Copyright © 2010-2019 Linux Foundation
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.
This version of the Yocto Project Mega-Manual is for the 2.5.3 release of the Yocto Project. To be sure you have the latest version of the manual for this release, go to the Yocto Project documentation page and select the manual from that site. Manuals from the site are more up-to-date than manuals derived from the Yocto Project released TAR files.
If you located this manual through a web search, the version of the manual might not be the one you want (e.g. the search might have returned a manual much older than the Yocto Project version with which you are working). You can see all Yocto Project major releases by visiting the Releases page. If you need a version of this manual for a different Yocto Project release, visit the Yocto Project documentation page and select the manual set by using the "ACTIVE RELEASES DOCUMENTATION" or "DOCUMENTS ARCHIVE" pull-down menus.
To report any inaccuracies or problems with this
manual, send an email to the Yocto Project
discussion group at
yocto@yoctoproject.com
or log into
the freenode #yocto
channel.
Revision History | |
---|---|
Revision 1.8 | April 2015 |
Released with the Yocto Project 1.8 Release. | |
Revision 2.0 | October 2015 |
Released with the Yocto Project 2.0 Release. | |
Revision 2.1 | April 2016 |
Released with the Yocto Project 2.1 Release. | |
Revision 2.2 | October 2016 |
Released with the Yocto Project 2.2 Release. | |
Revision 2.3 | May 2017 |
Released with the Yocto Project 2.3 Release. | |
Revision 2.4 | October 2017 |
Released with the Yocto Project 2.4 Release. | |
Revision 2.5 | May 2018 |
Released with the Yocto Project 2.5 Release. | |
Revision 2.5.1 | September 2018 |
The initial document released with the Yocto Project 2.5.1 Release. | |
Revision 2.5.2 | January 2019 |
The initial document released with the Yocto Project 2.5.2 Release. | |
Revision 2.5.3 | March 2019 |
The initial document released with the Yocto Project 2.5.3 Release. |
Abstract¶
The Yocto Project Mega-Manual is a concatenation of the published Yocto Project HTML manuals for the given release. The manual exists to help users efficiently search for strings across the entire Yocto Project documentation set.
Copyright © 2010-2019 Linux Foundation
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.
Abstract¶
Welcome! This short document steps you through the process for a typical image build using the Yocto Project. The document also introduces how to configure a build for specific hardware. You will use Yocto Project to build a reference embedded OS called Poky.
If you want more conceptual or background information on the Yocto Project, see the Yocto Project Overview and Concepts Manual.
Make sure your build host meets the following requirements:
50 Gbytes of free disk space
Runs a supported Linux distribution (i.e. recent releases of Fedora, openSUSE, CentOS, Debian, or Ubuntu). For a list of Linux distributions that support the Yocto Project, see the "Supported Linux Distributions" section in the Yocto Project Reference Manual.
Git 1.8.3.1 or greater
tar 1.27 or greater
Python 3.4.0 or greater.
If your build host does not meet any of these three listed version requirements, you can take steps to prepare the system so that you can still use the Yocto Project. See the "Required Git, tar, and Python Versions" section in the Yocto Project Reference Manual for information.
You must install essential host packages on your build host. The following command installs the host packages based on an Ubuntu distribution:
$ sudo apt-get install gawk wget git-core diffstat unzip texinfo gcc-multilib \ build-essential chrpath socat cpio python python3 python3-pip python3-pexpect \ xz-utils debianutils iputils-ping libsdl1.2-dev xterm
Once you complete the setup instructions for your machine, you need to get a copy of the Poky repository on your build host. Use the following commands to clone the Poky repository and then checkout the yocto-2.5.3 release:
$ git clone git://git.yoctoproject.org/poky Cloning into 'poky'... remote: Counting objects: 431956, done. remote: Compressing objects: 100% (101918/101918), done. remote: Total 431956 (delta 322982), reused 431910 (delta 322936) Receiving objects: 100% (431956/431956), 153.76 MiB | 6.86 MiB/s, done. Resolving deltas: 100% (322982/322982), done. Checking connectivity... done.
Move to the poky directory and take a look at the tags:
$ cd poky $ git fetch --tags $ git tag 1.1_M1.final 1.1_M1.rc1 1.1_M1.rc2 1.1_M2.final 1.1_M2.rc1 . . . yocto-2.5.2 yocto-2.5.3 yocto-2.6 yocto-2.6.1 yocto_1.5_M5.rc8
For this example, check out the branch based on the yocto-2.5.3 release:
$ git checkout tags/yocto-2.5.3 -b my-yocto-2.5.3 Switched to a new branch 'my-yocto-2.5.3'
The previous Git checkout command creates a local branch named my-yocto-2.5.3. The files available to you in that branch exactly match the repository's files in the "sumo" development branch at the time of the Yocto Project yocto-2.5.3 release.
For more options and information about accessing Yocto Project related repositories, see the "Locating Yocto Project Source Files" section in the Yocto Project Development Tasks Manual.
Use the following steps to build your image. The build process creates an entire Linux distribution, including the toolchain, from source.
If you are working behind a firewall and your build host is not set up for proxies, you could encounter problems with the build process when fetching source code (e.g. fetcher failures or Git failures).
If you do not know your proxy settings, consult your local network infrastructure resources and get that information. A good starting point could also be to check your web browser settings. Finally, you can find more information on the "Working Behind a Network Proxy" page of the Yocto Project Wiki.
Initialize the Build Environment:
Run the
oe-init-build-env
environment setup script to define Yocto Project's
build environment on your build host.
$ source oe-init-build-env
Among other things, the script 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.
Examine Your Local Configuration File:
When you set up the build environment, a local
configuration file named
local.conf
becomes available in
a conf
subdirectory of the
Build Directory.
For this example, the defaults are set to build
for a qemux86
target, which is
suitable for emulation.
The package manager used is set to the RPM package
manager.
local.conf
file in the Build
directory:
SSTATE_MIRRORS = "\ file://.* http://sstate.yoctoproject.org/dev/PATH;downloadfilename=PATH \n \ file://.* http://sstate.yoctoproject.org/2.4.4/PATH;downloadfilename=PATH \n \ file://.* http://sstate.yoctoproject.org/2.5.3/PATH;downloadfilename=PATH \n \ "The previous examples showed how to add sstate paths for Yocto Project 2.4.4, 2.5.3, and a development area. For a complete index of sstate locations, see http://sstate.yoctoproject.org/.
Start the Build:
Continue with the following command to build an OS image
for the target, which is
core-image-sato
in this example:
$ bitbake core-image-sato
For information on using the
bitbake
command, see the
"BitBake"
section in the Yocto Project Overview and Concepts Manual,
or see the
"BitBake Command"
section in the BitBake User Manual.
Simulate Your Image Using QEMU: Once this particular image is built, you can start QEMU, which is a Quick EMUlator that ships with the Yocto Project:
$ runqemu qemux86
If you want to learn more about running QEMU, see the "Using the Quick EMUlator (QEMU)" chapter in the Yocto Project Development Tasks Manual.
Exit QEMU:
Exit QEMU by either clicking on the shutdown icon or by
typing Ctrl-C
in the QEMU
transcript window from which you evoked QEMU.
So far, all you have done is quickly built an image suitable for emulation only. This section shows you how to customize your build for specific hardware by adding a hardware layer into the Yocto Project development environment.
In general, layers are repositories that contain related sets of instructions and configurations that tell the Yocto Project what to do. Isolating related metadata into functionally specific layers facilitates modular development and makes it easier to reuse the layer metadata.
Follow these steps to add a hardware layer:
Find a Layer: Lots of hardware layers exist. The Yocto Project Source Repositories has many hardware layers. This example adds the meta-altera hardware layer.
Clone the Layer Use Git to make a local copy of the layer on your machine. You can put the copy in the top level of the copy of the Poky repository created earlier:
$ cd ~/poky $ git clone https://github.com/kraj/meta-altera.git Cloning into 'meta-altera'... remote: Counting objects: 25170, done. remote: Compressing objects: 100% (350/350), done. remote: Total 25170 (delta 645), reused 719 (delta 538), pack-reused 24219 Receiving objects: 100% (25170/25170), 41.02 MiB | 1.64 MiB/s, done. Resolving deltas: 100% (13385/13385), done. Checking connectivity... done.
The hardware layer now exists with other layers inside
the Poky reference repository on your build host as
meta-altera
and contains all the
metadata needed to support hardware from Altera, which
is owned by Intel.
Change the Configuration to Build for a Specific Machine:
The
MACHINE
variable in the local.conf
file
specifies the machine for the build.
For this example, set the MACHINE
variable to "cyclone5".
These configurations are used:
https://github.com/kraj/meta-altera/blob/master/conf/machine/cyclone5.conf.
Add Your Layer to the Layer Configuration File:
Before you can use a layer during a build, you must add it
to your bblayers.conf
file, which
is found in the
Build Directory's
conf
directory.
Use the bitbake-layers add-layer
command to add the layer to the configuration file:
$ cd ~/poky/build $ bitbake-layers add-layer ../meta-altera NOTE: Starting bitbake server... Parsing recipes: 100% |##################################################################| Time: 0:00:32 Parsing of 918 .bb files complete (0 cached, 918 parsed). 1401 targets, 123 skipped, 0 masked, 0 errors.
You can find more information on adding layers in the
"Adding a Layer Using the bitbake-layers
Script"
section.
Completing these steps has added the
meta-altera
layer to your Yocto Project
development environment and configured it to build for the
"cyclone5" machine.
README
.
Maybe you have an application or specific set of behaviors you
need to isolate.
You can create your own general layer using the
bitbake-layers create-layer
command.
The tool automates layer creation by setting up a
subdirectory with a layer.conf
configuration file, a recipes-example
subdirectory that contains an example.bb
recipe, a licensing file, and a README
.
The following commands run the tool to create a layer named
meta-mylayer
in the
poky
directory:
$ cd ~/poky $ bitbake-layers create-layer meta-mylayer NOTE: Starting bitbake server... Add your new layer with 'bitbake-layers add-layer meta-mylayer'
For more information on layers and how to create them, see the
"Creating a General Layer Using the bitbake-layers
Script"
section in the Yocto Project Development Tasks Manual.
Now that you have experienced using the Yocto Project, you might be asking yourself "What now?" The Yocto Project has many sources of information including the website, wiki pages, and user manuals:
Website: The Yocto Project Website provides background information, the latest builds, breaking news, full development documentation, and access to a rich Yocto Project Development Community into which you can tap.
Developer Screencast: The Getting Started with the Yocto Project - New Developer Screencast Tutorial provides a 30-minute video created for users unfamiliar with the Yocto Project but familiar with Linux build hosts. While this screencast is somewhat dated, the introductory and fundamental concepts are useful for the beginner.
Yocto Project Overview and Concepts Manual: The Yocto Project Overview and Concepts Manual is a great place to start to learn about the Yocto Project. This manual introduces you to the Yocto Project and its development environment. The manual also provides conceptual information for various aspects of the Yocto Project.
Yocto Project Wiki: The Yocto Project Wiki provides additional information on where to go next when ramping up with the Yocto Project, release information, project planning, and QA information.
Yocto Project Mailing Lists: Related mailing lists provide a forum for discussion, patch submission and announcements. Several mailing lists exist and are grouped according to areas of concern. See the "Mailing lists" section in the Yocto Project Reference Manual for a complete list of Yocto Project mailing lists.
Comprehensive List of Links and Other Documentation: The "Links and Related Documentation" section in the Yocto Project Reference Manual provides a comprehensive list of all related links and other user documentation.
Welcome to the Yocto Project Overview and Concepts Manual! This manual introduces the Yocto Project by providing concepts, software overviews, best-known-methods (BKMs), and any other high-level introductory information suitable for a new Yocto Project user.
The following list describes what you can get from this manual:
Introducing the Yocto Project: This chapter provides an introduction to the Yocto Project. You will learn about features and challenges of the Yocto Project, the layer model, components and tools, development methods, the Poky reference distribution, the OpenEmbedded build system workflow, and some basic Yocto terms.
The Yocto Project Development Environment: This chapter helps you get started understanding the Yocto Project development environment. You will learn about open source, development hosts, Yocto Project source repositories, workflows using Git and the Yocto Project, a Git primer, and information about licensing.
Yocto Project Concepts: This chapter presents various concepts regarding the Yocto Project. You can find conceptual information about components, development, cross-toolchains, and so forth.
This manual does not give you the following:
Step-by-step Instructions for Development Tasks: Instructional procedures reside in other manuals within the Yocto Project documentation set. For example, the Yocto Project Development Tasks Manual provides examples on how to perform various development tasks. As another example, the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual contains detailed instructions on how to install an SDK, which is used to develop applications for target hardware.
Reference Material: This type of material resides in an appropriate reference manual. For example, system variables are documented in the Yocto Project Reference Manual. As another example, the Yocto Project Board Support Package (BSP) Developer's Guide contains reference information on BSPs.
Detailed Public Information Not Specific to the Yocto Project: For example, exhaustive information on how to use the Source Control Manager Git is better covered with Internet searches and official Git Documentation than through the Yocto Project documentation.
Because this manual presents information for many different topics, supplemental information is recommended for full comprehension. For additional introductory information on the Yocto Project, see the Yocto Project Website. If you want to build an image with no knowledge of Yocto Project as a way of quickly testing it out, see the Yocto Project Quick Build document. For a comprehensive list of links and other documentation, see the "Links and Related Documentation" section in the Yocto Project Reference Manual.
The Yocto Project is an open source collaboration project that helps developers create custom Linux-based systems that are designed for embedded products regardless of the product's hardware architecture. Yocto Project provides a flexible toolset and a development environment that allows embedded device developers across the world to collaborate through shared technologies, software stacks, configurations, and best practices used to create these tailored Linux images.
Thousands of developers worldwide have discovered that Yocto Project provides advantages in both systems and applications development, archival and management benefits, and customizations used for speed, footprint, and memory utilization. The project is a standard when it comes to delivering embedded software stacks. The project allows software customizations and build interchange for multiple hardware platforms as well as software stacks that can be maintained and scaled.
For further introductory information on the Yocto Project, you might be interested in this article by Drew Moseley and in this short introductory video.
The remainder of this section overviews advantages and challenges tied to the Yocto Project.
The following list describes features and advantages of the Yocto Project:
Widely Adopted Across the Industry: Semiconductor, operating system, software, and service vendors exist whose products and services adopt and support the Yocto Project. For a look at the Yocto Project community and the companies involved with the Yocto Project, see the "COMMUNITY" and "ECOSYSTEM" tabs on the Yocto Project home page.
Architecture Agnostic: Yocto Project supports Intel, ARM, MIPS, AMD, PPC and other architectures. Most ODMs, OSVs, and chip vendors create and supply BSPs that support their hardware. If you have custom silicon, you can create a BSP that supports that architecture.
Aside from lots of architecture support, the Yocto Project fully supports a wide range of device emulation through the Quick EMUlator (QEMU).
Images and Code Transfer Easily: Yocto Project output can easily move between architectures without moving to new development environments. Additionally, if you have used the Yocto Project to create an image or application and you find yourself not able to support it, commercial Linux vendors such as Wind River, Mentor Graphics, Timesys, and ENEA could take it and provide ongoing support. These vendors have offerings that are built using the Yocto Project.
Flexibility: Corporations use the Yocto Project many different ways. One example is to create an internal Linux distribution as a code base the corporation can use across multiple product groups. Through customization and layering, a project group can leverage the base Linux distribution to create a distribution that works for their product needs.
Ideal for Constrained Embedded and IoT devices: Unlike a full Linux distribution, you can use the Yocto Project to create exactly what you need for embedded devices. You only add the feature support or packages that you absolutely need for the device. For devices that have display hardware, you can use available system components such as X11, GTK+, Qt, Clutter, and SDL (among others) to create a rich user experience. For devices that do not have a display or where you want to use alternative UI frameworks, you can choose to not install these components.
Comprehensive Toolchain Capabilities: Toolchains for supported architectures satisfy most use cases. However, if your hardware supports features that are not part of a standard toolchain, you can easily customize that toolchain through specification of platform-specific tuning parameters. And, should you need to use a third-party toolchain, mechanisms built into the Yocto Project allow for that.
Mechanism Rules Over Policy: Focusing on mechanism rather than policy ensures that you are free to set policies based on the needs of your design instead of adopting decisions enforced by some system software provider.
Uses a Layer Model: The Yocto Project layer infrastructure groups related functionality into separate bundles. You can incrementally add these grouped functionalities to your project as needed. Using layers to isolate and group functionality reduces project complexity and redundancy, allows you to easily extend the system, make customizations, and keep functionality organized.
Supports Partial Builds: You can build and rebuild individual packages as needed. Yocto Project accomplishes this through its shared-state cache (sstate) scheme. Being able to build and debug components individually eases project development.
Releases According to a Strict Schedule: Major releases occur on a six-month cycle predictably in October and April. The most recent two releases support point releases to address common vulnerabilities and exposures. This predictability is crucial for projects based on the Yocto Project and allows development teams to plan activities.
Rich Ecosystem of Individuals and Organizations: For open source projects, the value of community is very important. Support forums, expertise, and active developers who continue to push the Yocto Project forward are readily available.
Binary Reproducibility:
The Yocto Project allows you to be very specific about
dependencies and achieves very high percentages of
binary reproducibility (e.g. 99.8% for
core-image-minimal
).
When distributions are not specific about which
packages are pulled in and in what order to support
dependencies, other build systems can arbitrarily
include packages.
License Manifest: The Yocto Project provides a license manifest for review by people who need to track the use of open source licenses (e.g.legal teams).
The following list presents challenges you might encounter when developing using the Yocto Project:
Steep Learning Curve: The Yocto Project has a steep learning curve and has many different ways to accomplish similar tasks. It can be difficult to choose how to proceed when varying methods exist by which to accomplish a given task.
Understanding What Changes You Need to Make For Your Design Requires Some Research: Beyond the simple tutorial stage, understanding what changes need to be made for your particular design can require a significant amount of research and investigation. For information that helps you transition from trying out the Yocto Project to using it for your project, see the "What I wish I'd Known" and "Transitioning to a Custom Environment for Systems Development" documents on the Yocto Project website.
Project Workflow Could Be Confusing: The Yocto Project workflow could be confusing if you are used to traditional desktop and server software development. In a desktop development environment, mechanisms exist to easily pull and install new packages, which are typically pre-compiled binaries from servers accessible over the Internet. Using the Yocto Project, you must modify your configuration and rebuild to add additional packages.
Working in a Cross-Build Environment Can Feel Unfamiliar: When developing code to run on a target, compilation, execution, and testing done on the actual target can be faster than running a BitBake build on a development host and then deploying binaries to the target for test. While the Yocto Project does support development tools on the target, the additional step of integrating your changes back into the Yocto Project build environment would be required. Yocto Project supports an intermediate approach that involves making changes on the development system within the BitBake environment and then deploying only the updated packages to the target.
The Yocto Project
OpenEmbedded build system
produces packages in standard formats (i.e. RPM,
DEB, IPK, and TAR).
You can deploy these packages into the running system
on the target by using utilities on the target such
as rpm
or
ipk
.
Initial Build Times Can be Significant: Long initial build times are unfortunately unavoidable due to the large number of packages initially built from scratch for a fully functioning Linux system. Once that initial build is completed, however, the shared-state (sstate) cache mechanism Yocto Project uses keeps the system from rebuilding packages that have not been "touched" since the last build. The sstate mechanism significantly reduces times for successive builds.
The Yocto Project's "Layer Model" is a development model for embedded and IoT Linux creation that distinguishes the Yocto Project from other simple build systems. The Layer Model simultaneously supports collaboration and customization. Layers are repositories that contain related sets of instructions that tell the OpenEmbedded build system what to do. You can collaborate, share, and reuse layers.
Layers can contain changes to previous instructions or settings at any time. This powerful override capability is what allows you to customize previously supplied collaborative or community layers to suit your product requirements.
You use different layers to logically separate information in your build. As an example, you could have BSP, GUI, distro configuration, middleware, or application layers. Putting your entire build into one layer limits and complicates future customization and reuse. Isolating information into layers, on the other hand, helps simplify future customizations and reuse. You might find it tempting to keep everything in one layer when working on a single project. However, the more modular your Metadata, the easier it is to cope with future changes.
Use Board Support Package (BSP) layers from silicon vendors when possible.
Familiarize yourself with the Yocto Project curated layer index or the OpenEmbedded layer index. The latter contains more layers but they are less universally validated.
Layers support the inclusion of technologies, hardware components, and software components. The Yocto Project Compatible designation provides a minimum level of standardization that contributes to a strong ecosystem. "YP Compatible" is applied to appropriate products and software components such as BSPs, other OE-compatible layers, and related open-source projects, allowing the producer to use Yocto Project badges and branding assets.
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 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.
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 names.
Layers typically have names that begin with the string
meta-
.
meta-
, but it is a commonly
accepted standard in the Yocto Project community.
For example, if you were to examine the
tree view
of the poky
repository, you will see several
layers: meta
,
meta-skeleton
,
meta-selftest
,
meta-poky
, and
meta-yocto-bsp
.
Each of these repositories represents a distinct layer.
For procedures on how to create layers, see the "Understanding and Creating Layers" section in the Yocto Project Development Tasks Manual.
The Yocto Project employs a collection of components and tools used by the project itself, by project developers, and by those using the Yocto Project. These components and tools are open source projects and metadata that are separate from the reference distribution (Poky) and the OpenEmbedded build system. Most of the components and tools are downloaded separately.
This section provides brief overviews of the components and tools associated with the Yocto Project.
The following list consists of tools that help you develop images and applications using the Yocto Project:
CROPS: CROPS is an open source, cross-platform development framework that leverages Docker Containers. CROPS provides an easily managed, extensible environment that allows you to build binaries for a variety of architectures on Windows, Linux and Mac OS X hosts.
devtool
:
This command-line tool is available as part of the
extensible SDK (eSDK) and is its cornerstone.
You can use devtool
to help build,
test, and package software within the eSDK.
You can use the tool to optionally integrate what you
build into an image built by the OpenEmbedded build
system.
The devtool
command employs
a number of sub-commands that allow you to add, modify,
and upgrade recipes.
As with the OpenEmbedded build system, “recipes”
represent software packages within
devtool
.
When you use devtool add
, a recipe
is automatically created.
When you use devtool modify
, the
specified existing recipe is used in order to determine
where to get the source code and how to patch it.
In both cases, an environment is set up so that when
you build the recipe a source tree that is under your
control is used in order to allow you to make changes
to the source as desired.
By default, both new recipes and the source go into
a “workspace” directory under the eSDK.
The devtool upgrade
command
updates an existing recipe so that you can build it
for an updated set of source files.
You can read about the
devtool
workflow in the Yocto
Project Application Development and Extensible
Software Development Kit (eSDK) Manual in the
"Using devtool
in Your SDK Workflow'"
section.
Extensible Software Development Kit (eSDK):
The eSDK provides a cross-development toolchain and
libraries tailored to the contents of a specific image.
The eSDK makes it easy to add new applications and
libraries to an image, modify the source for an
existing component, test changes on the target
hardware, and integrate into the rest of the
OpenEmbedded build system.
The eSDK gives you a toolchain experience supplemented
with the powerful set of devtool
commands tailored for the Yocto Project environment.
For information on the eSDK, see the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) Manual.
Eclipse™ IDE Plug-in: This plug-in enables you to use the popular Eclipse Integrated Development Environment (IDE), which allows for development using the Yocto Project all within the Eclipse IDE. You can work within Eclipse to cross-compile, deploy, and execute your output into a QEMU emulation session as well as onto actual target hardware.
The environment also supports performance enhancing tools that allow you to perform remote profiling, tracing, collection of power data, collection of latency data, and collection of performance data.
Once you enable the plug-in, standard Eclipse functions automatically use the cross-toolchain and target system libraries. You can build applications using any of these libraries.
For more information on the Eclipse plug-in, see the "Working Within Eclipse" section in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.
Toaster: Toaster is a web interface to the Yocto Project OpenEmbedded build system. Toaster allows you to configure, run, and view information about builds. For information on Toaster, see the Toaster User Manual.
The following list consists of tools that help production related activities using the Yocto Project:
Auto Upgrade Helper: This utility when used in conjunction with the OpenEmbedded build system (BitBake and OE-Core) automatically generates upgrades for recipes that are based on new versions of the recipes published upstream.
Recipe Reporting System: The Recipe Reporting System tracks recipe versions available for Yocto Project. The main purpose of the system is to help you manage the recipes you maintain and to offer a dynamic overview of the project. The Recipe Reporting System is built on top of the OpenEmbedded Layer Index, which is a website that indexes OpenEmbedded-Core layers.
Patchwork: Patchwork is a fork of a project originally started by OzLabs. The project is a web-based tracking system designed to streamline the process of bringing contributions into a project. The Yocto Project uses Patchwork as an organizational tool to handle patches, which number in the thousands for every release.
AutoBuilder: AutoBuilder is a project that automates build tests and quality assurance (QA). By using the public AutoBuilder, anyone can determine the status of the current "master" branch of Poky.
A goal of the Yocto Project is to lead the open source industry with a project that automates testing and QA procedures. In doing so, the project encourages a development community that publishes QA and test plans, publicly demonstrates QA and test plans, and encourages development of tools that automate and test and QA procedures for the benefit of the development community.
You can learn more about the AutoBuilder used by the Yocto Project here.
Cross-Prelink: Prelinking is the process of pre-computing the load addresses and link tables generated by the dynamic linker as compared to doing this at runtime. Doing this ahead of time results in performance improvements when the application is launched and reduced memory usage for libraries shared by many applications.
Historically, cross-prelink is a variant of
prelink, which was conceived by
Jakub Jelínek
a number of years ago.
Both prelink and cross-prelink are maintained in the
same repository albeit on separate branches.
By providing an emulated runtime dynamic linker
(i.e. glibc
-derived
ld.so
emulation), the
cross-prelink project extends the prelink software’s
ability to prelink a sysroot environment.
Additionally, the cross-prelink software enables the
ability to work in sysroot style environments.
The dynamic linker determines standard load address calculations based on a variety of factors such as mapping addresses, library usage, and library function conflicts. The prelink tool uses this information, from the dynamic linker, to determine unique load addresses for executable and linkable format (ELF) binaries that are shared libraries and dynamically linked. The prelink tool modifies these ELF binaries with the pre-computed information. The result is faster loading and often lower memory consumption because more of the library code can be re-used from shared Copy-On-Write (COW) pages.
The original upstream prelink project only supports running prelink on the end target device due to the reliance on the target device’s dynamic linker. This restriction causes issues when developing a cross-compiled system. The cross-prelink adds a synthesized dynamic loader that runs on the host, thus permitting cross-prelinking without ever having to run on a read-write target filesystem.
Pseudo: Pseudo is the Yocto Project implementation of fakeroot, which is used to run commands in an environment that seemingly has root privileges.
During a build, it can be necessary to perform
operations that require system administrator
privileges.
For example, file ownership or permissions might need
definition.
Pseudo is a tool that you can either use directly or
through the environment variable
LD_PRELOAD
.
Either method allows these operations to succeed as
if system administrator privileges exist even
when they do not.
You can read more about Pseudo in the "Fakeroot and Pseudo" section.
The following list consists of components associated with the OpenEmbedded build system:
BitBake: BitBake is a core component of the Yocto Project and is used by the OpenEmbedded build system to build images. While BitBake is key to the build system, BitBake is maintained separately from the Yocto Project.
BitBake is a generic task execution engine that allows shell and Python tasks to be run efficiently and in parallel while working within complex inter-task dependency constraints. In short, BitBake is a build engine that works through recipes written in a specific format in order to perform sets of tasks.
You can learn more about BitBake in the BitBake User Manual.
OpenEmbedded-Core: OpenEmbedded-Core (OE-Core) is a common layer of metadata (i.e. recipes, classes, and associated files) used by OpenEmbedded-derived systems, which includes the Yocto Project. The Yocto Project and the OpenEmbedded Project both maintain the OpenEmbedded-Core. You can find the OE-Core metadata in the Yocto Project Source Repositories.
Historically, the Yocto Project integrated the OE-Core metadata throughout the Yocto Project source repository reference system (Poky). After Yocto Project Version 1.0, the Yocto Project and OpenEmbedded agreed to work together and share a common core set of metadata (OE-Core), which contained much of the functionality previously found in Poky. This collaboration achieved a long-standing OpenEmbedded objective for having a more tightly controlled and quality-assured core. The results also fit well with the Yocto Project objective of achieving a smaller number of fully featured tools as compared to many different ones.
Sharing a core set of metadata results in Poky as an integration layer on top of OE-Core. You can see that in this figure. The Yocto Project combines various components such as BitBake, OE-Core, script “glue”, and documentation for its build system.
Poky is the Yocto Project reference distribution. It contains the Open-Embedded build system (BitBake and OE-Core) as well as a set of metadata to get you started building your own distribution. See the figure in "What is the Yocto Project?" section for an illustration that shows Poky and its relationship with other parts of the Yocto Project.
To use the Yocto Project tools and components, you
can download (clone
) Poky and use it
to bootstrap your own distribution.
You can read more about Poky in the "Reference Embedded Distribution (Poky)" section.
The following lists components associated with packages for finished targets:
Matchbox: Matchbox is an Open Source, base environment for the X Window System running on non-desktop, embedded platforms such as handhelds, set-top boxes, kiosks, and anything else for which screen space, input mechanisms, or system resources are limited.
Matchbox consists of a number of interchangeable and optional applications that you can tailor to a specific, non-desktop platform to enhance usability in constrained environments.
You can find the Matchbox source in the Yocto Project Source Repositories.
Opkg Open PacKaGe management (opkg) is a lightweight package management system based on the itsy package (ipkg) management system. Opkg is written in C and resembles Advanced Package Tool (APT) and Debian Package (dpkg) in operation.
Opkg is intended for use on embedded Linux devices and is used in this capacity in the OpenEmbedded and OpenWrt projects, as well as the Yocto Project.
The Build Appliance is a virtual machine image that enables you to build and boot a custom embedded Linux image with the Yocto Project using a non-Linux development system.
Historically, the Build Appliance was the second of three methods by which you could use the Yocto Project on a system that was not native to Linux.
Hob: Hob, which is now deprecated and is no longer available since the 2.1 release of the Yocto Project provided a rudimentary, GUI-based interface to the Yocto Project. Toaster has fully replaced Hob.
Build Appliance: Post Hob, the Build Appliance became available. It was never recommended that you use the Build Appliance as a day-to-day production development environment with the Yocto Project. Build Appliance was useful as a way to try out development in the Yocto Project environment.
CROPS: The final and best solution available now for developing using the Yocto Project on a system not native to Linux is with CROPS.
The Yocto Project development environment usually involves a Build Host and target hardware. You use the Build Host to build images and develop applications, while you use the target hardware to test deployed software.
This section provides an introduction to the choices or development methods you have when setting up your Build Host. Depending on the your particular workflow preference and the type of operating system your Build Host runs, several choices exist that allow you to use the Yocto Project.
Native Linux Host: By far the best option for a Build Host. A system running Linux as its native operating system allows you to develop software by directly using the BitBake tool. You can accomplish all aspects of development from a familiar shell of a supported Linux distribution.
For information on how to set up a Build Host on a system running Linux as its native operating system, see the "Setting Up a Native Linux Host" section in the Yocto Project Development Tasks Manual.
CROss PlatformS (CROPS): Typically, you use CROPS, which leverages Docker Containers, to set up a Build Host that is not running Linux (e.g. Microsoft® Windows™ or macOS®).
CROPS is an open source, cross-platform development framework that provides an easily managed, extensible environment for building binaries targeted for a variety of architectures on Windows, macOS, or Linux hosts. Once the Build Host is set up using CROPS, you can prepare a shell environment to mimic that of a shell being used on a system natively running Linux.
For information on how to set up a Build Host with CROPS, see the "Setting Up to Use CROss PlatformS (CROPS)" section in the Yocto Project Development Tasks Manual.
Toaster: Regardless of what your Build Host is running, you can use Toaster to develop software using the Yocto Project. Toaster is a web interface to the Yocto Project's Open-Embedded build system. The interface enables you to configure and run your builds. Information about builds is collected and stored in a database. You can use Toaster to configure and start builds on multiple remote build servers.
For information about and how to use Toaster, see the Toaster User Manual.
Eclipse™ IDE: If your Build Host supports and runs the popular Eclipse IDE, you can install the Yocto Project Eclipse plug-in and use the Yocto Project to develop software. The plug-in integrates the Yocto Project functionality into Eclipse development practices.
For information about how to install and use the Yocto Project Eclipse plug-in, see the "Developing Applications Using Eclipse" chapter in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) Manual.
"Poky", which is pronounced Pock-ee, is the name of the Yocto Project's reference distribution or Reference OS Kit. Poky contains the OpenEmbedded Build System (BitBake and OpenEmbedded-Core) as well as a set of metadata to get you started building your own distro. In other words, Poky is a base specification of the functionality needed for a typical embedded system as well as the components from the Yocto Project that allow you to build a distribution into a usable binary image.
Poky is a combined repository of BitBake, OpenEmbedded-Core
(which is found in meta
),
meta-poky
,
meta-yocto-bsp
, and documentation provided
all together and known to work well together.
You can view these items that make up the Poky repository in the
Source Repositories.
poky
Git repository, see the
"Top-Level Core Components"
section in the Yocto Project Reference Manual.
The following figure illustrates what generally comprises Poky:
BitBake is a task executor and scheduler that is the heart of the OpenEmbedded build system.
meta-poky
, which is Poky-specific
metadata.
meta-yocto-bsp
, which are Yocto
Project-specific Board Support Packages (BSPs).
OpenEmbedded-Core (OE-Core) metadata, which includes shared configurations, global variable definitions, shared classes, packaging, and recipes. Classes define the encapsulation and inheritance of build logic. Recipes are the logical units of software and images to be built.
Documentation, which contains the Yocto Project source files used to make the set of user manuals.
To use the Yocto Project tools, you can use Git to clone (download) the Poky repository then use your local copy of the reference distribution to bootstrap your own distribution.
Poky has a regular, well established, six-month release cycle under its own version. Major releases occur at the same time major releases (point releases) occur for the Yocto Project, which are typically in the Spring and Fall. For more information on the Yocto Project release schedule and cadence, see the "Yocto Project Releases and the Stable Release Process" chapter in the Yocto Project Reference Manual.
Much has been said about Poky being a "default configuration." A default configuration provides a starting image footprint. You can use Poky out of the box to create an image ranging from a shell-accessible minimal image all the way up to a Linux Standard Base-compliant image that uses a GNOME Mobile and Embedded (GMAE) based reference user interface called Sato.
One of the most powerful properties of Poky is that every aspect of a build is controlled by the metadata. You can use metadata to augment these base image types by adding metadata layers that extend functionality. These layers can provide, for example, an additional software stack for an image type, add a board support package (BSP) for additional hardware, or even create a new image type.
Metadata is loosely grouped into configuration files or package
recipes.
A recipe is a collection of non-executable metadata used by
BitBake to set variables or define additional build-time tasks.
A recipe contains fields such as the recipe description, the recipe
version, the license of the package and the upstream source
repository.
