, called 'programming languages'. Making programming languages easily available to apply to such problems given the specific format of data is called a 'programming language binding' for that data and language. Perf supports two programming language bindings, one for Python and one for Perl.

Tying it Together: Language bindings for manipulating and aggregating trace data are of course not a new idea. One of the first projects to do this was IBM's DProbes dpcc compiler, an ANSI C compiler which targeted a low-level assembly language running on an in-kernel interpreter on the target system. This is exactly analagous to what Sun's DTrace did, except that DTrace invented its own language for the purpose. Systemtap, heavily inspired by DTrace, also created its own one-off language, but rather than running the product on an in-kernel interpreter, created an elaborate compiler-based machinery to translate its language into kernel modules written in C.

Now that we have the trace data in perf.data, we can use 'perf script -g' to generate a skeleton script with handlers for the read/write entry/exit events we recorded:

     root@crownbay:~# perf script -g python
     generated Python script: perf-script.py
                

The skeleton script simply creates a python function for each event type in the perf.data file. The body of each function simply prints the event name along with its parameters. For example:

     def net__netif_rx(event_name, context, common_cpu,
            common_secs, common_nsecs, common_pid, common_comm,
            skbaddr, len, name):
                    print_header(event_name, common_cpu, common_secs, common_nsecs,
                            common_pid, common_comm)

		     print "skbaddr=%u, len=%u, name=%s\n" % (skbaddr, len, name),
                

We can run that script directly to print all of the events contained in the perf.data file:

     root@crownbay:~# perf script -s perf-script.py

     in trace_begin
     syscalls__sys_exit_read     0 11624.857082795     1262 perf                  nr=3, ret=0
     sched__sched_wakeup      0 11624.857193498     1262 perf                  comm=migration/0, pid=6, prio=0,      success=1, target_cpu=0
     irq__softirq_raise       1 11624.858021635     1262 wget                  vec=TIMER
     irq__softirq_entry       1 11624.858074075     1262 wget                  vec=TIMER
     irq__softirq_exit        1 11624.858081389     1262 wget                  vec=TIMER
     syscalls__sys_enter_read     1 11624.858166434     1262 wget                  nr=3, fd=3, buf=3213019456,      count=512
     syscalls__sys_exit_read     1 11624.858177924     1262 wget                  nr=3, ret=512
     skb__kfree_skb           1 11624.858878188     1262 wget                  skbaddr=3945041280,           location=3243922184, protocol=0
     skb__kfree_skb           1 11624.858945608     1262 wget                  skbaddr=3945037824,      location=3243922184, protocol=0
     irq__softirq_raise       1 11624.859020942     1262 wget                  vec=TIMER
     irq__softirq_entry       1 11624.859076935     1262 wget                  vec=TIMER
     irq__softirq_exit        1 11624.859083469     1262 wget                  vec=TIMER
     syscalls__sys_enter_read     1 11624.859167565     1262 wget                  nr=3, fd=3, buf=3077701632,      count=1024
     syscalls__sys_exit_read     1 11624.859192533     1262 wget                  nr=3, ret=471
     syscalls__sys_enter_read     1 11624.859228072     1262 wget                  nr=3, fd=3, buf=3077701632,      count=1024
     syscalls__sys_exit_read     1 11624.859233707     1262 wget                  nr=3, ret=0
     syscalls__sys_enter_read     1 11624.859573008     1262 wget                  nr=3, fd=3, buf=3213018496,      count=512
     syscalls__sys_exit_read     1 11624.859584818     1262 wget                  nr=3, ret=512
     syscalls__sys_enter_read     1 11624.859864562     1262 wget                  nr=3, fd=3, buf=3077701632,      count=1024
     syscalls__sys_exit_read     1 11624.859888770     1262 wget                  nr=3, ret=1024
     syscalls__sys_enter_read     1 11624.859935140     1262 wget                  nr=3, fd=3, buf=3077701632,      count=1024
     syscalls__sys_exit_read     1 11624.859944032     1262 wget                  nr=3, ret=1024
                

That in itself isn't very useful; after all, we can accomplish pretty much the same thing by simply running 'perf script' without arguments in the same directory as the perf.data file.

We can however replace the print statements in the generated function bodies with whatever we want, and thereby make it infinitely more useful.

As a simple example, let's just replace the print statements in the function bodies with a simple function that does nothing but increment a per-event count. When the program is run against a perf.data file, each time a particular event is encountered, a tally is incremented for that event. For example:

     def net__netif_rx(event_name, context, common_cpu,
            common_secs, common_nsecs, common_pid, common_comm,
            skbaddr, len, name):
		          inc_counts(event_name)
                

Each event handler function in the generated code is modified to do this. For convenience, we define a common function called inc_counts() that each handler calls; inc_counts simply tallies a count for each event using the 'counts' hash, which is a specialized has function that does Perl-like autovivification, a capability that's extremely useful for kinds of multi-level aggregation commonly used in processing traces (see perf's documentation on the Python language binding for details):

     counts = autodict()

     def inc_counts(event_name):
            try:
                    counts[event_name] += 1
            except TypeError:
                    counts[event_name] = 1
                

Finally, at the end of the trace processing run, we want to print the result of all the per-event tallies. For that, we use the special 'trace_end()' function:

     def trace_end():
            for event_name, count in counts.iteritems():
                    print "%-40s %10s\n" % (event_name, count)
                

The end result is a summary of all the events recorded in the trace:

     skb__skb_copy_datagram_iovec                  13148
     irq__softirq_entry                             4796
     irq__irq_handler_exit                          3805
     irq__softirq_exit                              4795
     syscalls__sys_enter_write                      8990
     net__net_dev_xmit                               652
     skb__kfree_skb                                 4047
     sched__sched_wakeup                            1155
     irq__irq_handler_entry                         3804
     irq__softirq_raise                             4799
     net__net_dev_queue                              652
     syscalls__sys_enter_read                      17599
     net__netif_receive_skb                         1743
     syscalls__sys_exit_read                       17598
     net__netif_rx                                     2
     napi__napi_poll                                1877
     syscalls__sys_exit_write                       8990
                

Note that this is pretty much exactly the same information we get from 'perf stat', which goes a little way to support the idea mentioned previously that given the right kind of trace data, higher-level profiling-type summaries can be derived from it.

Documentation on using the 'perf script' python binding.

3.1.2.3. System-Wide Tracing and Profiling

The examples so far have focused on tracing a particular program or workload - in other words, every profiling run has specified the program to profile in the command-line e.g. 'perf record wget ...'.

It's also possible, and more interesting in many cases, to run a system-wide profile or trace while running the workload in a separate shell.

To do system-wide profiling or tracing, you typically use the -a flag to 'perf record'.

To demonstrate this, open up one window and start the profile using the -a flag (press Ctrl-C to stop tracing):

     root@crownbay:~# perf record -g -a
     ^C[ perf record: Woken up 6 times to write data ]
     [ perf record: Captured and wrote 1.400 MB perf.data (~61172 samples) ]
                

In another window, run the wget test:

     root@crownbay:~# wget http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2
     Connecting to downloads.yoctoproject.org (140.211.169.59:80)
     linux-2.6.19.2.tar.b 100% |*******************************| 41727k  0:00:00 ETA
                

Here we see entries not only for our wget load, but for other processes running on the system as well:

In the snapshot above, we can see callchains that originate in libc, and a callchain from Xorg that demonstrates that we're using a proprietary X driver in userspace (notice the presence of 'PVR' and some other unresolvable symbols in the expanded Xorg callchain).

Note also that we have both kernel and userspace entries in the above snapshot. We can also tell perf to focus on userspace but providing a modifier, in this case 'u', to the 'cycles' hardware counter when we record a profile:

     root@crownbay:~# perf record -g -a -e cycles:u
     ^C[ perf record: Woken up 2 times to write data ]
     [ perf record: Captured and wrote 0.376 MB perf.data (~16443 samples) ]
                

Notice in the screenshot above, we see only userspace entries ([.])

Finally, we can press 'enter' on a leaf node and select the 'Zoom into DSO' menu item to show only entries associated with a specific DSO. In the screenshot below, we've zoomed into the 'libc' DSO which shows all the entries associated with the libc-xxx.so DSO.

