12 Using Quilt in Your Workflow

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

Note

With regard to preserving changes to source files, if you clean a recipe or have rm_work.bbclass 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.

Note

All the modifications you make to the temporary source code disappear once you run the 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.bbclass 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"
```