A recipe might also indicate that the build process uses autotools,
make, distutils or any other build process, in which case the basic
functionality can be defined by the classes it inherits from
the OE-Core layer's class definitions in
./meta/classes
.
Within a recipe you can also define additional tasks as well as
task prerequisites.
Recipe syntax through BitBake also supports both
_prepend
and _append
operators as a method of extending task functionality.
These operators inject code into the beginning or end of a task.
For information on these BitBake operators, see the
"Appending and Prepending (Override Style Syntax)"
section in the BitBake User's Manual.
The OpenEmbedded build system uses a "workflow" to accomplish image and SDK generation. The following figure overviews that workflow:
Following is a brief summary of the "workflow":
Developers specify architecture, policies, patches and configuration details.
The build system fetches and downloads the source code from the specified location. The build system supports standard methods such as tarballs or source code repositories systems such as Git.
Once source code is downloaded, the build system extracts the sources into a local work area where patches are applied and common steps for configuring and compiling the software are run.
The build system then installs the software into a temporary staging area where the binary package format you select (DEB, RPM, or IPK) is used to roll up the software.
Different QA and sanity checks run throughout entire build process.
After the binaries are created, the build system generates a binary package feed that is used to create the final root file image.
The build system generates the file system image and a customized Extensible SDK (eSDSK) for application development in parallel.
For a very detailed look at this workflow, see the "OpenEmbedded Build System Concepts" section.
It helps to understand some basic fundamental terms when learning the Yocto Project. Although a list of terms exists in the "Yocto Project Terms" section of the Yocto Project Reference Manual, this section provides the definitions of some terms helpful for getting started:
Configuration Files: Files that hold global definitions of variables, user-defined variables, and hardware configuration information. These files tell the Open-Embedded build system what to build and what to put into the image to support a particular platform.
Extensible Software Development Kit (eSDK): A custom SDK for application developers. This eSDK allows developers to incorporate their library and programming changes back into the image to make their code available to other application developers. For information on the eSDK, see the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.
Layer: A collection of related recipes. Layers allow you to consolidate related metadata to customize your build. Layers also isolate information used when building for multiple architectures. Layers are hierarchical in their ability to override previous specifications. You can include any number of available layers from the Yocto Project and customize the build by adding your layers after them. You can search the Layer Index for layers used within Yocto Project.
For more detailed information on layers, see the "Understanding and Creating Layers" section in the Yocto Project Development Tasks Manual. For a discussion specifically on BSP Layers, see the "BSP Layers" section in the Yocto Project Board Support Packages (BSP) Developer's Guide.
Metadata: A key element of the Yocto Project is the Metadata that is used to construct a Linux distribution and is contained in the files that the OpenEmbedded build system parses when building an image. In general, Metadata includes recipes, configuration files, and other information that refers to the build instructions themselves, as well as the data used to control what things get built and the effects of the build. Metadata also includes commands and data used to indicate what versions of software are used, from where they are obtained, and changes or additions to the software itself (patches or auxiliary files) that are used to fix bugs or customize the software for use in a particular situation. OpenEmbedded-Core is an important set of validated metadata.
OpenEmbedded Build System: The terms "BitBake" and "build system" are sometimes used for the OpenEmbedded Build System.
BitBake is a task scheduler and execution engine
that parses instructions (i.e. recipes) and configuration
data.
After a parsing phase, BitBake creates a dependency tree
to order the compilation, schedules the compilation of
the included code, and finally executes the building
of the specified custom Linux image (distribution).
BitBake is similar to the make
tool.
During a build process, the build system tracks dependencies and performs a native or cross-compilation of the package. As a first step in a cross-build setup, the framework attempts to create a cross-compiler toolchain (i.e. Extensible SDK) suited for the target platform.
OpenEmbedded-Core (OE-Core): OE-Core is metadata comprised of foundation recipes, classes, and associated files that are meant to be common among many different OpenEmbedded-derived systems, including the Yocto Project. OE-Core is a curated subset of an original repository developed by the OpenEmbedded community that has been pared down into a smaller, core set of continuously validated recipes. The result is a tightly controlled and quality-assured core set of recipes.
You can see the Metadata in the
meta
directory of the Yocto Project
Source Repositories.
Packages: In the context of the Yocto Project, this term refers to a recipe's packaged output produced by BitBake (i.e. 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 "Required Packages for the Host Development System" section in the Yocto Project Reference Manual 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
,
PV
,
and
PE
).
Poky: Poky is a reference embedded distribution and a reference test configuration. Poky provides the following:
A base-level functional distro used to illustrate how to customize a distribution.
A means by which to test the Yocto Project components (i.e. Poky is used to validate the Yocto Project).
A vehicle through which you can download the Yocto Project.
Poky is not a product level distro. Rather, it is a good starting point for customization.
Recipe: The most common form of metadata. A recipe contains a list of settings and tasks (i.e. instructions) for building packages that are then used to build the binary image. A recipe describes where you get source code and which patches to apply. Recipes describe dependencies for libraries or for other recipes as well as configuration and compilation options. Related recipes are consolidated into a layer.
This chapter takes a look at the Yocto Project development environment. The chapter provides Yocto Project Development environment concepts that help you understand how work is accomplished in an open source environment, which is very different as compared to work accomplished in a closed, proprietary environment.
Specifically, this chapter addresses open source philosophy, source repositories, workflows, Git, and licensing.
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) who 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.
A development host or build host is key to using the Yocto Project. Because the goal of the Yocto Project is to develop images or applications that run on embedded hardware, development of those images and applications generally takes place on a system not intended to run the software - the development host.
You need to set up a development host in order to use it with the Yocto Project. Most find that it is best to have a native Linux machine function as the development host. However, it is possible to use a system that does not run Linux as its operating system as your development host. When you have a Mac or Windows-based system, you can set it up as the development host by using CROPS, which leverages Docker Containers. Once you take the steps to set up a CROPS machine, you effectively have access to a shell environment that is similar to what you see when using a Linux-based development host. For the steps needed to set up a system using CROPS, see the "Setting Up to Use CROss PlatformS (CROPS)" section in the Yocto Project Development Tasks Manual.
If your development host is going to be a system that runs a Linux distribution, steps still exist that you must take to prepare the system for use with the Yocto Project. You need to be sure that the Linux distribution on the system is one that supports the Yocto Project. You also need to be sure that the correct set of host packages are installed that allow development using the Yocto Project. For the steps needed to set up a development host that runs Linux, see the "Setting Up a Native Linux Host" section in the Yocto Project Development Tasks Manual.
Once your development host is set up to use the Yocto Project, several methods exist for you to do work in the Yocto Project environment:
Command Lines, BitBake, and Shells: Traditional development in the Yocto Project involves using the OpenEmbedded build system, which uses BitBake, in a command-line environment from a shell on your development host. You can accomplish this from a host that is a native Linux machine or from a host that has been set up with CROPS. Either way, you create, modify, and build images and applications all within a shell-based environment using components and tools available through your Linux distribution and the Yocto Project.
For a general flow of the build procedures, see the "Building a Simple Image" section in the Yocto Project Development Tasks Manual.
Board Support Package (BSP) Development: Development of BSPs involves using the Yocto Project to create and test layers that allow easy development of images and applications targeted for specific hardware. To development BSPs, you need to take some additional steps beyond what was described in setting up a development host.
The Yocto Project Board Support Package (BSP) Developer's Guide provides BSP-related development information. For specifics on development host preparation, see the "Preparing Your Build Host to Work With BSP Layers" section in the Yocto Project Board Support Package (BSP) Developer's Guide.
Kernel Development:
If you are going to be developing kernels using the Yocto
Project you likely will be using devtool
.
A workflow using devtool
makes kernel
development quicker by reducing iteration cycle times.
The Yocto Project Linux Kernel Development Manual provides kernel-related development information. For specifics on development host preparation, see the "Preparing the Build Host to Work on the Kernel" section in the Yocto Project Linux Kernel Development Manual.
Using the Eclipse™ IDE: One of two Yocto Project development methods that involves an interface that effectively puts the Yocto Project into the background is the popular Eclipse IDE. This method of development is advantageous if you are already familiar with working within Eclipse. Development is supported through a plugin that you install onto your development host.
For steps that show you how to set up your development host to use the Eclipse Yocto Project plugin, see the "Developing Applications Using Eclipse™" Chapter in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.
Using Toaster: The other Yocto Project development method that involves an interface that effectively puts the Yocto Project into the background is Toaster. Toaster provides an interface to the OpenEmbedded build system. The interface enables you to configure and run your builds. Information about builds is collected and stored in a database. You can use Toaster to configure and start builds on multiple remote build servers.
For steps that show you how to set up your development host to use Toaster and on how to use Toaster in general, see the Toaster User Manual.
The Yocto Project team maintains complete source repositories for all Yocto Project files at http://git.yoctoproject.org. 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, which is usually named "poky", allows you to make changes, contribute to the history, and ultimately enhance the Yocto Project's tools, Board Support Packages, and so forth.
For any supported release of Yocto Project, you can also go to the
Yocto Project Website and
select the "DOWNLOADS" item from the "SOFTWARE" menu and get a
released tarball of the poky
repository, any
supported BSP tarball, or Yocto Project tools.
Unpacking these tarballs gives you a snapshot of the released
files.
The recommended method for setting up the Yocto Project
Source Directory
and the files for supported BSPs
(e.g., meta-intel
) is to use
Git to create a local copy of
the upstream repositories.
Be sure to always work in matching branches for both
the selected BSP repository and the Source Directory
(i.e. poky
) repository.
For example, if you have checked out the "master" branch
of poky
and you are going to use
meta-intel
, be sure to checkout the
"master" branch of meta-intel
.
In summary, here is where you can get the project files needed for development:
Source 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.
For steps on how to view and access these upstream Git repositories, see the "Accessing Source Repositories" Section in the Yocto Project Development Tasks Manual.
Index of /releases: This is an index of 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.
For steps on how to view and access these files, see the "Accessing Index of Releases" section in the Yocto Project Development Tasks Manual.
"DOWNLOADS" page for the Yocto Project Website:
The Yocto Project website includes a "DOWNLOADS" page accessible through the "SOFTWARE" menu that allows you to download any Yocto Project release, tool, and Board Support Package (BSP) in tarball form. The tarballs are similar to those found in the Index of /releases: area.
For steps on how to use the "DOWNLOADS" page, see the "Using the Downloads Page" section in the Yocto Project Development Tasks Manual.
Developing using the Yocto Project likely requires the use of Git. Git is a free, open source distributed version control system used as part of many collaborative design environments. This section provides workflow concepts using the Yocto Project and Git. In particular, the information covers basic practices that describe roles and actions in a collaborative development environment.
The Yocto Project files are maintained using Git in "branches" whose Git histories track every change and whose structures provide 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 integrity of the "master" branch of a given Git repository. The "master" branch is the “upstream” repository from which final or most recent builds of a project occur. The maintainer is responsible for accepting changes from other developers and for organizing the underlying branch structure to reflect release strategies and so forth.
The Yocto Project poky
Git repository also has an
upstream contribution Git repository named
poky-contrib
.
You can see all the branches in this repository using the web interface
of the
Source Repositories organized
within the "Poky Support" area.
These branches hold changes (commits) to the project that have been
submitted or committed by the Yocto Project development team and by
community members who contribute to the project.
The maintainer determines if the changes are qualified to be moved
from the "contrib" branches into the "master" branch of the Git
repository.
Developers (including contributing community members) create and maintain cloned repositories of upstream branches. The cloned 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 change to the appropriate "contrib" repository.
Developers are responsible for keeping their local repository up-to-date with whatever upstream branch they are working against. 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 development host 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 an upstream branch. This process is called “submitting a patch” or "submitting a change." For information on submitting patches and changes, see the "Submitting a Change to the Yocto Project" section in the Yocto Project Development Tasks Manual.
In summary, a single point of entry exists for changes into a "master" or development branch of the Git repository, which is controlled by the project’s maintainer. And, a set of developers exist 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.
Make Complete 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 on the development host. 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 in the Yocto Project Development Tasks Manual.
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
"Submitting a Change to the Yocto Project"
section in the Yocto Project Development Tasks Manual.
The Yocto Project makes extensive use of 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, it is recommended that you add Git to your system through your distribution's "software store" (e.g. for Ubuntu, use the Ubuntu Software feature). For the Git download page, see http://git-scm.com/download.
For information beyond the introductory nature in this section, see the "Locating Yocto Project Source Files" section in the Yocto Project Development Tasks Manual.
As mentioned briefly in the previous section and also in the "Git Workflows and the Yocto Project" section, the Yocto Project maintains source repositories at http://git.yoctoproject.org. 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 that repository 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
"Locating Yocto Project Source Files"
section in the Yocto Project Development Tasks Manual.
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
several branches that include the current "sumo"
branch, the "master" branch, and many branches for past
Yocto Project releases.
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 offshoots 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 upstream 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, consider the following example Git commands:
$ cd ~ $ git clone git://git.yoctoproject.org/poky $ cd poky $ git checkout -b sumo origin/sumo
In the previous example after moving to the home directory, the
git clone
command creates a
local copy of the upstream poky
Git repository.
By default, Git checks out the "master" branch for your work.
After changing the working directory to the new local repository
(i.e. poky
), the
git checkout
command creates
and checks out a local branch named "sumo", which
tracks the upstream "origin/sumo" branch.
Changes you make while in this branch would ultimately affect
the upstream "sumo" branch of the
poky
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 particular development branch at the time you created your local branch, which could be different from the files in the "master" branch of the upstream repository. In other words, creating and checking out a local branch based on the "sumo" branch name is not the same as checking out the "master" branch in the repository. 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 branch
structure.
Typically, a tag is used to mark a special point such as the final
change (or commit) 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 for the poky
repository are
jethro-14.0.3
,
morty-16.0.1
,
pyro-17.0.0
, and
sumo-20.0.3
.
These tags represent Yocto Project releases.
When you create a local copy of the Git repository, you also have access to all the tags in the upstream repository. 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 fetch --tags $ git checkout tags/rocko-18.0.0 -b my_rocko-18.0.0
In this example, the name of the top-level directory of your
local Yocto Project repository is poky
.
After moving to the poky
directory, the
git fetch
command makes all the upstream
tags available locally in your repository.
Finally, the git checkout
command
creates and checks out a branch named "my-rocko-18.0.0" that is
based on the upstream branch whose "HEAD" matches the
commit in the repository associated with the "rocko-18.0.0" tag.
The files in your repository now exactly match that particular
Yocto Project release as it is tagged in the upstream Git
repository.
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 (i.e. from the "tip" of the branch backwards).
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.
The following list of Git commands 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 it supports. 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 local clone of a Git repository that is on
equal footing with a fellow developer’s Git repository
or an upstream repository.
git add
:
Locally 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 local "commit" that documents the changes you
made.
Only changes that have been staged can be committed.
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 repository.
git status
:
Reports any modified files that possibly need to be
staged and gives you a status of where you stand regarding
local commits as compared to the upstream repository.
git checkout
branch-name
:
Changes your local working branch and in this form
assumes the local branch already exists.
This command is analogous to "cd".
git checkout –b
working-branch
upstream-branch
:
Creates and checks out a working branch on your local
machine.
The local branch tracks the upstream branch.
You can use your local branch to isolate your work.
It is a good idea to use local branches when adding
specific features or changes.
Using isolated branches facilitates easy removal of
changes if they do not work out.
git branch
:
Displays the existing local branches associated with your
local repository.
The branch that you have currently checked out is noted
with an asterisk character.
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 --rebase
:
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).
The "--rebase" option ensures that any local commits you
have in your branch are preserved at the top of your
local branch.
git push
repo-name
local-branch
:
upstream-branch
:
Sends all your committed local changes to the upstream Git
repository that your local repository is tracking
(e.g. a contribution repository).
The maintainer of the project draws from these repositories
to merge changes (commits) into the appropriate branch
of project's upstream repository.
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 that is
based off "master" that you would use for isolated work.
You would make your changes in that isolated branch,
stage and commit them locally, switch to the "master"
branch, and then use the git merge
command to apply the changes from your isolated branch
into the currently checked out branch (e.g. "master").
After the merge is complete and if you are done with
working in that isolated branch, you can safely delete
the isolated branch.
git cherry-pick
commits
:
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.
gitk
package on your development system to use this
command.
git log
:
Reports a history of your commits to the repository.
This report lists all commits regardless of whether you
have pushed them upstream or not.
git diff
:
Displays line-by-line differences between a local
working file and the same file as understood by Git.
This command is useful to see what you have changed
in any given file.
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 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 conform to the Open Source Definition (OSD).
You can find a list of the combined SPDX and OSI licenses that the
Yocto Project uses in the
meta/files/common-licenses
directory in your
Source Directory.
For information that can help you 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 in the Yocto Project Development Tasks Manual.
This chapter provides explanations for Yocto Project concepts that go beyond the surface of "how-to" information and reference (or look-up) material. Concepts such as components, the OpenEmbedded build system workflow, cross-development toolchains, shared state cache, and so forth are explained.
The BitBake task executor together with various types of configuration files form the OpenEmbedded-Core. This section overviews these components by describing their use and how they interact.
BitBake handles the parsing and execution of the data files. The data itself is of various types:
Recipes: Provides details about particular pieces of software.
Class Data: Abstracts common build information (e.g. how to build a Linux kernel).
Configuration Data: Defines machine-specific settings, policy decisions, and so forth. Configuration data acts as the glue to bind everything together.
BitBake knows how to combine multiple data sources together and refers to each data source as a layer. For information on layers, see the "Understanding and Creating Layers" section of the Yocto Project Development Tasks Manual.
Following are some brief details on these core components. For additional information on how these components interact during a build, see the "OpenEmbedded Build System Concepts" section.
BitBake is the tool at the heart of the OpenEmbedded build system and is responsible for parsing the Metadata, generating a list of tasks from it, and then executing those tasks.
This section briefly introduces BitBake. If you want more information on BitBake, see the BitBake User Manual.
To see a list of the options BitBake supports, use either of the following commands:
$ bitbake -h $ bitbake --help
The most common usage for BitBake is
bitbake
,
where packagename
packagename
is the name of the
package you want to build (referred to as the "target").
The target often equates to the first part of a recipe's
filename (e.g. "foo" for a recipe named
foo_1.3.0-r0.bb
).
So, to process the
matchbox-desktop_1.2.3.bb
recipe file, you
might type the following:
$ bitbake matchbox-desktop
Several different versions of
matchbox-desktop
might exist.
BitBake chooses the one selected by the distribution
configuration.
You can get more details about how BitBake chooses between
different target versions and providers in the
"Preferences"
section of the BitBake User Manual.
BitBake also tries to execute any dependent tasks first.
So for example, before building
matchbox-desktop
, BitBake would build a
cross compiler and glibc
if they had not
already been built.
A useful BitBake option to consider is the
-k
or --continue
option.
This option instructs BitBake to try and continue processing
the job as long as possible even after encountering an error.
When an error occurs, the target that failed and those that
depend on it cannot be remade.
However, when you use this option other dependencies can
still be processed.
Files that have the .bb
suffix are
"recipes" files.
In general, a recipe contains information about a single piece
of software.
This information includes the location from which to download
the unaltered source, any source patches to be applied to that
source (if needed), which special configuration options to
apply, how to compile the source files, and how to package the
compiled output.
The term "package" is sometimes used to refer to recipes.
However, since the word "package" is used for the packaged
output from the OpenEmbedded build system (i.e.
.ipk
or .deb
files),
this document avoids using the term "package" when referring
to recipes.
Class files (.bbclass
) contain information
that is useful to share between recipes files.
An example is the
autotools
class, which contains common settings for any application that
Autotools uses.
The
"Classes"
chapter in the Yocto Project Reference Manual provides
details about classes and how to use them.
The configuration files (.conf
) define
various configuration variables that govern the OpenEmbedded
build process.
These files fall into several areas that define machine
configuration options, distribution configuration options,
compiler tuning options, general common configuration options,
and user configuration options in
conf/local.conf
, which is found in the
Build Directory.
Layers are repositories that contain related metadata (i.e. sets of instructions) that tell the OpenEmbedded build system how to build a target. Yocto Project's layer model facilitates collaboration, sharing, customization, and reuse within the Yocto Project development environment. Layers logically separate information for your project. For example, you can use a layer to hold all the configurations for a particular piece of hardware. Isolating hardware-specific configurations allows you to share other metadata by using a different layer where that metadata might be common across several pieces of hardware.
Many layers exist that work in the Yocto Project development environment. The Yocto Project Curated Layer Index and OpenEmbedded Layer Index both contain layers from which you can use or leverage.
By convention, layers in the Yocto Project follow a specific form.
Conforming to a known structure allows BitBake to make assumptions
during builds on where to find types of metadata.
You can find procedures and learn about tools (i.e.
bitbake-layers
) for creating layers suitable
for the Yocto Project in the
"Understanding and Creating Layers"
section of the Yocto Project Development Tasks Manual.
This section takes a more detailed look inside the build process used by the OpenEmbedded build system, which is the build system specific to the Yocto Project. At the heart of the build system is BitBake, the task executor.
The following diagram represents the high-level workflow of a build. The remainder of this section expands on the fundamental input, output, process, and metadata logical blocks that make up the workflow.
In general, the build's workflow consists of several functional areas:
User Configuration: metadata you can use to control the build process.
Metadata Layers: Various layers that provide software, machine, and distro metadata.
Source Files: Upstream releases, local projects, and SCMs.
Build System: Processes under the control of BitBake. This block expands on how BitBake fetches source, applies patches, completes compilation, analyzes output for package generation, creates and tests packages, generates images, and generates cross-development tools.
Package Feeds: Directories containing output packages (RPM, DEB or IPK), which are subsequently used in the construction of an image or Software Development Kit (SDK), produced by the build system. These feeds can also be copied and shared using a web server or other means to facilitate extending or updating existing images on devices at runtime if runtime package management is enabled.
Images: Images produced by the workflow.
Application Development SDK: Cross-development tools that are produced along with an image or separately with BitBake.
User configuration helps define the build. Through user configuration, you can tell BitBake the target architecture for which you are building the image, where to store downloaded source, and other build properties.
The following figure shows an expanded representation of the "User Configuration" box of the general workflow figure:
BitBake needs some basic configuration files in order to
complete a build.
These files are *.conf
files.
The minimally necessary ones reside as example files in the
build/conf
directory of the
Source Directory.
For simplicity, this section refers to the Source Directory as
the "Poky Directory."
When you clone the
Poky
Git repository or you download and unpack a Yocto Project
release, you can set up the Source Directory to be named
anything you want.
For this discussion, the cloned repository uses the default
name poky
.
The meta-poky
layer inside Poky contains
a conf
directory that has example
configuration files.
These example files are used as a basis for creating actual
configuration files when you source
oe-init-build-env
,
which is the build environment script.
Sourcing the build environment script creates a
Build Directory
if one does not already exist.
BitBake uses the Build Directory for all its work during
builds.
The Build Directory has a conf
directory
that contains default versions of your
local.conf
and
bblayers.conf
configuration files.
These default configuration files are created only if versions
do not already exist in the Build Directory at the time you
source the build environment setup script.
Because the Poky repository is fundamentally an aggregation of
existing repositories, some users might be familiar with
running the oe-init-build-env
script
in the context of separate
OpenEmbedded-Core
and BitBake repositories rather than a single Poky repository.
This discussion assumes the script is executed from
within a cloned or unpacked version of Poky.
Depending on where the script is sourced, different
sub-scripts are called to set up the Build Directory
(Yocto or OpenEmbedded).
Specifically, the script
scripts/oe-setup-builddir
inside the
poky directory sets up the Build Directory and seeds the
directory (if necessary) with configuration files appropriate
for the Yocto Project development environment.
scripts/oe-setup-builddir
script
uses the $TEMPLATECONF
variable to
determine which sample configuration files to locate.
The local.conf
file provides many
basic variables that define a build environment.
Here is a list of a few.
To see the default configurations in a
local.conf
file created by the build
environment script, see the
local.conf.sample
in the meta-poky
layer:
Target Machine Selection:
Controlled by the
MACHINE
variable.
Download Directory:
Controlled by the
DL_DIR
variable.
Shared State Directory:
Controlled by the
SSTATE_DIR
variable.
Build Output:
Controlled by the
TMPDIR
variable.
Distribution Policy:
Controlled by the
DISTRO
variable.
Packaging Format:
Controlled by the
PACKAGE_CLASSES
variable.
SDK Target Architecture:
Controlled by the
SDKMACHINE
variable.
Extra Image Packages:
Controlled by the
EXTRA_IMAGE_FEATURES
variable.
conf/local.conf
file can also be set
in the conf/site.conf
and
conf/auto.conf
configuration files.
The bblayers.conf
file tells BitBake what
layers you want considered during the build.
By default, the layers listed in this file include layers
minimally needed by the build system.
However, you must manually add any custom layers you have
created.
You can find more information on working with the
bblayers.conf
file in the
"Enabling Your Layer"
section in the Yocto Project Development Tasks Manual.
The files site.conf
and
auto.conf
are not created by the
environment initialization script.
If you want the site.conf
file, you
need to create that yourself.
The auto.conf
file is typically created by
an autobuilder:
site.conf
:
You can use the conf/site.conf
configuration file to configure multiple
build directories.
For example, suppose you had several build environments
and they shared some common features.
You can set these default build properties here.
A good example is perhaps the packaging format to use
through the
PACKAGE_CLASSES
variable.
One useful scenario for using the
conf/site.conf
file is to extend
your
BBPATH
variable to include the path to a
conf/site.conf
.
Then, when BitBake looks for Metadata using
BBPATH
, it finds the
conf/site.conf
file and applies
your common configurations found in the file.
To override configurations in a particular build
directory, alter the similar configurations within
that build directory's
conf/local.conf
file.
auto.conf
:
The file is usually created and written to by
an autobuilder.
The settings put into the file are typically the
same as you would find in the
conf/local.conf
or the
conf/site.conf
files.
You can edit all configuration files to further define any particular build environment. This process is represented by the "User Configuration Edits" box in the figure.
When you launch your build with the
bitbake
command, BitBake sorts out the configurations to ultimately
define your build environment.
It is important to understand that the
OpenEmbedded build system
reads the configuration files in a specific order:
target
site.conf
, auto.conf
,
and local.conf
.
And, the build system applies the normal assignment statement
rules as described in the
"Syntax and Operators"
chapter of the BitBake User Manual.
Because the files are parsed in a specific order, variable
assignments for the same variable could be affected.
For example, if the auto.conf
file and
the local.conf
set
variable1
to different values,
because the build system parses local.conf
after auto.conf
,
variable1
is assigned the value from
the local.conf
file.
The previous section described the user configurations that define BitBake's global behavior. This section takes a closer look at the layers the build system uses to further control the build. These layers provide Metadata for the software, machine, and policies.
In general, three types of layer input exists. You can see them below the "User Configuration" box in the general workflow figure:
Metadata (.bb
+ Patches):
Software layers containing user-supplied recipe files,
patches, and append files.
A good example of a software layer might be the
meta-qt5
layer from the
OpenEmbedded Layer Index.
This layer is for version 5.0 of the popular
Qt
cross-platform application development framework for
desktop, embedded and mobile.
Machine BSP Configuration:
Board Support Package (BSP) layers (i.e. "BSP Layer"
in the following figure) providing machine-specific
configurations.
This type of information is specific to a particular
target architecture.
A good example of a BSP layer from the
Poky Reference Distribution
is the
meta-yocto-bsp
layer.
Policy Configuration:
Distribution Layers (i.e. "Distro Layer" in the
following figure) providing top-level or general
policies for the images or SDKs being built for a
particular distribution.
For example, in the Poky Reference Distribution the
distro layer is the
meta-poky
layer.
Within the distro layer is a
conf/distro
directory that
contains distro configuration files (e.g.
poky.conf
that contain many policy configurations for the
Poky distribution.
The following figure shows an expanded representation of these three layers from the general workflow figure:
In general, all layers have a similar structure.
They all contain a licensing file
(e.g. COPYING.MIT
) if the layer is to be
distributed, a README
file as good
practice and especially if the layer is to be distributed, a
configuration directory, and recipe directories.
You can learn about the general structure for layers used with
the Yocto Project in the
"Creating Your Own Layer"
section in the Yocto Project Development Tasks Manual.
For a general discussion on layers and the many layers from
which you can draw, see the
"Layers" and
"The Yocto Project Layer Model"
sections both earlier in this manual.
If you explored the previous links, you discovered some areas where many layers that work with the Yocto Project exist. The Source Repositories also shows layers categorized under "Yocto Metadata Layers."
BitBake uses the conf/bblayers.conf
file,
which is part of the user configuration, to find what layers it
should be using as part of the build.
The distribution layer provides policy configurations for
your distribution.
Best practices dictate that you isolate these types of
configurations into their own layer.
Settings you provide in
conf/distro/
override
similar settings that BitBake finds in your
distro
.confconf/local.conf
file in the Build
Directory.
The following list provides some explanation and references for what you typically find in the distribution layer:
classes:
Class files (.bbclass
) hold
common functionality that can be shared among
recipes in the distribution.
When your recipes inherit a class, they take on the
settings and functions for that class.
You can read more about class files in the
"Classes"
chapter of the Yocto Reference Manual.
conf:
This area holds configuration files for the
layer (conf/layer.conf
),
the distribution
(conf/distro/
),
and any distribution-wide include files.
distro
.conf
recipes-*:
Recipes and append files that affect common
functionality across the distribution.
This area could include recipes and append files
to add distribution-specific configuration,
initialization scripts, custom image recipes,
and so forth.
Examples of recipes-*
directories are recipes-core
and recipes-extra
.
Hierarchy and contents within a
recipes-*
directory can vary.
Generally, these directories contain recipe files
(*.bb
), recipe append files
(*.bbappend
), directories
that are distro-specific for configuration files,
and so forth.
The BSP Layer provides machine configurations that target specific hardware. Everything in this layer is specific to the machine for which you are building the image or the SDK. A common structure or form is defined for BSP layers. You can learn more about this structure in the Yocto Project Board Support Package (BSP) Developer's Guide.
The BSP Layer's configuration directory contains
configuration files for the machine
(conf/machine/
)
and, of course, the layer
(machine
.confconf/layer.conf
).
The remainder of the layer is dedicated to specific recipes
by function: recipes-bsp
,
recipes-core
,
recipes-graphics
,
recipes-kernel
, and so forth.
Metadata can exist for multiple formfactors, graphics
support systems, and so forth.
recipes-*
directories, not all
these directories appear in all BSP layers.
The software layer provides the Metadata for additional software packages used during the build. This layer does not include Metadata that is specific to the distribution or the machine, which are found in their respective layers.
This layer contains any recipes, append files, and patches, that your project needs.
In order for the OpenEmbedded build system to create an image or any target, it must be able to access source files. The general workflow figure represents source files using the "Upstream Project Releases", "Local Projects", and "SCMs (optional)" boxes. The figure represents mirrors, which also play a role in locating source files, with the "Source Materials" box.
The method by which source files are ultimately organized is a function of the project. For example, for released software, projects tend to use tarballs or other archived files that can capture the state of a release guaranteeing that it is statically represented. On the other hand, for a project that is more dynamic or experimental in nature, a project might keep source files in a repository controlled by a Source Control Manager (SCM) such as Git. Pulling source from a repository allows you to control the point in the repository (the revision) from which you want to build software. Finally, a combination of the two might exist, which would give the consumer a choice when deciding where to get source files.
BitBake uses the
SRC_URI
variable to point to source files regardless of their location.
Each recipe must have a SRC_URI
variable
that points to the source.
Another area that plays a significant role in where source
files come from is pointed to by the
DL_DIR
variable.
This area is a cache that can hold previously downloaded
source.
You can also instruct the OpenEmbedded build system to create
tarballs from Git repositories, which is not the default
behavior, and store them in the DL_DIR
by using the
BB_GENERATE_MIRROR_TARBALLS
variable.
Judicious use of a DL_DIR
directory can
save the build system a trip across the Internet when looking
for files.
A good method for using a download directory is to have
DL_DIR
point to an area outside of your
Build Directory.
Doing so allows you to safely delete the Build Directory
if needed without fear of removing any downloaded source file.
The remainder of this section provides a deeper look into the source files and the mirrors. Here is a more detailed look at the source file area of the general workflow figure:
Upstream project releases exist anywhere in the form of an archived file (e.g. tarball or zip file). These files correspond to individual recipes. For example, the figure uses specific releases each for BusyBox, Qt, and Dbus. An archive file can be for any released product that can be built using a recipe.
Local projects are custom bits of software the user provides. These bits reside somewhere local to a project - perhaps a directory into which the user checks in items (e.g. a local directory containing a development source tree used by the group).
The canonical method through which to include a local
project is to use the
externalsrc
class to include that local project.
You use either the local.conf
or a
recipe's append file to override or set the
recipe to point to the local directory on your disk to pull
in the whole source tree.
Another place the build system can get source files from is
through an SCM such as Git or Subversion.
In this case, a repository is cloned or checked out.
The
do_fetch
task inside BitBake uses
the SRC_URI
variable and the argument's prefix to determine the correct
fetcher module.
DL_DIR
directory, see the
BB_GENERATE_MIRROR_TARBALLS
variable.
When fetching a repository, BitBake uses the
SRCREV
variable to determine the specific revision from which to
build.
Two kinds of mirrors exist: pre-mirrors and regular
mirrors.
The
PREMIRRORS
and
MIRRORS
variables point to these, respectively.
BitBake checks pre-mirrors before looking upstream for any
source files.
Pre-mirrors are appropriate when you have a shared
directory that is not a directory defined by the
DL_DIR
variable.
A Pre-mirror typically points to a shared directory that is
local to your organization.
Regular mirrors can be any site across the Internet that is used as an alternative location for source code should the primary site not be functioning for some reason or another.
When the OpenEmbedded build system generates an image or an SDK, it gets the packages from a package feed area located in the Build Directory. The general workflow figure shows this package feeds area in the upper-right corner.
This section looks a little closer into the package feeds area used by the build system. Here is a more detailed look at the area:
Package feeds are an intermediary step in the build process.
The OpenEmbedded build system provides classes to generate
different package types, and you specify which classes to
enable through the
PACKAGE_CLASSES
variable.
Before placing the packages into package feeds,
the build process validates them with generated output quality
assurance checks through the
insane
class.
The package feed area resides in the Build Directory. The directory the build system uses to temporarily store packages is determined by a combination of variables and the particular package manager in use. See the "Package Feeds" box in the illustration and note the information to the right of that area. In particular, the following defines where package files are kept:
DEPLOY_DIR
:
Defined as tmp/deploy
in the Build
Directory.
DEPLOY_DIR_*
:
Depending on the package manager used, the package type
sub-folder.
Given RPM, IPK, or DEB packaging and tarball creation,
the
DEPLOY_DIR_RPM
,
DEPLOY_DIR_IPK
,
DEPLOY_DIR_DEB
,
or
DEPLOY_DIR_TAR
,
variables are used, respectively.
PACKAGE_ARCH
:
Defines architecture-specific sub-folders.
For example, packages could exist for the i586 or
qemux86 architectures.