We can also use the system-wide -a switch to do system-wide tracing. Here we'll trace a couple of scheduler events:

     root@crownbay:~# perf record -a -e sched:sched_switch -e sched:sched_wakeup
     ^C[ perf record: Woken up 38 times to write data ]
     [ perf record: Captured and wrote 9.780 MB perf.data (~427299 samples) ]
                

We can look at the raw output using 'perf script' with no arguments:

     root@crownbay:~# perf script

                perf  1383 [001]  6171.460045: sched_wakeup: comm=kworker/1:1 pid=21 prio=120 success=1 target_cpu=001
                perf  1383 [001]  6171.460066: sched_switch: prev_comm=perf prev_pid=1383 prev_prio=120 prev_state=R+ ==> next_comm=kworker/1:1 next_pid=21 next_prio=120
         kworker/1:1    21 [001]  6171.460093: sched_switch: prev_comm=kworker/1:1 prev_pid=21 prev_prio=120 prev_state=S ==> next_comm=perf next_pid=1383 next_prio=120
             swapper     0 [000]  6171.468063: sched_wakeup: comm=kworker/0:3 pid=1209 prio=120 success=1 target_cpu=000
             swapper     0 [000]  6171.468107: sched_switch: prev_comm=swapper/0 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=kworker/0:3 next_pid=1209 next_prio=120
         kworker/0:3  1209 [000]  6171.468143: sched_switch: prev_comm=kworker/0:3 prev_pid=1209 prev_prio=120 prev_state=S ==> next_comm=swapper/0 next_pid=0 next_prio=120
                perf  1383 [001]  6171.470039: sched_wakeup: comm=kworker/1:1 pid=21 prio=120 success=1 target_cpu=001
                perf  1383 [001]  6171.470058: sched_switch: prev_comm=perf prev_pid=1383 prev_prio=120 prev_state=R+ ==> next_comm=kworker/1:1 next_pid=21 next_prio=120
         kworker/1:1    21 [001]  6171.470082: sched_switch: prev_comm=kworker/1:1 prev_pid=21 prev_prio=120 prev_state=S ==> next_comm=perf next_pid=1383 next_prio=120
                perf  1383 [001]  6171.480035: sched_wakeup: comm=kworker/1:1 pid=21 prio=120 success=1 target_cpu=001
                

3.1.2.3.1. Filtering

Notice that there are a lot of events that don't really have anything to do with what we're interested in, namely events that schedule 'perf' itself in and out or that wake perf up. We can get rid of those by using the '--filter' option - for each event we specify using -e, we can add a --filter after that to filter out trace events that contain fields with specific values:

     root@crownbay:~# perf record -a -e sched:sched_switch --filter 'next_comm != perf && prev_comm != perf' -e sched:sched_wakeup --filter 'comm != perf'
     ^C[ perf record: Woken up 38 times to write data ]
     [ perf record: Captured and wrote 9.688 MB perf.data (~423279 samples) ]


     root@crownbay:~# perf script

             swapper     0 [000]  7932.162180: sched_switch: prev_comm=swapper/0 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=kworker/0:3 next_pid=1209 next_prio=120
         kworker/0:3  1209 [000]  7932.162236: sched_switch: prev_comm=kworker/0:3 prev_pid=1209 prev_prio=120 prev_state=S ==> next_comm=swapper/0 next_pid=0 next_prio=120
                perf  1407 [001]  7932.170048: sched_wakeup: comm=kworker/1:1 pid=21 prio=120 success=1 target_cpu=001
                perf  1407 [001]  7932.180044: sched_wakeup: comm=kworker/1:1 pid=21 prio=120 success=1 target_cpu=001
                perf  1407 [001]  7932.190038: sched_wakeup: comm=kworker/1:1 pid=21 prio=120 success=1 target_cpu=001
                perf  1407 [001]  7932.200044: sched_wakeup: comm=kworker/1:1 pid=21 prio=120 success=1 target_cpu=001
                perf  1407 [001]  7932.210044: sched_wakeup: comm=kworker/1:1 pid=21 prio=120 success=1 target_cpu=001
                perf  1407 [001]  7932.220044: sched_wakeup: comm=kworker/1:1 pid=21 prio=120 success=1 target_cpu=001
             swapper     0 [001]  7932.230111: sched_wakeup: comm=kworker/1:1 pid=21 prio=120 success=1 target_cpu=001
             swapper     0 [001]  7932.230146: sched_switch: prev_comm=swapper/1 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=kworker/1:1 next_pid=21 next_prio=120
         kworker/1:1    21 [001]  7932.230205: sched_switch: prev_comm=kworker/1:1 prev_pid=21 prev_prio=120 prev_state=S ==> next_comm=swapper/1 next_pid=0 next_prio=120
             swapper     0 [000]  7932.326109: sched_wakeup: comm=kworker/0:3 pid=1209 prio=120 success=1 target_cpu=000
             swapper     0 [000]  7932.326171: sched_switch: prev_comm=swapper/0 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=kworker/0:3 next_pid=1209 next_prio=120
         kworker/0:3  1209 [000]  7932.326214: sched_switch: prev_comm=kworker/0:3 prev_pid=1209 prev_prio=120 prev_state=S ==> next_comm=swapper/0 next_pid=0 next_prio=120
                    

In this case, we've filtered out all events that have 'perf' in their 'comm' or 'comm_prev' or 'comm_next' fields. Notice that there are still events recorded for perf, but notice that those events don't have values of 'perf' for the filtered fields. To completely filter out anything from perf will require a bit more work, but for the purpose of demonstrating how to use filters, it's close enough.

Tying it Together: These are exactly the same set of event filters defined by the trace event subsystem. See the ftrace/tracecmd/kernelshark section for more discussion about these event filters.
Tying it Together: These event filters are implemented by a special-purpose pseudo-interpreter in the kernel and are an integral and indispensable part of the perf design as it relates to tracing. kernel-based event filters provide a mechanism to precisely throttle the event stream that appears in user space, where it makes sense to provide bindings to real programming languages for postprocessing the event stream. This architecture allows for the intelligent and flexible partitioning of processing between the kernel and user space. Contrast this with other tools such as SystemTap, which does all of its processing in the kernel and as such requires a special project-defined language in order to accommodate that design, or LTTng, where everything is sent to userspace and as such requires a super-efficient kernel-to-userspace transport mechanism in order to function properly. While perf certainly can benefit from for instance advances in the design of the transport, it doesn't fundamentally depend on them. Basically, if you find that your perf tracing application is causing buffer I/O overruns, it probably means that you aren't taking enough advantage of the kernel filtering engine.

3.1.2.4. Using Dynamic Tracepoints

perf isn't restricted to the fixed set of static tracepoints listed by 'perf list'. Users can also add their own 'dynamic' tracepoints anywhere in the kernel. For instance, suppose we want to define our own tracepoint on do_fork(). We can do that using the 'perf probe' perf subcommand:

     root@crownbay:~# perf probe do_fork
     Added new event:
       probe:do_fork        (on do_fork)

     You can now use it in all perf tools, such as:

	     perf record -e probe:do_fork -aR sleep 1
                

Adding a new tracepoint via 'perf probe' results in an event with all the expected files and format in /sys/kernel/debug/tracing/events, just the same as for static tracepoints (as discussed in more detail in the trace events subsystem section:

     root@crownbay:/sys/kernel/debug/tracing/events/probe/do_fork# ls -al
     drwxr-xr-x    2 root     root             0 Oct 28 11:42 .
     drwxr-xr-x    3 root     root             0 Oct 28 11:42 ..
     -rw-r--r--    1 root     root             0 Oct 28 11:42 enable
     -rw-r--r--    1 root     root             0 Oct 28 11:42 filter
     -r--r--r--    1 root     root             0 Oct 28 11:42 format
     -r--r--r--    1 root     root             0 Oct 28 11:42 id

     root@crownbay:/sys/kernel/debug/tracing/events/probe/do_fork# cat format
     name: do_fork
     ID: 944
     format:
	     field:unsigned short common_type;	offset:0;	size:2;	signed:0;
	     field:unsigned char common_flags;	offset:2;	size:1;	signed:0;
	     field:unsigned char common_preempt_count;	offset:3;	size:1;	signed:0;
	     field:int common_pid;	offset:4;	size:4;	signed:1;
	     field:int common_padding;	offset:8;	size:4;	signed:1;

	     field:unsigned long __probe_ip;	offset:12;	size:4;	signed:0;

     print fmt: "(%lx)", REC->__probe_ip
                

We can list all dynamic tracepoints currently in existence:

     root@crownbay:~# perf probe -l
      probe:do_fork        (on do_fork)
      probe:schedule       (on schedule)
                

Let's record system-wide ('sleep 30' is a trick for recording system-wide but basically do nothing and then wake up after 30 seconds):

     root@crownbay:~# perf record -g -a -e probe:do_fork sleep 30
     [ perf record: Woken up 1 times to write data ]
     [ perf record: Captured and wrote 0.087 MB perf.data (~3812 samples) ]
                

Using 'perf script' we can see each do_fork event that fired:

     root@crownbay:~# perf script

     # ========
     # captured on: Sun Oct 28 11:55:18 2012
     # hostname : crownbay
     # os release : 3.4.11-yocto-standard
     # perf version : 3.4.11
     # arch : i686
     # nrcpus online : 2
     # nrcpus avail : 2
     # cpudesc : Intel(R) Atom(TM) CPU E660 @ 1.30GHz
     # cpuid : GenuineIntel,6,38,1
     # total memory : 1017184 kB
     # cmdline : /usr/bin/perf record -g -a -e probe:do_fork sleep 30
     # event : name = probe:do_fork, type = 2, config = 0x3b0, config1 = 0x0, config2 = 0x0, excl_usr = 0, excl_kern
      = 0, id = { 5, 6 }
     # HEADER_CPU_TOPOLOGY info available, use -I to display
     # ========
     #
      matchbox-deskto  1197 [001] 34211.378318: do_fork: (c1028460)
      matchbox-deskto  1295 [001] 34211.380388: do_fork: (c1028460)
              pcmanfm  1296 [000] 34211.632350: do_fork: (c1028460)
              pcmanfm  1296 [000] 34211.639917: do_fork: (c1028460)
      matchbox-deskto  1197 [001] 34217.541603: do_fork: (c1028460)
      matchbox-deskto  1299 [001] 34217.543584: do_fork: (c1028460)
               gthumb  1300 [001] 34217.697451: do_fork: (c1028460)
               gthumb  1300 [001] 34219.085734: do_fork: (c1028460)
               gthumb  1300 [000] 34219.121351: do_fork: (c1028460)
               gthumb  1300 [001] 34219.264551: do_fork: (c1028460)
              pcmanfm  1296 [000] 34219.590380: do_fork: (c1028460)
      matchbox-deskto  1197 [001] 34224.955965: do_fork: (c1028460)
      matchbox-deskto  1306 [001] 34224.957972: do_fork: (c1028460)
      matchbox-termin  1307 [000] 34225.038214: do_fork: (c1028460)
      matchbox-termin  1307 [001] 34225.044218: do_fork: (c1028460)
      matchbox-termin  1307 [000] 34225.046442: do_fork: (c1028460)
      matchbox-deskto  1197 [001] 34237.112138: do_fork: (c1028460)
      matchbox-deskto  1311 [001] 34237.114106: do_fork: (c1028460)
                 gaku  1312 [000] 34237.202388: do_fork: (c1028460)
                

And using 'perf report' on the same file, we can see the callgraphs from starting a few programs during those 30 seconds:

Tying it Together: The trace events subsystem accomodate static and dynamic tracepoints in exactly the same way - there's no difference as far as the infrastructure is concerned. See the ftrace section for more details on the trace event subsystem.
Tying it Together: Dynamic tracepoints are implemented under the covers by kprobes and uprobes. kprobes and uprobes are also used by and in fact are the main focus of SystemTap.

