This post was originally published on linkedin.
Yocto delivered with great “devtool” tool that allow to work on specific package locally. This tool allow you create patches to any recipes like this:
devtool modify package
cd workspace/sources/package
# Edit source as you want
devtool build package
# Finish editing
git commit -am 'This new commit in sources will be exported as patch to yocto recipe'
devtool finish package /path/to/meta-layer-with-package
You can find full description for “devtool modify” utility in yocto documentation.
For recipe with S="${WORKDIR}/internal/subpath/for/sources" devtool will export directory "${WORKDIR}/internal" as source directory and reuse “externalsrc” mechanism to allow to build from exported sources. To track changes and generate patches devtool create “git” repository at a root of exported sources.
All this mechanisms can fail because of yocto flexibility. Let’s describe a possible issues with examples based on current (yocto 2.4) poky distro.
externalsrc.bbclass change “fetch” task to fetch only “file://” URI’s, while ‘devtool’ save only one subdirectory of “${WORKDIR}” as sources. As result if you fetch more that one remote URI for recipe “devtool modify” will lose part of files required for build.
devtool modify libxml2 && devtool build libxml2
This command will fail to build because libxml2 fetch two tarballs, but devtool save content only from one of tarballs as a sources.
If you have git repository in subdirectory of “${S}” than “devtool” will lose all your changes in this subdirectory, because “devtool finish” looks only at toplevel git.
devtool modify cross-localedef-native
cd workspace/sources/cross-localedef-native/localedef/
# Change files
git commit -am 'This changes will be lost'
devtool finish cross-localedef-native /path/to/meta-layer
devtool also can fail if you recipe patch some files fetched with “file://” fetcher. There is no such recipes in poky, but it possible to imagine next example:
recipe.bb:
SRC_URI = "https://recipe.org/recipe.tar.gz file://additional_file"
recipe.bbappend
SRC_URI += "file://patch_for_additional_file.patch;patchdir=../"
In this case after “devtool modify” you will work with original “additional_file” without patches.