BitBake uses the
do_package_write_*
tasks to generate packages and place them into the package
holding area (e.g. do_package_write_ipk
for IPK packages).
See the
"do_package_write_deb
",
"do_package_write_ipk
",
"do_package_write_rpm
",
and
"do_package_write_tar
"
sections in the Yocto Project Reference Manual
for additional information.
As an example, consider a scenario where an IPK packaging
manager is being used and package architecture support for
both i586 and qemux86 exist.
Packages for the i586 architecture are placed in
build/tmp/deploy/ipk/i586
, while packages
for the qemux86 architecture are placed in
build/tmp/deploy/ipk/qemux86
.
The OpenEmbedded build system uses BitBake to produce images and Software Development Kits (SDKs). You can see from the general workflow figure, the BitBake area consists of several functional areas. This section takes a closer look at each of those areas.
The first stages of building a recipe are to fetch and unpack the source code:
The
do_fetch
and
do_unpack
tasks fetch the source files and unpack them into the
Build Directory.
file://
)
that is part of a recipe's
SRC_URI
statement, the OpenEmbedded build system takes a
checksum of the file for the recipe and inserts the
checksum into the signature for the
do_fetch
task.
If any local file has been modified, the
do_fetch
task and all tasks that
depend on it are re-executed.
By default, everything is accomplished in the Build
Directory, which has a defined structure.
For additional general information on the Build Directory,
see the
"build/
"
section in the Yocto Project Reference Manual.
Each recipe has an area in the Build Directory where the
unpacked source code resides.
The
S
variable points to this area for a recipe's unpacked source
code.
The name of that directory for any given recipe is defined
from several different variables.
The preceding figure and the following list describe
the Build Directory's hierarchy:
TMPDIR
:
The base directory where the OpenEmbedded build
system performs all its work during the build.
The default base directory is the
tmp
directory.
PACKAGE_ARCH
:
The architecture of the built package or packages.
Depending on the eventual destination of the
package or packages (i.e. machine architecture,
build host,
SDK, or specific machine),
PACKAGE_ARCH
varies.
See the variable's description for details.
TARGET_OS
:
The operating system of the target device.
A typical value would be "linux" (e.g.
"qemux86-poky-linux").
PN
:
The name of the recipe used to build the package.
This variable can have multiple meanings.
However, when used in the context of input files,
PN
represents the the name
of the recipe.
WORKDIR
:
The location where the OpenEmbedded build system
builds a recipe (i.e. does the work to create the
package).
S
:
Contains the unpacked source files for a given
recipe.
PACKAGE_ARCH
) and one based on a
machine (i.e. MACHINE
).
The underlying structures are identical.
The differentiator being what the OpenEmbedded build
system is using as a build target (e.g. general
architecture, a build host, an SDK, or a specific
machine).
Once source code is fetched and unpacked, BitBake locates patch files and applies them to the source files:
The
do_patch
task uses a recipe's
SRC_URI
statements and the
FILESPATH
variable to locate applicable patch files.
Default processing for patch files assumes the files have
either *.patch
or
*.diff
file types.
You can use SRC_URI
parameters to
change the way the build system recognizes patch files.
See the
do_patch
task for more information.
BitBake finds and applies multiple patches for a single
recipe in the order in which it locates the patches.
The FILESPATH
variable defines the
default set of directories that the build system uses to
search for patch files.
Once found, patches are applied to the recipe's source
files, which are located in the
S
directory.
For more information on how the source directories are
created, see the
"Source Fetching"
section.
For more information on how to create patches and how the
build system processes patches, see the
"Patching Code"
section in the Yocto Project Development Tasks Manual.
You can also see the
"Use devtool modify
to Modify the Source of an Existing Component"
section in the Yocto Project Application Development and
the Extensible Software Development Kit (SDK) manual and
the
"Using Traditional Kernel Development to Patch the Kernel"
section in the Yocto Project Linux Kernel Development
Manual.
After source code is patched, BitBake executes tasks that configure and compile the source code. Once compilation occurs, the files are copied to a holding area (staged) in preparation for packaging:
This step in the build process consists of the following tasks:
do_prepare_recipe_sysroot
:
This task sets up the two sysroots in
${
WORKDIR
}
(i.e. recipe-sysroot
and
recipe-sysroot-native
) so that
during the packaging phase the sysroots can contain
the contents of the
do_populate_sysroot
tasks of the recipes on which the recipe
containing the tasks depends.
A sysroot exists for both the target and for the
native binaries, which run on the host system.
do_configure
:
This task configures the source by enabling and
disabling any build-time and configuration options
for the software being built.
Configurations can come from the recipe itself as
well as from an inherited class.
Additionally, the software itself might configure
itself depending on the target for which it is
being built.
The configurations handled by the
do_configure
task are specific to configurations for the source
code being built by the recipe.
If you are using the
autotools
class, you can add additional configuration options
by using the
EXTRA_OECONF
or
PACKAGECONFIG_CONFARGS
variables.
For information on how this variable works within
that class, see the
autotools
class
here.
do_compile
:
Once a configuration task has been satisfied,
BitBake compiles the source using the
do_compile
task.
Compilation occurs in the directory pointed to by
the
B
variable.
Realize that the B
directory
is, by default, the same as the
S
directory.
do_install
:
After compilation completes, BitBake executes the
do_install
task.
This task copies files from the
B
directory and places them
in a holding area pointed to by the
D
variable.
Packaging occurs later using files from this
holding directory.
After source code is configured, compiled, and staged, the build system analyzes the results and splits the output into packages:
The
do_package
and
do_packagedata
tasks combine to analyze the files found in the
D
directory and split them into subsets based on available
packages and files.
Analysis involves the following as well as other items:
splitting out debugging symbols, looking at shared library
dependencies between packages, and looking at package
relationships.
The do_packagedata
task creates
package metadata based on the analysis such that the
build system can generate the final packages.
The
do_populate_sysroot
task stages (copies) a subset of the files installed by
the
do_install
task into the appropriate sysroot.
Working, staged, and intermediate results of the analysis
and package splitting process use several areas:
PKGD
:
The destination directory
(i.e. package
) for packages
before they are split into individual packages.
PKGDESTWORK
:
A temporary work area (i.e.
pkgdata
) used by the
do_package
task to save
package metadata.
PKGDEST
:
The parent directory (i.e.
packages-split
) for packages
after they have been split.
PKGDATA_DIR
:
A shared, global-state directory that holds
packaging metadata generated during the packaging
process.
The packaging process copies metadata from
PKGDESTWORK
to the
PKGDATA_DIR
area where it
becomes globally available.
STAGING_DIR_HOST
:
The path for the sysroot for the system on which
a component is built to run (i.e.
recipe-sysroot
).
STAGING_DIR_NATIVE
:
The path for the sysroot used when building
components for the build host (i.e.
recipe-sysroot-native
).
STAGING_DIR_TARGET
:
The path for the sysroot used when a component that
is built to execute on a system and it generates
code for yet another machine (e.g. cross-canadian
recipes).
The
FILES
variable defines the files that go into each package in
PACKAGES
.
If you want details on how this is accomplished, you can
look at
package.bbclass
.
Depending on the type of packages being created (RPM, DEB,
or IPK), the
do_package_write_*
task creates the actual packages and places them in the
Package Feed area, which is
${TMPDIR}/deploy
.
You can see the
"Package Feeds"
section for more detail on that part of the build process.
deploy/*
directories does not
exist.
Creating such feeds usually requires some kind of feed
maintenance mechanism that would upload the new
packages into an official package feed (e.g. the
Ångström distribution).
This functionality is highly distribution-specific
and thus is not provided out of the box.
Once packages are split and stored in the Package Feeds area, the build system uses BitBake to generate the root filesystem image:
The image generation process consists of several stages and
depends on several tasks and variables.
The
do_rootfs
task creates the root filesystem (file and directory
structure) for an image.
This task uses several key variables to help create the
list of packages to actually install:
IMAGE_INSTALL
:
Lists out the base set of packages from which to
install from the Package Feeds area.
PACKAGE_EXCLUDE
:
Specifies packages that should not be installed
into the image.
IMAGE_FEATURES
:
Specifies features to include in the image.
Most of these features map to additional packages
for installation.
PACKAGE_CLASSES
:
Specifies the package backend (e.g. RPM, DEB, or
IPK) to use and consequently helps determine where
to locate packages within the Package Feeds area.
IMAGE_LINGUAS
:
Determines the language(s) for which additional
language support packages are installed.
PACKAGE_INSTALL
:
The final list of packages passed to the package
manager for installation into the image.
With
IMAGE_ROOTFS
pointing to the location of the filesystem under
construction and the PACKAGE_INSTALL
variable providing the final list of packages to install,
the root file system is created.
Package installation is under control of the package manager (e.g. dnf/rpm, opkg, or apt/dpkg) regardless of whether or not package management is enabled for the target. At the end of the process, if package management is not enabled for the target, the package manager's data files are deleted from the root filesystem. As part of the final stage of package installation, post installation scripts that are part of the packages are run. Any scripts that fail to run on the build host are run on the target when the target system is first booted. If you are using a read-only root filesystem, all the post installation scripts must succeed on the build host during the package installation phase since the root filesystem on the target is read-only.
The final stages of the do_rootfs
task
handle post processing.
Post processing includes creation of a manifest file and
optimizations.
The manifest file (.manifest
) resides
in the same directory as the root filesystem image.
This file lists out, line-by-line, the installed packages.
The manifest file is useful for the
testimage
class, for example, to determine whether or not to run
specific tests.
See the
IMAGE_MANIFEST
variable for additional information.
Optimizing processes that are run across the image include
mklibs
, prelink
,
and any other post-processing commands as defined by the
ROOTFS_POSTPROCESS_COMMAND
variable.
The mklibs
process optimizes the size
of the libraries, while the prelink
process optimizes the dynamic linking of shared libraries
to reduce start up time of executables.
After the root filesystem is built, processing begins on
the image through the
do_image
task.
The build system runs any pre-processing commands as
defined by the
IMAGE_PREPROCESS_COMMAND
variable.
This variable specifies a list of functions to call before
the build system creates the final image output files.
The build system dynamically creates
do_image_*
tasks as needed, based
on the image types specified in the
IMAGE_FSTYPES
variable.
The process turns everything into an image file or a set of
image files and can compress the root filesystem image to
reduce the overall size of the image.
The formats used for the root filesystem depend on the
IMAGE_FSTYPES
variable.
Compression depends on whether the formats support
compression.
As an example, a dynamically created task when creating a
particular image type
would
take the following form:
do_image_type
So, if the type
as specified by
the IMAGE_FSTYPES
were
ext4
, the dynamically generated task
would be as follows:
do_image_ext4
The final task involved in image creation is the
do_image_complete
task.
This task completes the image by applying any image
post processing as defined through the
IMAGE_POSTPROCESS_COMMAND
variable.
The variable specifies a list of functions to call once the
build system has created the final image output files.
The OpenEmbedded build system uses BitBake to generate the Software Development Kit (SDK) installer scripts for both the standard SDK and the extensible SDK (eSDK):
do_populate_sdk
task, see the
"Building an SDK Installer"
section in the Yocto Project Application Development
and the Extensible Software Development Kit (eSDK)
manual.
Like image generation, the SDK script process consists of
several stages and depends on many variables.
The
do_populate_sdk
and
do_populate_sdk_ext
tasks use these key variables to help create the list of
packages to actually install.
For information on the variables listed in the figure,
see the
"Application Development SDK"
section.
The do_populate_sdk
task helps create
the standard SDK and handles two parts: a target part and a
host part.
The target part is the part built for the target hardware
and includes libraries and headers.
The host part is the part of the SDK that runs on the
SDKMACHINE
.
The do_populate_sdk_ext
task helps
create the extensible SDK and handles host and target parts
differently than its counter part does for the standard SDK.
For the extensible SDK, the task encapsulates the build
system, which includes everything needed (host and target)
for the SDK.
Regardless of the type of SDK being constructed, the
tasks perform some cleanup after which a cross-development
environment setup script and any needed configuration files
are created.
The final output is the Cross-development
toolchain installation script (.sh
file), which includes the environment setup script.
For each task that completes successfully, BitBake writes a
stamp file into the
STAMPS_DIR
directory.
The beginning of the stamp file's filename is determined
by the
STAMP
variable, and the end of the name consists of the task's
name and current
input checksum.
BB_SIGNATURE_HANDLER
is "OEBasicHash", which is almost always the case in
current OpenEmbedded.
To determine if a task needs to be rerun, BitBake checks if a stamp file with a matching input checksum exists for the task. If such a stamp file exists, the task's output is assumed to exist and still be valid. If the file does not exist, the task is rerun.
The stamp mechanism is more general than the shared state (sstate) cache mechanism described in the "Setscene Tasks and Shared State" section. BitBake avoids rerunning any task that has a valid stamp file, not just tasks that can be accelerated through the sstate cache.
However, you should realize that stamp files only
serve as a marker that some work has been done and that
these files do not record task output.
The actual task output would usually be somewhere in
TMPDIR
(e.g. in some recipe's
WORKDIR
.)
What the sstate cache mechanism adds is a way to cache
task output that can then be shared between build
machines.
Since STAMPS_DIR
is usually a
subdirectory of TMPDIR
, removing
TMPDIR
will also remove
STAMPS_DIR
, which means tasks will
properly be rerun to repopulate
TMPDIR
.
If you want some task to always be considered "out of
date", you can mark it with the
nostamp
varflag.
If some other task depends on such a task, then that
task will also always be considered out of date, which
might not be what you want.
For details on how to view information about a task's signature, see the "Viewing Task Variable Dependencies" section in the Yocto Project Development Tasks Manual.
The description of tasks so far assumes that BitBake needs to build everything and no available prebuilt objects exist. BitBake does support skipping tasks if prebuilt objects are available. These objects are usually made available in the form of a shared state (sstate) cache.
SSTATE_DIR
and
SSTATE_MIRRORS
variables.
The idea of a setscene task (i.e
do_
taskname
_setscene
)
is a version of the task where
instead of building something, BitBake can skip to the end
result and simply place a set of files into specific
locations as needed.
In some cases, it makes sense to have a setscene task
variant (e.g. generating package files in the
do_package_write_*
task).
In other cases, it does not make sense (e.g. a
do_patch
task or a
do_unpack
task) since the work involved would be equal to or greater
than the underlying task.
In the build system, the common tasks that have setscene
variants are
do_package
,
do_package_write_*
,
do_deploy
,
do_packagedata
,
and
do_populate_sysroot
.
Notice that these tasks represent most of the tasks whose
output is an end result.
The build system has knowledge of the relationship between
these tasks and other preceding tasks.
For example, if BitBake runs
do_populate_sysroot_setscene
for
something, it does not make sense to run any of the
do_fetch
,
do_unpack
,
do_patch
,
do_configure
,
do_compile
, and
do_install
tasks.
However, if do_package
needs to be
run, BitBake needs to run those other tasks.
It becomes more complicated if everything can come
from an sstate cache because some objects are simply
not required at all.
For example, you do not need a compiler or native tools,
such as quilt, if nothing exists to compile or patch.
If the do_package_write_*
packages
are available from sstate, BitBake does not need the
do_package
task data.
To handle all these complexities, BitBake runs in two phases. The first is the "setscene" stage. During this stage, BitBake first checks the sstate cache for any targets it is planning to build. BitBake does a fast check to see if the object exists rather than a complete download. If nothing exists, the second phase, which is the setscene stage, completes and the main build proceeds.
If objects are found in the sstate cache, the build system works backwards from the end targets specified by the user. For example, if an image is being built, the build system first looks for the packages needed for that image and the tools needed to construct an image. If those are available, the compiler is not needed. Thus, the compiler is not even downloaded. If something was found to be unavailable, or the download or setscene task fails, the build system then tries to install dependencies, such as the compiler, from the cache.
The availability of objects in the sstate cache is
handled by the function specified by the
BB_HASHCHECK_FUNCTION
variable and returns a list of available objects.
The function specified by the
BB_SETSCENE_DEPVALID
variable is the function that determines whether a given
dependency needs to be followed, and whether for any given
relationship the function needs to be passed.
The function returns a True or False value.
The images produced by the build system are compressed forms of the root filesystem and are ready to boot on a target device. You can see from the general workflow figure that BitBake output, in part, consists of images. This section takes a closer look at this output:
The build process writes images out to the
Build Directory
inside the
tmp/deploy/images/
folder as shown in the figure.
This folder contains any files expected to be loaded on the
target device.
The
machine
/DEPLOY_DIR
variable points to the deploy
directory,
while the
DEPLOY_DIR_IMAGE
variable points to the appropriate directory containing images
for the current configuration.
kernel-image
:
A kernel binary file.
The
KERNEL_IMAGETYPE
variable determines the naming scheme for the
kernel image file.
Depending on this variable, the file could begin with
a variety of naming strings.
The
deploy/images/
machine
directory can contain multiple image files for the
machine.
root-filesystem-image
:
Root filesystems for the target device (e.g.
*.ext3
or
*.bz2
files).
The
IMAGE_FSTYPES
variable determines the root filesystem image type.
The
deploy/images/
machine
directory can contain multiple root filesystems for the
machine.
kernel-modules
:
Tarballs that contain all the modules built for the
kernel.
Kernel module tarballs exist for legacy purposes and
can be suppressed by setting the
MODULE_TARBALL_DEPLOY
variable to "0".
The
deploy/images/
machine
directory can contain multiple kernel module tarballs
for the machine.
bootloaders
:
If applicable to the target machine, bootloaders
supporting the image.
The deploy/images/
machine
directory can contain multiple bootloaders for the
machine.
symlinks
:
The
deploy/images/
machine
folder contains a symbolic link that points to the
most recently built file for each machine.
These links might be useful for external scripts that
need to obtain the latest version of each file.
In the
general workflow figure,
the output labeled "Application Development SDK" represents an
SDK.
The SDK generation process differs depending on whether you
build an extensible SDK (e.g.
bitbake -c populate_sdk_ext
imagename
)
or a standard SDK (e.g.
bitbake -c populate_sdk
imagename
).
This section takes a closer look at this output:
The specific form of this output is a set of files that
includes a self-extracting SDK installer
(*.sh
), host and target manifest files,
and files used for SDK testing.
When the SDK installer file is run, it installs the SDK.
The SDK consists of a cross-development toolchain, a set of
libraries and headers, and an SDK environment setup script.
Running this installer essentially sets up your
cross-development environment.
You can think of the cross-toolchain as the "host"
part because it runs on the SDK machine.
You can think of the libraries and headers as the "target"
part because they are built for the target hardware.
The environment setup script is added so that you can
initialize the environment before using the tools.
The Yocto Project supports several methods by which you can set up this cross-development environment. These methods include downloading pre-built SDK installers or building and installing your own SDK installer.
For background information on cross-development toolchains in the Yocto Project development environment, see the "Cross-Development Toolchain Generation" section.
For information on setting up a cross-development environment, see the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.
All the output files for an SDK are written to the
deploy/sdk
folder inside the
Build Directory
as shown in the previous figure.
Depending on the type of SDK, several variables exist that help
configure these files.
The following list shows the variables associated with an
extensible SDK:
DEPLOY_DIR
:
Points to the deploy
directory.
SDK_EXT_TYPE
:
Controls whether or not shared state artifacts are
copied into the extensible SDK.
By default, all required shared state artifacts are
copied into the SDK.
SDK_INCLUDE_PKGDATA
:
Specifies whether or not packagedata is included in the
extensible SDK for all recipes in the "world" target.
SDK_INCLUDE_TOOLCHAIN
:
Specifies whether or not the toolchain is included
when building the extensible SDK.
SDK_LOCAL_CONF_WHITELIST
:
A list of variables allowed through from the build
system configuration into the extensible SDK
configuration.
SDK_LOCAL_CONF_BLACKLIST
:
A list of variables not allowed through from the build
system configuration into the extensible SDK
configuration.
SDK_INHERIT_BLACKLIST
:
A list of classes to remove from the
INHERIT
value globally within the extensible SDK configuration.
This next list, shows the variables associated with a standard SDK:
DEPLOY_DIR
:
Points to the deploy
directory.
SDKMACHINE
:
Specifies the architecture of the machine on which the
cross-development tools are run to create packages for
the target hardware.
SDKIMAGE_FEATURES
:
Lists the features to include in the "target" part
of the SDK.
TOOLCHAIN_HOST_TASK
:
Lists packages that make up the host part of the SDK
(i.e. the part that runs on the
SDKMACHINE
).
When you use
bitbake -c populate_sdk
to create the SDK, a set of default packages apply.
This variable allows you to add more packages.
imagename
TOOLCHAIN_TARGET_TASK
:
Lists packages that make up the target part of the SDK
(i.e. the part built for the target hardware).
SDKPATH
:
Defines the default SDK installation path offered by
the installation script.
SDK_HOST_MANIFEST
:
Lists all the installed packages that make up the host
part of the SDK.
This variable also plays a minor role for extensible
SDK development as well.
However, it is mainly used for the standard SDK.
SDK_TARGET_MANIFEST
:
Lists all the installed packages that make up the
target part of the SDK.
This variable also plays a minor role for extensible
SDK development as well.
However, it is mainly used for the standard SDK.
The Yocto Project does most of the work for you when it comes to creating cross-development toolchains. This section provides some technical background on how cross-development toolchains are created and used. For more information on toolchains, you can also see the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.
In the Yocto Project development environment, cross-development toolchains are used to build images and applications that run on the target hardware. With just a few commands, the OpenEmbedded build system creates these necessary toolchains for you.
The following figure shows a high-level build environment regarding toolchain construction and use.
Most of the work occurs on the Build Host.
This is the machine used to build images and generally work within
the the Yocto Project environment.
When you run
BitBake
to create an image, the OpenEmbedded build system
uses the host gcc
compiler to bootstrap a
cross-compiler named gcc-cross
.
The gcc-cross
compiler is what BitBake uses to
compile source files when creating the target image.
You can think of gcc-cross
simply as an
automatically generated cross-compiler that is used internally
within BitBake only.
gcc-cross-canadian
since this SDK
ships a copy of the OpenEmbedded build system and the sysroot
within it contains gcc-cross
.
The chain of events that occurs when gcc-cross
is
bootstrapped is as follows:
gcc -> binutils-cross -> gcc-cross-initial -> linux-libc-headers -> glibc-initial -> glibc -> gcc-cross -> gcc-runtime
gcc
:
The build host's GNU Compiler Collection (GCC).
binutils-cross
:
The bare minimum binary utilities needed in order to run
the gcc-cross-initial
phase of the
bootstrap operation.
gcc-cross-initial
:
An early stage of the bootstrap process for creating
the cross-compiler.
This stage builds enough of the gcc-cross
,
the C library, and other pieces needed to finish building the
final cross-compiler in later stages.
This tool is a "native" package (i.e. it is designed to run on
the build host).
linux-libc-headers
:
Headers needed for the cross-compiler.
glibc-initial
:
An initial version of the Embedded GNU C Library
(GLIBC) needed to bootstrap glibc
.
glibc
:
The GNU C Library.
gcc-cross
:
The final stage of the bootstrap process for the
cross-compiler.
This stage results in the actual cross-compiler that
BitBake uses when it builds an image for a targeted
device.
gcc-cross
.
This tool is also a "native" package (i.e. it is designed to run on the build host).
gcc-runtime
:
Runtime libraries resulting from the toolchain bootstrapping
process.
This tool produces a binary that consists of the
runtime libraries need for the targeted device.
You can use the OpenEmbedded build system to build an installer for
the relocatable SDK used to develop applications.
When you run the installer, it installs the toolchain, which
contains the development tools (e.g.,
gcc-cross-canadian
,
binutils-cross-canadian
, and other
nativesdk-*
tools),
which are tools native to the SDK (i.e. native to
SDK_ARCH
),
you need to cross-compile and test your software.
The figure shows the commands you use to easily build out this
toolchain.
This cross-development toolchain is built to execute on the
SDKMACHINE
,
which might or might not be the same
machine as the Build Host.
Here is the bootstrap process for the relocatable toolchain:
gcc -> binutils-crosssdk -> gcc-crosssdk-initial -> linux-libc-headers -> glibc-initial -> nativesdk-glibc -> gcc-crosssdk -> gcc-cross-canadian
gcc
:
The build host's GNU Compiler Collection (GCC).
binutils-crosssdk
:
The bare minimum binary utilities needed in order to run
the gcc-crosssdk-initial
phase of the
bootstrap operation.
gcc-crosssdk-initial
:
An early stage of the bootstrap process for creating
the cross-compiler.
This stage builds enough of the
gcc-crosssdk
and supporting pieces so that
the final stage of the bootstrap process can produce the
finished cross-compiler.
This tool is a "native" binary that runs on the build host.
linux-libc-headers
:
Headers needed for the cross-compiler.
glibc-initial
:
An initial version of the Embedded GLIBC needed to bootstrap
nativesdk-glibc
.
nativesdk-glibc
:
The Embedded GLIBC needed to bootstrap the
gcc-crosssdk
.
gcc-crosssdk
:
The final stage of the bootstrap process for the
relocatable cross-compiler.
The gcc-crosssdk
is a transitory
compiler and never leaves the build host.
Its purpose is to help in the bootstrap process to create
the eventual gcc-cross-canadian
compiler, which is relocatable.
This tool is also a "native" package (i.e. it is
designed to run on the build host).
gcc-cross-canadian
:
The final relocatable cross-compiler.
When run on the
SDKMACHINE
,
this tool
produces executable code that runs on the target device.
Only one cross-canadian compiler is produced per architecture
since they can be targeted at different processor optimizations
using configurations passed to the compiler through the
compile commands.
This circumvents the need for multiple compilers and thus
reduces the size of the toolchains.
By design, the OpenEmbedded build system builds everything from scratch unless BitBake can determine that parts do not need to be rebuilt. Fundamentally, building from scratch is attractive as it means all parts are built fresh and no possibility of stale data exists that can cause problems. When developers hit problems, they typically default back to building from scratch so they have a know state from the start.
Building an image from scratch is both an advantage and a disadvantage to the process. As mentioned in the previous paragraph, building from scratch ensures that everything is current and starts from a known state. However, building from scratch also takes much longer as it generally means rebuilding things that do not necessarily need to be rebuilt.
The Yocto Project implements shared state code that supports incremental builds. The implementation of the shared state code answers the following questions that were fundamental roadblocks within the OpenEmbedded incremental build support system:
What pieces of the system have changed and what pieces have not changed?
How are changed pieces of software removed and replaced?
How are pre-built components that do not need to be rebuilt from scratch used when they are available?
For the first question, the build system detects changes in the "inputs" to a given task by creating a checksum (or signature) of the task's inputs. If the checksum changes, the system assumes the inputs have changed and the task needs to be rerun. For the second question, the shared state (sstate) code tracks which tasks add which output to the build process. This means the output from a given task can be removed, upgraded or otherwise manipulated. The third question is partly addressed by the solution for the second question assuming the build system can fetch the sstate objects from remote locations and install them if they are deemed to be valid.
The build system does not maintain
PR
information as part of the shared state packages.
Consequently, considerations exist that affect
maintaining shared state feeds.
For information on how the build system works with
packages and can track incrementing
PR
information, see the
"Automatically Incrementing a Binary Package Revision Number"
section in the Yocto Project Development Tasks Manual.
The code in the build system that supports incremental builds is not simple code. For techniques that help you work around issues related to shared state code, see the "Viewing Metadata Used to Create the Input Signature of a Shared State Task" and "Invalidating Shared State to Force a Task to Run" sections both in the Yocto Project Development Tasks Manual.
The rest of this section goes into detail about the overall incremental build architecture, the checksums (signatures), and shared state.
When determining what parts of the system need to be built,
BitBake works on a per-task basis rather than a per-recipe
basis.
You might wonder why using a per-task basis is preferred over
a per-recipe basis.
To help explain, consider having the IPK packaging backend
enabled and then switching to DEB.
In this case, the
do_install
and
do_package
task outputs are still valid.
However, with a per-recipe approach, the build would not
include the .deb
files.
Consequently, you would have to invalidate the whole build and
rerun it.
Rerunning everything is not the best solution.
Also, in this case, the core must be "taught" much about
specific tasks.
This methodology does not scale well and does not allow users
to easily add new tasks in layers or as external recipes
without touching the packaged-staging core.
The shared state code uses a checksum, which is a unique signature of a task's inputs, to determine if a task needs to be run again. Because it is a change in a task's inputs that triggers a rerun, the process needs to detect all the inputs to a given task. For shell tasks, this turns out to be fairly easy because the build process generates a "run" shell script for each task and it is possible to create a checksum that gives you a good idea of when the task's data changes.
To complicate the problem, there are things that should not be
included in the checksum.
First, there is the actual specific build path of a given
task - the
WORKDIR
.
It does not matter if the work directory changes because it
should not affect the output for target packages.
Also, the build process has the objective of making native
or cross packages relocatable.
The checksum therefore needs to exclude
WORKDIR
.
The simplistic approach for excluding the work directory is to
set WORKDIR
to some fixed value and
create the checksum for the "run" script.
Another problem results from the "run" scripts containing functions that might or might not get called. The incremental build solution contains code that figures out dependencies between shell functions. This code is used to prune the "run" scripts down to the minimum set, thereby alleviating this problem and making the "run" scripts much more readable as a bonus.
So far, solutions for shell scripts exist. What about Python tasks? The same approach applies even though these tasks are more difficult. The process needs to figure out what variables a Python function accesses and what functions it calls. Again, the incremental build solution contains code that first figures out the variable and function dependencies, and then creates a checksum for the data used as the input to the task.
Like the WORKDIR
case, situations exist
where dependencies should be ignored.
For these situations, you can instruct the build process to
ignore a dependency by using a line like the following:
PACKAGE_ARCHS[vardepsexclude] = "MACHINE"
This example ensures that the
PACKAGE_ARCHS
variable does not depend on the value of
MACHINE
,
even if it does reference it.
Equally, there are cases where you need to add dependencies BitBake is not able to find. You can accomplish this by using a line like the following:
PACKAGE_ARCHS[vardeps] = "MACHINE"
This example explicitly adds the MACHINE
variable as a dependency for
PACKAGE_ARCHS
.
As an example, consider a case with in-line Python where
BitBake is not able to figure out dependencies.
When running in debug mode (i.e. using
-DDD
), BitBake produces output when it
discovers something for which it cannot figure out dependencies.
The Yocto Project team has currently not managed to cover
those dependencies in detail and is aware of the need to fix
this situation.
Thus far, this section has limited discussion to the direct inputs into a task. Information based on direct inputs is referred to as the "basehash" in the code. However, the question of a task's indirect inputs still exits - items already built and present in the Build Directory. The checksum (or signature) for a particular task needs to add the hashes of all the tasks on which the particular task depends. Choosing which dependencies to add is a policy decision. However, the effect is to generate a master checksum that combines the basehash and the hashes of the task's dependencies.
At the code level, a variety of ways exist by which both the basehash and the dependent task hashes can be influenced. Within the BitBake configuration file, you can give BitBake some extra information to help it construct the basehash. The following statement effectively results in a list of global variable dependency excludes (i.e. variables never included in any checksum):
BB_HASHBASE_WHITELIST ?= "TMPDIR FILE PATH PWD BB_TASKHASH BBPATH DL_DIR \ SSTATE_DIR THISDIR FILESEXTRAPATHS FILE_DIRNAME HOME LOGNAME SHELL TERM \ USER FILESPATH STAGING_DIR_HOST STAGING_DIR_TARGET COREBASE PRSERV_HOST \ PRSERV_DUMPDIR PRSERV_DUMPFILE PRSERV_LOCKDOWN PARALLEL_MAKE \ CCACHE_DIR EXTERNAL_TOOLCHAIN CCACHE CCACHE_DISABLE LICENSE_PATH SDKPKGSUFFIX"
The previous example excludes
WORKDIR
since that variable is actually constructed as a path within
TMPDIR
,
which is on the whitelist.
The rules for deciding which hashes of dependent tasks to
include through dependency chains are more complex and are
generally accomplished with a Python function.
The code in meta/lib/oe/sstatesig.py
shows
two examples of this and also illustrates how you can insert
your own policy into the system if so desired.
This file defines the two basic signature generators
OE-Core
uses: "OEBasic" and "OEBasicHash".
By default, a dummy "noop" signature handler is enabled
in BitBake.
This means that behavior is unchanged from previous versions.
OE-Core uses the "OEBasicHash" signature handler by default
through this setting in the bitbake.conf
file:
BB_SIGNATURE_HANDLER ?= "OEBasicHash"
The "OEBasicHash" BB_SIGNATURE_HANDLER
is the same as the "OEBasic" version but adds the task hash to
the
stamp files.
This results in any metadata change that changes the task hash,
automatically causing the task to be run again.
This removes the need to bump
PR
values, and changes to metadata automatically ripple across
the build.
It is also worth noting that the end result of these signature generators is to make some dependency and hash information available to the build. This information includes:
BB_BASEHASH_task-
taskname
:
The base hashes for each task in the recipe.
BB_BASEHASH_
filename
:
taskname
:
The base hashes for each dependent task.
BBHASHDEPS_
filename
:
taskname
:
The task dependencies for each task.
BB_TASKHASH
:
The hash of the currently running task.
Checksums and dependencies, as discussed in the previous section, solve half the problem of supporting a shared state. The other half of the problem is being able to use checksum information during the build and being able to reuse or rebuild specific components.
The
sstate
class is a relatively generic implementation of how to
"capture" a snapshot of a given task.
The idea is that the build process does not care about the
source of a task's output.
Output could be freshly built or it could be downloaded and
unpacked from somewhere.
In other words, the build process does not need to worry about
its origin.
Two types of output exist.
One type is just about creating a directory in
WORKDIR
.
A good example is the output of either
do_install
or
do_package
.
The other type of output occurs when a set of data is merged
into a shared directory tree such as the sysroot.
The Yocto Project team has tried to keep the details of the
implementation hidden in sstate
class.
From a user's perspective, adding shared state wrapping to a
task is as simple as this
do_deploy
example taken from the
deploy
class:
DEPLOYDIR = "${WORKDIR}/deploy-${PN}" SSTATETASKS += "do_deploy" do_deploy[sstate-inputdirs] = "${DEPLOYDIR}" do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}" python do_deploy_setscene () { sstate_setscene(d) } addtask do_deploy_setscene do_deploy[dirs] = "${DEPLOYDIR} ${B}" do_deploy[stamp-extra-info] = "${MACHINE_ARCH}"
The following list explains the previous example:
Adding "do_deploy" to SSTATETASKS
adds some required sstate-related processing, which is
implemented in the
sstate
class, to before and after the
do_deploy
task.
The
do_deploy[sstate-inputdirs] = "${DEPLOYDIR}"
declares that do_deploy
places its
output in ${DEPLOYDIR}
when run
normally (i.e. when not using the sstate cache).
This output becomes the input to the shared state cache.
The
do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}"
line causes the contents of the shared state cache to be
copied to ${DEPLOY_DIR_IMAGE}
.
do_deploy
is not already in
the shared state cache or if its input checksum
(signature) has changed from when the output was
cached, the task runs to populate the shared
state cache, after which the contents of the shared
state cache is copied to
${DEPLOY_DIR_IMAGE}
.