3.1.3. Documentation

Online versions of the man pages for the commands discussed in this section can be found here:

Normally, you should be able to invoke the man pages via perf itself e.g. 'perf help' or 'perf help record'.

However, by default Yocto doesn't install man pages, but perf invokes the man pages for most help functionality. This is a bug and is being addressed by a Yocto bug: Bug 3388 - perf: enable man pages for basic 'help' functionality.

The man pages in text form, along with some other files, such as a set of examples, can be found in the 'perf' directory of the kernel tree:

     tools/perf/Documentation
            

There's also a nice perf tutorial on the perf wiki that goes into more detail than we do here in certain areas: Perf Tutorial

3.2. ftrace

'ftrace' literally refers to the 'ftrace function tracer' but in reality this encompasses a number of related tracers along with the infrastructure that they all make use of.

3.2.1. Setup

For this section, we'll assume you've already performed the basic setup outlined in the General Setup section.

ftrace, trace-cmd, and kernelshark run on the target system, and are ready to go out-of-the-box - no additional setup is necessary. For the rest of this section we assume you've ssh'ed to the host and will be running ftrace on the target. kernelshark is a GUI application and if you use the '-X' option to ssh you can have the kernelshark GUI run on the target but display remotely on the host if you want.

3.2.2. Basic ftrace usage

'ftrace' essentially refers to everything included in the /tracing directory of the mounted debugfs filesystem (Yocto follows the standard convention and mounts it at /sys/kernel/debug). Here's a listing of all the files found in /sys/kernel/debug/tracing on a Yocto system.:

     root@sugarbay:/sys/kernel/debug/tracing# ls
     README                      kprobe_events               trace
     available_events            kprobe_profile              trace_clock
     available_filter_functions  options                     trace_marker
     available_tracers           per_cpu                     trace_options
     buffer_size_kb              printk_formats              trace_pipe
     buffer_total_size_kb        saved_cmdlines              tracing_cpumask
     current_tracer              set_event                   tracing_enabled
     dyn_ftrace_total_info       set_ftrace_filter           tracing_on
     enabled_functions           set_ftrace_notrace          tracing_thresh
     events                      set_ftrace_pid
     free_buffer                 set_graph_function
            

The files listed above are used for various purposes - some relate directly to the tracers themselves, others are used to set tracing options, and yet others actually contain the tracing output when a tracer is in effect. Some of the functions can be guessed from their names, others need explanation; in any case, we'll cover some of the files we see here below but for an explanation of the others, please see the ftrace documentation.

We'll start by looking at some of the available built-in tracers.

cat'ing the 'available_tracers' file lists the set of available tracers:

     root@sugarbay:/sys/kernel/debug/tracing# cat available_tracers
     blk function_graph function nop
            

The 'current_tracer' file contains the tracer currently in effect:

     root@sugarbay:/sys/kernel/debug/tracing# cat current_tracer
     nop
            

The above listing of current_tracer shows that the 'nop' tracer is in effect, which is just another way of saying that there's actually no tracer currently in effect.

echo'ing one of the available_tracers into current_tracer makes the specified tracer the current tracer:

     root@sugarbay:/sys/kernel/debug/tracing# echo function > current_tracer
     root@sugarbay:/sys/kernel/debug/tracing# cat current_tracer
     function
            

The above sets the current tracer to be the 'function tracer'. This tracer traces every function call in the kernel and makes it available as the contents of the 'trace' file. Reading the 'trace' file lists the currently buffered function calls that have been traced by the function tracer:

     root@sugarbay:/sys/kernel/debug/tracing# cat trace | less

     # tracer: function
     #
     # entries-in-buffer/entries-written: 310629/766471   #P:8
     #
     #                              _-----=> irqs-off
     #                             / _----=> need-resched
     #                            | / _---=> hardirq/softirq
     #                            || / _--=> preempt-depth
     #                            ||| /     delay
     #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
     #              | |       |   ||||       |         |
              <idle>-0     [004] d..1   470.867169: ktime_get_real <-intel_idle
              <idle>-0     [004] d..1   470.867170: getnstimeofday <-ktime_get_real
              <idle>-0     [004] d..1   470.867171: ns_to_timeval <-intel_idle
              <idle>-0     [004] d..1   470.867171: ns_to_timespec <-ns_to_timeval
              <idle>-0     [004] d..1   470.867172: smp_apic_timer_interrupt <-apic_timer_interrupt
              <idle>-0     [004] d..1   470.867172: native_apic_mem_write <-smp_apic_timer_interrupt
              <idle>-0     [004] d..1   470.867172: irq_enter <-smp_apic_timer_interrupt
              <idle>-0     [004] d..1   470.867172: rcu_irq_enter <-irq_enter
              <idle>-0     [004] d..1   470.867173: rcu_idle_exit_common.isra.33 <-rcu_irq_enter
              <idle>-0     [004] d..1   470.867173: local_bh_disable <-irq_enter
              <idle>-0     [004] d..1   470.867173: add_preempt_count <-local_bh_disable
              <idle>-0     [004] d.s1   470.867174: tick_check_idle <-irq_enter
              <idle>-0     [004] d.s1   470.867174: tick_check_oneshot_broadcast <-tick_check_idle
              <idle>-0     [004] d.s1   470.867174: ktime_get <-tick_check_idle
              <idle>-0     [004] d.s1   470.867174: tick_nohz_stop_idle <-tick_check_idle
              <idle>-0     [004] d.s1   470.867175: update_ts_time_stats <-tick_nohz_stop_idle
              <idle>-0     [004] d.s1   470.867175: nr_iowait_cpu <-update_ts_time_stats
              <idle>-0     [004] d.s1   470.867175: tick_do_update_jiffies64 <-tick_check_idle
              <idle>-0     [004] d.s1   470.867175: _raw_spin_lock <-tick_do_update_jiffies64
              <idle>-0     [004] d.s1   470.867176: add_preempt_count <-_raw_spin_lock
              <idle>-0     [004] d.s2   470.867176: do_timer <-tick_do_update_jiffies64
              <idle>-0     [004] d.s2   470.867176: _raw_spin_lock <-do_timer
              <idle>-0     [004] d.s2   470.867176: add_preempt_count <-_raw_spin_lock
              <idle>-0     [004] d.s3   470.867177: ntp_tick_length <-do_timer
              <idle>-0     [004] d.s3   470.867177: _raw_spin_lock_irqsave <-ntp_tick_length
              .
              .
              .
            

Each line in the trace above shows what was happening in the kernel on a given cpu, to the level of detail of function calls. Each entry shows the function called, followed by its caller (after the arrow).

The function tracer gives you an extremely detailed idea of what the kernel was doing at the point in time the trace was taken, and is a great way to learn about how the kernel code works in a dynamic sense.

Tying it Together: The ftrace function tracer is also available from within perf, as the ftrace:function tracepoint.

It is a little more difficult to follow the call chains than it needs to be - luckily there's a variant of the function tracer that displays the callchains explicitly, called the 'function_graph' tracer:

     root@sugarbay:/sys/kernel/debug/tracing# echo function_graph > current_tracer
     root@sugarbay:/sys/kernel/debug/tracing# cat trace | less

      tracer: function_graph

      CPU  DURATION                  FUNCTION CALLS
      |     |   |                     |   |   |   |
     7)   0.046 us    |      pick_next_task_fair();
     7)   0.043 us    |      pick_next_task_stop();
     7)   0.042 us    |      pick_next_task_rt();
     7)   0.032 us    |      pick_next_task_fair();
     7)   0.030 us    |      pick_next_task_idle();
     7)               |      _raw_spin_unlock_irq() {
     7)   0.033 us    |        sub_preempt_count();
     7)   0.258 us    |      }
     7)   0.032 us    |      sub_preempt_count();
     7) + 13.341 us   |    } /* __schedule */
     7)   0.095 us    |  } /* sub_preempt_count */
     7)               |  schedule() {
     7)               |    __schedule() {
     7)   0.060 us    |      add_preempt_count();
     7)   0.044 us    |      rcu_note_context_switch();
     7)               |      _raw_spin_lock_irq() {
     7)   0.033 us    |        add_preempt_count();
     7)   0.247 us    |      }
     7)               |      idle_balance() {
     7)               |        _raw_spin_unlock() {
     7)   0.031 us    |          sub_preempt_count();
     7)   0.246 us    |        }
     7)               |        update_shares() {
     7)   0.030 us    |          __rcu_read_lock();
     7)   0.029 us    |          __rcu_read_unlock();
     7)   0.484 us    |        }
     7)   0.030 us    |        __rcu_read_lock();
     7)               |        load_balance() {
     7)               |          find_busiest_group() {
     7)   0.031 us    |            idle_cpu();
     7)   0.029 us    |            idle_cpu();
     7)   0.035 us    |            idle_cpu();
     7)   0.906 us    |          }
     7)   1.141 us    |        }
     7)   0.022 us    |        msecs_to_jiffies();
     7)               |        load_balance() {
     7)               |          find_busiest_group() {
     7)   0.031 us    |            idle_cpu();
     .
     .
     .
     4)   0.062 us    |        msecs_to_jiffies();
     4)   0.062 us    |        __rcu_read_unlock();
     4)               |        _raw_spin_lock() {
     4)   0.073 us    |          add_preempt_count();
     4)   0.562 us    |        }
     4) + 17.452 us   |      }
     4)   0.108 us    |      put_prev_task_fair();
     4)   0.102 us    |      pick_next_task_fair();
     4)   0.084 us    |      pick_next_task_stop();
     4)   0.075 us    |      pick_next_task_rt();
     4)   0.062 us    |      pick_next_task_fair();
     4)   0.066 us    |      pick_next_task_idle();
     ------------------------------------------
     4)   kworker-74   =>    <idle>-0
     ------------------------------------------

     4)               |      finish_task_switch() {
     4)               |        _raw_spin_unlock_irq() {
     4)   0.100 us    |          sub_preempt_count();
     4)   0.582 us    |        }
     4)   1.105 us    |      }
     4)   0.088 us    |      sub_preempt_count();
     4) ! 100.066 us  |    }
     .
     .
     .
     3)               |  sys_ioctl() {
     3)   0.083 us    |    fget_light();
     3)               |    security_file_ioctl() {
     3)   0.066 us    |      cap_file_ioctl();
     3)   0.562 us    |    }
     3)               |    do_vfs_ioctl() {
     3)               |      drm_ioctl() {
     3)   0.075 us    |        drm_ut_debug_printk();
     3)               |        i915_gem_pwrite_ioctl() {
     3)               |          i915_mutex_lock_interruptible() {
     3)   0.070 us    |            mutex_lock_interruptible();
     3)   0.570 us    |          }
     3)               |          drm_gem_object_lookup() {
     3)               |            _raw_spin_lock() {
     3)   0.080 us    |              add_preempt_count();
     3)   0.620 us    |            }
     3)               |            _raw_spin_unlock() {
     3)   0.085 us    |              sub_preempt_count();
     3)   0.562 us    |            }
     3)   2.149 us    |          }
     3)   0.133 us    |          i915_gem_object_pin();
     3)               |          i915_gem_object_set_to_gtt_domain() {
     3)   0.065 us    |            i915_gem_object_flush_gpu_write_domain();
     3)   0.065 us    |            i915_gem_object_wait_rendering();
     3)   0.062 us    |            i915_gem_object_flush_cpu_write_domain();
     3)   1.612 us    |          }
     3)               |          i915_gem_object_put_fence() {
     3)   0.097 us    |            i915_gem_object_flush_fence.constprop.36();
     3)   0.645 us    |          }
     3)   0.070 us    |          add_preempt_count();
     3)   0.070 us    |          sub_preempt_count();
     3)   0.073 us    |          i915_gem_object_unpin();
     3)   0.068 us    |          mutex_unlock();
     3)   9.924 us    |        }
     3) + 11.236 us   |      }
     3) + 11.770 us   |    }
     3) + 13.784 us   |  }
     3)               |  sys_ioctl() {
            

As you can see, the function_graph display is much easier to follow. Also note that in addition to the function calls and associated braces, other events such as scheduler events are displayed in context. In fact, you can freely include any tracepoint available in the trace events subsystem described in the next section by simply enabling those events, and they'll appear in context in the function graph display. Quite a powerful tool for understanding kernel dynamics.

Also notice that there are various annotations on the left hand side of the display. For example if the total time it took for a given function to execute is above a certain threshold, and exclamation point or plus sign appears on the left hand side. Please see the ftrace documentation for details on all these fields.

3.2.3. The 'trace events' Subsystem

One especially important directory contained within the /sys/kernel/debug/tracing directory is the 'events' subdirectory, which contains representations of every tracepoint in the system. Listing out the contents of the 'events' subdirectory, we see mainly another set of subdirectories:

     root@sugarbay:/sys/kernel/debug/tracing# cd events
     root@sugarbay:/sys/kernel/debug/tracing/events# ls -al
     drwxr-xr-x   38 root     root             0 Nov 14 23:19 .
     drwxr-xr-x    5 root     root             0 Nov 14 23:19 ..
     drwxr-xr-x   19 root     root             0 Nov 14 23:19 block
     drwxr-xr-x   32 root     root             0 Nov 14 23:19 btrfs
     drwxr-xr-x    5 root     root             0 Nov 14 23:19 drm
     -rw-r--r--    1 root     root             0 Nov 14 23:19 enable
     drwxr-xr-x   40 root     root             0 Nov 14 23:19 ext3
     drwxr-xr-x   79 root     root             0 Nov 14 23:19 ext4
     drwxr-xr-x   14 root     root             0 Nov 14 23:19 ftrace
     drwxr-xr-x    8 root     root             0 Nov 14 23:19 hda
     -r--r--r--    1 root     root             0 Nov 14 23:19 header_event
     -r--r--r--    1 root     root             0 Nov 14 23:19 header_page
     drwxr-xr-x   25 root     root             0 Nov 14 23:19 i915
     drwxr-xr-x    7 root     root             0 Nov 14 23:19 irq
     drwxr-xr-x   12 root     root             0 Nov 14 23:19 jbd
     drwxr-xr-x   14 root     root             0 Nov 14 23:19 jbd2
     drwxr-xr-x   14 root     root             0 Nov 14 23:19 kmem
     drwxr-xr-x    7 root     root             0 Nov 14 23:19 module
     drwxr-xr-x    3 root     root             0 Nov 14 23:19 napi
     drwxr-xr-x    6 root     root             0 Nov 14 23:19 net
     drwxr-xr-x    3 root     root             0 Nov 14 23:19 oom
     drwxr-xr-x   12 root     root             0 Nov 14 23:19 power
     drwxr-xr-x    3 root     root             0 Nov 14 23:19 printk
     drwxr-xr-x    8 root     root             0 Nov 14 23:19 random
     drwxr-xr-x    4 root     root             0 Nov 14 23:19 raw_syscalls
     drwxr-xr-x    3 root     root             0 Nov 14 23:19 rcu
     drwxr-xr-x    6 root     root             0 Nov 14 23:19 rpm
     drwxr-xr-x   20 root     root             0 Nov 14 23:19 sched
     drwxr-xr-x    7 root     root             0 Nov 14 23:19 scsi
     drwxr-xr-x    4 root     root             0 Nov 14 23:19 signal
     drwxr-xr-x    5 root     root             0 Nov 14 23:19 skb
     drwxr-xr-x    4 root     root             0 Nov 14 23:19 sock
     drwxr-xr-x   10 root     root             0 Nov 14 23:19 sunrpc
     drwxr-xr-x  538 root     root             0 Nov 14 23:19 syscalls
     drwxr-xr-x    4 root     root             0 Nov 14 23:19 task
     drwxr-xr-x   14 root     root             0 Nov 14 23:19 timer
     drwxr-xr-x    3 root     root             0 Nov 14 23:19 udp
     drwxr-xr-x   21 root     root             0 Nov 14 23:19 vmscan
     drwxr-xr-x    3 root     root             0 Nov 14 23:19 vsyscall
     drwxr-xr-x    6 root     root             0 Nov 14 23:19 workqueue
     drwxr-xr-x   26 root     root             0 Nov 14 23:19 writeback
            

Each one of these subdirectories corresponds to a 'subsystem' and contains yet again more subdirectories, each one of those finally corresponding to a tracepoint. For example, here are the contents of the 'kmem' subsystem:

     root@sugarbay:/sys/kernel/debug/tracing/events# cd kmem
     root@sugarbay:/sys/kernel/debug/tracing/events/kmem# ls -al
     drwxr-xr-x   14 root     root             0 Nov 14 23:19 .
     drwxr-xr-x   38 root     root             0 Nov 14 23:19 ..
     -rw-r--r--    1 root     root             0 Nov 14 23:19 enable
     -rw-r--r--    1 root     root             0 Nov 14 23:19 filter
     drwxr-xr-x    2 root     root             0 Nov 14 23:19 kfree
     drwxr-xr-x    2 root     root             0 Nov 14 23:19 kmalloc
     drwxr-xr-x    2 root     root             0 Nov 14 23:19 kmalloc_node
     drwxr-xr-x    2 root     root             0 Nov 14 23:19 kmem_cache_alloc
     drwxr-xr-x    2 root     root             0 Nov 14 23:19 kmem_cache_alloc_node
     drwxr-xr-x    2 root     root             0 Nov 14 23:19 kmem_cache_free
     drwxr-xr-x    2 root     root             0 Nov 14 23:19 mm_page_alloc
     drwxr-xr-x    2 root     root             0 Nov 14 23:19 mm_page_alloc_extfrag
     drwxr-xr-x    2 root     root             0 Nov 14 23:19 mm_page_alloc_zone_locked
     drwxr-xr-x    2 root     root             0 Nov 14 23:19 mm_page_free
     drwxr-xr-x    2 root     root             0 Nov 14 23:19 mm_page_free_batched
     drwxr-xr-x    2 root     root             0 Nov 14 23:19 mm_page_pcpu_drain
            