If do_deploy
is in the shared
state cache and its signature indicates that the
cached output is still valid (i.e. if no
relevant task inputs have changed), then the
contents of the shared state cache copies
directly to
${DEPLOY_DIR_IMAGE}
by the
do_deploy_setscene
task
instead, skipping the
do_deploy
task.
The following task definition is glue logic needed to make the previous settings effective:
python do_deploy_setscene () { sstate_setscene(d) } addtask do_deploy_setscene
sstate_setscene()
takes the flags
above as input and accelerates the
do_deploy
task through the
shared state cache if possible.
If the task was accelerated,
sstate_setscene()
returns True.
Otherwise, it returns False, and the normal
do_deploy
task runs.
For more information, see the
"setscene"
section in the BitBake User Manual.
The do_deploy[dirs] = "${DEPLOYDIR} ${B}"
line creates ${DEPLOYDIR}
and
${B}
before the
do_deploy
task runs, and also sets
the current working directory of
do_deploy
to
${B}
.
For more information, see the
"Variable Flags"
section in the BitBake User Manual.
sstate-inputdirs
and
sstate-outputdirs
would be the
same, you can use
sstate-plaindirs
.
For example, to preserve the
${PKGD}
and
${PKGDEST}
output from the
do_package
task, use the following:
do_package[sstate-plaindirs] = "${PKGD} ${PKGDEST}"
The do_deploy[stamp-extra-info] = "${MACHINE_ARCH}"
line appends extra metadata to the
stamp file.
In this case, the metadata makes the task specific
to a machine's architecture.
See
"The Task List"
section in the BitBake User Manual for more
information on the stamp-extra-info
flag.
sstate-inputdirs
and
sstate-outputdirs
can also be used
with multiple directories.
For example, the following declares
PKGDESTWORK
and
SHLIBWORK
as shared state
input directories, which populates the shared state
cache, and PKGDATA_DIR
and
SHLIBSDIR
as the corresponding
shared state output directories:
do_package[sstate-inputdirs] = "${PKGDESTWORK} ${SHLIBSWORKDIR}" do_package[sstate-outputdirs] = "${PKGDATA_DIR} ${SHLIBSDIR}"
These methods also include the ability to take a lockfile when manipulating shared state directory structures, for cases where file additions or removals are sensitive:
do_package[sstate-lockfile] = "${PACKAGELOCK}"
Behind the scenes, the shared state code works by looking in
SSTATE_DIR
and
SSTATE_MIRRORS
for shared state files.
Here is an example:
SSTATE_MIRRORS ?= "\ file://.* http://someserver.tld/share/sstate/PATH;downloadfilename=PATH \n \ file://.* file:///some/local/dir/sstate/PATH"
SSTATE_DIR
) is organized into
two-character subdirectories, where the subdirectory
names are based on the first two characters of the hash.
If the shared state directory structure for a mirror has the
same structure as SSTATE_DIR
, you must
specify "PATH" as part of the URI to enable the build system
to map to the appropriate subdirectory.
The shared state package validity can be detected just by looking at the filename since the filename contains the task checksum (or signature) as described earlier in this section. If a valid shared state package is found, the build process downloads it and uses it to accelerate the task.
The build processes use the *_setscene
tasks for the task acceleration phase.
BitBake goes through this phase before the main execution
code and tries to accelerate any tasks for which it can find
shared state packages.
If a shared state package for a task is available, the
shared state package is used.
This means the task and any tasks on which it is dependent
are not executed.
As a real world example, the aim is when building an IPK-based
image, only the
do_package_write_ipk
tasks would have their shared state packages fetched and
extracted.
Since the sysroot is not used, it would never get extracted.
This is another reason why a task-based approach is preferred
over a recipe-based approach, which would have to install the
output from every task.
The OpenEmbedded build system automatically adds common types of
runtime dependencies between packages, which means that you do not
need to explicitly declare the packages using
RDEPENDS
.
Three automatic mechanisms exist (shlibdeps
,
pcdeps
, and depchains
)
that handle shared libraries, package configuration (pkg-config)
modules, and -dev
and
-dbg
packages, respectively.
For other types of runtime dependencies, you must manually declare
the dependencies.
shlibdeps
:
During the
do_package
task of each recipe, all shared libraries installed by the
recipe are located.
For each shared library, the package that contains the
shared library is registered as providing the shared
library.
More specifically, the package is registered as providing
the
soname
of the library.
The resulting shared-library-to-package mapping
is saved globally in
PKGDATA_DIR
by the
do_packagedata
task.
Simultaneously, all executables and shared libraries
installed by the recipe are inspected to see what shared
libraries they link against.
For each shared library dependency that is found,
PKGDATA_DIR
is queried to
see if some package (likely from a different recipe)
contains the shared library.
If such a package is found, a runtime dependency is added
from the package that depends on the shared library to the
package that contains the library.
The automatically added runtime dependency also
includes a version restriction.
This version restriction specifies that at least the
current version of the package that provides the shared
library must be used, as if
"package
(>= version
)"
had been added to RDEPENDS
.
This forces an upgrade of the package containing the shared
library when installing the package that depends on the
library, if needed.
If you want to avoid a package being registered as
providing a particular shared library (e.g. because the library
is for internal use only), then add the library to
PRIVATE_LIBS
inside the package's recipe.
pcdeps
:
During the do_package
task of each
recipe, all pkg-config modules
(*.pc
files) installed by the recipe
are located.
For each module, the package that contains the module is
registered as providing the module.
The resulting module-to-package mapping is saved globally in
PKGDATA_DIR
by the
do_packagedata
task.
Simultaneously, all pkg-config modules installed by
the recipe are inspected to see what other pkg-config
modules they depend on.
A module is seen as depending on another module if it
contains a "Requires:" line that specifies the other module.
For each module dependency,
PKGDATA_DIR
is queried to see if some
package contains the module.
If such a package is found, a runtime dependency is added
from the package that depends on the module to the package
that contains the module.
pcdeps
mechanism most often
infers dependencies between -dev
packages.
depchains
:
If a package foo
depends on a package
bar
, then foo-dev
and foo-dbg
are also made to depend on
bar-dev
and
bar-dbg
, respectively.
Taking the -dev
packages as an
example, the bar-dev
package might
provide headers and shared library symlinks needed by
foo-dev
, which shows the need
for a dependency between the packages.
The dependencies added by
depchains
are in the form of
RRECOMMENDS
.
foo-dev
also has an
RDEPENDS
-style dependency on
foo
, because the default value of
RDEPENDS_${PN}-dev
(set in
bitbake.conf
) includes
"${PN}".
To ensure that the dependency chain is never broken,
-dev
and -dbg
packages are always generated by default, even if the
packages turn out to be empty.
See the
ALLOW_EMPTY
variable for more information.
The do_package
task depends on the
do_packagedata
task of each recipe in
DEPENDS
through use of a
[
deptask
]
declaration, which guarantees that the required
shared-library/module-to-package mapping information will be available
when needed as long as DEPENDS
has been
correctly set.
Some tasks are easier to implement when allowed to perform certain
operations that are normally reserved for the root user (e.g.
do_install
,
do_package_write*
,
do_rootfs
,
and
do_image*
).
For example, the do_install
task benefits
from being able to set the UID and GID of installed files to
arbitrary values.
One approach to allowing tasks to perform root-only operations would be to require BitBake to run as root. However, this method is cumbersome and has security issues. The approach that is actually used is to run tasks that benefit from root privileges in a "fake" root environment. Within this environment, the task and its child processes believe that they are running as the root user, and see an internally consistent view of the filesystem. As long as generating the final output (e.g. a package or an image) does not require root privileges, the fact that some earlier steps ran in a fake root environment does not cause problems.
The capability to run tasks in a fake root environment is known as "fakeroot", which is derived from the BitBake keyword/variable flag that requests a fake root environment for a task.
In the
OpenEmbedded build system,
the program that implements fakeroot is known as Pseudo.
Pseudo overrides system calls by using the environment variable
LD_PRELOAD
, which results in the illusion
of running as root.
To keep track of "fake" file ownership and permissions resulting
from operations that require root permissions, Pseudo uses
an SQLite 3 database.
This database is stored in
${
WORKDIR
}/pseudo/files.db
for individual recipes.
Storing the database in a file as opposed to in memory
gives persistence between tasks and builds, which is not
accomplished using fakeroot.
virtual/fakeroot-native:do_populate_sysroot
,
giving the following:
fakeroot do_mytask () { ... } do_mytask[depends] += "virtual/fakeroot-native:do_populate_sysroot"
For more information, see the
FAKEROOT*
variables in the BitBake User Manual.
You can also reference the
"Pseudo"
and
"Why Not Fakeroot?"
articles for background information on Pseudo.
Welcome to the Yocto Project Development Tasks Manual! This manual provides relevant procedures necessary for developing in the Yocto Project environment (i.e. developing embedded Linux images and user-space applications that run on targeted devices). The manual groups related procedures into higher-level sections. Procedures can consist of high-level steps or low-level steps depending on the topic.
The following list describes what you can get from this manual:
Procedures that help you get going with the Yocto Project. For example, procedures that show you how to set up a build host and work with the Yocto Project source repositories.
Procedures that show you how to submit changes to the Yocto Project. Changes can be improvements, new features, or bug fixes.
Procedures related to "everyday" tasks you perform while developing images and applications using the Yocto Project. For example, procedures to create a layer, customize an image, write a new recipe, and so forth.
This manual will not give you the following:
Redundant Step-by-step Instructions: For example, the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual contains detailed instructions on how to install an SDK, which is used to develop applications for target hardware.
Reference or Conceptual 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 Not Specific to the Yocto Project: For example, exhaustive information on how to use the Source Control Manager Git is better covered with Internet searches and official Git Documentation than through the Yocto Project documentation.
Because this manual presents information for many different topics, supplemental information is recommended for full comprehension. For introductory information on the Yocto Project, see the Yocto Project Website. If you want to build an image with no knowledge of Yocto Project as a way of quickly testing it out, see the Yocto Project Quick Build document.
For a comprehensive list of links and other documentation, see the "Links and Related Documentation" section in the Yocto Project Reference Manual.
This chapter provides procedures related to getting set up to use the Yocto Project. You can learn about creating a team environment that develops using the Yocto Project, how to set up a build host, how to locate Yocto Project source repositories, and how to create local Git repositories.
It might not be immediately clear how you can use the Yocto Project in a team development 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 you understand how to set up this type of environment, this section presents a procedure that gives you the information to learn how to get the results you want. The procedure is high-level and presents some of the project's most successful experiences, practices, solutions, and available technologies that work well. Keep in mind, the procedure here is a starting point. You can build off it and customize it to fit any particular working environment and set of practices.
Determine Who is Going to be Developing: You need to understand who is going to be doing anything related to the Yocto Project and what their roles would be. Making this determination is essential to completing the steps two and three, which are to get your equipment together and set up your development environment's hardware topology.
The following roles exist:
Application Development: These types of developers do application level work on top of an existing software stack.
Core System Development: These types of developers work on the contents of the operating system image itself.
Build Engineer: This type of developer manages Autobuilders and releases. Not all environments need a Build Engineer.
Test Engineer: This type of developer creates and manages automated tests needed to ensure all application and core system development meets desired quality standards.
Gather the Hardware: Based on the size and make-up of the team, get the hardware together. Any development, build, or test engineer should be using a system that is running a supported Linux distribution. Systems, in general, should be high performance (e.g. dual, six-core Xeons with 24 Gbytes of RAM and plenty of disk space). You can help ensure efficiency by having any machines used for testing or that run Autobuilders be as high performance as possible.
Understand the Hardware Topology of the Environment: Once you understand the hardware involved and the make-up of the team, you can understand the hardware topology of the development environment. You can get a visual idea of the machines and their roles across the development environment.
Use Git as Your Source Control Manager (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, allows you to work remotely, and then connects back to the infrastructure.
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.
Git documentation:
Describes how to install gitolite
on the server.
Gitolite:
Information for gitolite
.
Interfaces, frontends, and tools: Documentation on how to create interfaces and frontends for Git.
Set up the Application Development Machines: As mentioned earlier, application developers are creating applications on top of existing software stacks. Following are some best practices for setting up machines that do application development:
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 SDK development practices. For more information, see the "Yocto Project Application Development and the Extensible Software Development Kit (eSDK)" manual.
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.
Set up the Core Development Machines: As mentioned earlier, these types of developers work on the contents of the operating system itself. Following are some best practices for setting up machines used for developing images:
Have the Yocto Project build system itself available on the developer workstations so developers can run their own builds and directly rebuild the software stack.
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).
Share layers amongst the developers of a particular project and contain the policy configuration that defines the project.
Set up an Autobuilder: Autobuilders are often the core of the development environment. 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 "Yocto Project Autobuilder" for more information and links to 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.
Set up Test Machines: Use a small number of shared, high performance systems for testing purposes. Developers can use these systems for wider, more extensive testing while they continue to develop locally using their primary development system.
Document 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.
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.
Development Environment Summary: Aside from the previous steps, some best practices exist within the Yocto Project development environment. Consider the following:
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 "Locating Yocto Project Source Files" section for information on how to set up local Git repositories for related upstream Yocto Project 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 "Submitting a Change to the Yocto Project" section.
Send changes to the core sooner than later as others are likely to run into the same issues. For some guidance on mailing lists to use, see the list in the "Submitting a Change to the Yocto Project" section. For a description of the available mailing lists, see the "Mailing Lists" section in the Yocto Project Reference Manual.
This section provides procedures to set up your development host to use the Yocto Project. You can use the Yocto Project on a native Linux development host or you can use CROPS, which leverages Docker Containers, to prepare any Linux, Mac, or Windows development host.
Once your development host is set up to use the Yocto Project, further steps are necessary depending on what you want to accomplish. See the following references for information on how to prepare for Board Support Package (BSP) development, kernel development, and development using the Eclipse™ IDE:
BSP Development: See the "Preparing Your Build Host to Work With BSP Layers" section in the Yocto Project Board Support Package (BSP) Developer's Guide.
Kernel Development: See the "Preparing the Build Host to Work on the Kernel" section in the Yocto Project Linux Kernel Development Manual.
Eclipse Development: See the "Developing Applications Using Eclipse™" Chapter in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.
Follow these steps to prepare a native Linux machine as your Yocto Project development host:
Use a Supported Linux Distribution: 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.
Have Enough Free Memory: You should have at least 50 Gbytes of free disk space for building images.
Meet Minimal Version Requirements: The OpenEmbedded build system should be able to run on any modern distribution that has the following versions for Git, tar, and Python.
Git 1.8.3.1 or greater
tar 1.27 or greater
Python 3.4.0 or greater.
If your build host does not meet any of these three listed version requirements, you can take steps to prepare the system so that you can still use the Yocto Project. See the "Required Git, tar, and Python Versions" section in the Yocto Project Reference Manual for information.
Install Development Host Packages: Required development host packages vary depending on your build machine and what you want to do with the Yocto Project. Collectively, the number of required packages is large if you want to be able to cover all cases.
For lists of required packages for all scenarios, see the "Required Packages for the Host Development System" section in the Yocto Project Reference Manual.
Once you have completed the previous steps, you are ready to
continue using a given development path on your native Linux
machine.
If you are going to use BitBake, see the
"Cloning the poky
Repository"
section.
If you are going to use the Extensible SDK, see the
"Using the Extensible SDK"
Chapter in the Yocto Project Application Development and the
Extensible Software Development Kit (eSDK) manual.
If you want to work on the kernel, see the
Yocto Project Linux Kernel Development Manual.
If you are going to use Toaster, see the
"Setting Up and Using Toaster"
section in the Toaster User Manual.
With CROPS, which leverages Docker Containers, you can create a Yocto Project development environment that is operating system agnostic. You can set up a container in which you can develop using the Yocto Project on a Windows, Mac, or Linux machine.
Follow these general steps to prepare a Windows, Mac, or Linux machine as your Yocto Project development host:
Go to the Docker Installation Site: Docker is a software container platform that you need to install on the host development machine. To start the installation process, see the Docker Installation site.
Choose Your Docker Edition: Docker comes in several editions. For the Yocto Project, the stable community edition (i.e. "Docker CE Stable") is adequate. You can learn more about the Docker editions from the site.
Go to the Install Site for Your Platform: Click the link for the Docker edition associated with your development host machine's native software. For example, if your machine is running Microsoft Windows Version 10 and you want the Docker CE Stable edition, click that link under "Supported Platforms".
Understand What You Need: The install page has pre-requisites your machine must meet. Be sure you read through this page and make sure your machine meets the requirements to run Docker. If your machine does not meet the requirements, the page has instructions to handle exceptions. For example, to run Docker on Windows 10, you must have the pro version of the operating system. If you have the home version, you need to install the Docker Toolbox.
Another example is that a Windows machine needs to have Microsoft Hyper-V. If you have a legacy version of the the Microsoft operating system or for any other reason you do not have Microsoft Hyper-V, you would have to enter the BIOS and enable virtualization.
Install the Software: Once you have understood all the pre-requisites, you can download and install the appropriate software. Follow the instructions for your specific machine and the type of the software you need to install.
Optionally Orient Yourself With Docker: If you are unfamiliar with Docker and the container concept, you can learn more here - https://docs.docker.com/get-started/. You should be able to launch Docker or the Docker Toolbox and have a terminal shell on your development host.
Set Up the Containers to Use the Yocto Project: Go to https://github.com/crops/docker-win-mac-docs/wiki and follow the directions for your particular development host (i.e. Linux, Mac, or Windows).
Once you complete the setup instructions for your machine, you have the Poky, Extensible SDK, and Toaster containers available. You can click those links from the page and learn more about using each of those containers.
Once you have a container set up, everything is in place to
develop just as if you were running on a native Linux machine.
If you are going to use the Poky container, see the
"Cloning the poky
Repository"
section.
If you are going to use the Extensible SDK container, see the
"Using the Extensible SDK"
Chapter in the Yocto Project Application Development and the
Extensible Software Development Kit (eSDK) manual.
If you are going to use the Toaster container, see the
"Setting Up and Using Toaster"
section in the Toaster User Manual.
This section contains procedures related to locating Yocto Project files. You establish and use these local files to work on projects.
For concepts and introductory information about Git as it is used in the Yocto Project, see the "Git" section in the Yocto Project Overview and Concepts Manual.
For concepts on Yocto Project source repositories, see the "Yocto Project Source Repositories" section in the Yocto Project Overview and Concepts Manual."
Working from a copy of the upstream Yocto Project
Source Repositories
is the preferred method for obtaining and using a Yocto Project
release.
You can view the Yocto Project Source Repositories at
http://git.yoctoproject.org.
In particular, you can find the
poky
repository at
http://git.yoctoproject.org/cgit/cgit.cgi/poky/.
Use the following procedure to locate the latest upstream copy of
the poky
Git repository:
Access Repositories: Open a browser and go to http://git.yoctoproject.org to access the GUI-based interface into the Yocto Project source repositories.
Select the Repository:
Click on the repository in which you are interested (i.e.
poky
).
Find the URL Used to Clone the Repository:
At the bottom of the page, note the URL used to
clone
that repository (e.g.
http://git.yoctoproject.org/poky
).
poky
Repository"
section.
Yocto Project maintains an Index of Releases area that contains related files that contribute to the Yocto Project. Rather than Git repositories, these files are tarballs that represent snapshots in time of a given component.
Access the Index of Releases:
Open a browser and go to
http://downloads.yoctoproject.org/releases to access the
Index of Releases.
The list represents released components (e.g.
eclipse-plugin
,
sato
, and so on).
yocto
directory contains the
full array of released Poky tarballs.
The poky
directory in the
Index of Releases was historically used for very
early releases and exists now only for retroactive
completeness.
Select a Component:
Click on any released component in which you are interested
(e.g. yocto
).
Find the Tarball:
Drill down to find the associated tarball.
For example, click on yocto-2.5.3
to
view files associated with the Yocto Project 2.5.3
release (e.g. poky-sumo-20.0.3.tar.bz2
,
which is the released Poky tarball).
Download the Tarball: Click the tarball to download and save a snapshot of the given component.
The Yocto Project Website uses a "DOWNLOADS" page from which you can locate and download tarballs of any Yocto Project release. Rather than Git repositories, these files represent snapshot tarballs.
Go to the Yocto Project Website: Open The Yocto Project Website in your browser.
Get to the Downloads Area: Select the "DOWNLOADS" item from the pull-down "SOFTWARE" tab menu.
Select a Yocto Project Release: Use the menu next to "RELEASE" to display and choose a Yocto Project release (e.g. sumo, rocko, pyro, and so forth. For a "map" of Yocto Project releases to version numbers, see the Releases wiki page.
Download Tools or Board Support Packages (BSPs): From the "DOWNLOADS" page, you can download tools or BSPs as well. Just scroll down the page and look for what you need.
Yocto Project maintains an area for nightly builds that contains tarball releases at https://autobuilder.yocto.io//pub/nightly/. These builds include Yocto Project releases, SDK installation scripts, and experimental builds.
Should you ever want to access a nightly build of a particular Yocto Project component, use the following procedure:
Access the Nightly Builds: Open a browser and go to https://autobuilder.yocto.io//pub/nightly/ to access the Nightly Builds.
Select a Build: Click on any build by date in which you are interested.
Find the Tarball: Drill down to find the associated tarball.
Download the Tarball: Click the tarball to download and save a snapshot of the given component.
To use the Yocto Project, you need a release of the Yocto Project locally installed on your development system. The locally installed set of files is referred to as the Source Directory in the Yocto Project documentation.
You create your Source Directory by using
Git to clone a local
copy of the upstream poky
repository.
Working from a copy of the upstream repository allows you to contribute back into the Yocto Project or simply work with the latest software on a development branch. Because Git maintains and creates an upstream repository with a complete history of changes and you are working with a local clone of that repository, you have access to all the Yocto Project development branches and tag names used in the upstream repository.
poky
Repository¶
Follow these steps to create a local version of the
upstream
poky
Git repository.
Set Your Directory: Be in the directory where you want to create your local copy of poky.
Clone the Repository: The following command clones the repository and uses the default name "poky" for your local repository:
$ git clone git://git.yoctoproject.org/poky Cloning into 'poky'... remote: Counting objects: 431956, done. remote: Compressing objects: 100% (101918/101918), done. remote: Total 431956 (delta 322982), reused 431910 (delta 322936) Receiving objects: 100% (431956/431956), 153.76 MiB | 6.86 MiB/s, done. Resolving deltas: 100% (322982/322982), done. Checking connectivity... done.
Unless you specify a specific development branch or tag name, Git clones the "master" branch, which results in a snapshot of the latest development changes for "master". For information on how to check out a specific development branch or on how to check out a local branch based on a tag name, see the "Checking Out By Branch in Poky" and Checking Out By Tag in Poky" sections, respectively.
Once the repository is created, you can change to that directory and check its status. Here, the single "master" branch exists on your system and by default, it is checked out:
$ cd ~/poky $ git status On branch master Your branch is up-to-date with 'origin/master'. nothing to commit, working directory clean $ git branch * master
Your local repository of poky is identical to the upstream poky repository at the time from which it was cloned.
When you clone the upstream poky repository, you have access to all its development branches. Each development branch in a repository is unique as it forks off the "master" branch. To see and use the files of a particular development branch locally, you need to know the branch name and then specifically check out that development branch.
Switch to the Poky Directory:
If you have a local poky Git repository, switch to that
directory.
If you do not have the local copy of poky, see the
"Cloning the poky
Repository"
section.
Determine Existing Branch Names:
$ git branch -a * master remotes/origin/1.1_M1 remotes/origin/1.1_M2 remotes/origin/1.1_M3 remotes/origin/1.1_M4 remotes/origin/1.2_M1 remotes/origin/1.2_M2 remotes/origin/1.2_M3 . . . remotes/origin/rocko remotes/origin/rocko-next remotes/origin/sumo remotes/origin/sumo-next remotes/origin/thud remotes/origin/thud-next
Checkout the Branch: Checkout the development branch in which you want to work. For example, to access the files for the Yocto Project 2.5.3 Release (Sumo), use the following command:
$ git checkout -b sumo origin/sumo Branch sumo set up to track remote branch sumo from origin. Switched to a new branch 'sumo'
The previous command checks out the "sumo" development branch and reports that the branch is tracking the upstream "origin/sumo" branch.
The following command displays the branches that are now part of your local poky repository. The asterisk character indicates the branch that is currently checked out for work:
$ git branch master * sumo
Similar to branches, the upstream repository uses tags to mark specific commits associated with significant points in a development branch (i.e. a release point or stage of a release). You might want to set up a local branch based on one of those points in the repository. The process is similar to checking out by branch name except you use tag names.
Switch to the Poky Directory:
If you have a local poky Git repository, switch to that
directory.
If you do not have the local copy of poky, see the
"Cloning the poky
Repository"
section.
Fetch the Tag Names: To checkout the branch based on a tag name, you need to fetch the upstream tags into your local repository:
$ git fetch --tags $
List the Tag Names: You can list the tag names now:
$ git tag 1.1_M1.final 1.1_M1.rc1 1.1_M1.rc2 1.1_M2.final 1.1_M2.rc1 . . . yocto-2.5.2 yocto-2.5.3 yocto-2.6 yocto-2.6.1 yocto_1.5_M5.rc8
Checkout the Branch:
$ git checkout tags/yocto-2.5.3 -b my_yocto_2.5.3 Switched to a new branch 'my_yocto_2.5.3' $ git branch master * my_yocto_2.5.3
The previous command creates and checks out a local
branch named "my_yocto_2.5.3", which is based on
the commit in the upstream poky repository that has
the same tag.
In this example, the files you have available locally
as a result of the checkout
command are a snapshot of the
"sumo" development branch at the point
where Yocto Project 2.5.3 was released.
bitbake-layers
Scriptbitbake-layers
Scriptbmaptool
oe-pkgdata-util
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 that the procedures documented here occur often in the development cycle using the Yocto Project.
The OpenEmbedded build system supports organizing Metadata into multiple layers. Layers allow you to isolate different types of customizations from each other. For introductory information on the Yocto Project Layer Model, see the "The Yocto Project Layer Model" section in the Yocto Project Overview and Concepts Manual.
It is very easy to create your own layers to use with the
OpenEmbedded build system.
The Yocto Project ships with tools that speed up creating
layers.
This section describes the steps you perform by hand to create
layers so that you can better understand them.
For information about the layer-creation tools, see the
"Creating a New BSP Layer Using the bitbake-layers
Script"
section in the Yocto Project Board Support Package (BSP)
Developer's Guide and the
"Creating a General Layer Using the bitbake-layers
Script"
section further down in this manual.
Follow these general steps to create your layer without using tools:
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. You could find a layer that is identical or close to what you need.
Create a Directory:
Create the directory for your layer.
When you create the layer, be sure to create the
directory in an area not associated with the
Yocto Project
Source Directory
(e.g. the cloned poky
repository).
While not strictly required, prepend the name of the directory with the string "meta-". For example:
meta-mylayer meta-GUI_xyz meta-mymachine
With rare exceptions, a layer's name follows this form:
meta-root_name
Following this layer naming convention can save you trouble later when tools, components, or variables "assume" your layer name begins with "meta-". A notable example is in configuration files as shown in the following step where layer names without the "meta-" string are appended to several variables used in the configuration.
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
in the Yocto Project
Source Repositories
demonstrates the required syntax.
For your layer, you need to replace "yoctobsp" with
a unique identifier for your layer (e.g. "machinexyz"
for a layer named "meta-machinexyz"):
# 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" LAYERVERSION_yoctobsp = "4" LAYERSERIES_COMPAT_yoctobsp = "sumo"
Following is an explanation of the layer configuration file:
BBPATH
:
Adds the layer's root directory to BitBake's
search path.
Through the use of the
BBPATH
variable, BitBake
locates class files
(.bbclass
),
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.
It is recommended, therefore, that you use
unique class and configuration filenames in
your custom layer.
BBFILES
:
Defines the location for all recipes in the
layer.
BBFILE_COLLECTIONS
:
Establishes the current layer through a
unique identifier that is used throughout the
OpenEmbedded build system to refer to the layer.
In this example, the identifier "yoctobsp" is
the representation for the container layer
named "meta-yocto-bsp".
BBFILE_PATTERN
:
Expands immediately during parsing to
provide the directory of the layer.
BBFILE_PRIORITY
:
Establishes a priority to use for
recipes in the layer when the OpenEmbedded build
finds recipes of the same name in different
layers.
LAYERVERSION
:
Establishes a version number for the layer.
You can use this version number to specify this
exact version of the layer as a dependency when
using the
LAYERDEPENDS
variable.
LAYERSERIES_COMPAT
:
Lists the
Yocto Project
releases for which the current version is
compatible.
This variable is a good way to indicate how
up-to-date your particular layer is.
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 within the layer.
If the layer introduces new recipes, put the recipes
you need in recipes-*
subdirectories within the layer.
Optionally Test for Compatibility: If you want permission to use the Yocto Project Compatibility logo with your layer or application that uses your layer, perform the steps to apply for compatibility. See the "Making Sure Your Layer is Compatible With Yocto Project" section for more information.
To create layers that are easier to maintain and that will not impact builds for other machines, you should consider the information in the following list:
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.
Rather, use an append file
(.bbappend
) to override only those
parts of the original recipe you need to modify.
Avoid Duplicating Include Files:
Use append files (.bbappend
)
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/
package
/
file
.inc
instead of
require
file
.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 should try to address that
deficiency instead of overlaying the include file.
For example, you could address this by getting the
maintainer of the include file to add a variable or
variables to make it easy to override the parts needing
to be overridden.
Structure Your Layers: Proper use of overrides within append files and placement of machine-specific files within your layer can ensure that a build is not using the wrong Metadata and negatively impacting a build for a different machine. Following are some examples:
Modify Variables to Support a
Different Machine:
Suppose you have a layer named
meta-one
that adds support
for building machine "one".
To do so, you use an append file named
base-files.bbappend
and
create a dependency on "foo" by altering the
DEPENDS
variable:
DEPENDS = "foo"
The dependency is created during any build that
includes the layer
meta-one
.
However, you might not want this dependency
for all machines.
For example, suppose you are building for
machine "two" but your
bblayers.conf
file has the
meta-one
layer included.
During the build, the
base-files
for machine
"two" will also have the dependency on
foo
.
To make sure your changes apply only when
building machine "one", use a machine override
with the DEPENDS
statement:
DEPENDS_one = "foo"
You should follow the same strategy when using
_append
and
_prepend
operations:
DEPENDS_append_one = " foo" DEPENDS_prepend_one = "foo "
As an actual example, here's a line from the recipe for gnutls, which adds dependencies on "argp-standalone" when building with the musl C library:
DEPENDS_append_libc-musl = " argp-standalone"
_append
and _prepend
operations
is recommended as well.
Place Machine-Specific Files in
Machine-Specific Locations:
When you have a base recipe, such as
base-files.bb
, that
contains a
SRC_URI
statement to a file, you can use an append file
to cause the build to use your own version of
the file.
For example, an append file in your layer at
meta-one/recipes-core/base-files/base-files.bbappend
could extend
FILESPATH
using
FILESEXTRAPATHS
as follows:
FILESEXTRAPATHS_prepend := "${THISDIR}/${BPN}:"
The build for machine "one" will pick up your
machine-specific file as long as you have the
file in
meta-one/recipes-core/base-files/base-files/
.
However, if you are building for a different
machine and the
bblayers.conf
file includes
the meta-one
layer and
the location of your machine-specific file is
the first location where that file is found
according to FILESPATH
,
builds for all machines will also use that
machine-specific file.
You can make sure that a machine-specific
file is used for a particular machine by putting
the file in a subdirectory specific to the
machine.
For example, rather than placing the file in
meta-one/recipes-core/base-files/base-files/
as shown above, put it in
meta-one/recipes-core/base-files/base-files/one/
.
Not only does this make sure the file is used
only when building for machine "one", but the
build process locates the file more quickly.
In summary, you need to place all files
referenced from SRC_URI
in a machine-specific subdirectory within the
layer in order to restrict those files to
machine-specific builds.
Perform Steps to Apply for Yocto Project Compatibility: If you want permission to use the Yocto Project Compatibility logo with your layer or application that uses your layer, perform the steps to apply for compatibility. See the "Making Sure Your Layer is Compatible With Yocto Project" section for more information.
Follow the Layer Naming Convention:
Store custom layers in a Git repository that use the
meta-
format.
layer_name
Group Your Layers Locally:
Clone your repository alongside other cloned
meta
directories from the
Source Directory.
When you create a layer used with the Yocto Project, it is advantageous to make sure that the layer interacts well with existing Yocto Project layers (i.e. the layer is compatible with the Yocto Project). Ensuring compatibility makes the layer easy to be consumed by others in the Yocto Project community and could allow you permission to use the Yocto Project Compatible Logo.
The Yocto Project Compatibility Program consists of a layer application process that requests permission to use the Yocto Project Compatibility Logo for your layer and application. The process consists of two parts:
Successfully passing a script
(yocto-check-layer
) that
when run against your layer, tests it against
constraints based on experiences of how layers have
worked in the real world and where pitfalls have been
found.
Getting a "PASS" result from the script is required for
successful compatibility registration.
Completion of an application acceptance form, which you can find at https://www.yoctoproject.org/webform/yocto-project-compatible-registration.
To be granted permission to use the logo, you need to satisfy the following:
Be able to check the box indicating that you got a "PASS" when running the script against your layer.
Answer "Yes" to the questions on the form or have an acceptable explanation for any questions answered "No".
Be a Yocto Project Member Organization.
The remainder of this section presents information on the
registration form and on the
yocto-check-layer
script.
Use the form to apply for your layer's approval. Upon successful application, you can use the Yocto Project Compatibility Logo with your layer and the application that uses your layer.
To access the form, use this link: https://www.yoctoproject.org/webform/yocto-project-compatible-registration. Follow the instructions on the form to complete your application.
The application consists of the following sections:
Contact Information: Provide your contact information as the fields require. Along with your information, provide the released versions of the Yocto Project for which your layer is compatible.
Acceptance Criteria: Provide "Yes" or "No" answers for each of the items in the checklist. Space exists at the bottom of the form for any explanations for items for which you answered "No".
Recommendations: Provide answers for the questions regarding Linux kernel use and build success.
yocto-check-layer
Script¶
The yocto-check-layer
script
provides you a way to assess how compatible your layer is
with the Yocto Project.
You should run this script prior to using the form to
apply for compatibility as described in the previous
section.
You need to achieve a "PASS" result in order to have
your application form successfully processed.
The script divides tests into three areas: COMMON, BSP, and DISTRO. For example, given a distribution layer (DISTRO), the layer must pass both the COMMON and DISTRO related tests. Furthermore, if your layer is a BSP layer, the layer must pass the COMMON and BSP set of tests.
To execute the script, enter the following commands from your build directory:
$ source oe-init-build-env
$ yocto-check-layer your_layer_directory
Be sure to provide the actual directory for your layer as part of the command.
Entering the command causes the script to determine the type of layer and then to execute a set of specific tests against the layer. The following list overviews the test:
common.test_readme
:
Tests if a README
file
exists in the layer and the file is not empty.
common.test_parse
:
Tests to make sure that BitBake can parse the
files without error (i.e.
bitbake -p
).
common.test_show_environment
:
Tests that the global or per-recipe environment
is in order without errors (i.e.
bitbake -e
).
common.test_signatures
:
Tests to be sure that BSP and DISTRO layers do not
come with recipes that change signatures.
bsp.test_bsp_defines_machines
:
Tests if a BSP layer has machine configurations.
bsp.test_bsp_no_set_machine
:
Tests to ensure a BSP layer does not set the
machine when the layer is added.
distro.test_distro_defines_distros
:
Tests if a DISTRO layer has distro configurations.
distro.test_distro_no_set_distro
:
Tests to ensure a DISTRO layer does not set the
distribution when the layer is added.
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
:
# POKY_BBLAYERS_CONF_VERSION is increased each time build/conf/bblayers.conf # changes incompatibly POKY_BBLAYERS_CONF_VERSION = "2" BBPATH = "${TOPDIR}" BBFILES ?= "" BBLAYERS ?= " \ /home/user
/poky/meta \ /home/user
/poky/meta-poky \ /home/user
/poky/meta-yocto-bsp \ /home/user
/poky/meta-mylayer \ "
BitBake parses each conf/layer.conf
file
from the top down 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.
A recipe that appends Metadata to another recipe is called a
BitBake append file.
A BitBake append file uses the .bbappend
file type suffix, while the corresponding recipe to which
Metadata is being appended uses the .bb
file type suffix.
You can use a .bbappend
file in your
layer to make additions or changes to the content of another
layer's recipe without having to copy the other layer's
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.
Being able to append information to an existing recipe not only avoids duplication, but also automatically applies recipe changes from a different layer into your layer. If you were copying recipes, you would have to manually merge changes as they occur.
When you create an append file, you must use the same root
name as the corresponding recipe file.
For example, the append file
someapp_2.5.3.bbappend
must apply to
someapp_2.5.3.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, you must also rename and possibly update
the corresponding .bbappend
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.
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
:
SUMMARY = "Device formfactor information" SECTION = "base" LICENSE = "MIT" LIC_FILES_CHKSUM = "file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420" PR = "r45" SRC_URI = "file://config file://machconfig" S = "${WORKDIR}" PACKAGE_ARCH = "${MACHINE_ARCH}" INHIBIT_DEFAULT_DEPS = "1" do_install() { # Install file only if it has 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
Raspberry Pi BSP Layer named
meta-raspberrypi
.
The file is in the layer at
recipes-bsp/formfactor
:
FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
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-raspberrypi/recipes-bsp/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.
BitBake automatically defines the
THISDIR
variable.
You should never set this variable yourself.
Using "_prepend" as part of the
FILESEXTRAPATHS
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, your append file would not even
use the FILESEXTRAPATHS
statement.
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 and append the layer's root name:
BBFILE_PRIORITY_mylayer = "1"
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.
You can use the BitBake layer management tool
bitbake-layers
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.
For help on the BitBake layer management tool, use the following command:
$ bitbake-layers --help NOTE: Starting bitbake server... usage: bitbake-layers [-d] [-q] [-F] [--color COLOR] [-h] <subcommand> ... BitBake layers utility optional arguments: -d, --debug Enable debug output -q, --quiet Print only errors -F, --force Force add without recipe parse verification --color COLOR Colorize output (where COLOR is auto, always, never) -h, --help show this help message and exit subcommands: <subcommand> show-layers show current configured layers. show-overlayed list overlayed recipes (where the same recipe exists in another layer) show-recipes list available recipes, showing the layer they are provided by show-appends list bbappend files and recipe files they apply to show-cross-depends Show dependencies between recipes that cross layer boundaries. add-layer Add one or more layers to bblayers.conf. remove-layer Remove one or more layers from bblayers.conf. flatten flatten layer configuration into a separate output directory. layerindex-fetch Fetches a layer from a layer index along with its dependent layers, and adds them to conf/bblayers.conf. layerindex-show-depends Find layer dependencies from layer index. create-layer Create a basic layer Use bitbake-layers <subcommand> --help to get help on a specific command
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-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-recipes:
Lists available recipes and the layers that provide them.
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.
add-layer:
Adds a layer to bblayers.conf
.
remove-layer:
Removes a layer from bblayers.conf
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" ...
layerindex-fetch
:
Fetches a layer from a layer index, along with its
dependent layers, and adds the layers to the
conf/bblayers.conf
file.
layerindex-show-depends
:
Finds layer dependencies from the layer index.
create-layer
:
Creates a basic layer.
bitbake-layers
Script¶
The bitbake-layers
script with the
create-layer
subcommand simplifies
creating a new general layer.
For information on BSP layers, see the "BSP Layers" section in the Yocto Project Board Specific (BSP) Developer's Guide.
In order to use a layer with the OpenEmbedded
build system, you need to add the layer to your
bblayers.conf
configuration
file.
See the
"Adding a Layer Using the bitbake-layers
Script"
section for more information.
The default mode of the script's operation with this subcommand is to create a layer with the following:
A layer priority of 6.
A conf
subdirectory that contains a
layer.conf
file.
A recipes-example
subdirectory
that contains a further subdirectory named
example
, which contains
an example.bb
recipe file.
A COPYING.MIT
,
which is the license statement for the layer.
The script assumes you want to use the MIT license,
which is typical for most layers, for the contents of
the layer itself.
A README
file, which is a file
describing the contents of your new layer.
In its simplest form, you can use the following command form
to create a layer.
The command creates a layer whose name corresponds to
your_layer_name
in the current
directory:
$ bitbake-layers create-layer your_layer_name
As an example, the following command creates a layer named
meta-scottrif
in your home directory:
$ cd /usr/home $ bitbake-layers create-layer meta-scottrif NOTE: Starting bitbake server... Add your new layer with 'bitbake-layers add-layer meta-scottrif'
If you want to set the priority of the layer to other than the
default value of "6", you can either use the
‐‐priority
option or you can
edit the
BBFILE_PRIORITY
value in the conf/layer.conf
after the
script creates it.
Furthermore, if you want to give the example recipe file
some name other than the default, you can
use the
‐‐example-recipe-name
option.
The easiest way to see how the
bitbake-layers create-layer
command
works is to experiment with the script.
You can also read the usage information by entering the
following:
$ bitbake-layers create-layer --help NOTE: Starting bitbake server... usage: bitbake-layers create-layer [-h] [--priority PRIORITY] [--example-recipe-name EXAMPLERECIPE] layerdir Create a basic layer positional arguments: layerdir Layer directory to create optional arguments: -h, --help show this help message and exit --priority PRIORITY, -p PRIORITY Layer directory to create --example-recipe-name EXAMPLERECIPE, -e EXAMPLERECIPE Filename of the example recipe
bitbake-layers
Script¶
Once you create your general layer, you must add it to your
bblayers.conf
file.
Adding the layer to this configuration file makes the
OpenEmbedded build system aware of your layer so that it can
search it for metadata.
Add your layer by using the
bitbake-layers add-layer
command:
$ bitbake-layers add-layer your_layer_name
Here is an example that adds a layer named
meta-scottrif
to the configuration file.
Following the command that adds the layer is another
bitbake-layers
command that shows the
layers that are in your bblayers.conf
file:
$ bitbake-layers add-layer meta-scottrif NOTE: Starting bitbake server... Parsing recipes: 100% |##########################################################| Time: 0:00:49 Parsing of 1441 .bb files complete (0 cached, 1441 parsed). 2055 targets, 56 skipped, 0 masked, 0 errors. $ bitbake-layers show-layers NOTE: Starting bitbake server... layer path priority ========================================================================== meta /home/scottrif/poky/meta 5 meta-poky /home/scottrif/poky/meta-poky 5 meta-yocto-bsp /home/scottrif/poky/meta-yocto-bsp 5 workspace /home/scottrif/poky/build/workspace 99 meta-scottrif /home/scottrif/poky/build/meta-scottrif 6
Adding the layer to this file enables the build system to locate the layer during the build.
You can customize images to satisfy particular requirements. This section describes several methods and provides guidelines for each.
local.conf
¶
Probably the easiest way to customize an image is to add a
package by way of the local.conf
configuration 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 are in effect for every
build and consequently affect all images, which might not
be what you require.
To add a package to your image using the local configuration
file, use 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 the
core-image-minimal
image 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.
IMAGE_FEATURES
and
EXTRA_IMAGE_FEATURES
¶
Another method for customizing your image is to enable or
disable 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
.
This class lists out the available
IMAGE_FEATURES
of which most map to
package groups while some, such as
debug-tweaks
and
read-only-rootfs
, resolve as general
configuration settings.
In summary, the file looks at the contents of the
IMAGE_FEATURES
variable and then maps
or configures the feature accordingly.
Based on this information, the build system automatically
adds the appropriate packages or configurations 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-full-cmdline
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
.
You can also customize an image by creating a custom recipe that defines additional software as part of the image. The following example shows the form for the two lines you need:
IMAGE_INSTALL = "packagegroup-core-x11-base package1 package2" inherit core-image
Defining the software using a custom recipe gives you 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. glibc-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"
For complex custom images, the best approach for customizing
an image 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-base.bb
.
If you examine that recipe, you see that the
PACKAGES
variable lists the package group packages to produce.
The inherit packagegroup
statement
sets appropriate default values and automatically adds
-dev
, -dbg
, and
-ptest
complementary packages for each
package specified in the PACKAGES
statement.
inherit packages
should be
located near the top of the recipe, certainly before
the PACKAGES
statement.
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.
You can see examples of these further down in the
packagegroup-base.bb
recipe.
Here is a short, fabricated example showing the same basic pieces:
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-tools" 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.
By default, the configured hostname (i.e.
/etc/hostname
) in an image is the
same as the machine name.
For example, if
MACHINE
equals "qemux86", the configured hostname written to
/etc/hostname
is "qemux86".
You can customize this name by altering the value of the
"hostname" variable in the
base-files
recipe using either
an append file or a configuration file.
Use the following in an append file:
hostname="myhostname"
Use the following in a configuration file:
hostname_pn-base-files = "myhostname"
Changing the default value of the variable "hostname" can be useful in certain situations. For example, suppose you need to do extensive testing on an image and you would like to easily identify the image under test from existing images with typical default hostnames. In this situation, you could change the default hostname to "testme", which results in all the images using the name "testme". Once testing is complete and you do not need to rebuild the image for test any longer, you can easily reset the default hostname.
Another point of interest is that if you unset the variable, the image will have no default hostname in the filesystem. Here is an example that unsets the variable in a configuration file:
hostname_pn-base-files = ""
Having no default hostname in the filesystem is suitable for environments that use dynamic hostnames such as virtual machines.
Recipes (.bb
files) are fundamental components
in the Yocto Project environment.
Each software component built by the OpenEmbedded build system
requires a recipe to define the component.
This section describes how to create, write, and test a new
recipe.
The following figure shows the basic process for creating a new recipe. The remainder of the section provides details for the steps.
You can always write a recipe from scratch. However, three choices exist that can help you quickly get a start on a new recipe:
devtool add
:
A command that assists in creating a recipe and
an environment conducive to development.
recipetool create
:
A command provided by the Yocto Project that automates
creation of a base recipe based on the source
files.
Existing Recipes: Location and modification of an existing recipe that is similar in function to the recipe you need.
devtool add
¶
The devtool add
command uses the same
logic for auto-creating the recipe as
recipetool create
, which is listed
below.
Additionally, however, devtool add
sets up an environment that makes it easy for you to
patch the source and to make changes to the recipe as
is often necessary when adding a recipe to build a new
piece of software to be included in a build.
You can find a complete description of the
devtool add
command in the
"A Closer Look at devtool
add"
section in the Yocto Project Application Development
and the Extensible Software Development Kit (eSDK) manual.
recipetool create
¶
recipetool create
automates creation
of a base recipe given a set of source code files.
As long as you can extract or point to the source files,
the tool will construct a recipe and automatically
configure all pre-build information into the recipe.
For example, suppose you have an application that builds
using Autotools.
Creating the base recipe using
recipetool
results in a recipe
that has the pre-build dependencies, license requirements,
and checksums configured.
To run the tool, you just need to be in your
Build Directory
and have sourced the build environment setup script
(i.e.
oe-init-build-env
).
To get help on the tool, use the following command:
$ recipetool -h NOTE: Starting bitbake server... usage: recipetool [-d] [-q] [--color COLOR] [-h] <subcommand> ... OpenEmbedded recipe tool options: -d, --debug Enable debug output -q, --quiet Print only errors --color COLOR Colorize output (where COLOR is auto, always, never) -h, --help show this help message and exit subcommands: create Create a new recipe newappend Create a bbappend for the specified target in the specified layer setvar Set a variable within a recipe appendfile Create/update a bbappend to replace a target file appendsrcfiles Create/update a bbappend to add or replace source files appendsrcfile Create/update a bbappend to add or replace a source file Use recipetool <subcommand> --help to get help on a specific command
Running
recipetool create -o
OUTFILE
creates the base recipe and locates it properly in the
layer that contains your source files.
Following are some syntax examples:
Use this syntax to generate a recipe based on
source
.
Once generated, the recipe resides in the existing source
code layer:
recipetool create -oOUTFILE
source
Use this syntax to generate a recipe using code that you
extract from source
.
The extracted code is placed in its own layer defined
by EXTERNALSRC
.
recipetool create -oOUTFILE
-xEXTERNALSRC
source
Use this syntax to generate a recipe based on
source
.
The options direct recipetool
to
generate debugging information.
Once generated, the recipe resides in the existing source
code layer:
recipetool create -d -oOUTFILE
source
Before writing a recipe from scratch, it is often useful to discover whether someone else has already written one that meets (or comes close to meeting) your needs. The Yocto Project and OpenEmbedded communities maintain many recipes that might be candidates for what you are doing. You can find a good central index of these recipes in the OpenEmbedded Layer Index.
Working from an existing recipe or a skeleton recipe is the best way to get started. Here are some points on both methods:
Locate and modify a recipe that is close to what you want to do: This method works when you are familiar with the current recipe space. The method does not work so well for those new to the Yocto Project or writing recipes.
Some risks associated with this method are using a recipe that has areas totally unrelated to what you are trying to accomplish with your recipe, not recognizing areas of the recipe that you might have to add from scratch, and so forth. All these risks stem from unfamiliarity with the existing recipe space.
Use and modify the following
skeleton recipe:
If for some reason you do not want to use
recipetool
and you cannot
find an existing recipe that is close to meeting
your needs, you can use the following structure to
provide the fundamental areas of a new recipe.
DESCRIPTION = "" HOMEPAGE = "" LICENSE = "" SECTION = "" DEPENDS = "" LIC_FILES_CHKSUM = "" SRC_URI = ""
Once you have your base recipe, you should put it in your own layer and name it appropriately. Locating it correctly ensures that the OpenEmbedded build system can find it when you use BitBake to process the recipe.
Storing Your Recipe:
The OpenEmbedded build system locates your recipe
through the layer's conf/layer.conf
file and the
BBFILES
variable.
This variable sets up a path from which the build system can
locate recipes.
Here is the typical use:
BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \ ${LAYERDIR}/recipes-*/*/*.bbappend"
Consequently, you need to be sure you locate your new recipe inside your layer such that it can be found.
You can find more information on how layers are structured in the "Understanding and Creating Layers" section.
Naming Your Recipe: When you name your recipe, you need to follow this naming convention:
basename
_version
.bb
Use lower-cased characters and do not include the reserved
suffixes -native
,
-cross
, -initial
,
or -dev
casually (i.e. do not use them
as part of your recipe name unless the string applies).
Here are some examples:
cups_1.7.0.bb gawk_4.0.2.bb irssi_0.8.16-rc1.bb
Creating a new recipe is usually an iterative process that requires using BitBake to process the recipe multiple times in order to progressively discover and add information to the recipe file.
Assuming you have sourced the build environment setup script (i.e.
oe-init-build-env
)
and you are in the
Build Directory,
use BitBake to process your recipe.
All you need to provide is the
of the recipe as described
in the previous section:
basename
$ bitbake basename
During the build, the OpenEmbedded build system creates a
temporary work directory for each recipe
(${
WORKDIR
}
)
where it keeps extracted source files, log files, intermediate
compilation and packaging files, and so forth.
The path to the per-recipe temporary work directory depends on the context in which it is being built. The quickest way to find this path is to have BitBake return it by running the following:
$ bitbake -e basename
| grep ^WORKDIR=
As an example, assume a Source Directory top-level folder named
poky
, a default Build Directory at
poky/build
, and a
qemux86-poky-linux
machine target system.
Furthermore, suppose your recipe is named
foo_1.3.0.bb
.
In this case, the work directory the build system uses to
build the package would be as follows:
poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0
Inside this directory you can find sub-directories such as
image
, packages-split
,
and temp
.
After the build, you can examine these to determine how well
the build went.
temp
directory (e.g.
poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0/temp
).
Log files are named log.taskname
(e.g. log.do_configure
,
log.do_fetch
, and
log.do_compile
).
You can find more information about the build process in "The Yocto Project Development Environment" chapter of the Yocto Project Overview and Concepts Manual.
The first thing your recipe must do is specify how to fetch
the source files.
Fetching is controlled mainly through the
SRC_URI
variable.
Your recipe must have a SRC_URI
variable
that points to where the source is located.
For a graphical representation of source locations, see the
"Sources"
section in the Yocto Project Overview and Concepts Manual.
The
do_fetch
task uses the prefix of each entry in the
SRC_URI
variable value to determine which
fetcher to use to get your source files.
It is the SRC_URI
variable that triggers
the fetcher.
The
do_patch
task uses the variable after source is fetched to apply
patches.
The OpenEmbedded build system uses
FILESOVERRIDES
for scanning directory locations for local files in
SRC_URI
.
The SRC_URI
variable in your recipe must
define each unique location for your source files.
It is good practice to not hard-code pathnames in an URL used
in SRC_URI
.
Rather than hard-code these paths, use
${
PV
}
,
which causes the fetch process to use the version specified in
the recipe filename.
Specifying the version in this manner means that upgrading the
recipe to a future version is as simple as renaming the recipe
to match the new version.
Here is a simple example from the
meta/recipes-devtools/cdrtools/cdrtools-native_3.01a20.bb
recipe where the source comes from a single tarball.
Notice the use of the
PV
variable:
SRC_URI = "ftp://ftp.berlios.de/pub/cdrecord/alpha/cdrtools-${PV}.tar.bz2"
Files mentioned in SRC_URI
whose names end
in a typical archive extension (e.g. .tar
,
.tar.gz
, .tar.bz2
,
.zip
, and so forth), are automatically
extracted during the
do_unpack
task.
For another example that specifies these types of files, see
the
"Autotooled Package"
section.
Another way of specifying source is from an SCM.
For Git repositories, you must specify
SRCREV
and you should specify
PV
to include the revision with
SRCPV
.
Here is an example from the recipe
meta/recipes-kernel/blktrace/blktrace_git.bb
:
SRCREV = "d6918c8832793b4205ed3bfede78c2f915c23385" PR = "r6" PV = "1.0.5+git${SRCPV}" SRC_URI = "git://git.kernel.dk/blktrace.git \ file://ldflags.patch"
If your SRC_URI
statement includes
URLs pointing to individual files fetched from a remote server
other than a version control system, BitBake attempts to
verify the files against checksums defined in your recipe to
ensure they have not been tampered with or otherwise modified
since the recipe was written.
Two checksums are used:
SRC_URI[md5sum]
and
SRC_URI[sha256sum]
.
If your SRC_URI
variable points to
more than a single URL (excluding SCM URLs), you need to
provide the md5
and
sha256
checksums for each URL.
For these cases, you provide a name for each URL as part of
the SRC_URI
and then reference that name
in the subsequent checksum statements.
Here is an example:
SRC_URI = "${DEBIAN_MIRROR}/main/a/apmd/apmd_3.2.2.orig.tar.gz;name=tarball \ ${DEBIAN_MIRROR}/main/a/apmd/apmd_${PV}.diff.gz;name=patch" SRC_URI[tarball.md5sum] = "b1e6309e8331e0f4e6efd311c2d97fa8" SRC_URI[tarball.sha256sum] = "7f7d9f60b7766b852881d40b8ff91d8e39fccb0d1d913102a5c75a2dbb52332d" SRC_URI[patch.md5sum] = "57e1b689264ea80f78353519eece0c92" SRC_URI[patch.sha256sum] = "7905ff96be93d725544d0040e425c42f9c05580db3c272f11cff75b9aa89d430"
Proper values for md5
and
sha256
checksums might be available
with other signatures on the download page for the upstream
source (e.g. md5
,
sha1
, sha256
,
GPG
, and so forth).
Because the OpenEmbedded build system only deals with
sha256sum
and md5sum
,
you should verify all the signatures you find by hand.
If no SRC_URI
checksums are specified
when you attempt to build the recipe, or you provide an
incorrect checksum, the build will produce an error for each
missing or incorrect checksum.
As part of the error message, the build system provides
the checksum string corresponding to the fetched file.
Once you have the correct checksums, you can copy and paste
them into your recipe and then run the build again to continue.
This final example is a bit more complicated and is from the
meta/recipes-sato/rxvt-unicode/rxvt-unicode_9.20.bb
recipe.
The example's SRC_URI
statement identifies
multiple files as the source files for the recipe: a tarball, a
patch file, a desktop file, and an icon.
SRC_URI = "http://dist.schmorp.de/rxvt-unicode/Attic/rxvt-unicode-${PV}.tar.bz2 \ file://xwc.patch \ file://rxvt.desktop \ file://rxvt.png"
When you specify local files using the
file://
URI protocol, the build system
fetches files from the local machine.
The path is relative to the
FILESPATH
variable and searches specific directories in a certain order:
${
BP
}
,
${
BPN
}
,
and files
.
The directories are assumed to be subdirectories of the
directory in which the recipe or append file resides.
For another example that specifies these types of files, see the
"Single .c File Package (Hello World!)"
section.
The previous example also specifies a patch file.
Patch files are files whose names usually end in
.patch
or .diff
but
can end with compressed suffixes such as
diff.gz
and
patch.bz2
, for example.
The build system automatically applies patches as described
in the
"Patching Code" section.
During the build, the
do_unpack
task unpacks the source with
${
S
}
pointing to where it is unpacked.
If you are fetching your source files from an upstream source
archived tarball and the tarball's internal structure matches
the common convention of a top-level subdirectory named
${
BPN
}-${
PV
}
,
then you do not need to set S
.
However, if SRC_URI
specifies to fetch
source from an archive that does not use this convention,
or from an SCM like Git or Subversion, your recipe needs to
define S
.
If processing your recipe using BitBake successfully unpacks
the source files, you need to be sure that the directory
pointed to by ${S}
matches the structure
of the source.
Sometimes it is necessary to patch code after it has been
fetched.
Any files mentioned in SRC_URI
whose
names end in .patch
or
.diff
or compressed versions of these
suffixes (e.g. diff.gz
are treated as
patches.
The
do_patch
task automatically applies these patches.
The build system should be able to apply patches with the "-p1"
option (i.e. one directory level in the path will be stripped
off).
If your patch needs to have more directory levels stripped off,
specify the number of levels using the "striplevel" option in
the SRC_URI
entry for the patch.
Alternatively, if your patch needs to be applied in a specific
subdirectory that is not specified in the patch file, use the
"patchdir" option in the entry.
As with all local files referenced in
SRC_URI
using file://
, you should place
patch files in a directory next to the recipe either
named the same as the base name of the recipe
(BP
and
BPN
)
or "files".
Your recipe needs to have both the
LICENSE
and
LIC_FILES_CHKSUM
variables:
LICENSE
:
This variable specifies the license for the software.
If you do not know the license under which the software
you are building is distributed, you should go to the
source code and look for that information.
Typical files containing this information include
COPYING
,
LICENSE
, and
README
files.
You could also find the information near the top of
a source file.
For example, given a piece of software licensed under
the GNU General Public License version 2, you would
set LICENSE
as follows:
LICENSE = "GPLv2"
The licenses you specify within
LICENSE
can have any name as long
as you do not use spaces, since spaces are used as
separators between license names.
For standard licenses, use the names of the files in
meta/files/common-licenses/
or the SPDXLICENSEMAP
flag names
defined in meta/conf/licenses.conf
.
LIC_FILES_CHKSUM
:
The OpenEmbedded build system uses this variable to
make sure the license text has not changed.
If it has, the build produces an error and it affords
you the chance to figure it out and correct the problem.
You need to specify all applicable licensing
files for the software.
At the end of the configuration step, the build process
will compare the checksums of the files to be sure
the text has not changed.
Any differences result in an error with the message
containing the current checksum.
For more explanation and examples of how to set the
LIC_FILES_CHKSUM
variable, see the
"Tracking License Changes"
section.
To determine the correct checksum string, you
can list the appropriate files in the
LIC_FILES_CHKSUM
variable with
incorrect md5 strings, attempt to build the software,
and then note the resulting error messages that will
report the correct md5 strings.
See the
"Fetching Code"
section for additional information.
Here is an example that assumes the software has a
COPYING
file:
LIC_FILES_CHKSUM = "file://COPYING;md5=xxx"
When you try to build the software, the build system will produce an error and give you the correct string that you can substitute into the recipe file for a subsequent build.
Most software packages have a short list of other packages that they require, which are called dependencies. These dependencies fall into two main categories: build-time dependencies, which are required when the software is built; and runtime dependencies, which are required to be installed on the target in order for the software to run.
Within a recipe, you specify build-time dependencies using the
DEPENDS
variable.
Although nuances exist, items specified in
DEPENDS
should be names of other recipes.
It is important that you specify all build-time dependencies
explicitly.
If you do not, due to the parallel nature of BitBake's
execution, you can end up with a race condition where the
dependency is present for one task of a recipe (e.g.
do_configure
)
and then gone when the next task runs (e.g.
do_compile
).
Another consideration is that configure scripts might
automatically check for optional dependencies and enable
corresponding functionality if those dependencies are found.
This behavior means that to ensure deterministic results and
thus avoid more race conditions, you need to either explicitly
specify these dependencies as well, or tell the configure
script explicitly to disable the functionality.
If you wish to make a recipe that is more generally useful
(e.g. publish the recipe in a layer for others to use),
instead of hard-disabling the functionality, you can use the
PACKAGECONFIG
variable to allow functionality and the corresponding
dependencies to be enabled and disabled easily by other
users of the recipe.
Similar to build-time dependencies, you specify runtime
dependencies through a variable -
RDEPENDS
,
which is package-specific.
All variables that are package-specific need to have the name
of the package added to the end as an override.
Since the main package for a recipe has the same name as the
recipe, and the recipe's name can be found through the
${
PN
}
variable, then you specify the dependencies for the main
package by setting RDEPENDS_${PN}
.
If the package were named ${PN}-tools
,
then you would set RDEPENDS_${PN}-tools
,
and so forth.
Some runtime dependencies will be set automatically at packaging time. These dependencies include any shared library dependencies (i.e. if a package "example" contains "libexample" and another package "mypackage" contains a binary that links to "libexample" then the OpenEmbedded build system will automatically add a runtime dependency to "mypackage" on "example"). See the "Automatically Added Runtime Dependencies" section in the Yocto Project Overview and Concepts Manual for further details.
Most software provides some means of setting build-time configuration options before compilation. Typically, setting these options is accomplished by running a configure script with some options, or by modifying a build configuration file.
pkg-config
now, which is much more
robust.
You can find a list of the *-config
scripts that are disabled list in the
"Binary Configuration Scripts Disabled"
section in the Yocto Project Reference Manual.
A major part of build-time configuration is about checking for
build-time dependencies and possibly enabling optional
functionality as a result.
You need to specify any build-time dependencies for the
software you are building in your recipe's
DEPENDS
value, in terms of other recipes that satisfy those
dependencies.
You can often find build-time or runtime
dependencies described in the software's documentation.
The following list provides configuration items of note based on how your software is built:
Autotools:
If your source files have a
configure.ac
file, then your
software is built using Autotools.
If this is the case, you just need to worry about
modifying the configuration.
When using Autotools, your recipe needs to inherit
the
autotools
class and your recipe does not have to contain a
do_configure
task.
However, you might still want to make some adjustments.
For example, you can set
EXTRA_OECONF
or
PACKAGECONFIG_CONFARGS
to pass any needed configure options that are specific
to the recipe.
CMake:
If your source files have a
CMakeLists.txt
file, then your
software is built using CMake.
If this is the case, you just need to worry about
modifying the configuration.
When you use CMake, your recipe needs to inherit
the
cmake
class and your recipe does not have to contain a
do_configure
task.
You can make some adjustments by setting
EXTRA_OECMAKE
to pass any needed configure options that are specific
to the recipe.
Other:
If your source files do not have a
configure.ac
or
CMakeLists.txt
file, then your
software is built using some method other than Autotools
or CMake.
If this is the case, you normally need to provide a
do_configure
task in your recipe
unless, of course, there is nothing to configure.
Even if your software is not being built by Autotools or CMake, you still might not need to deal with any configuration issues. You need to determine if configuration is even a required step. You might need to modify a Makefile or some configuration file used for the build to specify necessary build options. Or, perhaps you might need to run a provided, custom configure script with the appropriate options.
For the case involving a custom configure
script, you would run
./configure --help
and look for
the options you need to set.
Once configuration succeeds, it is always good practice to
look at the log.do_configure
file to
ensure that the appropriate options have been enabled and no
additional build-time dependencies need to be added to
DEPENDS
.
For example, if the configure script reports that it found
something not mentioned in DEPENDS
, or
that it did not find something that it needed for some
desired optional functionality, then you would need to add
those to DEPENDS
.
Looking at the log might also reveal items being checked for,
enabled, or both that you do not want, or items not being found
that are in DEPENDS
, in which case
you would need to look at passing extra options to the
configure script as needed.
For reference information on configure options specific to the
software you are building, you can consult the output of the
./configure --help
command within
${S}
or consult the software's upstream
documentation.
If your recipe builds an application that needs to
communicate with some device or needs an API into a custom
kernel, you will need to provide appropriate header files.
Under no circumstances should you ever modify the existing
meta/recipes-kernel/linux-libc-headers/linux-libc-headers.inc
file.
These headers are used to build libc
and
must not be compromised with custom or machine-specific
header information.
If you customize libc
through modified
headers all other applications that use
libc
thus become affected.
libc
header file (i.e.
meta/recipes-kernel/linux-libc-headers/linux-libc-headers.inc
).
The correct way to interface to a device or custom kernel is to use a separate package that provides the additional headers for the driver or other unique interfaces. When doing so, your application also becomes responsible for creating a dependency on that specific provider.
Consider the following:
Never modify
linux-libc-headers.inc
.
Consider that file to be part of the
libc
system, and not something
you use to access the kernel directly.
You should access libc
through
specific libc
calls.
Applications that must talk directly to devices should either provide necessary headers themselves, or establish a dependency on a special headers package that is specific to that driver.
For example, suppose you want to modify an existing header that adds I/O control or network support. If the modifications are used by a small number programs, providing a unique version of a header is easy and has little impact. When doing so, bear in mind the guidelines in the previous list.
libc
, and subsequently all
other applications on the system, use a
.bbappend
to modify the
linux-kernel-headers.inc
file.
However, take care to not make the changes
machine specific.
Consider a case where your kernel is older and you need
an older libc
ABI.
The headers installed by your recipe should still be a
standard mainline kernel, not your own custom one.
When you use custom kernel headers you need to get them from
STAGING_KERNEL_DIR
,
which is the directory with kernel headers that are
required to build out-of-tree modules.
Your recipe will also need the following:
do_configure[depends] += "virtual/kernel:do_shared_workdir"
During a build, the do_compile
task
happens after source is fetched, unpacked, and configured.
If the recipe passes through do_compile
successfully, nothing needs to be done.
However, if the compile step fails, you need to diagnose the failure. Here are some common issues that cause failures.
pkg-config
.
See the note in section
"Configuring the Recipe"
for additional information.
Parallel build failures: These failures manifest themselves as intermittent errors, or errors reporting that a file or directory that should be created by some other part of the build process could not be found. This type of failure can occur even if, upon inspection, the file or directory does exist after the build has failed, because that part of the build process happened in the wrong order.
To fix the problem, you need to either satisfy
the missing dependency in the Makefile or whatever
script produced the Makefile, or (as a workaround)
set
PARALLEL_MAKE
to an empty string:
PARALLEL_MAKE = ""
For information on parallel Makefile issues, see the "Debugging Parallel Make Races" section.
Improper host path usage:
This failure applies to recipes building for the target
or nativesdk
only.
The failure occurs when the compilation process uses
improper headers, libraries, or other files from the
host system when cross-compiling for the target.
To fix the problem, examine the
log.do_compile
file to identify
the host paths being used (e.g.
/usr/include
,
/usr/lib
, and so forth) and then
either add configure options, apply a patch, or do both.
Failure to find required
libraries/headers:
If a build-time dependency is missing because it has
not been declared in
DEPENDS
,
or because the dependency exists but the path used by
the build process to find the file is incorrect and the
configure step did not detect it, the compilation
process could fail.
For either of these failures, the compilation process
notes that files could not be found.
In these cases, you need to go back and add additional
options to the configure script as well as possibly
add additional build-time dependencies to
DEPENDS
.
Occasionally, it is necessary to apply a patch
to the source to ensure the correct paths are used.
If you need to specify paths to find files staged
into the sysroot from other recipes, use the variables
that the OpenEmbedded build system provides
(e.g.
STAGING_BINDIR
,
STAGING_INCDIR
,
STAGING_DATADIR
, and so forth).
During do_install
, the task copies the
built files along with their hierarchy to locations that
would mirror their locations on the target device.
The installation process copies files from the
${
S
}
,
${
B
}
,
and
${
WORKDIR
}
directories to the
${
D
}
directory to create the structure as it should appear on the
target system.
How your software is built affects what you must do to be sure your software is installed correctly. The following list describes what you must do for installation depending on the type of build system used by the software being built:
Autotools and CMake:
If the software your recipe is building uses Autotools
or CMake, the OpenEmbedded build
system understands how to install the software.
Consequently, you do not have to have a
do_install
task as part of your
recipe.
You just need to make sure the install portion of the
build completes with no issues.
However, if you wish to install additional files not
already being installed by
make install
, you should do this
using a do_install_append
function
using the install command as described in
the "Manual" bulleted item later in this list.
Other (using
make install
):
You need to define a
do_install
function in your
recipe.
The function should call
oe_runmake install
and will likely
need to pass in the destination directory as well.
How you pass that path is dependent on how the
Makefile
being run is written
(e.g. DESTDIR=${D}
,
PREFIX=${D}
,
INSTALLROOT=${D}
, and so forth).
For an example recipe using
make install
, see the
"Makefile-Based Package"
section.
Manual:
You need to define a
do_install
function in your
recipe.
The function must first use
install -d
to create the
directories under
${
D
}
.
Once the directories exist, your function can use
install
to manually install the
built software into the directories.
You can find more information on
install
at
http://www.gnu.org/software/coreutils/manual/html_node/install-invocation.html.