Let's see what's inside the subdirectory for a specific tracepoint, in this case the one for kmalloc:

     root@sugarbay:/sys/kernel/debug/tracing/events/kmem# cd kmalloc
     root@sugarbay:/sys/kernel/debug/tracing/events/kmem/kmalloc# ls -al
     drwxr-xr-x    2 root     root             0 Nov 14 23:19 .
     drwxr-xr-x   14 root     root             0 Nov 14 23:19 ..
     -rw-r--r--    1 root     root             0 Nov 14 23:19 enable
     -rw-r--r--    1 root     root             0 Nov 14 23:19 filter
     -r--r--r--    1 root     root             0 Nov 14 23:19 format
     -r--r--r--    1 root     root             0 Nov 14 23:19 id
            

The 'format' file for the tracepoint describes the event in memory, which is used by the various tracing tools that now make use of these tracepoint to parse the event and make sense of it, along with a 'print fmt' field that allows tools like ftrace to display the event as text. Here's what the format of the kmalloc event looks like:

     root@sugarbay:/sys/kernel/debug/tracing/events/kmem/kmalloc# cat format
     name: kmalloc
     ID: 313
     format:
	     field:unsigned short common_type;	offset:0;	size:2;	signed:0;
	     field:unsigned char common_flags;	offset:2;	size:1;	signed:0;
	     field:unsigned char common_preempt_count;	offset:3;	size:1;	signed:0;
	     field:int common_pid;	offset:4;	size:4;	signed:1;
	     field:int common_padding;	offset:8;	size:4;	signed:1;

	     field:unsigned long call_site;	offset:16;	size:8;	signed:0;
	     field:const void * ptr;	offset:24;	size:8;	signed:0;
	     field:size_t bytes_req;	offset:32;	size:8;	signed:0;
	     field:size_t bytes_alloc;	offset:40;	size:8;	signed:0;
	     field:gfp_t gfp_flags;	offset:48;	size:4;	signed:0;

     print fmt: "call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s", REC->call_site, REC->ptr, REC->bytes_req, REC->bytes_alloc,
     (REC->gfp_flags) ? __print_flags(REC->gfp_flags, "|", {(unsigned long)(((( gfp_t)0x10u) | (( gfp_t)0x40u) | (( gfp_t)0x80u) | ((
     gfp_t)0x20000u) | (( gfp_t)0x02u) | (( gfp_t)0x08u)) | (( gfp_t)0x4000u) | (( gfp_t)0x10000u) | (( gfp_t)0x1000u) | (( gfp_t)0x200u) | ((
     gfp_t)0x400000u)), "GFP_TRANSHUGE"}, {(unsigned long)((( gfp_t)0x10u) | (( gfp_t)0x40u) | (( gfp_t)0x80u) | (( gfp_t)0x20000u) | ((
     gfp_t)0x02u) | (( gfp_t)0x08u)), "GFP_HIGHUSER_MOVABLE"}, {(unsigned long)((( gfp_t)0x10u) | (( gfp_t)0x40u) | (( gfp_t)0x80u) | ((
     gfp_t)0x20000u) | (( gfp_t)0x02u)), "GFP_HIGHUSER"}, {(unsigned long)((( gfp_t)0x10u) | (( gfp_t)0x40u) | (( gfp_t)0x80u) | ((
     gfp_t)0x20000u)), "GFP_USER"}, {(unsigned long)((( gfp_t)0x10u) | (( gfp_t)0x40u) | (( gfp_t)0x80u) | (( gfp_t)0x80000u)), GFP_TEMPORARY"},
     {(unsigned long)((( gfp_t)0x10u) | (( gfp_t)0x40u) | (( gfp_t)0x80u)), "GFP_KERNEL"}, {(unsigned long)((( gfp_t)0x10u) | (( gfp_t)0x40u)),
     "GFP_NOFS"}, {(unsigned long)((( gfp_t)0x20u)), "GFP_ATOMIC"}, {(unsigned long)((( gfp_t)0x10u)), "GFP_NOIO"}, {(unsigned long)((
     gfp_t)0x20u), "GFP_HIGH"}, {(unsigned long)(( gfp_t)0x10u), "GFP_WAIT"}, {(unsigned long)(( gfp_t)0x40u), "GFP_IO"}, {(unsigned long)((
     gfp_t)0x100u), "GFP_COLD"}, {(unsigned long)(( gfp_t)0x200u), "GFP_NOWARN"}, {(unsigned long)(( gfp_t)0x400u), "GFP_REPEAT"}, {(unsigned
     long)(( gfp_t)0x800u), "GFP_NOFAIL"}, {(unsigned long)(( gfp_t)0x1000u), "GFP_NORETRY"},      {(unsigned long)(( gfp_t)0x4000u), "GFP_COMP"},
     {(unsigned long)(( gfp_t)0x8000u), "GFP_ZERO"}, {(unsigned long)(( gfp_t)0x10000u), "GFP_NOMEMALLOC"}, {(unsigned long)(( gfp_t)0x20000u),
     "GFP_HARDWALL"}, {(unsigned long)(( gfp_t)0x40000u), "GFP_THISNODE"}, {(unsigned long)(( gfp_t)0x80000u), "GFP_RECLAIMABLE"}, {(unsigned
     long)(( gfp_t)0x08u), "GFP_MOVABLE"}, {(unsigned long)(( gfp_t)0), "GFP_NOTRACK"}, {(unsigned long)(( gfp_t)0x400000u), "GFP_NO_KSWAPD"},
     {(unsigned long)(( gfp_t)0x800000u), "GFP_OTHER_NODE"} ) : "GFP_NOWAIT"
            

The 'enable' file in the tracepoint directory is what allows the user (or tools such as trace-cmd) to actually turn the tracepoint on and off. When enabled, the corresponding tracepoint will start appearing in the ftrace 'trace' file described previously. For example, this turns on the kmalloc tracepoint:

     root@sugarbay:/sys/kernel/debug/tracing/events/kmem/kmalloc# echo 1 > enable
            

At the moment, we're not interested in the function tracer or some other tracer that might be in effect, so we first turn it off, but if we do that, we still need to turn tracing on in order to see the events in the output buffer:

     root@sugarbay:/sys/kernel/debug/tracing# echo nop > current_tracer
     root@sugarbay:/sys/kernel/debug/tracing# echo 1 > tracing_on
            

Now, if we look at the the 'trace' file, we see nothing but the kmalloc events we just turned on:

     root@sugarbay:/sys/kernel/debug/tracing# cat trace | less
     # tracer: nop
     #
     # entries-in-buffer/entries-written: 1897/1897   #P:8
     #
     #                              _-----=> irqs-off
     #                             / _----=> need-resched
     #                            | / _---=> hardirq/softirq
     #                            || / _--=> preempt-depth
     #                            ||| /     delay
     #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
     #              | |       |   ||||       |         |
            dropbear-1465  [000] ...1 18154.620753: kmalloc: call_site=ffffffff816650d4 ptr=ffff8800729c3000 bytes_req=2048 bytes_alloc=2048 gfp_flags=GFP_KERNEL
              <idle>-0     [000] ..s3 18154.621640: kmalloc: call_site=ffffffff81619b36 ptr=ffff88006d555800 bytes_req=512 bytes_alloc=512 gfp_flags=GFP_ATOMIC
              <idle>-0     [000] ..s3 18154.621656: kmalloc: call_site=ffffffff81619b36 ptr=ffff88006d555800 bytes_req=512 bytes_alloc=512 gfp_flags=GFP_ATOMIC
     matchbox-termin-1361  [001] ...1 18154.755472: kmalloc: call_site=ffffffff81614050 ptr=ffff88006d5f0e00 bytes_req=512 bytes_alloc=512 gfp_flags=GFP_KERNEL|GFP_REPEAT
                Xorg-1264  [002] ...1 18154.755581: kmalloc: call_site=ffffffff8141abe8 ptr=ffff8800734f4cc0 bytes_req=168 bytes_alloc=192 gfp_flags=GFP_KERNEL|GFP_NOWARN|GFP_NORETRY
                Xorg-1264  [002] ...1 18154.755583: kmalloc: call_site=ffffffff814192a3 ptr=ffff88001f822520 bytes_req=24 bytes_alloc=32 gfp_flags=GFP_KERNEL|GFP_ZERO
                Xorg-1264  [002] ...1 18154.755589: kmalloc: call_site=ffffffff81419edb ptr=ffff8800721a2f00 bytes_req=64 bytes_alloc=64 gfp_flags=GFP_KERNEL|GFP_ZERO
     matchbox-termin-1361  [001] ...1 18155.354594: kmalloc: call_site=ffffffff81614050 ptr=ffff88006db35400 bytes_req=576 bytes_alloc=1024 gfp_flags=GFP_KERNEL|GFP_REPEAT
                Xorg-1264  [002] ...1 18155.354703: kmalloc: call_site=ffffffff8141abe8 ptr=ffff8800734f4cc0 bytes_req=168 bytes_alloc=192 gfp_flags=GFP_KERNEL|GFP_NOWARN|GFP_NORETRY
                Xorg-1264  [002] ...1 18155.354705: kmalloc: call_site=ffffffff814192a3 ptr=ffff88001f822520 bytes_req=24 bytes_alloc=32 gfp_flags=GFP_KERNEL|GFP_ZERO
                Xorg-1264  [002] ...1 18155.354711: kmalloc: call_site=ffffffff81419edb ptr=ffff8800721a2f00 bytes_req=64 bytes_alloc=64 gfp_flags=GFP_KERNEL|GFP_ZERO
              <idle>-0     [000] ..s3 18155.673319: kmalloc: call_site=ffffffff81619b36 ptr=ffff88006d555800 bytes_req=512 bytes_alloc=512 gfp_flags=GFP_ATOMIC
            dropbear-1465  [000] ...1 18155.673525: kmalloc: call_site=ffffffff816650d4 ptr=ffff8800729c3000 bytes_req=2048 bytes_alloc=2048 gfp_flags=GFP_KERNEL
              <idle>-0     [000] ..s3 18155.674821: kmalloc: call_site=ffffffff81619b36 ptr=ffff88006d554800 bytes_req=512 bytes_alloc=512 gfp_flags=GFP_ATOMIC
              <idle>-0     [000] ..s3 18155.793014: kmalloc: call_site=ffffffff81619b36 ptr=ffff88006d554800 bytes_req=512 bytes_alloc=512 gfp_flags=GFP_ATOMIC
            dropbear-1465  [000] ...1 18155.793219: kmalloc: call_site=ffffffff816650d4 ptr=ffff8800729c3000 bytes_req=2048 bytes_alloc=2048 gfp_flags=GFP_KERNEL
              <idle>-0     [000] ..s3 18155.794147: kmalloc: call_site=ffffffff81619b36 ptr=ffff88006d555800 bytes_req=512 bytes_alloc=512 gfp_flags=GFP_ATOMIC
              <idle>-0     [000] ..s3 18155.936705: kmalloc: call_site=ffffffff81619b36 ptr=ffff88006d555800 bytes_req=512 bytes_alloc=512 gfp_flags=GFP_ATOMIC
            dropbear-1465  [000] ...1 18155.936910: kmalloc: call_site=ffffffff816650d4 ptr=ffff8800729c3000 bytes_req=2048 bytes_alloc=2048 gfp_flags=GFP_KERNEL
              <idle>-0     [000] ..s3 18155.937869: kmalloc: call_site=ffffffff81619b36 ptr=ffff88006d554800 bytes_req=512 bytes_alloc=512 gfp_flags=GFP_ATOMIC
     matchbox-termin-1361  [001] ...1 18155.953667: kmalloc: call_site=ffffffff81614050 ptr=ffff88006d5f2000 bytes_req=512 bytes_alloc=512 gfp_flags=GFP_KERNEL|GFP_REPEAT
                Xorg-1264  [002] ...1 18155.953775: kmalloc: call_site=ffffffff8141abe8 ptr=ffff8800734f4cc0 bytes_req=168 bytes_alloc=192 gfp_flags=GFP_KERNEL|GFP_NOWARN|GFP_NORETRY
                Xorg-1264  [002] ...1 18155.953777: kmalloc: call_site=ffffffff814192a3 ptr=ffff88001f822520 bytes_req=24 bytes_alloc=32 gfp_flags=GFP_KERNEL|GFP_ZERO
                Xorg-1264  [002] ...1 18155.953783: kmalloc: call_site=ffffffff81419edb ptr=ffff8800721a2f00 bytes_req=64 bytes_alloc=64 gfp_flags=GFP_KERNEL|GFP_ZERO
              <idle>-0     [000] ..s3 18156.176053: kmalloc: call_site=ffffffff81619b36 ptr=ffff88006d554800 bytes_req=512 bytes_alloc=512 gfp_flags=GFP_ATOMIC
            dropbear-1465  [000] ...1 18156.176257: kmalloc: call_site=ffffffff816650d4 ptr=ffff8800729c3000 bytes_req=2048 bytes_alloc=2048 gfp_flags=GFP_KERNEL
              <idle>-0     [000] ..s3 18156.177717: kmalloc: call_site=ffffffff81619b36 ptr=ffff88006d555800 bytes_req=512 bytes_alloc=512 gfp_flags=GFP_ATOMIC
              <idle>-0     [000] ..s3 18156.399229: kmalloc: call_site=ffffffff81619b36 ptr=ffff88006d555800 bytes_req=512 bytes_alloc=512 gfp_flags=GFP_ATOMIC
            dropbear-1465  [000] ...1 18156.399434: kmalloc: call_site=ffffffff816650d4 ptr=ffff8800729c3000 bytes_http://rostedt.homelinux.com/kernelshark/req=2048 bytes_alloc=2048 gfp_flags=GFP_KERNEL
              <idle>-0     [000] ..s3 18156.400660: kmalloc: call_site=ffffffff81619b36 ptr=ffff88006d554800 bytes_req=512 bytes_alloc=512 gfp_flags=GFP_ATOMIC
     matchbox-termin-1361  [001] ...1 18156.552800: kmalloc: call_site=ffffffff81614050 ptr=ffff88006db34800 bytes_req=576 bytes_alloc=1024 gfp_flags=GFP_KERNEL|GFP_REPEAT
            

To again disable the kmalloc event, we need to send 0 to the enable file:

     root@sugarbay:/sys/kernel/debug/tracing/events/kmem/kmalloc# echo 0 > enable
            

You can enable any number of events or complete subsystems (by using the 'enable' file in the subsystem directory) and get am arbitrarily fine-grained idea of what's going on in the system by enabling as many of the appropriate tracepoints as applicable.

A number of the tools described in this HOWTO do just that, including trace-cmd and kernelshark in the next section.

Tying it Together: These tracepoints and their representation are used not only by ftrace, but by many of the other tools covered in this document and they form a central point of integration for the various tracers available in Linux. They form a central part of the instrumentation for the following tools: perf, lttng, ftrace, blktrace and SystemTap
Tying it Together: Eventually all the special-purpose tracers currently available in /sys/kernel/debug/tracing will be removed and replaced with equivalent tracers based on the 'trace events' subsystem.

3.2.4. trace-cmd/kernelshark

trace-cmd is essentially an extensive command-line 'wrapper' interface that hides the details of all the individual files in /sys/kernel/debug/tracing, allowing users to specify specific particular events within the /sys/kernel/debug/tracing/events/ subdirectory and to collect traces and avoiding having to deal with those details directly.

As yet another layer on top of that, kernelshark provides a GUI that allows users to start and stop traces and specify sets of events using an intuitive interface, and view the output as both trace events and as a per-cpu graphical display. It directly uses 'trace-cmd' as the plumbing that accomplishes all that underneath the covers (and actually displays the trace-cmd command it uses, as we'll see).

To start a trace using kernelshark, first start kernelshark:

     root@sugarbay:~# kernelshark
            

The bring up the 'Capture' dialog by choosing from the kernelshark menu:

     Capture | Record
            

That will display the following dialog, which allows you to choose on or more events (or even one or more complete subsystems) to trace:

Note that these are exactly the same set of events described in the previous trace events subsystem section, and in fact is where trace-cmd gets them for kernelshark.

In the above screenshot, we've decided to explore the graphics subsystem a bit and so have chosen to trace all the tracepoints contained within the 'i915' and 'drm' subsystems.

After doing that, we can start and stop the trace using the 'Run' and 'Stop' button on the lower right corner of the dialog (the same button will turn into the 'Stop' button after the trace has started):

Notice that the right-hand pane shows the exact trace-cmd command-line that's used to run the trace, along with the results of the trace-cmd run.

Once the 'Stop' button is pressed, the graphical view magically fills up with a colorful per-cpu display of the trace data, along with the detailed event listing below that:

Here's another example, this time a display resulting from tracing 'all events':

The tool is pretty self-explanatory, but for more detailed information on navigating through the data, see the kernelshark website.

3.2.5. Documentation

The documentation for ftrace can be found in the kernel Documentation directory:

     Documentation/trace/ftrace.txt
            

The documentation for the trace event subsystem can also be found in the kernel Documentation directory:

     Documentation/trace/events.txt
            

There are a nice series of articles on using ftrace and trace-cmd at LWN:

There's more detailed documentation kernelshark usage here: KernelShark

An amusing yet useful README (a tracing mini-HOWTO) can be found in /sys/kernel/debug/tracing/README.

3.3. systemtap

SystemTap is a system-wide script-based tracing and profiling tool.

SystemTap scripts are C-like programs that are executed in the kernel to gather/print/aggregate data extracted from the context they end up being invoked under.

For example, this probe from the SystemTap tutorial simply prints a line every time any process on the system open()s a file. For each line, it prints the executable name of the program that opened the file, along with its pid, and the name of the file it opened (or tried to open), which it extracts from the open syscall's argstr.

     probe syscall.open
     {
             printf ("%s(%d) open (%s)\n", execname(), pid(), argstr)
     }

     probe timer.ms(4000) # after 4 seconds
     {
             exit ()
     }
        

Normally, to execute this probe, you'd simply install systemtap on the system you want to probe, and directly run the probe on that system e.g. assuming the name of the file containing the above text is trace_open.stp:

     # stap trace_open.stp
        

What systemtap does under the covers to run this probe is 1) parse and convert the probe to an equivalent 'C' form, 2) compile the 'C' form into a kernel module, 3) insert the module into the kernel, which arms it, and 4) collect the data generated by the probe and display it to the user.

In order to accomplish steps 1 and 2, the 'stap' program needs access to the kernel build system that produced the kernel that the probed system is running. In the case of a typical embedded system (the 'target'), the kernel build system unfortunately isn't typically part of the image running on the target. It is normally available on the 'host' system that produced the target image however; in such cases, steps 1 and 2 are executed on the host system, and steps 3 and 4 are executed on the target system, using only the systemtap 'runtime'.

The systemtap support in Yocto assumes that only steps 3 and 4 are run on the target; it is possible to do everything on the target, but this section assumes only the typical embedded use-case.

So basically what you need to do in order to run a systemtap script on the target is to 1) on the host system, compile the probe into a kernel module that makes sense to the target, 2) copy the module onto the target system and 3) insert the module into the target kernel, which arms it, and 4) collect the data generated by the probe and display it to the user.