For the scenarios that do not use Autotools or
CMake, you need to track the installation
and diagnose and fix any issues until everything installs
correctly.
You need to look in the default location of
${D}
, which is
${WORKDIR}/image
, to be sure your
files have been installed correctly.
During the installation process, you might need to
modify some of the installed files to suit the target
layout.
For example, you might need to replace hard-coded paths
in an initscript with values of variables provided by
the build system, such as replacing
/usr/bin/
with
${bindir}
.
If you do perform such modifications during
do_install
, be sure to modify the
destination file after copying rather than before
copying.
Modifying after copying ensures that the build system
can re-execute do_install
if
needed.
oe_runmake install
, which can be
run directly or can be run indirectly by the
autotools
and
cmake
classes, runs make install
in
parallel.
Sometimes, a Makefile can have missing dependencies
between targets that can result in race conditions.
If you experience intermittent failures during
do_install
, you might be able to
work around them by disabling parallel Makefile
installs by adding the following to the recipe:
PARALLEL_MAKEINST = ""
See
PARALLEL_MAKEINST
for additional information.
If you want to install a service, which is a process that usually starts on boot and runs in the background, then you must include some additional definitions in your recipe.
If you are adding services and the service initialization
script or the service file itself is not installed, you must
provide for that installation in your recipe using a
do_install_append
function.
If your recipe already has a do_install
function, update the function near its end rather than
adding an additional do_install_append
function.
When you create the installation for your services, you need
to accomplish what is normally done by
make install
.
In other words, make sure your installation arranges the output
similar to how it is arranged on the target system.
The OpenEmbedded build system provides support for starting services two different ways:
SysVinit: SysVinit is a system and service manager that manages the init system used to control the very basic functions of your system. The init program is the first program started by the Linux kernel when the system boots. Init then controls the startup, running and shutdown of all other programs.
To enable a service using SysVinit, your recipe
needs to inherit the
update-rc.d
class.
The class helps facilitate safely installing the
package on the target.
You will need to set the
INITSCRIPT_PACKAGES
,
INITSCRIPT_NAME
,
and
INITSCRIPT_PARAMS
variables within your recipe.
systemd: System Management Daemon (systemd) was designed to replace SysVinit and to provide enhanced management of services. For more information on systemd, see the systemd homepage at http://freedesktop.org/wiki/Software/systemd/.
To enable a service using systemd, your recipe
needs to inherit the
systemd
class.
See the systemd.bbclass
file
located in your
Source Directory.
section for more information.
Successful packaging is a combination of automated processes performed by the OpenEmbedded build system and some specific steps you need to take. The following list describes the process:
Splitting Files:
The do_package
task splits the
files produced by the recipe into logical components.
Even software that produces a single binary might
still have debug symbols, documentation, and other
logical components that should be split out.
The do_package
task ensures
that files are split up and packaged correctly.
Running QA Checks:
The
insane
class adds a step to
the package generation process so that output quality
assurance checks are generated by the OpenEmbedded
build system.
This step performs a range of checks to be sure the
build's output is free of common problems that show
up during runtime.
For information on these checks, see the
insane
class and the
"QA Error and Warning Messages"
chapter in the Yocto Project Reference Manual.
Hand-Checking Your Packages:
After you build your software, you need to be sure
your packages are correct.
Examine the
${
WORKDIR
}/packages-split
directory and make sure files are where you expect
them to be.
If you discover problems, you can set
PACKAGES
,
FILES
,
do_install(_append)
, and so forth as
needed.
Splitting an Application into Multiple Packages: If you need to split an application into several packages, see the "Splitting an Application into Multiple Packages" section for an example.
Installing a Post-Installation Script: For an example showing how to install a post-installation script, see the "Post-Installation Scripts" section.
Marking Package Architecture: Depending on what your recipe is building and how it is configured, it might be important to mark the packages produced as being specific to a particular machine, or to mark them as not being specific to a particular machine or architecture at all.
By default, packages apply to any machine with the
same architecture as the target machine.
When a recipe produces packages that are
machine-specific (e.g. the
MACHINE
value is passed into the configure script or a patch
is applied only for a particular machine), you should
mark them as such by adding the following to the
recipe:
PACKAGE_ARCH = "${MACHINE_ARCH}"
On the other hand, if the recipe produces packages
that do not contain anything specific to the target
machine or architecture at all (e.g. recipes
that simply package script files or configuration
files), you should use the
allarch
class to do this for you by adding this to your
recipe:
inherit allarch
Ensuring that the package architecture is correct is not critical while you are doing the first few builds of your recipe. However, it is important in order to ensure that your recipe rebuilds (or does not rebuild) appropriately in response to changes in configuration, and to ensure that you get the appropriate packages installed on the target machine, particularly if you run separate builds for more than one target machine.
Recipes often need to use files provided by other recipes on
the build host.
For example, an application linking to a common library needs
access to the library itself and its associated headers.
The way this access is accomplished is by populating a sysroot
with files.
Each recipe has two sysroots in its work directory, one for
target files
(recipe-sysroot
) and one for files that
are native to the build host
(recipe-sysroot-native
).
STAGING_DIR
variable).
Recipes should never populate the sysroot directly (i.e. write
files into sysroot).
Instead, files should be installed into standard locations
during the
do_install
task within the
${
D
}
directory.
The reason for this limitation is that almost all files that
populate the sysroot are cataloged in manifests in order to
ensure the files can be removed later when a recipe is either
modified or removed.
Thus, the sysroot is able to remain free from stale files.
A subset of the files installed by the
do_install
task are used by the
do_populate_sysroot
task as defined by the the
SYSROOT_DIRS
variable to automatically populate the sysroot.
It is possible to modify the list of directories that populate
the sysroot.
The following example shows how you could add the
/opt
directory to the list of
directories within a recipe:
SYSROOT_DIRS += "/opt"
For a more complete description of the
do_populate_sysroot
task and its associated functions, see the
staging
class.
Prior to a build, if you know that several different recipes
provide the same functionality, you can use a virtual provider
(i.e. virtual/*
) as a placeholder for the
actual provider.
The actual provider is determined at build-time.
A common scenario where a virtual provider is used would be
for the kernel recipe.
Suppose you have three kernel recipes whose
PN
values map to kernel-big
,
kernel-mid
, and
kernel-small
.
Furthermore, each of these recipes in some way uses a
PROVIDES
statement that essentially identifies itself as being able
to provide virtual/kernel
.
Here is one way through the
kernel
class:
PROVIDES += "${@ "virtual/kernel" if (d.getVar("KERNEL_PACKAGE_NAME") == "kernel") else "" }"
Any recipe that inherits the kernel
class
is going to utilize a PROVIDES
statement
that identifies that recipe as being able to provide the
virtual/kernel
item.
Now comes the time to actually build an image and you need a
kernel recipe, but which one?
You can configure your build to call out the kernel recipe
you want by using the
PREFERRED_PROVIDER
variable.
As an example, consider the
x86-base.inc
include file, which is a machine
(i.e. MACHINE
)
configuration file.
This include file is the reason all x86-based machines use the
linux-yocto
kernel.
Here are the relevant lines from the include file:
PREFERRED_PROVIDER_virtual/kernel ??= "linux-yocto" PREFERRED_VERSION_linux-yocto ??= "4.15%"
When you use a virtual provider, you do not have to
"hard code" a recipe name as a build dependency.
You can use the
DEPENDS
variable to state the build is dependent on
virtual/kernel
for example:
DEPENDS = "virtual/kernel"
During the build, the OpenEmbedded build system picks
the correct recipe needed for the
virtual/kernel
dependency based on the
PREFERRED_PROVIDER
variable.
If you want to use the small kernel mentioned at the beginning
of this section, configure your build as follows:
PREFERRED_PROVIDER_virtual/kernel ??= "kernel-small"
PROVIDES
a virtual/*
item that is ultimately
not selected through
PREFERRED_PROVIDER
does not get built.
Preventing these recipes from building is usually the
desired behavior since this mechanism's purpose is to
select between mutually exclusive alternative providers.
The following lists specific examples of virtual providers:
virtual/kernel
:
Provides the name of the kernel recipe to use when
building a kernel image.
virtual/bootloader
:
Provides the name of the bootloader to use when
building an image.
virtual/mesa
:
Provides gbm.pc
.
virtual/egl
:
Provides egl.pc
and possibly
wayland-egl.pc
.
virtual/libgl
:
Provides gl.pc
(i.e. libGL).
virtual/libgles1
:
Provides glesv1_cm.pc
(i.e. libGLESv1_CM).
virtual/libgles2
:
Provides glesv2.pc
(i.e. libGLESv2).
Sometimes the name of a recipe can lead to versioning
problems when the recipe is upgraded to a final release.
For example, consider the
irssi_0.8.16-rc1.bb
recipe file in
the list of example recipes in the
"Storing and Naming the Recipe"
section.
This recipe is at a release candidate stage (i.e.
"rc1").
When the recipe is released, the recipe filename becomes
irssi_0.8.16.bb
.
The version change from 0.8.16-rc1
to 0.8.16
is seen as a decrease by the
build system and package managers, so the resulting packages
will not correctly trigger an upgrade.
In order to ensure the versions compare properly, the
recommended convention is to set
PV
within the recipe to
"previous_version
+current_version
".
You can use an additional variable so that you can use the
current version elsewhere.
Here is an example:
REALPV = "0.8.16-rc1" PV = "0.8.15+${REALPV}"
Post-installation scripts run immediately after installing
a package on the target or during image creation when a
package is included in an image.
To add a post-installation script to a package, add a
pkg_postinst_
PACKAGENAME
()
function to
the recipe file (.bb
) and replace
PACKAGENAME
with the name of the package
you want to attach to the postinst
script.
To apply the post-installation script to the main package
for the recipe, which is usually what is required, specify
${
PN
}
in place of PACKAGENAME
.
A post-installation function has the following structure:
pkg_postinst_PACKAGENAME
() {
# Commands to carry out
}
The script defined in the post-installation function is called when the root filesystem is created. If the script succeeds, the package is marked as installed. If the script fails, the package is marked as unpacked and the script is executed when the image boots again.
Sometimes it is necessary for the execution of a post-installation script to be delayed until the first boot. For example, the script might need to be executed on the device itself. To delay script execution until boot time, use the following structure in the post-installation script:
pkg_postinst_PACKAGENAME
() {
if [ x"$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 environment variable D
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.
If you have recipes that use pkg_postinst
scripts and they require the use of non-standard native
tools that have dependencies during rootfs construction, you
need to use the
PACKAGE_WRITE_DEPS
variable in your recipe to list these tools.
If you do not use this variable, the tools might be missing and
execution of the post-installation script is deferred until
first boot.
Deferring the script to first boot is undesirable and for
read-only rootfs impossible.
pkg_preinst
,
pkg_prerm
, and
pkg_postrm
, respectively.
These scrips work in exactly the same way as does
pkg_postinst
with the exception that they
run at different times.
Also, because of when they run, they are not applicable to
being run at image creation time like
pkg_postinst
.
The final step for completing your recipe is to be sure that the software you built runs correctly. To accomplish runtime testing, add the build's output packages to your image and test them on the target.
For information on how to customize your image by adding specific packages, see the "Customizing Images" section.
To help summarize how to write a recipe, this section provides some examples given various scenarios:
Recipes that use local files
Using an Autotooled package
Using a Makefile-based package
Splitting an application into multiple packages
Adding binaries to an image
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.
SUMMARY = "Simple helloworld application" SECTION = "examples" LICENSE = "MIT" LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302" SRC_URI = "file://helloworld.c" S = "${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.
Applications that use Autotools such as autoconf
and
automake
require a recipe that has a source archive listed in
SRC_URI
and
also inherit the
autotools
class, 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
)
SUMMARY = "GNU Helloworld application" SECTION = "examples" LICENSE = "GPLv2+" LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe" 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 in the Yocto Project Overview and Concepts Manual.
You can quickly create Autotool-based recipes in a manner
similar to the previous example.
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
or
PACKAGECONFIG_CONFARGS
variables.
BitBake passes these options into the GNU make
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 ${S}/include "
In the following example, mtd-utils
is a makefile-based package:
SUMMARY = "Tools for managing memory technology devices" SECTION = "base" DEPENDS = "zlib lzo e2fsprogs util-linux" HOMEPAGE = "http://www.linux-mtd.infradead.org/" LICENSE = "GPLv2+" LIC_FILES_CHKSUM = "file://COPYING;md5=0636e73ff0215e8d672dc4c32c317bb3 \ file://include/common.h;beginline=1;endline=17;md5=ba05b07912a44ea2bf81ce409380049c" # Use the latest version at 26 Oct, 2013 SRCREV = "9f107132a6a073cce37434ca9cda6917dd8d866b" SRC_URI = "git://git.infradead.org/mtd-utils.git \ file://add-exclusion-to-mkfs-jffs2-git-2.patch \ " PV = "1.5.1+git${SRCPV}" S = "${WORKDIR}/git" EXTRA_OEMAKE = "'CC=${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=${includedir} } PACKAGES =+ "mtd-utils-jffs2 mtd-utils-ubifs mtd-utils-misc" FILES_mtd-utils-jffs2 = "${sbindir}/mkfs.jffs2 ${sbindir}/jffs2dump ${sbindir}/jffs2reader ${sbindir}/sumtool" FILES_mtd-utils-ubifs = "${sbindir}/mkfs.ubifs ${sbindir}/ubi*" FILES_mtd-utils-misc = "${sbindir}/nftl* ${sbindir}/ftl* ${sbindir}/rfd* ${sbindir}/doc* ${sbindir}/serve_image ${sbindir}/recv_image" PARALLEL_MAKE = "" BBCLASSEXTEND = "native"
You can use the variables
PACKAGES
and
FILES
to split an application into multiple packages.
Following is an example that uses the libxpm
recipe.
By default, this recipe generates a single package that contains the library along
with a few binaries.
You can modify the recipe to split the binaries into separate packages:
require xorg-lib-common.inc SUMMARY = "Xpm: X Pixmap extension library" LICENSE = "BSD" LIC_FILES_CHKSUM = "file://COPYING;md5=51f4270b012ecd4ab1a164f5f4ed6cf7" DEPENDS += "libxext libsm libxt" PE = "1" XORG_PN = "libXpm" PACKAGES =+ "sxpm cxpm" FILES_cxpm = "${bindir}/cxpm" FILES_sxpm = "${bindir}/sxpm"
In the previous example, we want to ship the sxpm
and cxpm
binaries in separate packages.
Since bindir
would be packaged into the main
PN
package by default, we prepend the PACKAGES
variable so additional package names are added to the start of list.
This results in the extra FILES_*
variables then containing information that define which files and
directories go into which packages.
Files included by earlier packages are skipped by latter packages.
Thus, the main PN
package
does not include the above listed files.
Sometimes, you need to add pre-compiled binaries to an
image.
For example, suppose that binaries for proprietary code
exist, which are created by a particular division of a
company.
Your part of the company needs to use those binaries as
part of an image that you are building using the
OpenEmbedded build system.
Since you only have the binaries and not the source code,
you cannot use a typical recipe that expects to fetch the
source specified in
SRC_URI
and then compile it.
One method is to package the binaries and then install them as part of the image. Generally, it is not a good idea to package binaries since, among other things, it can hinder the ability to reproduce builds and could lead to compatibility problems with ABI in the future. However, sometimes you have no choice.
The easiest solution is to create a recipe that uses
the
bin_package
class and to be sure that you are using default locations
for build artifacts.
In most cases, the bin_package
class
handles "skipping" the configure and compile steps as well
as sets things up to grab packages from the appropriate
area.
In particular, this class sets noexec
on both the
do_configure
and
do_compile
tasks, sets
FILES_${PN}
to "/" so that it picks
up all files, and sets up a
do_install
task, which effectively copies all files from
${S}
to ${D}
.
The bin_package
class works well when
the files extracted into ${S}
are
already laid out in the way they should be laid out
on the target.
For more information on these variables, see the
FILES
,
PN
,
S
,
and
D
variables in the Yocto Project Reference Manual's variable
glossary.
Using
DEPENDS
is a good idea even for components distributed
in binary form, and is often necessary for
shared libraries.
For a shared library, listing the library
dependencies in
DEPENDS
makes sure that
the libraries are available in the staging
sysroot when other recipes link against the
library, which might be necessary for
successful linking.
Using DEPENDS
also
allows runtime dependencies between packages
to be added automatically.
See the
"Automatically Added Runtime Dependencies"
section in the Yocto Project Overview and
Concepts Manual for more information.
If you cannot use the bin_package
class, you need to be sure you are doing the following:
Create a recipe where the
do_configure
and
do_compile
tasks do nothing:
It is usually sufficient to just not define these
tasks in the recipe, because the default
implementations do nothing unless a Makefile is
found in
${
S
}
.
If
${S}
might contain a Makefile,
or if you inherit some class that replaces
do_configure
and
do_compile
with custom
versions, then you can use the
[
noexec
]
flag to turn the tasks into no-ops, as follows:
do_configure[noexec] = "1" do_compile[noexec] = "1"
Unlike
deleting the tasks
,
using the flag preserves the dependency chain from
the
do_fetch
, do_unpack
,
and
do_patch
tasks to the
do_install
task.
Make sure your
do_install
task installs the
binaries appropriately.
Ensure that you set up
FILES
(usually
FILES_${
PN
}
)
to point to the files you have installed, which of
course depends on where you have installed them
and whether those files are in different locations
than the defaults.
When writing recipes, it is good to conform to existing style guidelines. The OpenEmbedded Styleguide wiki page provides rough guidelines for preferred recipe style.
It is common for existing recipes to deviate a bit from this
style.
However, aiming for at least a consistent style is a good idea.
Some practices, such as omitting spaces around
=
operators in assignments or ordering
recipe components in an erratic way, are widely seen as poor
style.
Understanding recipe file syntax is important for writing recipes. The following list overviews the basic items that make up a BitBake recipe file. For more complete BitBake syntax descriptions, see the "Syntax and Operators" chapter of the BitBake User Manual.
Variable Assignments and Manipulations: Variable assignments allow a value to be assigned to a variable. The assignment can be static text or might include the contents of other variables. In addition to the assignment, appending and prepending operations are also supported.
The following example shows some of the ways you can use variables in recipes:
S = "${WORKDIR}/postfix-${PV}" CFLAGS += "-DNO_ASM" SRC_URI_append = " file://fixup.patch"
Functions:
Functions provide a series of actions to be performed.
You usually use functions to override the default
implementation of a task function or to complement
a default function (i.e. append or prepend to an
existing function).
Standard functions use sh
shell
syntax, although access to OpenEmbedded variables and
internal methods are also available.
The following is an example function from the
sed
recipe:
do_install () { autotools_do_install install -d ${D}${base_bindir} mv ${D}${bindir}/sed ${D}${base_bindir}/sed rmdir ${D}${bindir}/ }
It is also possible to implement new functions that are called between existing tasks as long as the new functions are not replacing or complementing the default functions. You can implement functions in Python instead of shell. Both of these options are not seen in the majority of recipes.
Keywords:
BitBake recipes use only a few keywords.
You use keywords to include common
functions (inherit
), load parts
of a recipe from other files
(include
and
require
) and export variables
to the environment (export
).
The following example shows the use of some of these keywords:
export POSTCONF = "${STAGING_BINDIR}/postconf" inherit autoconf require otherfile.inc
Comments (#):
Any lines that begin with the hash character
(#
) are treated as comment lines
and are ignored:
# This is a comment
This next list summarizes the most important and most commonly used parts of the recipe syntax. For more information on these parts of the syntax, you can reference the Syntax and Operators chapter in the BitBake User Manual.
Line Continuation (\):
Use the backward slash (\
)
character to split a statement over multiple lines.
Place the slash character at the end of the line that
is to be continued on the next line:
VAR = "A really long \ line"
Using Variables (${VARNAME
}):
Use the ${
syntax to access the contents of a variable:
VARNAME
}
SRC_URI = "${SOURCEFORGE_MIRROR}/libpng/zlib-${PV}.tar.gz"
:=
operator instead of
=
when you make the
assignment, but this is not generally needed.
Quote All Assignments ("value
"):
Use double quotes around values in all variable
assignments (e.g.
"
).
Following is an example:
value
"
VAR1 = "${OTHERVAR}" VAR2 = "The version is ${PV}"
Conditional Assignment (?=):
Conditional assignment is used to assign a
value to a variable, but only when the variable is
currently unset.
Use the question mark followed by the equal sign
(?=
) to make a "soft" assignment
used for conditional assignment.
Typically, "soft" assignments are used in the
local.conf
file for variables
that are allowed to come through from the external
environment.
Here is an example where
VAR1
is set to "New value" if
it is currently empty.
However, if VAR1
has already been
set, it remains unchanged:
VAR1 ?= "New value"
In this next example, VAR1
is left with the value "Original value":
VAR1 = "Original value" VAR1 ?= "New value"
Appending (+=):
Use the plus character followed by the equals sign
(+=
) to append values to existing
variables.
Here is an example:
SRC_URI += "file://fix-makefile.patch"
Prepending (=+):
Use the equals sign followed by the plus character
(=+
) to prepend values to existing
variables.
Here is an example:
VAR =+ "Starts"
Appending (_append):
Use the _append
operator to
append values to existing variables.
This operator does not add any additional space.
Also, the operator is applied after all the
+=
, and
=+
operators have been applied and
after all =
assignments have
occurred.
The following example shows the space being explicitly added to the start to ensure the appended value is not merged with the existing value:
SRC_URI_append = " file://fix-makefile.patch"
You can also use the _append
operator with overrides, which results in the actions
only being performed for the specified target or
machine:
SRC_URI_append_sh4 = " file://fix-makefile.patch"
Prepending (_prepend):
Use the _prepend
operator to
prepend values to existing variables.
This operator does not add any additional space.
Also, the operator is applied after all the
+=
, and
=+
operators have been applied and
after all =
assignments have
occurred.
The following example shows the space being explicitly added to the end to ensure the prepended value is not merged with the existing value:
CFLAGS_prepend = "-I${S}/myincludes "
You can also use the _prepend
operator with overrides, which results in the actions
only being performed for the specified target or
machine:
CFLAGS_prepend_sh4 = "-I${S}/myincludes "
Overrides:
You can use overrides to set a value conditionally,
typically based on how the recipe is being built.
For example, to set the
KBRANCH
variable's value to "standard/base" for any target
MACHINE
,
except for qemuarm where it should be set to
"standard/arm-versatile-926ejs", you would do the
following:
KBRANCH = "standard/base" KBRANCH_qemuarm = "standard/arm-versatile-926ejs"
Overrides are also used to separate alternate values
of a variable in other situations.
For example, when setting variables such as
FILES
and
RDEPENDS
that are specific to individual packages produced by
a recipe, you should always use an override that
specifies the name of the package.
Indentation: Use spaces for indentation rather than than tabs. For shell functions, both currently work. However, it is a policy decision of the Yocto Project to use tabs in shell functions. Realize that some layers have a policy to use spaces for all indentation.
Using Python for Complex Operations: For more advanced processing, it is possible to use Python code during variable assignments (e.g. search and replacement on a variable).
You indicate Python code using the
${@
syntax for the variable assignment:
python_code
}
SRC_URI = "ftp://ftp.info-zip.org/pub/infozip/src/zip${@d.getVar('PV',1).replace('.', '')}.tgz
Shell Function Syntax:
Write shell functions as if you were writing a shell
script when you describe a list of actions to take.
You should ensure that your script works with a generic
sh
and that it does not require
any bash
or other shell-specific
functionality.
The same considerations apply to various system
utilities (e.g. sed
,
grep
, awk
,
and so forth) that you might wish to use.
If in doubt, you should check with multiple
implementations - including those from BusyBox.
Adding a new machine to the Yocto Project is a straightforward process. This section describes how to add machines that are similar to those that the Yocto Project already supports.
gcc/glibc
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 bitbake-layers
Script"
section in the Yocto Project Board Support Package (BSP)
Developer's Guide.
To add a new machine, you need to add a new machine
configuration file to the layer's
conf/machine
directory.
This configuration file provides details about the device
you are adding.
The OpenEmbedded build system uses the root name of the
machine configuration file to reference the new machine.
For example, given a machine configuration file named
crownbay.conf
, the build system
recognizes the machine as "crownbay".
The most important variables you must set in your machine configuration file or include from a lower-level configuration file are as follows:
TARGET_ARCH
(e.g. "arm")
PREFERRED_PROVIDER_virtual/kernel
MACHINE_FEATURES
(e.g. "apm screen wifi")
You might also need these variables:
SERIAL_CONSOLES
(e.g. "115200;ttyS0 115200;ttyS1")
KERNEL_IMAGETYPE
(e.g. "zImage")
IMAGE_FSTYPES
(e.g. "tar.gz jffs2")
You can find full details on these variables in the reference
section.
You can leverage existing machine .conf
files from meta-yocto-bsp/conf/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 kernel recipe.
You can find several kernel recipe examples in the
Source Directory at
meta/recipes-kernel/linux
that you can use as references.
If you are creating a new kernel 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 do_configure
task that
configures the unpacked kernel with a
defconfig
file.
You can do this by using a make defconfig
command or, more commonly, by copying in a suitable
defconfig
file 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 defaults of the
class normally work well.
If you are extending an existing kernel recipe, 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 recipe.
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)'
For more information on defconfig
files,
see the
"Changing the Configuration"
section in the Yocto Project Linux Kernel Development Manual.
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" machine:
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
Over time, upstream developers publish new versions for software
built by layer recipes.
It is recommended to keep recipes up-to-date with upstream
version releases.
You can use the Automated Upgrade Helper (AUH) to set up
automatic version upgrades.
Alternatively, you can use devtool upgrade
to set up semi-automatic version upgrades.
Finally, you can even manually upgrade a recipe by editing the
recipe itself.
The AUH utility works in conjunction with the OpenEmbedded build system in order to automatically generate upgrades for recipes based on new versions being published upstream. Use AUH when you want to create a service that performs the upgrades automatically and optionally sends you an email with the results.
AUH allows you to update several recipes with a single use. You can also optionally perform build and integration tests using images with the results saved to your hard drive and emails of results optionally sent to recipe maintainers. Finally, AUH creates Git commits with appropriate commit messages in the layer's tree for the changes made to recipes.
devtool upgrade
or upgrade your
recipes manually:
When AUH cannot complete the upgrade sequence.
This situation usually results because custom
patches carried by the recipe cannot be
automatically rebased to the new version.
In this case, devtool upgrade
allows you to manually resolve conflicts.
When for any reason you want fuller control over the upgrade process. For example, when you want special arrangements for testing.
The following steps describe how to set up the AUH utility:
Be Sure the Development Host is Set Up: You need to be sure that your development host is set up to use the Yocto Project. For information on how to set up your host, see the "Preparing the Build Host" section.
Make Sure Git is Configured: The AUH utility requires Git to be configured because AUH uses Git to save upgrades. Thus, you must have Git user and email configured. The following command shows your configurations:
$ git config --list
If you do not have the user and email configured, you can use the following commands to do so:
$ git config --global user.namesome_name
$ git config --global user.emailusername
@domain
.com
Clone the AUH Repository: To use AUH, you must clone the repository onto your development host. The following command uses Git to create a local copy of the repository on your system:
$ git clone git://git.yoctoproject.org/auto-upgrade-helper Cloning into 'auto-upgrade-helper'... remote: Counting objects: 768, done. remote: Compressing objects: 100% (300/300), done. remote: Total 768 (delta 499), reused 703 (delta 434) Receiving objects: 100% (768/768), 191.47 KiB | 98.00 KiB/s, done. Resolving deltas: 100% (499/499), done. Checking connectivity... done.
AUH is not part of the OpenEmbedded-Core (OE-Core) or Poky repositories.
Create a Dedicated Build Directory:
Run the
oe-init-build-env
script to create a fresh build directory that you
use exclusively for running the AUH utility:
$ cd ~/poky
$ source oe-init-build-env your_AUH_build_directory
Re-using an existing build directory and its configurations is not recommended as existing settings could cause AUH to fail or behave undesirably.
Make Configurations in Your Local Configuration File:
Several settings need to exist in the
local.conf
file in the build
directory you just created for AUH.
Make these following configurations:
Enable "distrodata" as follows:
INHERIT =+ "distrodata"
If you want to enable
Build History,
which is optional, you need the following
lines in the
conf/local.conf
file:
INHERIT =+ "buildhistory" BUILDHISTORY_COMMIT = "1"
With this configuration and a successful
upgrade, a build history "diff" file appears in
the
upgrade-helper/work/recipe/buildhistory-diff.txt
file found in your build directory.
If you want to enable testing through the
testimage
class, which is optional, you need to have the
following set in your
conf/local.conf
file:
INHERIT += "testimage"
local.conf
file:
DISTRO_FEATURES_append = " ptest"
Optionally Start a vncserver: If you are running in a server without an X11 session, you need to start a vncserver:
$ vncserver :1 $ export DISPLAY=:1
Create and Edit an AUH Configuration File:
You need to have the
upgrade-helper/upgrade-helper.conf
configuration file in your build directory.
You can find a sample configuration file in the
AUH source repository.
Read through the sample file and make
configurations as needed.
For example, if you enabled build history in your
local.conf
as described earlier,
you must enable it in
upgrade-helper.conf
.
Also, if you are using the default
maintainers.inc
file supplied
with Poky and located in
meta-yocto
and you do not set a
"maintainers_whitelist" or "global_maintainer_override"
in the upgrade-helper.conf
configuration, and you specify "-e all" on the
AUH command-line, the utility automatically sends out
emails to all the default maintainers.
Please avoid this.
This next set of examples describes how to use the AUH:
Upgrading a Specific Recipe: To upgrade a specific recipe, use the following form:
$ upgrade-helper.py recipe_name
For example, this command upgrades the
xmodmap
recipe:
$ upgrade-helper.py xmodmap
Upgrading a Specific Recipe to a Particular Version: To upgrade a specific recipe to a particular version, use the following form:
$ upgrade-helper.pyrecipe_name
-tversion
For example, this command upgrades the
xmodmap
recipe to version
1.2.3:
$ upgrade-helper.py xmodmap -t 1.2.3
Upgrading all Recipes to the Latest Versions and Suppressing Email Notifications: To upgrade all recipes to their most recent versions and suppress the email notifications, use the following command:
$ upgrade-helper.py all
Upgrading all Recipes to the Latest Versions and Send Email Notifications: To upgrade all recipes to their most recent versions and send email messages to maintainers for each attempted recipe as well as a status email, use the following command:
$ upgrade-helper.py -e all
Once you have run the AUH utility, you can find the results in the AUH build directory:
${BUILDDIR}/upgrade-helper/timestamp
The AUH utility also creates recipe update commits from successful upgrade attempts in the layer tree.
You can easily set up to run the AUH utility on a regular
basis by using a cron job.
See the
weeklyjob.sh
file distributed with the utility for an example.
devtool upgrade
¶
As mentioned earlier, an alternative method for upgrading
recipes to newer versions is to use
devtool upgrade
.
You can read about devtool upgrade
in
general in the
"Use devtool upgrade
to Create a Version of the Recipe that Supports a Newer Version of the Software"
section in the Yocto Project Application Development and the
Extensible Software Development Kit (eSDK) Manual.
To see all the command-line options available with
devtool upgrade
, use the following help
command:
$ devtool upgrade -h
If you want to find out what version a recipe is currently at upstream without any attempt to upgrade your local version of the recipe, you can use the following command:
$ devtool latest-version recipe_name
As mentioned in the previous section describing AUH,
devtool upgrade
works in a
less-automated manner than AUH.
Specifically, devtool upgrade
only
works on a single recipe that you name on the command line,
cannot perform build and integration testing using images,
and does not automatically generate commits for changes in
the source tree.
Despite all these "limitations",
devtool upgrade
updates the recipe file
to the new upstream version and attempts to rebase custom
patches contained by the recipe as needed.
devtool upgrade
behind the scenes making AUH somewhat of a "wrapper"
application for devtool upgrade
.
A typical scenario involves having used Git to clone an
upstream repository that you use during build operations.
Because you are (or have) built the recipe in the past, the
layer is likely added to your configuration already.
If for some reason, the layer is not added, you could add
it easily using the
bitbake-layers
script.
For example, suppose you use the nano.bb
recipe from the meta-oe
layer in the
meta-openembedded
repository.
For this example, assume that the layer has been cloned into
following area:
/home/scottrif/meta-openembedded
The following command from your
Build Directory
adds the layer to your build configuration (i.e.
${BUILDDIR}/conf/bblayers.conf
):
$ bitbake-layers add-layer /home/scottrif/meta-openembedded/meta-oe NOTE: Starting bitbake server... Parsing recipes: 100% |##########################################| Time: 0:00:55 Parsing of 1431 .bb files complete (0 cached, 1431 parsed). 2040 targets, 56 skipped, 0 masked, 0 errors. Removing 12 recipes from the x86_64 sysroot: 100% |##############| Time: 0:00:00 Removing 1 recipes from the x86_64_i586 sysroot: 100% |##########| Time: 0:00:00 Removing 5 recipes from the i586 sysroot: 100% |#################| Time: 0:00:00 Removing 5 recipes from the qemux86 sysroot: 100% |##############| Time: 0:00:00
For this example, assume that the nano.bb
recipe that is upstream has a 2.9.3 version number.
However, the version in the local repository is 2.7.4.
The following command from your build directory automatically
upgrades the recipe for you:
-V
option is not necessary.
Omitting the version number causes
devtool upgrade
to upgrade the recipe
to the most recent version.
$ devtool upgrade nano -V 2.9.3 NOTE: Starting bitbake server... NOTE: Creating workspace layer in /home/scottrif/poky/build/workspace Parsing recipes: 100% |##########################################| Time: 0:00:46 Parsing of 1431 .bb files complete (0 cached, 1431 parsed). 2040 targets, 56 skipped, 0 masked, 0 errors. NOTE: Extracting current version source... NOTE: Resolving any missing task queue dependencies . . . NOTE: Executing SetScene Tasks NOTE: Executing RunQueue Tasks NOTE: Tasks Summary: Attempted 74 tasks of which 72 didn't need to be rerun and all succeeded. Adding changed files: 100% |#####################################| Time: 0:00:00 NOTE: Upgraded source extracted to /home/scottrif/poky/build/workspace/sources/nano NOTE: New recipe is /home/scottrif/poky/build/workspace/recipes/nano/nano_2.9.3.bb
Continuing with this example, you can use
devtool build
to build the newly upgraded
recipe:
$ devtool build nano NOTE: Starting bitbake server... Loading cache: 100% |################################################################################################| Time: 0:00:01 Loaded 2040 entries from dependency cache. Parsing recipes: 100% |##############################################################################################| Time: 0:00:00 Parsing of 1432 .bb files complete (1431 cached, 1 parsed). 2041 targets, 56 skipped, 0 masked, 0 errors. NOTE: Resolving any missing task queue dependencies . . . NOTE: Executing SetScene Tasks NOTE: Executing RunQueue Tasks NOTE: nano: compiling from external source tree /home/scottrif/poky/build/workspace/sources/nano NOTE: Tasks Summary: Attempted 520 tasks of which 304 didn't need to be rerun and all succeeded.