3.3.1. Setup

Those are a lot of steps and a lot of details, but fortunately Yocto includes a script called 'crosstap' that will take care of those details, allowing you to simply execute a systemtap script on the remote target, with arguments if necessary.

In order to do this from a remote host, however, you need to have access to the build for the image you booted. The 'crosstap' script provides details on how to do this if you run the script on the host without having done a build:

     $ crosstap root@192.168.1.88 trace_open.stp

     Error: No target kernel build found.
     Did you forget to create a local build of your image?

     'crosstap' requires a local sdk build of the target system
     (or a build that includes 'tools-profile') in order to build
     kernel modules that can probe the target system.

     Practically speaking, that means you need to do the following:
      - If you're running a pre-built image, download the release
        and/or BSP tarballs used to build the image.
      - If you're working from git sources, just clone the metadata
        and BSP layers needed to build the image you'll be booting.
      - Make sure you're properly set up to build a new image (see
        the BSP README and/or the widely available basic documentation
        that discusses how to build images).
      - Build an -sdk version of the image e.g.:
          $ bitbake core-image-sato-sdk
      OR
      - Build a non-sdk image but include the profiling tools:
          [ edit local.conf and add 'tools-profile' to the end of
            the EXTRA_IMAGE_FEATURES variable ]
          $ bitbake core-image-sato

      [ NOTE that 'crosstap' needs to be able to ssh into the target
        system, which isn't enabled by default in -minimal images. ]

     Once you've build the image on the host system, you're ready to
     boot it (or the equivalent pre-built image) and use 'crosstap'
     to probe it (you need to source the environment as usual first):

        $ source oe-init-build-env
        $ cd ~/my/systemtap/scripts
        $ crosstap root@192.168.1.xxx myscript.stp
            

So essentially what you need to do is build an SDK image or image with 'tools-profile' as detailed in the "General Setup" section of this manual, and boot the resulting target image.

Note

If you have a build directory containing multiple machines, you need to have the MACHINE you're connecting to selected in local.conf, and the kernel in that machine's build directory must match the kernel on the booted system exactly, or you'll get the above 'crosstap' message when you try to invoke a script.

3.3.2. Running a Script on a Target

Once you've done that, you should be able to run a systemtap script on the target:

     $ cd /path/to/yocto
     $ source oe-init-build-env

     ### Shell environment set up for builds. ###

     You can now run 'bitbake <target>'

     Common targets are:
        core-image-minimal
        core-image-sato
        meta-toolchain
        meta-toolchain-sdk
        adt-installer
        meta-ide-support

     You can also run generated qemu images with a command like 'runqemu qemux86'
            

Once you've done that, you can cd to whatever directory contains your scripts and use 'crosstap' to run the script:

     $ cd /path/to/my/systemap/script
     $ crosstap root@192.168.7.2 trace_open.stp
            

If you get an error connecting to the target e.g.:

     $ crosstap root@192.168.7.2 trace_open.stp
     error establishing ssh connection on remote 'root@192.168.7.2'
            

Try ssh'ing to the target and see what happens:

     $ ssh root@192.168.7.2
            

A lot of the time, connection problems are due specifying a wrong IP address or having a 'host key verification error'.

If everything worked as planned, you should see something like this (enter the password when prompted, or press enter if its set up to use no password):

     $ crosstap root@192.168.7.2 trace_open.stp
     root@192.168.7.2's password:
     matchbox-termin(1036) open ("/tmp/vte3FS2LW", O_RDWR|O_CREAT|O_EXCL|O_LARGEFILE, 0600)
     matchbox-termin(1036) open ("/tmp/vteJMC7LW", O_RDWR|O_CREAT|O_EXCL|O_LARGEFILE, 0600)
            

3.3.3. Documentation

The SystemTap language reference can be found here: SystemTap Language Reference

Links to other SystemTap documents, tutorials, and examples can be found here: SystemTap documentation page

3.4. oprofile

oprofile itself is a command-line application that runs on the target system.

3.4.1. Setup

For this section, we'll assume you've already performed the basic setup outlined in the "General Setup" section.

For the the section that deals with oprofile from the command-line, we assume you've ssh'ed to the host and will be running oprofile on the target.

oprofileui (oprofile-viewer) is a GUI-based program that runs on the host and interacts remotely with the target. See the oprofileui section for the exact steps needed to install oprofileui on the host.

3.4.2. Basic Usage

Oprofile as configured in Yocto is a system-wide profiler (i.e. the version in Yocto doesn't yet make use of the perf_events interface which would allow it to profile specific processes and workloads). It's relies on hardware counter support in the hardware (but can fall back to a timer-based mode), which means that it doesn't take advantage of tracepoints or other event sources for example.

It consists of a kernel module that collects samples and a userspace daemon that writes the sample data to disk.

The 'opcontrol' shell script is used for transparently managing these components and starting and stopping profiles, and the 'opreport' command is used to display the results.

The oprofile daemon should already be running, but before you start profiling, you may need to change some settings and some of these settings may require the daemon not be running. One of these settings is the path the the vmlinux file, which you'll want to set using the --vmlinux option if you want the kernel profiled:

     root@crownbay:~# opcontrol --vmlinux=/boot/vmlinux-`uname -r`
     The profiling daemon is currently active, so changes to the configuration
     will be used the next time you restart oprofile after a --shutdown or --deinit.
            

You can check if vmlinux file: is set using opcontrol --status:

     root@crownbay:~# opcontrol --status
     Daemon paused: pid 1334
     Separate options: library
     vmlinux file: none
     Image filter: none
     Call-graph depth: 6
            

If it's not, you need to shutdown the daemon, add the setting and restart the daemon:

     root@crownbay:~# opcontrol --shutdown
     Killing daemon.

     root@crownbay:~# opcontrol --vmlinux=/boot/vmlinux-`uname -r`
     root@crownbay:~# opcontrol --start-daemon
     Using default event: CPU_CLK_UNHALTED:100000:0:1:1
     Using 2.6+ OProfile kernel interface.
     Reading module info.
     Using log file /var/lib/oprofile/samples/oprofiled.log
     Daemon started.
            

If we get the status again we now see our updated settings:

     root@crownbay:~# opcontrol --status
     Daemon paused: pid 1649
     Separate options: library
     vmlinux file: /boot/vmlinux-3.4.11-yocto-standard
     Image filter: none
     Call-graph depth: 6
            

We're now in a position to run a profile. For that we used 'opcontrol --start':

     root@crownbay:~# opcontrol --start
     Profiler running.
            

In another window, run our wget workload:

     root@crownbay:~# rm linux-2.6.19.2.tar.bz2; wget http://downloads.yoctoproject.org/mirror/sources/linux-2.6.19.2.tar.bz2; sync
     Connecting to downloads.yoctoproject.org (140.211.169.59:80)
     linux-2.6.19.2.tar.b 100% |*******************************| 41727k  0:00:00 ETA
            

To stop the profile we use 'opcontrol --shudown', which not only stops the profile but shuts down the daemon as well:

     root@crownbay:~# opcontrol --start
     Stopping profiling.
     Killing daemon.
            

Oprofile writes sample data to /var/lib/oprofile/samples, which you can look at if you're interested in seeing how the samples are structured. This is also interesting because it's related to how you dive down to get further details about specific executables in OProfile.

To see the default display output for a profile, simply type 'opreport', which will show the results using the data in /var/lib/oprofile/samples:

     root@crownbay:~# opreport

     WARNING! The OProfile kernel driver reports sample buffer overflows.
     Such overflows can result in incorrect sample attribution, invalid sample
     files and other symptoms.  See the oprofiled.log for details.
     You should adjust your sampling frequency to eliminate (or at least minimize)
     these overflows.
     CPU: Intel Architectural Perfmon, speed 1.3e+06 MHz (estimated)
     Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (No unit mask) count 100000
     CPU_CLK_UNHALT...|
      samples|      %|
     ------------------
       464365 79.8156 vmlinux-3.4.11-yocto-standard
        65108 11.1908 oprofiled
	     CPU_CLK_UNHALT...|
	       samples|      %|
 	     ------------------
 	         64416 98.9372 oprofiled
 	           692  1.0628 libc-2.16.so
        36959  6.3526 no-vmlinux
         4378  0.7525 busybox
	     CPU_CLK_UNHALT...|
	       samples|      %|
	     ------------------
	          2844 64.9612 libc-2.16.so
	          1337 30.5391 busybox
	           193  4.4084 ld-2.16.so
	             2  0.0457 libnss_compat-2.16.so
	             1  0.0228 libnsl-2.16.so
	             1  0.0228 libnss_files-2.16.so
         4344  0.7467 bash
	     CPU_CLK_UNHALT...|
	       samples|      %|
	     ------------------
	          2657 61.1648 bash
	          1665 38.3287 libc-2.16.so
	            18  0.4144 ld-2.16.so
	             3  0.0691 libtinfo.so.5.9
	             1  0.0230 libdl-2.16.so
         3118  0.5359 nf_conntrack
          686  0.1179 matchbox-terminal
	     CPU_CLK_UNHALT...|
	       samples|      %|
	     ------------------
	           214 31.1953 libglib-2.0.so.0.3200.4
	           114 16.6181 libc-2.16.so
	            79 11.5160 libcairo.so.2.11200.2
	            78 11.3703 libgdk-x11-2.0.so.0.2400.8
	            51  7.4344 libpthread-2.16.so
	            45  6.5598 libgobject-2.0.so.0.3200.4
	            29  4.2274 libvte.so.9.2800.2
	            25  3.6443 libX11.so.6.3.0
	            19  2.7697 libxcb.so.1.1.0
	            17  2.4781 libgtk-x11-2.0.so.0.2400.8
	            12  1.7493 librt-2.16.so
	             3  0.4373 libXrender.so.1.3.0
          671  0.1153 emgd
          411  0.0706 nf_conntrack_ipv4
          391  0.0672 iptable_nat
          378  0.0650 nf_nat
          263  0.0452 Xorg
	     CPU_CLK_UNHALT...|
	       samples|      %|
	     ------------------
	           106 40.3042 Xorg
	            53 20.1521 libc-2.16.so
	            31 11.7871 libpixman-1.so.0.27.2
	            26  9.8859 emgd_drv.so
	            16  6.0837 libemgdsrv_um.so.1.5.15.3226
	            11  4.1825 libEMGD2d.so.1.5.15.3226
	             9  3.4221 libfb.so
	             7  2.6616 libpthread-2.16.so
	             1  0.3802 libudev.so.0.9.3
	             1  0.3802 libdrm.so.2.4.0
	             1  0.3802 libextmod.so
	             1  0.3802 mouse_drv.so
     .
     .
     .
           9  0.0015 connmand
	     CPU_CLK_UNHALT...|
	       samples|      %|
	     ------------------
	             4 44.4444 libglib-2.0.so.0.3200.4
	             2 22.2222 libpthread-2.16.so
	             1 11.1111 connmand
	             1 11.1111 libc-2.16.so
	             1 11.1111 librt-2.16.so
            6  0.0010 oprofile-server
     	 CPU_CLK_UNHALT...|
	       samples|      %|
	     ------------------
	             3 50.0000 libc-2.16.so
	             1 16.6667 oprofile-server
	             1 16.6667 libpthread-2.16.so
	             1 16.6667 libglib-2.0.so.0.3200.4
           5 8.6e-04 gconfd-2
	     CPU_CLK_UNHALT...|
	       samples|      %|
	     ------------------
	             2 40.0000 libdbus-1.so.3.7.2
	             2 40.0000 libglib-2.0.so.0.3200.4
	             1 20.0000 libc-2.16.so
            