Within the devtool upgrade
workflow,
opportunity exists to deploy and test your rebuilt software.
For this example, however, running
devtool finish
cleans up the workspace
once the source in your workspace is clean.
This usually means using Git to stage and submit commits
for the changes generated by the upgrade process.
Once the tree is clean, you can clean things up in this
example with the following command from the
${BUILDDIR}/workspace/sources/nano
directory:
$ devtool finish nano meta-oe NOTE: Starting bitbake server... Loading cache: 100% |################################################################################################| Time: 0:00:00 Loaded 2040 entries from dependency cache. Parsing recipes: 100% |##############################################################################################| Time: 0:00:01 Parsing of 1432 .bb files complete (1431 cached, 1 parsed). 2041 targets, 56 skipped, 0 masked, 0 errors. NOTE: Adding new patch 0001-nano.bb-Stuff-I-changed-when-upgrading-nano.bb.patch NOTE: Updating recipe nano_2.9.3.bb NOTE: Removing file /home/scottrif/meta-openembedded/meta-oe/recipes-support/nano/nano_2.7.4.bb NOTE: Moving recipe file to /home/scottrif/meta-openembedded/meta-oe/recipes-support/nano NOTE: Leaving source tree /home/scottrif/poky/build/workspace/sources/nano as-is; if you no longer need it then please delete it manually
Using the devtool finish
command cleans
up the workspace and creates a patch file based on your
commits.
The tool puts all patch files back into the source directory
in a sub-directory named nano
in this
case.
If for some reason you choose not to upgrade recipes using the
Auto Upgrade Helper (AUH)
or by using
devtool upgrade
,
you can manually edit the recipe files to upgrade the versions.
devtool upgrade
, both of which
automate some steps and provide guidance for others needed
for the manual process.
To manually upgrade recipe versions, follow these general steps:
Change the Version:
Rename the recipe such that the version (i.e. the
PV
part of the recipe name) changes appropriately.
If the version is not part of the recipe name, change
the value as it is set for PV
within the recipe itself.
Update SRCREV
if Needed:
If the source code your recipe builds is fetched from
Git or some other version control system, update
SRCREV
to point to the commit hash that matches the new
version.
Build the Software: Try to build the recipe using BitBake. Typical build failures include the following:
License statements were updated for the new
version.
For this case, you need to review any changes
to the license and update the values of
LICENSE
and
LIC_FILES_CHKSUM
as needed.
Custom patches carried by the older version of the recipe might fail to apply to the new version. For these cases, you need to review the failures. Patches might not be necessary for the new version of the software if the upgraded version has fixed those issues. If a patch is necessary and failing, you need to rebase it into the new version.
Optionally Attempt to Build for Several Architectures:
Once you successfully build the new software for a
given architecture, you could test the build for
other architectures by changing the
MACHINE
variable and rebuilding the software.
This optional step is especially important if the
recipe is to be released publicly.
Check the Upstream Change Log or Release Notes: Checking both these reveals if new features exist that could break backwards-compatibility. If so, you need to take steps to mitigate or eliminate that situation.
Optionally Create a Bootable Image and Test: If you want, you can test the new software by booting it onto actual hardware.
Create a Commit with the Change in the Layer Repository: After all builds work and any testing is successful, you can create commits for any changes in the layer holding your upgraded recipe.
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.
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 ${WORKDIR}/git
.
BP
represents the base recipe name, which consists of the name
and version:
BP = "${BPN}-${PV}"
The path to the work directory for the recipe
(WORKDIR
)
is defined as follows:
${TMPDIR}/work/${MULTIMACH_TARGET_SYS}/${PN}/${EXTENDPE}${PV}-${PR}
The actual directory depends on several things:
As an example, assume a Source Directory top-level folder
named poky
, a default Build Directory at
poky/build
, and a
qemux86-poky-linux
machine target
system.
Furthermore, suppose your recipe is named
foo_1.3.0.bb
.
In this case, the work directory the build system uses to
build the package would be as follows:
poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0
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 source code, test changes, and then preserve the changes in the form of a patch all using Quilt.
rm_work
enabled,
the
devtool
workflow
as described in the Yocto Project Application Development
and the Extensible Software Development Kit (eSDK) manual
is a safer development flow than the flow that uses Quilt.
Follow these general steps:
Find the Source Code: Temporary source code used by the OpenEmbedded build system is kept in the Build Directory. See the "Finding Temporary Source Code" section to learn how to locate the directory that has the temporary source code for a particular package.
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.
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
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
Edit the Files: Make your changes in the source code to the files you added to the patch.
Test Your Changes:
Once you have modified the source code, the easiest way to
test your changes is by calling the
do_compile
task as shown in the
following example:
$ bitbake -c compile -f 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.
do_clean
or
do_cleanall
tasks using BitBake (i.e.
bitbake -c clean package
and
bitbake -c cleanall package
).
Modifications will also disappear if you use the
rm_work
feature as described
in the
"Conserving Disk Space During Builds"
section.
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.
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"
When debugging certain commands or even when just editing packages,
devshell
can be a useful tool.
When you invoke devshell
, all tasks up to and
including
do_patch
are run for the specified target.
Then, a new terminal is opened and you are placed in
${
S
}
,
the source 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
).
To manually run a specific task using devshell
,
run the corresponding run.*
script in
the
${
WORKDIR
}/temp
directory (e.g.,
run.do_configure.
pid
).
If a task's script does not exist, which would be the case if the task was
skipped by way of the sstate cache, you can create the task by first running
it outside of the devshell
:
$ bitbake -c task
Execution of a task's run.*
script and BitBake's execution of a task are identical.
In other words, running the script re-runs the task
just as it would be run using the
bitbake -c
command.
Any run.*
file that does not
have a .pid
extension is a
symbolic link (symlink) to the most recent version of that
file.
Remember, that the devshell
is a mechanism that allows
you to get into the BitBake task execution environment.
And as such, all commands must be called just as BitBake would call them.
That means you need to provide the appropriate options for
cross-compilation and so forth as applicable.
When you are finished using devshell
, exit the shell
or close the terminal window.
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.
Similar to working within a development shell as described in
the previous section, you can also spawn and work within an
interactive Python development shell.
When debugging certain commands or even when just editing packages,
devpyshell
can be a useful tool.
When you invoke devpyshell
, all tasks up to and
including
do_patch
are run for the specified target.
Then a new terminal is opened.
Additionally, key Python objects and code are available in the same
way they are to BitBake tasks, in particular, the data store 'd'.
So, commands such as the following are useful when exploring the data
store and running functions:
pydevshell> d.getVar("STAGING_DIR", True) '/media/build1/poky/build/tmp/sysroots' pydevshell> d.getVar("STAGING_DIR", False) '${TMPDIR}/sysroots' pydevshell> d.setVar("FOO", "bar") pydevshell> d.getVar("FOO", True) 'bar' pydevshell> d.delVar("FOO") pydevshell> d.getVar("FOO", True) pydevshell> bb.build.exec_func("do_unpack", d) pydevshell>
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 devpyshell
on a target named
matchbox-desktop
:
$ bitbake matchbox-desktop -c devpyshell
This command spawns a terminal and places you in an interactive
Python interpreter within the OpenEmbedded build environment.
The OE_TERMINAL
variable controls what type of shell is opened.
When you are finished using devpyshell
, you
can exit the shell either by using Ctrl+d or closing the terminal
window.
This section describes various build procedures. For example, the steps needed for a simple build, a target that uses multiple configurations, building an image for more than one machine, and so forth.
In the development environment, you need to build an image whenever you change hardware support, add or change system libraries, or add or change services that have dependencies. Several methods exist that allow you to build an image within the Yocto Project. This section presents the basic steps you need to build a simple image using BitBake from a build host running Linux.
For information on how to build an image using Toaster, see the Toaster User Manual.
For information on how to use
devtool
to build images, see
the
"Using devtool
in Your SDK Workflow"
section in the Yocto Project Application
Development and the Extensible Software Development
Kit (eSDK) manual.
For a quick example on how to build an image using the OpenEmbedded build system, see the Yocto Project Quick Build document.
The build process creates an entire Linux distribution from
source and places it in your
Build Directory
under tmp/deploy/images
.
For detailed information on the build process using BitBake,
see the
"Images"
section in the Yocto Project Overview and Concepts Manual.
The following figure and list overviews the build process:
Set up Your Host Development System to Support Development Using the Yocto Project: See the "Setting Up to Use the Yocto Project" section for options on how to get a build host ready to use the Yocto Project.
Initialize the Build Environment:
Initialize the build environment by sourcing the build
environment script (i.e.
oe-init-build-env
):
$ source oe-init-build-env [build_dir
]
When you use the initialization script, the
OpenEmbedded build system uses
build
as the default Build
Directory in your current work directory.
You can use a build_dir
argument with the script to specify a different build
directory.
~/build/x86
for a
qemux86
target, and
~/build/arm
for a
qemuarm
target.
Make Sure Your local.conf
File is Correct:
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 packaging format used during the build
(PACKAGE_CLASSES
),
and a centralized tarball download directory through the
DL_DIR
variable.
Build the Image:
Build the image using the bitbake
command:
$ bitbake target
The target
is the name of the
recipe you want to build.
Common targets are the images in
meta/recipes-core/images
,
meta/recipes-sato/images
, and so
forth all found in the
Source Directory.
Or, the target can be the name of a recipe for a
specific piece of software such as BusyBox.
For more details about the images the OpenEmbedded build
system supports, see the
"Images"
chapter in the Yocto Project Reference Manual.
As an example, the following command builds the
core-image-minimal
image:
$ bitbake core-image-minimal
Once an image has been built, it often needs to be
installed.
The images and kernels built by the OpenEmbedded
build system are placed in the Build Directory in
tmp/deploy/images
.
For information on how to run pre-built images such as
qemux86
and qemuarm
,
see the
Yocto Project Application Development and the Extensible Software Development Kit (eSDK)
manual.
For information about how to install these images,
see the documentation for your particular board or
machine.
Bitbake also has functionality that allows you to build multiple targets at the same time, where each target uses a different configuration.
In order to accomplish this, you setup each of the configurations
you need to use in parallel by placing the configuration files in
your current build directory alongside the usual
local.conf
file.
Follow these guidelines to create an environment that supports multiple configurations:
Create Configuration Files: You need to create a single configuration file for each configuration for which you want to add support. These files would contain lines such as the following:
MACHINE = "A"
The files would contain any other variables that can be set and built in the same directory.
TMPDIR
to not conflict.
Furthermore, the configuration file must be located in the
current build directory in a directory named
multiconfig
under the build's
conf
directory where
local.conf
resides.
The reason for this restriction is because the
BBPATH
variable is not constructed
until the layers are parsed.
Consequently, using the configuration file as a
pre-configuration file is not possible unless it is
located in the current working directory.
Add the BitBake Multi-Config Variable to you Local Configuration File:
Use the
BBMULTICONFIG
variable in your conf/local.conf
configuration file to specify each separate configuration.
For example, the following line tells BitBake it should load
conf/multiconfig/configA.conf
,
conf/multiconfig/configB.conf
, and
conf/multiconfig/configC.conf
.
BBMULTICONFIG = "configA configB configC"
Launch BitBake: Use the following BitBake command form to launch the build:
$ bitbake [multiconfig:multiconfigname
:]target
[[[multiconfig:multiconfigname
:]target
] ... ]
Following is an example that supports building a minimal
image for configuration A alongside a standard
core-image-sato
, which takes its
configuration from local.conf
:
$ bitbake multiconfig:configA:core-image-minimal core-image-sato
Support for multiple configurations in this current release of the Yocto Project (Sumo 2.5.3) has some known issues:
No inter-multi-configuration dependencies exist.
Shared State (sstate) optimizations do not exist.
Consequently, if the build uses the same object twice
in, for example, two different
TMPDIR
directories, the build
will either load from an existing sstate cache at the
start or build the object twice.
An initial RAM filesystem (initramfs) image provides a temporary root filesystem used for early system initialization (e.g. loading of modules needed to locate and mount the "real" root filesystem).
Follow these steps to create an initramfs image:
Create the initramfs Image Recipe:
You can reference the
core-image-minimal-initramfs.bb
recipe found in the meta/recipes-core
directory of the
Source Directory
as an example from which to work.
Decide if You Need to Bundle the initramfs Image
Into the Kernel Image:
If you want the initramfs image that is built to be
bundled in with the kernel image, set the
INITRAMFS_IMAGE_BUNDLE
variable to "1" in your local.conf
configuration file and set the
INITRAMFS_IMAGE
variable in the recipe that builds the kernel image.
Setting the INITRAMFS_IMAGE_BUNDLE
flag causes the initramfs image to be unpacked
into the ${B}/usr/
directory.
The unpacked initramfs image is then passed to the kernel's
Makefile
using the
CONFIG_INITRAMFS_SOURCE
variable, allowing the initramfs image to be built into
the kernel normally.
INITRD_IMAGE
,
INITRD_LIVE
, and
INITRD_IMAGE_LIVE
variables.
For more information, see the
image-live.bbclass
file.
Optionally Add Items to the initramfs Image
Through the initramfs Image Recipe:
If you add items to the initramfs image by way of its
recipe, you should use
PACKAGE_INSTALL
rather than
IMAGE_INSTALL
.
PACKAGE_INSTALL
gives more direct
control of what is added to the image as compared to
the defaults you might not necessarily want that are
set by the
image
or
core-image
classes.
Build the Kernel Image and the initramfs
Image:
Build your kernel image using BitBake.
Because the initramfs image recipe is a dependency of the
kernel image, the initramfs image is built as well and
bundled with the kernel image if you used the
INITRAMFS_IMAGE_BUNDLE
variable described earlier.
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.
The following list presents the overall steps you need to consider and perform to create distributions with smaller root filesystems, achieve faster boot times, maintain your critical functionality, and avoid initial RAM disks:
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.
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
.
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 represents 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/tiny/
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 help 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 repositories
(i.e. linux-yocto-3.14
,
linux-yocto-3.10
,
linux-yocto-3.8
, and so forth)
in the
scripts/kconfig
directory.
For more information on configuration fragments, see the "Creating Configuration Fragments" section in the Yocto Project Linux Kernel Development Manual.
bitbake -u taskexp -g
:
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.bitbake_target
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 modify 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. The previous example filters out any files 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:
$ cdimage-directory
$ bitbake -u taskexp -gimage
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 your 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.
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?
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.
Packaging requirements add size to the image. One way to reduce the size of the image is to remove all the packaging requirements from the image. This reduction includes both removing the package manager and its unique dependencies as well as removing the package management data itself.
To eliminate all the packaging requirements for an image,
be sure that "package-management" is not part of your
IMAGE_FEATURES
statement for the image.
When you remove this feature, you are removing the package
manager as well as its dependencies from the root filesystem.
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:
glibc
:
In general, follow this process:
Remove glibc
features from
DISTRO_FEATURES
that you think you do not need.
Build your distribution.
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 glibc
features provide the support and restore the
configuration.
Rebuild and repeat the process.
busybox
:
For BusyBox, use a process similar as described for
glibc
.
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.
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.
A common scenario developers face is creating images for several
different machines that use the same software environment.
In this situation, it is tempting to set the
tunings and optimization flags for each build specifically for
the targeted hardware (i.e. "maxing out" the tunings).
Doing so can considerably add to build times and package feed
maintenance collectively for the machines.
For example, selecting tunes that are extremely specific to a
CPU core used in a system might enable some micro optimizations
in GCC for that particular system but would otherwise not gain
you much of a performance difference across the other systems
as compared to using a more general tuning across all the builds
(e.g. setting
DEFAULTTUNE
specifically for each machine's build).
Rather than "max out" each build's tunings, you can take steps that
cause the OpenEmbedded build system to reuse software across the
various machines where it makes sense.
If build speed and package feed maintenance are considerations, you should consider the points in this section that can help you optimize your tunings to best consider build times and package feed maintenance.
Share the Build Directory:
If at all possible, share the
TMPDIR
across builds.
The Yocto Project supports switching between different
MACHINE
values in the same TMPDIR
.
This practice is well supported and regularly used by
developers when building for multiple machines.
When you use the same TMPDIR
for
multiple machine builds, the OpenEmbedded build system can
reuse the existing native and often cross-recipes for
multiple machines.
Thus, build time decreases.
DISTRO
settings change or fundamental configuration settings
such as the filesystem layout, you need to work with
a clean TMPDIR
.
Sharing TMPDIR
under these
circumstances might work but since it is not
guaranteed, you should use a clean
TMPDIR
.
Enable the Appropriate Package Architecture: By default, the OpenEmbedded build system enables three levels of package architectures: "all", "tune" or "package", and "machine". Any given recipe usually selects one of these package architectures (types) for its output. Depending for what a given recipe creates packages, making sure you enable the appropriate package architecture can directly impact the build time.
A recipe that just generates scripts can enable
"all" architecture because there are no binaries to build.
To specifically enable "all" architecture, be sure your
recipe inherits the
allarch
class.
This class is useful for "all" architectures because it
configures many variables so packages can be used across
multiple architectures.
If your recipe needs to generate packages that are
machine-specific or when one of the build or runtime
dependencies is already machine-architecture dependent,
which makes your recipe also machine-architecture dependent,
make sure your recipe enables the "machine" package
architecture through the
MACHINE_ARCH
variable:
PACKAGE_ARCH = "${MACHINE_ARCH}"
When you do not specifically enable a package
architecture through the
PACKAGE_ARCH
,
The OpenEmbedded build system defaults to the
TUNE_PKGARCH
setting:
PACKAGE_ARCH = "${TUNE_PKGARCH}"
Choose a Generic Tuning File if Possible:
Some tunes are more generic and can run on multiple targets
(e.g. an armv5
set of packages could
run on armv6
and
armv7
processors in most cases).
Similarly, i486
binaries could work
on i586
and higher processors.
You should realize, however, that advances on newer
processor versions would not be used.
If you select the same tune for several different machines, the OpenEmbedded build system reuses software previously built, thus speeding up the overall build time. Realize that even though a new sysroot for each machine is generated, the software is not recompiled and only one package feed exists.
Manage Granular Level Packaging:
Sometimes cases exist where injecting another level of
package architecture beyond the three higher levels noted
earlier can be useful.
For example, consider how NXP (formerly Freescale) allows
for the easy reuse of binary packages in their layer
meta-freescale
.
In this example, the
fsl-dynamic-packagearch
class shares GPU packages for i.MX53 boards because
all boards share the AMD GPU.
The i.MX6-based boards can do the same because all boards
share the Vivante GPU.
This class inspects the BitBake datastore to identify if
the package provides or depends on one of the
sub-architecture values.
If so, the class sets the
PACKAGE_ARCH
value based on the MACHINE_SUBARCH
value.
If the package does not provide or depend on one of the
sub-architecture values but it matches a value in the
machine-specific filter, it sets
MACHINE_ARCH
.
This behavior reduces the number of packages built and
saves build time by reusing binaries.
Use Tools to Debug Issues:
Sometimes you can run into situations where software is
being rebuilt when you think it should not be.
For example, the OpenEmbedded build system might not be
using shared state between machines when you think it
should be.
These types of situations are usually due to references
to machine-specific variables such as
MACHINE
,
SERIAL_CONSOLES
,
XSERVER
,
MACHINE_FEATURES
,
and so forth in code that is supposed to only be
tune-specific or when the recipe depends
(DEPENDS
,
RDEPENDS
,
RRECOMMENDS
,
RSUGGESTS
,
and so forth) on some other recipe that already has
PACKAGE_ARCH
defined as "${MACHINE_ARCH}".
For such cases, you can use some tools to help you sort out the situation:
sstate-diff-machines.sh
:
You can find this tool in the
scripts
directory of the
Source Repositories.
See the comments in the script for information on
how to use the tool.
BitBake's "-S printdiff" Option:
Using this option causes BitBake to try to
establish the closest signature match it can
(e.g. in the shared state cache) and then run
bitbake-diffsigs
over the
matches to determine the stamps and delta where
these two stamp trees diverge.
By default, the OpenEmbedded build system uses the Build Directory when building source code. 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
OpenEmbedded build system.
For example, suppose you have a project that includes a new BSP with
a heavily customized kernel.
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 inherit the
externalsrc
class and then set the
EXTERNALSRC
variable to point to your external source code.
Here are the statements to put in your
local.conf
file:
INHERIT += "externalsrc" EXTERNALSRC_pn-myrecipe
= "path-to-your-source-tree
"
This next example shows how to accomplish the same thing by setting
EXTERNALSRC
in the recipe itself or in the
recipe's append file:
EXTERNALSRC = "path
" EXTERNALSRC_BUILD = "path
"
externalsrc
class.
By default, externalsrc.bbclass
builds
the source code in a directory separate from the external source
directory as specified by
EXTERNALSRC
.
If you need to have the source built in the same directory in
which it resides, or some other nominated directory, you can set
EXTERNALSRC_BUILD
to point to that directory:
EXTERNALSRC_BUILD_pn-myrecipe
= "path-to-your-source-tree
"
Build time can be an issue. By default, the build system uses simple controls to try and maximize build efficiency. In general, the default settings for all the following variables result in the most efficient build times when dealing with single socket systems (i.e. a single CPU). If you have multiple CPUs, you might try increasing the default values to gain more speed. See the descriptions in the glossary for each variable for more information:
BB_NUMBER_THREADS
:
The maximum number of threads BitBake simultaneously executes.
BB_NUMBER_PARSE_THREADS
:
The number of threads BitBake uses during parsing.
PARALLEL_MAKE
:
Extra options passed to the make
command
during the
do_compile
task in order to specify parallel compilation on the
local build host.
PARALLEL_MAKEINST
:
Extra options passed to the make
command
during the
do_install
task in order to specify parallel installation on the
local build host.
As mentioned, these variables all scale to the number of processor cores available on the build system. For single socket systems, this auto-scaling ensures that the build system fundamentally takes advantage of potential parallel operations during the build based on the build machine's capabilities.
Following are additional factors that can affect build speed:
File system type:
The file system type that the build is being performed on can
also influence performance.
Using ext4
is recommended as compared
to ext2
and ext3
due to ext4
improved features
such as extents.
Disabling the updating of access time using
noatime
:
The noatime
mount option prevents the
build system from updating file and directory access times.
Setting a longer commit: Using the "commit=" mount option increases the interval in seconds between disk cache writes. Changing this interval from the five second default to something longer increases the risk of data loss but decreases the need to write to the disk, thus increasing the build performance.
Choosing the packaging backend: Of the available packaging backends, IPK is the fastest. Additionally, selecting a singular packaging backend also helps.
Using tmpfs
for
TMPDIR
as a temporary file system:
While this can help speed up the build, the benefits are
limited due to the compiler using
-pipe
.
The build system goes to some lengths to avoid
sync()
calls into the
file system on the principle that if there was a significant
failure, the
Build Directory
contents could easily be rebuilt.
Inheriting the
rm_work
class:
Inheriting this class has shown to speed up builds due to
significantly lower amounts of data stored in the data
cache as well as on disk.
Inheriting this class also makes cleanup of
TMPDIR
faster, at the expense of being easily able to dive into the
source code.
File system maintainers have recommended that the fastest way
to clean up large numbers of files is to reformat partitions
rather than delete files due to the linear nature of
partitions.
This, of course, assumes you structure the disk partitions and
file systems in a way that this is practical.
Aside from the previous list, you should keep some trade offs in mind that can help you speed up the build:
Remove items from
DISTRO_FEATURES
that you might not need.
Exclude debug symbols and other debug information:
If you do not need these symbols and other debug information,
disabling the *-dbg
package generation
can speed up the build.
You can disable this generation by setting the
INHIBIT_PACKAGE_DEBUG_SPLIT
variable to "1".
Disable static library generation for recipes derived from
autoconf
or libtool
:
Following is an example showing how to disable static
libraries and still provide an override to handle exceptions:
STATICLIBCONF = "--disable-static" STATICLIBCONF_sqlite3-native = "" EXTRA_OECONF += "${STATICLIBCONF}"
Some recipes need static libraries in order to work
correctly (e.g. pseudo-native
needs sqlite3-native
).
Overrides, as in the previous example, account for
these kinds of exceptions.
Some packages have packaging code that assumes the presence of the static libraries. If so, you might need to exclude them as well.
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:
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 includes
${PN}-staticdev
, which represents all static library files.
${PN}-dev
.
Following is part of the BitBake configuration file, where you can see how the static library files are defined:
PACKAGE_BEFORE_PN ?= "" PACKAGES = "${PN}-dbg ${PN}-staticdev ${PN}-dev ${PN}-doc ${PN}-locale ${PACKAGE_BEFORE_PN} ${PN}" PACKAGES_DYNAMIC = "^${PN}-locale-.*" FILES = "" FILES_${PN} = "${bindir}/* ${sbindir}/* ${libexecdir}/* ${libdir}/lib*${SOLIBS} \ ${sysconfdir} ${sharedstatedir} ${localstatedir} \ ${base_bindir}/* ${base_sbindir}/* \ ${base_libdir}/*${SOLIBS} \ ${base_prefix}/lib/udev/rules.d ${prefix}/lib/udev/rules.d \ ${datadir}/${BPN} ${libdir}/${BPN}/* \ ${datadir}/pixmaps ${datadir}/applications \ ${datadir}/idl ${datadir}/omf ${datadir}/sounds \ ${libdir}/bonobo/servers" FILES_${PN}-bin = "${bindir}/* ${sbindir}/*" FILES_${PN}-doc = "${docdir} ${mandir} ${infodir} ${datadir}/gtk-doc \ ${datadir}/gnome/help" SECTION_${PN}-doc = "doc" FILES_SOLIBSDEV ?= "${base_libdir}/lib*${SOLIBSDEV} ${libdir}/lib*${SOLIBSDEV}" FILES_${PN}-dev = "${includedir} ${FILES_SOLIBSDEV} ${libdir}/*.la \ ${libdir}/*.o ${libdir}/pkgconfig ${datadir}/pkgconfig \ ${datadir}/aclocal ${base_libdir}/*.o \ ${libdir}/${BPN}/*.la ${base_libdir}/*.la" SECTION_${PN}-dev = "devel" ALLOW_EMPTY_${PN}-dev = "1" RDEPENDS_${PN}-dev = "${PN} (= ${EXTENDPKGV})" FILES_${PN}-staticdev = "${libdir}/*.a ${base_libdir}/*.a ${libdir}/${BPN}/*.a" SECTION_${PN}-staticdev = "devel" RDEPENDS_${PN}-staticdev = "${PN}-dev (= ${EXTENDPKGV})"
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 a different set of libraries. The libraries could differ in architecture, compiler options, or other optimizations.
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
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
not be needed.
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
.
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_append = " lib32-glib-2.0"
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-glib-2.0
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-glib-2.0
Generic implementation details as well as details that are specific to package management systems exist. Following are implementation details that exist regardless of the package management system:
The typical convention used for the
class extension code as used by
Multilib assumes that all package names specified
in
PACKAGES
that contain ${PN}
have
${PN}
at the start of the name.
When that convention is not followed and
${PN}
appears at
the middle or the end of a name, problems occur.
The
TARGET_VENDOR
value under Multilib will be extended to
"-vendor
mlmultilib
"
(e.g. "-pokymllib32" for a "lib32" Multilib with
Poky).
The reason for this slightly unwieldy contraction
is that any "-" characters in the vendor
string presently break Autoconf's
config.sub
, and
other separators are problematic for different
reasons.
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.
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 straightforward 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"
x32 processor-specific Application Binary Interface (x32 psABI) is a native 32-bit processor-specific ABI for Intel® 64 (x86-64) architectures. An ABI defines the calling conventions between functions in a processing environment. The interface determines what registers are used and what the sizes are for various C data types.
Some processing environments prefer using 32-bit applications even when running on Intel 64-bit platforms. Consider the i386 psABI, which is a very old 32-bit ABI for Intel 64-bit platforms. The i386 psABI does not provide efficient use and access of the Intel 64-bit processor resources, leaving the system underutilized. Now consider the x86_64 psABI. This ABI is newer and uses 64-bits for data sizes and program pointers. The extra bits increase the footprint size of the programs, libraries, and also increases the memory and file system size requirements. Executing under the x32 psABI enables user programs to utilize CPU and system resources more efficiently while keeping the memory footprint of the applications low. Extra bits are used for registers but not for addressing mechanisms.
The Yocto Project supports the final specifications of x32 psABI as follows:
You can create packages and images in x32 psABI format on x86_64 architecture targets.
You can successfully build recipes with the x32 toolchain.
You can create and boot
core-image-minimal
and
core-image-sato
images.
RPM Package Manager (RPM) support exists for x32 binaries.
Support for large images exists.
To use the x32 psABI, you need to edit your
conf/local.conf
configuration file as
follows:
MACHINE = "qemux86-64" DEFAULTTUNE = "x86-64-x32" baselib = "${@d.getVar('BASE_LIB_tune-' + (d.getVar('DEFAULTTUNE', True) \ or 'INVALID'), True) or 'lib'}"
Once you have set up your configuration file, use BitBake to build an image that supports the x32 psABI. Here is an example:
$ bitbake core-image-sato
GObject introspection is the standard mechanism for accessing GObject-based software from runtime environments. GObject is a feature of the GLib library that provides an object framework for the GNOME desktop and related software. GObject Introspection adds information to GObject that allows objects created within it to be represented across different programming languages. If you want to construct GStreamer pipelines using Python, or control UPnP infrastructure using Javascript and GUPnP, GObject introspection is the only way to do it.
This section describes the Yocto Project support for generating
and packaging GObject introspection data.
GObject introspection data is a description of the
API provided by libraries built on top of GLib framework,
and, in particular, that framework's GObject mechanism.
GObject Introspection Repository (GIR) files go to
-dev
packages,
typelib
files go to main packages as they
are packaged together with libraries that are introspected.
The data is generated when building such a library, by linking the library with a small executable binary that asks the library to describe itself, and then executing the binary and processing its output.
Generating this data in a cross-compilation environment is difficult because the library is produced for the target architecture, but its code needs to be executed on the build host. This problem is solved with the OpenEmbedded build system by running the code through QEMU, which allows precisely that. Unfortunately, QEMU does not always work perfectly as mentioned in the xxx section.
Enabling the generation of introspection data (GIR files) in your library package involves the following:
Inherit the
gobject-introspection
class.
Make sure introspection is not disabled anywhere in
the recipe or from anything the recipe includes.
Also, make sure that "gobject-introspection-data" is
not in
DISTRO_FEATURES_BACKFILL_CONSIDERED
and that "qemu-usermode" is not in
MACHINE_FEATURES_BACKFILL_CONSIDERED
.
If either of these conditions exist, nothing will
happen.
Try to build the recipe.
If you encounter build errors that look like
something is unable to find
.so
libraries, check where these
libraries are located in the source tree and add
the following to the recipe:
GIR_EXTRA_LIBS_PATH = "${B}/something
/.libs"
oe-core
repository that use that
GIR_EXTRA_LIBS_PATH
variable
as an example.
Look for any other errors, which probably mean that introspection support in a package is not entirely standard, and thus breaks down in a cross-compilation environment. For such cases, custom-made fixes are needed. A good place to ask and receive help in these cases is the Yocto Project mailing lists.
You might find that you do not want to generate introspection data. Or, perhaps QEMU does not work on your build host and target architecture combination. If so, you can use either of the following methods to disable GIR file generations:
Add the following to your distro configuration:
DISTRO_FEATURES_BACKFILL_CONSIDERED = "gobject-introspection-data"
Adding this statement disables generating introspection data using QEMU but will still enable building introspection tools and libraries (i.e. building them does not require the use of QEMU).
Add the following to your machine configuration:
MACHINE_FEATURES_BACKFILL_CONSIDERED = "qemu-usermode"
Adding this statement disables the use of QEMU when building packages for your machine. Currently, this feature is used only by introspection recipes and has the same effect as the previously described option.
If you disable introspection data, you can still obtain it through other means such as copying the data from a suitable sysroot, or by generating it on the target hardware. The OpenEmbedded build system does not currently provide specific support for these techniques.
Use the following procedure to test if generating introspection data is working in an image:
Make sure that "gobject-introspection-data" is not in
DISTRO_FEATURES_BACKFILL_CONSIDERED
and that "qemu-usermode" is not in
MACHINE_FEATURES_BACKFILL_CONSIDERED
.
Build core-image-sato
.
Launch a Terminal and then start Python in the terminal.
Enter the following in the terminal:
>>> from gi.repository import GLib >>> GLib.get_host_name()
For something a little more advanced, enter the following:
http://python-gtk-3-tutorial.readthedocs.org/en/latest/introduction.html
The following know issues exist for GObject Introspection Support:
qemu-ppc64
immediately crashes.
Consequently, you cannot build introspection data on
that architecture.
x32 is not supported by QEMU. Consequently, introspection data is disabled.
musl causes transient GLib binaries to crash on assertion failures. Consequently, generating introspection data is disabled.
Because QEMU is not able to run the binaries correctly,
introspection is disabled for some specific packages
under specific architectures (e.g.
gcr
,
libsecret
, and
webkit
).
QEMU usermode might not work properly when running 64-bit binaries under 32-bit host machines. In particular, "qemumips64" is known to not work under i686.
You might want to use an external toolchain as part of your development. If this is the case, the fundamental steps you need to accomplish are as follows:
Understand where the installed toolchain resides. For cases where you need to build the external toolchain, you would need to take separate steps to build and install the toolchain.
Make sure you add the layer that contains the toolchain to
your bblayers.conf
file through the
BBLAYERS
variable.
Set the EXTERNAL_TOOLCHAIN
variable in your local.conf
file
to the location in which you installed the toolchain.
A good example of an external toolchain used with the Yocto Project
is Mentor Graphics®
Sourcery G++ Toolchain.
You can see information on how to use that particular layer in the
README
file at
http://github.com/MentorEmbedded/meta-sourcery/.
You can find further information by reading about the
TCMODE
variable in the Yocto Project Reference Manual's variable glossary.
Creating an image for a particular hardware target using the OpenEmbedded build system does not necessarily mean you can boot that image as is on your device. Physical devices accept and boot images in various ways depending on the specifics of the device. Usually, information about the hardware can tell you what image format the device requires. Should your device require multiple partitions on an SD card, flash, or an HDD, you can use the OpenEmbedded Image Creator, Wic, to create the properly partitioned image.
The wic
command generates partitioned
images from existing OpenEmbedded build artifacts.
Image generation is driven by partitioning commands
contained in an Openembedded kickstart file
(.wks
) specified either directly on
the command line or as one of a selection of canned
kickstart files as shown with the
wic list images
command in the
"Using an Existing Kickstart File"
section.
When you apply the command to a given set of build
artifacts, the result is an image or set of images that
can be directly written onto media and used on a particular
system.
.wks
) Reference"
Chapter in the Yocto Project Reference Manual.
The wic
command and the infrastructure
it is based on is by definition incomplete.
The purpose of the command is to allow the generation of
customized images, and as such, was designed to be
completely extensible through a plug-in interface.
See the
"Using the Wic Plug-Ins Interface"
section for information on these plug-ins.