The output above shows the breakdown or samples by both number of samples and percentage for each executable. Within an executable, the sample counts are broken down further into executable and shared libraries (DSOs) used by the executable.

To get even more detailed breakdowns by function, we need to have the full paths to the DSOs, which we can get by using -f with opreport:

     root@crownbay:~# opreport -f

     CPU: Intel Architectural Perfmon, speed 1.3e+06 MHz (estimated)
     Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (No unit mask) count 100000
     CPU_CLK_UNHALT...|
      samples|      %|

       464365 79.8156 /boot/vmlinux-3.4.11-yocto-standard
       65108 11.1908 /usr/bin/oprofiled
	     CPU_CLK_UNHALT...|
	       samples|      %|
	     ------------------
	         64416 98.9372 /usr/bin/oprofiled
	           692  1.0628 /lib/libc-2.16.so
        36959  6.3526 /no-vmlinux
         4378  0.7525 /bin/busybox
	     CPU_CLK_UNHALT...|
	       samples|      %|
	     ------------------
	          2844 64.9612 /lib/libc-2.16.so
	          1337 30.5391 /bin/busybox
	           193  4.4084 /lib/ld-2.16.so
	             2  0.0457 /lib/libnss_compat-2.16.so
	             1  0.0228 /lib/libnsl-2.16.so
	             1  0.0228 /lib/libnss_files-2.16.so
         4344  0.7467 /bin/bash
	     CPU_CLK_UNHALT...|
	       samples|      %|
	     ------------------
	          2657 61.1648 /bin/bash
	          1665 38.3287 /lib/libc-2.16.so
	            18  0.4144 /lib/ld-2.16.so
	             3  0.0691 /lib/libtinfo.so.5.9
	             1  0.0230 /lib/libdl-2.16.so
     .
     .
     .
            

Using the paths shown in the above output and the -l option to opreport, we can see all the functions that have hits in the profile and their sample counts and percentages. Here's a portion of what we get for the kernel:

     root@crownbay:~# opreport -l /boot/vmlinux-3.4.11-yocto-standard

     CPU: Intel Architectural Perfmon, speed 1.3e+06 MHz (estimated)
     Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (No unit mask) count 100000
     samples  %        symbol name
     233981   50.3873  intel_idle
     15437     3.3243  rb_get_reader_page
     14503     3.1232  ring_buffer_consume
     14092     3.0347  mutex_spin_on_owner
     13024     2.8047  read_hpet
     8039      1.7312  sub_preempt_count
     7096      1.5281  ioread32
     6997      1.5068  add_preempt_count
     3985      0.8582  rb_advance_reader
     3488      0.7511  add_event_entry
     3303      0.7113  get_parent_ip
     3104      0.6684  rb_buffer_peek
     2960      0.6374  op_cpu_buffer_read_entry
     2614      0.5629  sync_buffer
     2545      0.5481  debug_smp_processor_id
     2456      0.5289  ohci_irq
     2397      0.5162  memset
     2349      0.5059  __copy_to_user_ll
     2185      0.4705  ring_buffer_event_length
     1918      0.4130  in_lock_functions
     1850      0.3984  __schedule
     1767      0.3805  __copy_from_user_ll_nozero
     1575      0.3392  rb_event_data_length
     1256      0.2705  memcpy
     1233      0.2655  system_call
     1213      0.2612  menu_select
            

Notice that above we see an entry for the __copy_to_user_ll() function that we've looked at with other profilers as well.

Here's what we get when we do the same thing for the busybox executable:

     CPU: Intel Architectural Perfmon, speed 1.3e+06 MHz (estimated)
     Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (No unit mask) count 100000
     samples  %        image name               symbol name
     349       8.4198  busybox                  retrieve_file_data
     308       7.4306  libc-2.16.so             _IO_file_xsgetn
     283       6.8275  libc-2.16.so             __read_nocancel
     235       5.6695  libc-2.16.so             syscall
     233       5.6212  libc-2.16.so             clearerr
     215       5.1870  libc-2.16.so             fread
     181       4.3667  libc-2.16.so             __write_nocancel
     158       3.8118  libc-2.16.so             __underflow
     151       3.6429  libc-2.16.so             _dl_addr
     150       3.6188  busybox                  progress_meter
     150       3.6188  libc-2.16.so             __poll_nocancel
     148       3.5706  libc-2.16.so             _IO_file_underflow@@GLIBC_2.1
     137       3.3052  busybox                  safe_poll
     125       3.0157  busybox                  bb_progress_update
     122       2.9433  libc-2.16.so             __x86.get_pc_thunk.bx
     95        2.2919  busybox                  full_write
     81        1.9542  busybox                  safe_write
     77        1.8577  busybox                  xwrite
     72        1.7370  libc-2.16.so             _IO_file_read
     71        1.7129  libc-2.16.so             _IO_sgetn
     67        1.6164  libc-2.16.so             poll
     52        1.2545  libc-2.16.so             _IO_switch_to_get_mode
     45        1.0856  libc-2.16.so             read
     34        0.8203  libc-2.16.so             write
     32        0.7720  busybox                  monotonic_sec
     25        0.6031  libc-2.16.so             vfprintf
     22        0.5308  busybox                  get_mono
     14        0.3378  ld-2.16.so               strcmp
     14        0.3378  libc-2.16.so             __x86.get_pc_thunk.cx
     .
     .
     .
            

Since we recorded the profile with a callchain depth of 6, we should be able to see our __copy_to_user_ll() callchains in the output, and indeed we can if we search around a bit in the 'opreport --callgraph' output:

     root@crownbay:~# opreport --callgraph /boot/vmlinux-3.4.11-yocto-standard

       392       6.9639  vmlinux-3.4.11-yocto-standard sock_aio_read
       736      13.0751  vmlinux-3.4.11-yocto-standard __generic_file_aio_write
       3255     57.8255  vmlinux-3.4.11-yocto-standard inet_recvmsg
     785       0.1690  vmlinux-3.4.11-yocto-standard tcp_recvmsg
       1790     31.7940  vmlinux-3.4.11-yocto-standard local_bh_enable
       1238     21.9893  vmlinux-3.4.11-yocto-standard __kfree_skb
       992      17.6199  vmlinux-3.4.11-yocto-standard lock_sock_nested
       785      13.9432  vmlinux-3.4.11-yocto-standard tcp_recvmsg [self]
       525       9.3250  vmlinux-3.4.11-yocto-standard release_sock
       112       1.9893  vmlinux-3.4.11-yocto-standard tcp_cleanup_rbuf
       72        1.2789  vmlinux-3.4.11-yocto-standard skb_copy_datagram_iovec

     170       0.0366  vmlinux-3.4.11-yocto-standard skb_copy_datagram_iovec
       1491     73.3038  vmlinux-3.4.11-yocto-standard memcpy_toiovec
       327      16.0767  vmlinux-3.4.11-yocto-standard skb_copy_datagram_iovec
       170       8.3579  vmlinux-3.4.11-yocto-standard skb_copy_datagram_iovec [self]
       20        0.9833  vmlinux-3.4.11-yocto-standard copy_to_user

       2588     98.2909  vmlinux-3.4.11-yocto-standard copy_to_user
     2349      0.5059  vmlinux-3.4.11-yocto-standard __copy_to_user_ll
       2349     89.2138  vmlinux-3.4.11-yocto-standard __copy_to_user_ll [self]
       166       6.3046  vmlinux-3.4.11-yocto-standard do_page_fault
            

Remember that by default OProfile sessions are cumulative i.e. if you start and stop a profiling session, then start a new one, the new one will not erase the previous run(s) but will build on it. If you want to restart a profile from scratch, you need to reset:

     root@crownbay:~# opcontrol --reset