This section provides some background information on Wic, describes what you need to have in place to run the tool, provides instruction on how to use the Wic utility, provides information on using the Wic plug-ins interface, and provides several examples that show how to use Wic.
This section provides some background on the Wic utility. While none of this information is required to use Wic, you might find it interesting.
The name "Wic" is derived from OpenEmbedded Image Creator (oeic). The "oe" diphthong in "oeic" was promoted to the letter "w", because "oeic" is both difficult to remember and to pronounce.
Wic is loosely based on the
Meego Image Creator (mic
)
framework.
The Wic implementation has been
heavily modified to make direct use of OpenEmbedded
build artifacts instead of package installation and
configuration, which are already incorporated within
the OpenEmbedded artifacts.
Wic is a completely independent
standalone utility that initially provides
easier-to-use and more flexible replacements for an
existing functionality in OE-Core's
image-live
class and mkefidisk.sh
script.
The difference between
Wic and those examples is
that with Wic the
functionality of those scripts is implemented
by a general-purpose partitioning language, which is
based on Redhat kickstart syntax.
In order to use the Wic utility with the OpenEmbedded Build system, your system needs to meet the following requirements:
The Linux distribution on your development host must support the Yocto Project. See the "Supported Linux Distributions" section in the Yocto Project Reference Manual for the list of distributions that support the Yocto Project.
The standard system utilities, such as
cp
, must be installed on your
development host system.
You must have sourced the build environment
setup script (i.e.
oe-init-build-env
)
found in the
Build Directory.
You need to have the build artifacts already
available, which typically means that you must
have already created an image using the
Openembedded build system (e.g.
core-image-minimal
).
While it might seem redundant to generate an image
in order to create an image using
Wic, the current version of
Wic requires the artifacts
in the form generated by the OpenEmbedded build
system.
You must build several native tools, which are built to run on the build system:
$ bitbake parted-native dosfstools-native mtools-native
Include "wic" as part of the
IMAGE_FSTYPES
variable.
Include the name of the
wic kickstart file
as part of the
WKS_FILE
variable
You can get general help for the wic
command by entering the wic
command
by itself or by entering the command with a help argument
as follows:
$ wic -h $ wic --help $ wic help
Currently, Wic supports seven commands:
cp
, create
,
help
, list
,
ls
, rm
, and
write
.
You can get help for all these commands except "help" by
using the following form:
$ wic help command
For example, the following command returns help for the
write
command:
$ wic help write
Wic supports help for three topics:
overview
,
plugins
, and
kickstart
.
You can get help for any topic using the following form:
$ wic help topic
For example, the following returns overview help for Wic:
$ wic help overview
One additional level of help exists for Wic.
You can get help on individual images through the
list
command.
You can use the list
command to return the
available Wic images as follows:
$ wic list images mpc8315e-rdb Create SD card image for MPC8315E-RDB genericx86 Create an EFI disk image for genericx86* beaglebone-yocto Create SD card image for Beaglebone edgerouter Create SD card image for Edgerouter qemux86-directdisk Create a qemu machine 'pcbios' direct disk image directdisk-gpt Create a 'pcbios' direct disk image mkefidisk Create an EFI disk image directdisk Create a 'pcbios' direct disk image systemd-bootdisk Create an EFI disk image with systemd-boot mkhybridiso Create a hybrid ISO image sdimage-bootpart Create SD card image with a boot partition directdisk-multi-rootfs Create multi rootfs image using rootfs plugin directdisk-bootloader-config Create a 'pcbios' direct disk image with custom bootloader config
Once you know the list of available Wic images, you can use
help
with the command to get help on a
particular image.
For example, the following command returns help on the
"beaglebone-yocto" image:
$ wic list beaglebone-yocto help Creates a partitioned SD card image for Beaglebone. Boot files are located in the first vfat partition.
You can use Wic in two different modes, depending on how much control you need for specifying the Openembedded build artifacts that are used for creating the image: Raw and Cooked:
Raw Mode: You explicitly specify build artifacts through Wic command-line arguments.
Cooked Mode:
The current
MACHINE
setting and image name are used to automatically
locate and provide the build artifacts.
You just supply a kickstart file and the name
of the image from which to use artifacts.
Regardless of the mode you use, you need to have the build artifacts ready and available.
Running Wic in raw mode allows you to specify all the
partitions through the wic
command line.
The primary use for raw mode is if you have built
your kernel outside of the Yocto Project
Build Directory.
In other words, you can point to arbitrary kernel,
root filesystem locations, and so forth.
Contrast this behavior with cooked mode where Wic
looks in the Build Directory (e.g.
tmp/deploy/images/
machine
).
The general form of the
wic
command in raw mode is:
$ wic createwks_file
options
... Where:wks_file
: An OpenEmbedded kickstart file. You can provide your own custom file or use a file from a set of existing files as described by further options. optional arguments: -h, --help show this help message and exit -oOUTDIR
, --outdirOUTDIR
name of directory to create image in -eIMAGE_NAME
, --image-nameIMAGE_NAME
name of the image to use the artifacts from e.g. core- image-sato -rROOTFS_DIR
, --rootfs-dirROOTFS_DIR
path to the /rootfs dir to use as the .wks rootfs source -bBOOTIMG_DIR
, --bootimg-dirBOOTIMG_DIR
path to the dir containing the boot artifacts (e.g. /EFI or /syslinux dirs) to use as the .wks bootimg source -kKERNEL_DIR
, --kernel-dirKERNEL_DIR
path to the dir containing the kernel to use in the .wks bootimg -nNATIVE_SYSROOT
, --native-sysrootNATIVE_SYSROOT
path to the native sysroot containing the tools to use to build the image -s, --skip-build-check skip the build check -f, --build-rootfs build rootfs -c {gzip,bzip2,xz}, --compress-with {gzip,bzip2,xz} compress image with specified compressor -m, --bmap generate .bmap --no-fstab-update Do not change fstab file. -vVARS_DIR
, --varsVARS_DIR
directory with <image>.env files that store bitbake variables -D, --debug output debug information
Running Wic in cooked mode leverages off artifacts in
the Build Directory.
In other words, you do not have to specify kernel or
root filesystem locations as part of the command.
All you need to provide is a kickstart file and the
name of the image from which to use artifacts by using
the "-e" option.
Wic looks in the Build Directory (e.g.
tmp/deploy/images/
machine
)
for artifacts.
The general form of the wic
command using Cooked Mode is as follows:
$ wic createwks_file
-eIMAGE_NAME
Where:wks_file
: An OpenEmbedded kickstart file. You can provide your own custom file or use a file from a set of existing files provided with the Yocto Project release. required argument: -eIMAGE_NAME
, --image-nameIMAGE_NAME
name of the image to use the artifacts from e.g. core- image-sato
If you do not want to create your own kickstart file, you can use an existing file provided by the Wic installation. As shipped, kickstart files can be found in the Yocto Project Source Repositories in the following two locations:
poky/meta-yocto-bsp/wic poky/scripts/lib/wic/canned-wks
Use the following command to list the available kickstart files:
$ wic list images mpc8315e-rdb Create SD card image for MPC8315E-RDB genericx86 Create an EFI disk image for genericx86* beaglebone-yocto Create SD card image for Beaglebone edgerouter Create SD card image for Edgerouter qemux86-directdisk Create a qemu machine 'pcbios' direct disk image directdisk-gpt Create a 'pcbios' direct disk image mkefidisk Create an EFI disk image directdisk Create a 'pcbios' direct disk image systemd-bootdisk Create an EFI disk image with systemd-boot mkhybridiso Create a hybrid ISO image sdimage-bootpart Create SD card image with a boot partition directdisk-multi-rootfs Create multi rootfs image using rootfs plugin directdisk-bootloader-config Create a 'pcbios' direct disk image with custom bootloader config
When you use an existing file, you do not have to use the
.wks
extension.
Here is an example in Raw Mode that uses the
directdisk
file:
$ wic create directdisk -rrootfs_dir
-bbootimg_dir
\ -kkernel_dir
-nnative_sysroot
Here are the actual partition language commands
used in the genericx86.wks
file to
generate an image:
# short-description: Create an EFI disk image for genericx86* # long-description: Creates a partitioned EFI disk image for genericx86* machines part /boot --source bootimg-efi --sourceparams="loader=grub-efi" --ondisk sda --label msdos --active --align 1024 part / --source rootfs --ondisk sda --fstype=ext4 --label platform --align 1024 --use-uuid part swap --ondisk sda --size 44 --label swap1 --fstype=swap bootloader --ptable gpt --timeout=5 --append="rootfstype=ext4 console=ttyS0,115200 console=tty0"
You can extend and specialize Wic functionality by using Wic plug-ins. This section explains the Wic plug-in interface.
Source plug-ins provide a mechanism to customize partition
content during the Wic image generation process.
You can use source plug-ins to map values that you specify
using --source
commands in kickstart
files (i.e. *.wks
) to a plug-in
implementation used to populate a given partition.
WKS_FILE_DEPENDS
variable.
Source plug-ins are subclasses defined in plug-in files. As shipped, the Yocto Project provides several plug-in files. You can see the source plug-in files that ship with the Yocto Project here. Each of these plug-in files contains source plug-ins that are designed to populate a specific Wic image partition.
Source plug-ins are subclasses of the
SourcePlugin
class, which is
defined in the
poky/scripts/lib/wic/pluginbase.py
file.
For example, the BootimgEFIPlugin
source plug-in found in the
bootimg-efi.py
file is a subclass of
the SourcePlugin
class, which is found
in the pluginbase.py
file.
You can also implement source plug-ins in a layer outside
of the Source Repositories (external layer).
To do so, be sure that your plug-in files are located in
a directory whose path is
scripts/lib/wic/plugins/source/
within your external layer.
When the plug-in files are located there, the source
plug-ins they contain are made available to Wic.
When the Wic implementation needs to invoke a
partition-specific implementation, it looks for the plug-in
with the same name as the --source
parameter used in the kickstart file given to that
partition.
For example, if the partition is set up using the following
command in a kickstart file:
part /boot --source bootimg-pcbios --ondisk sda --label boot --active --align 1024
The methods defined as class members of the matching
source plug-in (i.e. bootimg-pcbios
)
in the bootimg-pcbios.py
plug-in file
are used.
To be more concrete, here is the corresponding plug-in
definition from the bootimg-pcbios.py
file for the previous command along with an example
method called by the Wic implementation when it needs to
prepare a partition using an implementation-specific
function:
. . . class BootimgPcbiosPlugin(SourcePlugin): """ Create MBR boot partition and install syslinux on it. """ name = 'bootimg-pcbios' . . . @classmethod def do_prepare_partition(cls, part, source_params, creator, cr_workdir, oe_builddir, bootimg_dir, kernel_dir, rootfs_dir, native_sysroot): """ Called to do the actual content population for a partition i.e. it 'prepares' the partition to be incorporated into the image. In this case, prepare content for legacy bios boot partition. """ . . .
If a subclass (plug-in) itself does not implement a
particular function, Wic locates and uses the default
version in the superclass.
It is for this reason that all source plug-ins are derived
from the SourcePlugin
class.
The SourcePlugin
class defined in
the pluginbase.py
file defines
a set of methods that source plug-ins can implement or
override.
Any plug-ins (subclass of
SourcePlugin
) that do not implement
a particular method inherit the implementation of the
method from the SourcePlugin
class.
For more information, see the
SourcePlugin
class in the
pluginbase.py
file for details:
The following list describes the methods implemented in the
SourcePlugin
class:
do_prepare_partition()
:
Called to populate a partition with actual content.
In other words, the method prepares the final
partition image that is incorporated into the
disk image.
do_configure_partition()
:
Called before
do_prepare_partition()
to
create custom configuration files for a partition
(e.g. syslinux or grub configuration files).
do_install_disk()
:
Called after all partitions have been prepared and
assembled into a disk image.
This method provides a hook to allow finalization
of a disk image (e.g. writing an MBR).
do_stage_partition()
:
Special content-staging hook called before
do_prepare_partition()
.
This method is normally empty.
Typically, a partition just uses the passed-in
parameters (e.g. the unmodified value of
bootimg_dir
).
However, in some cases, things might need to be
more tailored.
As an example, certain files might additionally
need to be taken from
bootimg_dir + /boot
.
This hook allows those files to be staged in a
customized fashion.
get_bitbake_var()
allows you to access non-standard variables
that you might want to use for this
behavior.
You can extend the source plug-in mechanism.
To add more hooks, create more source plug-in methods
within SourcePlugin
and the
corresponding derived subclasses.
The code that calls the plug-in methods uses the
plugin.get_source_plugin_methods()
function to find the method or methods needed by the call.
Retrieval of those methods is accomplished by filling up
a dict with keys that contain the method names of interest.
On success, these will be filled in with the actual
methods.
See the Wic implementation for examples and details.
This section provides several examples that show how to use
the Wic utility.
All the examples assume the list of requirements in the
"Requirements"
section have been met.
The examples assume the previously generated image is
core-image-minimal
.
This example runs in Cooked Mode and uses the
mkefidisk
kickstart file:
$ wic create mkefidisk -e core-image-minimal INFO: Building wic-tools... . . . INFO: The new image(s) can be found here: ./mkefidisk-201804191017-sda.direct The following build artifacts were used to create the image(s): ROOTFS_DIR: /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/rootfs BOOTIMG_DIR: /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share KERNEL_DIR: /home/stephano/build/master/build/tmp-glibc/deploy/images/qemux86 NATIVE_SYSROOT: /home/stephano/build/master/build/tmp-glibc/work/i586-oe-linux/wic-tools/1.0-r0/recipe-sysroot-native INFO: The image(s) were created using OE kickstart file: /home/stephano/build/master/openembedded-core/scripts/lib/wic/canned-wks/mkefidisk.wks
The previous example shows the easiest way to create
an image by running in cooked mode and supplying
a kickstart file and the "-e" option to point to the
existing build artifacts.
Your local.conf
file needs to have
the
MACHINE
variable set to the machine you are using, which is
"qemux86" in this example.
Once the image builds, the output provides image location, artifact use, and kickstart file information.
Continuing with the example, you can now write the
image from the Build Directory onto a USB stick, or
whatever media for which you built your image, and boot
from the media.
You can write the image by using
bmaptool
or
dd
:
$ oe-run-native bmaptool copy mkefidisk-201804191017-sda.direct /dev/sdX
or
$ sudo dd if=mkefidisk-201804191017-sda.direct of=/dev/sdX
bmaptool
to flash a device
with an image, see the
"Flashing Images Using bmaptool
"
section.
Because partitioned image creation is driven by the
kickstart file, it is easy to affect image creation by
changing the parameters in the file.
This next example demonstrates that through modification
of the directdisk-gpt
kickstart
file.
As mentioned earlier, you can use the command
wic list images
to show the list
of existing kickstart files.
The directory in which the
directdisk-gpt.wks
file resides is
scripts/lib/image/canned-wks/
,
which is located in the
Source Directory
(e.g. poky
).
Because available files reside in this directory,
you can create and add your own custom files to the
directory.
Subsequent use of the
wic list images
command would then
include your kickstart files.
In this example, the existing
directdisk-gpt
file already does
most of what is needed.
However, for the hardware in this example, the image
will need to boot from sdb
instead
of sda
, which is what the
directdisk-gpt
kickstart file
uses.
The example begins by making a copy of the
directdisk-gpt.wks
file in the
scripts/lib/image/canned-wks
directory and then by changing the lines that specify
the target disk from which to boot.
$ cp /home/stephano/poky/scripts/lib/wic/canned-wks/directdisk-gpt.wks \ /home/stephano/poky/scripts/lib/wic/canned-wks/directdisksdb-gpt.wks
Next, the example modifies the
directdisksdb-gpt.wks
file and
changes all instances of
"--ondisk sda
" to
"--ondisk sdb
".
The example changes the following two lines and leaves
the remaining lines untouched:
part /boot --source bootimg-pcbios --ondisk sdb --label boot --active --align 1024 part / --source rootfs --ondisk sdb --fstype=ext4 --label platform --align 1024 --use-uuid
Once the lines are changed, the example generates the
directdisksdb-gpt
image.
The command points the process at the
core-image-minimal
artifacts for
the Next Unit of Computing (nuc)
MACHINE
the local.conf
.
$ wic create directdisksdb-gpt -e core-image-minimal INFO: Building wic-tools... . . . Initialising tasks: 100% |#######################################| Time: 0:00:01 NOTE: Executing SetScene Tasks NOTE: Executing RunQueue Tasks NOTE: Tasks Summary: Attempted 1161 tasks of which 1157 didn't need to be rerun and all succeeded. INFO: Creating image(s)... INFO: The new image(s) can be found here: ./directdisksdb-gpt-201710090938-sdb.direct The following build artifacts were used to create the image(s): ROOTFS_DIR: /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/rootfs BOOTIMG_DIR: /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share KERNEL_DIR: /home/stephano/build/master/build/tmp-glibc/deploy/images/qemux86 NATIVE_SYSROOT: /home/stephano/build/master/build/tmp-glibc/work/i586-oe-linux/wic-tools/1.0-r0/recipe-sysroot-native INFO: The image(s) were created using OE kickstart file: /home/stephano/poky/scripts/lib/wic/canned-wks/directdisksdb-gpt.wks
Continuing with the example, you can now directly
dd
the image to a USB stick, or
whatever media for which you built your image,
and boot the resulting media:
$ sudo dd if=directdisksdb-gpt-201710090938-sdb.direct of=/dev/sdb 140966+0 records in 140966+0 records out 72174592 bytes (72 MB, 69 MiB) copied, 78.0282 s, 925 kB/s $ sudo eject /dev/sdb
This next example manually specifies each build artifact
(runs in Raw Mode) and uses a modified kickstart file.
The example also uses the -o
option
to cause Wic to create the output
somewhere other than the default output directory,
which is the current directory:
$ wic create /home/stephano/my_yocto/test.wks -o /home/stephano/testwic \ --rootfs-dir /home/stephano/build/master/build/tmp/work/qemux86-poky-linux/core-image-minimal/1.0-r0/rootfs \ --bootimg-dir /home/stephano/build/master/build/tmp/work/qemux86-poky-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share \ --kernel-dir /home/stephano/build/master/build/tmp/deploy/images/qemux86 \ --native-sysroot /home/stephano/build/master/build/tmp/work/i586-poky-linux/wic-tools/1.0-r0/recipe-sysroot-native INFO: Creating image(s)... INFO: The new image(s) can be found here: /home/stephano/testwic/test-201710091445-sdb.direct The following build artifacts were used to create the image(s): ROOTFS_DIR: /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/rootfs BOOTIMG_DIR: /home/stephano/build/master/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share KERNEL_DIR: /home/stephano/build/master/build/tmp-glibc/deploy/images/qemux86 NATIVE_SYSROOT: /home/stephano/build/master/build/tmp-glibc/work/i586-oe-linux/wic-tools/1.0-r0/recipe-sysroot-native INFO: The image(s) were created using OE kickstart file: /home/stephano/my_yocto/test.wks
For this example,
MACHINE
did not have to be specified in the
local.conf
file since the
artifact is manually specified.
Wic image manipulation allows you to shorten turnaround time during image development. For example, you can use Wic to delete the kernel partition of a Wic image and then insert a newly built kernel. This saves you time from having to rebuild the entire image each time you modify the kernel.
mtools
package installed.
The following example examines the contents of the Wic image, deletes the existing kernel, and then inserts a new kernel:
List the Partitions:
Use the wic ls
command to list
all the partitions in the Wic image:
$ wic ls tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic Num Start End Size Fstype 1 1048576 25041919 23993344 fat16 2 25165824 72157183 46991360 ext4
The previous output shows two partitions in the
core-image-minimal-qemux86.wic
image.
Examine a Particular Partition:
Use the wic ls
command again
but in a different form to examine a particular
partition.
$ wic help command
For example, the following command shows you
the various ways to use the
wic ls
command:
$ wic help ls
The following command shows what is in Partition one:
$ wic ls tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic:1 Volume in drive : is boot Volume Serial Number is E894-1809 Directory for ::/ libcom32 c32 186500 2017-10-09 16:06 libutil c32 24148 2017-10-09 16:06 syslinux cfg 220 2017-10-09 16:06 vesamenu c32 27104 2017-10-09 16:06 vmlinuz 6904608 2017-10-09 16:06 5 files 7 142 580 bytes 16 582 656 bytes free
The previous output shows five files, with the
vmlinuz
being the kernel.
~/.mtoolsrc
file and
be sure to have the line “mtools_skip_check=1“
in the file.
Then, run the Wic command again:
ERROR: _exec_cmd: /usr/bin/mdir -i /tmp/wic-parttfokuwra ::/ returned '1' instead of 0 output: Total number of sectors (47824) not a multiple of sectors per track (32)! Add mtools_skip_check=1 to your .mtoolsrc file to skip this test
Remove the Old Kernel:
Use the wic rm
command to
remove the vmlinuz
file
(kernel):
$ wic rm tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic:1/vmlinuz
Add In the New Kernel:
Use the wic cp
command to
add the updated kernel to the Wic image.
Depending on how you built your kernel, it could
be in different places.
If you used devtool
and
an SDK to build your kernel, it resides in the
tmp/work
directory of the
extensible SDK.
If you used make
to build the
kernel, the kernel will be in the
workspace/sources
area.
The following example assumes
devtool
was used to build
the kernel:
cp ~/poky_sdk/tmp/work/qemux86-poky-linux/linux-yocto/4.12.12+git999-r0/linux-yocto-4.12.12+git999/arch/x86/boot/bzImage \ ~/poky/build/tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic:1/vmlinuz
Once the new kernel is added back into the image,
you can use the dd
command or
bmaptool
to flash your wic image onto an SD card
or USB stick and test your target.
bmaptool
is
generally 10 to 20 times faster than using
dd
.
bmaptool
¶A fast and easy way to flash an image to a bootable device is to use Bmaptool, which is integrated into the OpenEmbedded build system. Bmaptool is a generic tool that creates a file's block map (bmap) and then uses that map to copy the file. As compared to traditional tools such as dd or cp, Bmaptool can copy (or flash) large files like raw system image files much faster.
If you are using Ubuntu or Debian distributions, you
can install the bmap-tools
package
using the following command and then use the tool
without specifying PATH
even from
the root account:
$ sudo apt-get install bmap-tools
If you are unable to install the
bmap-tools
package, you will
need to build Bmaptool before using it.
Use the following command:
$ bitbake bmap-tools-native
Following, is an example that shows how to flash a Wic image. Realize that while this example uses a Wic image, you can use Bmaptool to flash any type of image. Use these steps to flash an image using Bmaptool:
Update your local.conf
File:
You need to have the following set in your
local.conf
file before building
your image:
IMAGE_FSTYPES += "wic wic.bmap"
Get Your Image:
Either have your image ready (pre-built with the
IMAGE_FSTYPES
setting previously mentioned) or take the step to build
the image:
$ bitbake image
Flash the Device:
Flash the device with the image by using Bmaptool
depending on your particular setup.
The following commands assume the image resides in the
Build Directory's deploy/images/
area:
If you have write access to the media, use this command form:
$ oe-run-native bmap-tools-native bmaptool copybuild-directory
/tmp/deploy/images/machine
/image
.wic /dev/sdX
If you do not have write access to the media, set your permissions first and then use the same command form:
$ sudo chmod 666 /dev/sdX
$ oe-run-native bmap-tools-native bmaptool copybuild-directory
/tmp/deploy/images/machine
/image
.wic /dev/sdX
For help on the bmaptool
command, use the
following command:
$ bmaptool --help
Security is of increasing concern for embedded devices. Consider the issues and problems discussed in just this sampling of work found across the Internet:
"Security Risks of Embedded Systems" by Bruce Schneier
"Internet Census 2012" by Carna Botnet
"Security Issues for Embedded Devices" by Jake Edge
When securing your image is of concern, there are steps, tools, and variables that you can consider to help you reach the security goals you need for your particular device. Not all situations are identical when it comes to making an image secure. Consequently, this section provides some guidance and suggestions for consideration when you want to make your image more secure.
General considerations exist that help you create more secure images. You should consider the following suggestions to help make your device more secure:
Scan additional code you are adding to the system (e.g. application code) by using static analysis tools. Look for buffer overflows and other potential security problems.
Pay particular attention to the security for any web-based administration interface.
Web interfaces typically need to perform administrative functions and tend to need to run with elevated privileges. Thus, the consequences resulting from the interface's security becoming compromised can be serious. Look for common web vulnerabilities such as cross-site-scripting (XSS), unvalidated inputs, and so forth.
As with system passwords, the default credentials for accessing a web-based interface should not be the same across all devices. This is particularly true if the interface is enabled by default as it can be assumed that many end-users will not change the credentials.
Ensure you can update the software on the device to mitigate vulnerabilities discovered in the future. This consideration especially applies when your device is network-enabled.
Ensure you remove or disable debugging functionality before producing the final image. For information on how to do this, see the "Considerations Specific to the OpenEmbedded Build System" section.
Ensure you have no network services listening that are not needed.
Remove any software from the image that is not needed.
Enable hardware support for secure boot functionality when your device supports this functionality.
The Yocto Project has security flags that you can enable that
help make your build output more secure.
The security flags are in the
meta/conf/distro/include/security_flags.inc
file in your
Source Directory
(e.g. poky
).
Use the following line in your
local.conf
file or in your custom
distribution configuration file to enable the security
compiler and linker flags for your build:
require conf/distro/include/security_flags.inc
You can take some steps that are specific to the OpenEmbedded build system to make your images more secure:
Ensure "debug-tweaks" is not one of your selected
IMAGE_FEATURES
.
When creating a new project, the default is to provide you
with an initial local.conf
file that
enables this feature using the
EXTRA_IMAGE_FEATURES
variable with the line:
EXTRA_IMAGE_FEATURES = "debug-tweaks"
To disable that feature, simply comment out that line in your
local.conf
file, or
make sure IMAGE_FEATURES
does not contain
"debug-tweaks" before producing your final image.
Among other things, leaving this in place sets the
root password as blank, which makes logging in for
debugging or inspection easy during
development but also means anyone can easily log in
during production.
It is possible to set a root password for the image and also to set passwords for any extra users you might add (e.g. administrative or service type users). When you set up passwords for multiple images or users, you should not duplicate passwords.
To set up passwords, use the
extrausers
class, which is the preferred method.
For an example on how to set up both root and user
passwords, see the
"extrausers.bbclass
"
section.
Consider enabling a Mandatory Access Control (MAC)
framework such as SMACK or SELinux and tuning it
appropriately for your device's usage.
You can find more information in the
meta-selinux
layer.
The Yocto Project provides tools for making your image
more secure.
You can find these tools in the
meta-security
layer of the
Yocto Project Source Repositories.
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 bitbake-layers
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
DISTRO_VERSION
These following variables are optional and you typically set them from the distribution configuration file:
DISTRO_FEATURES
DISTRO_EXTRA_RDEPENDS
DISTRO_EXTRA_RRECOMMENDS
TCLIBC
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 an append file (.bbappend
)
for those.
For general information and recommendations
on how to add recipes to your layer, see the
"Creating Your Own Layer"
and
"Following Best Practices When Creating Layers"
sections.
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 in Your Layer"
section.
Add any other append files to make custom changes that are specific to individual recipes.
If you are producing your own customized version
of the build system for use by other users, you might
want to customize the message shown by the setup script or
you might want to change the template configuration files (i.e.
local.conf
and
bblayers.conf
) that are created in
a new build directory.
The OpenEmbedded build system uses the environment variable
TEMPLATECONF
to locate the directory
from which it gathers configuration information that ultimately
ends up in the
Build Directory
conf
directory.
By default, TEMPLATECONF
is set as
follows in the poky
repository:
TEMPLATECONF=${TEMPLATECONF:-meta-poky/conf}
This is the directory used by the build system to find templates
from which to build some key configuration files.
If you look at this directory, you will see the
bblayers.conf.sample
,
local.conf.sample
, and
conf-notes.txt
files.
The build system uses these files to form the respective
bblayers.conf
file,
local.conf
file, and display the list of
BitBake targets when running the setup script.
To override these default configuration files with
configurations you want used within every new
Build Directory, simply set the
TEMPLATECONF
variable to your directory.
The TEMPLATECONF
variable is set in the
.templateconf
file, which is in the
top-level
Source Directory
folder (e.g. poky
).
Edit the .templateconf
so that it can locate
your directory.
Best practices dictate that you should keep your
template configuration directory in your custom distribution layer.
For example, suppose you have a layer named
meta-mylayer
located in your home directory
and you want your template configuration directory named
myconf
.
Changing the .templateconf
as follows
causes the OpenEmbedded build system to look in your directory
and base its configuration files on the
*.sample
configuration files it finds.
The final configuration files (i.e.
local.conf
and
bblayers.conf
ultimately still end up in
your Build Directory, but they are based on your
*.sample
files.
TEMPLATECONF=${TEMPLATECONF:-meta-mylayer/myconf}
Aside from the *.sample
configuration files,
the conf-notes.txt
also resides in the
default meta-poky/conf
directory.
The script that sets up the build environment
(i.e.
oe-init-build-env
)
uses this file to display BitBake targets as part of the script
output.
Customizing this conf-notes.txt
file is a
good way to make sure your list of custom targets appears
as part of the script's output.
Here is the default list of targets displayed as a result of running either of the setup scripts:
You can now run 'bitbake <target>' Common targets are: core-image-minimal core-image-sato meta-toolchain meta-ide-support
Changing the listed common targets is as easy as editing your
version of conf-notes.txt
in your
custom template configuration directory and making sure you
have TEMPLATECONF
set to your directory.
To help conserve disk space during builds, you can add the
following statement to your project's
local.conf
configuration file found in the
Build Directory:
INHERIT += "rm_work"
Adding this statement deletes the work directory used for building
a recipe once the recipe is built.
For more information on "rm_work", see the
rm_work
class in the Yocto Project Reference Manual.
This section describes a few tasks that involve packages:
You might find it necessary to prevent specific packages from being installed into an image. If so, you can use several variables to direct the build system to essentially ignore installing recommended packages or to not install a package at all.
The following list introduces variables you can use to
prevent packages from being installed into your image.
Each of these variables only works with IPK and RPM
package types.
Support for Debian packages does not exist.
Also, you can use these variables from your
local.conf
file or attach them to a
specific image recipe by using a recipe name override.
For more detail on the variables, see the descriptions in the
Yocto Project Reference Manual's glossary chapter.
BAD_RECOMMENDATIONS
:
Use this variable to specify "recommended-only"
packages that you do not want installed.
NO_RECOMMENDATIONS
:
Use this variable to prevent all "recommended-only"
packages from being installed.
PACKAGE_EXCLUDE
:
Use this variable to prevent specific packages from
being installed regardless of whether they are
"recommended-only" or not.
You need to realize that the build process could
fail with an error when you
prevent the installation of a package whose presence
is required by an installed package.
This section provides some background on how binary package versioning is accomplished and presents some of the services, variables, and terminology involved.
In order to understand binary package versioning, you need to consider the following:
Binary Package: The binary package that is eventually built and installed into an image.
Binary Package Version: The binary package version is composed of two components - a version and a revision.
PE
)
is involved but this discussion for the most part
ignores PE
.
The version and revision are taken from the
PV
and
PR
variables, respectively.
PV
: The recipe version.
PV
represents the version of the
software being packaged.
Do not confuse PV
with the
binary package version.
PR
: The recipe revision.
SRCPV
:
The OpenEmbedded build system uses this string
to help define the value of PV
when the source code revision needs to be included
in it.
PR Service: A network-based service that helps automate keeping package feeds compatible with existing package manager applications such as RPM, APT, and OPKG.
Whenever the binary package content changes, the binary package
version must change.
Changing the binary package version is accomplished by changing
or "bumping" the PR
and/or
PV
values.
Increasing these values occurs one of two ways:
Automatically using a Package Revision Service (PR Service).
Manually incrementing the
PR
and/or
PV
variables.
Given a primary challenge of any build system and its users 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 binary package version numbering increases in a linear fashion and that a number of version components exist that support that linear progression. For information on how to ensure package revisioning remains linear, see the "Automatically Incrementing a Binary Package Revision Number" section.
The following three sections provide related information on the
PR Service, the manual method for "bumping"
PR
and/or PV
, and
on how to ensure binary package revisioning remains linear.
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.
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
, PV
, and
PE
numbers to trigger a rebuild.
The signatures, however, can be used to generate
these 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 a local PR Service by
setting
PRSERV_HOST
in 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 takes 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 --hostip
--portport
--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 binary 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.
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 Overview and Concepts Manual.
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 "${INC_PR}.0" initially, incrementing the last number
when the recipe is changed.
If the .inc
file is changed then its
INC_PR
should be incremented.
When upgrading the version of a binary package, assuming the
PV
changes, the PR
variable should be
reset to "r0" (or "${INC_PR}.0" if you are using
INC_PR
).
Usually, version increases occur only to binary 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".
Binary package version numbering strives to follow the Debian Version Field Policy Guidelines. These guidelines define how versions are compared and what "increasing" a version means.
When fetching a repository, BitBake uses the
SRCREV
variable to determine the specific source code revision
from which to build.
You set the SRCREV
variable to
AUTOREV
to cause the OpenEmbedded build system to automatically use the
latest revision of the software:
SRCREV = "${AUTOREV}"
Furthermore, you need to reference SRCPV
in PV
in order to automatically update
the version whenever the revision of the source code
changes.
Here is an example:
PV = "1.0+git${SRCPV}"
The OpenEmbedded build system substitutes
SRCPV
with the following:
AUTOINC+source_code_revision
The build system replaces the AUTOINC
with
a number.
The number used depends on the state of the PR Service:
If PR Service is enabled, the build system increments
the number, which is similar to the behavior of
PR
.
This behavior results in linearly increasing package
versions, which is desirable.
Here is an example:
hello-world-git_0.0+git0+b6558dd387-r0.0_armv7a-neon.ipk hello-world-git_0.0+git1+dd2f5c3565-r0.0_armv7a-neon.ipk
If PR Service is not enabled, the build system
replaces the AUTOINC
placeholder with zero (i.e. "0").
This results in changing the package version since
the source revision is included.
However, package versions are not increased linearly.
Here is an example:
hello-world-git_0.0+git0+b6558dd387-r0.0_armv7a-neon.ipk hello-world-git_0.0+git0+dd2f5c3565-r0.0_armv7a-neon.ipk
In summary, the OpenEmbedded build system does not track the
history of binary package versions for this purpose.
AUTOINC
, in this case, is comparable to
PR
.
If PR server is not enabled, AUTOINC
in the package version is simply replaced by "0".
If PR server is enabled, the build system keeps track of the
package versions and bumps the number when the package
revision changes.
Many pieces of software split functionality into optional modules (or plug-ins) and the plug-ins 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.
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 used 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 summary Summary to set for each package. Must include %s; defaults to description if not set.
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
.
During a build, BitBake always transforms a recipe into one or
more packages.
For example, BitBake takes the bash
recipe
and produces a number of packages (e.g.
bash
, bash-bashbug
,
bash-completion
,
bash-completion-dbg
,
bash-completion-dev
,
bash-completion-extra
,
bash-dbg
, and so forth).
Not all generated packages are included in an image.
In several situations, you might need to update, add, remo