Introduction

This guide provides a list of the backwards-incompatible changes you might need to adapt to in your existing Yocto Project configuration when upgrading to a new release.

If you are upgrading over multiple releases, you will need to follow the sections from the version following the one you were previously using up to the new version you are upgrading to.

General Migration Considerations

Some considerations are not tied to a specific Yocto Project release. This section presents information you should consider when migrating to any new Yocto Project release.

  • Dealing with Customized Recipes:

    Issues could arise if you take older recipes that contain customizations and simply copy them forward expecting them to work after you migrate to new Yocto Project metadata. For example, suppose you have a recipe in your layer that is a customized version of a core recipe copied from the earlier release, rather than through the use of an append file. When you migrate to a newer version of Yocto Project, the metadata (e.g. perhaps an include file used by the recipe) could have changed in a way that would break the build. Say, for example, a function is removed from an include file and the customized recipe tries to call that function.

    You could “forward-port” all your customizations in your recipe so that everything works for the new release. However, this is not the optimal solution as you would have to repeat this process with each new release if changes occur that give rise to problems.

    The better solution (where practical) is to use append files (*.bbappend) to capture any customizations you want to make to a recipe. Doing so isolates your changes from the main recipe, making them much more manageable. However, sometimes it is not practical to use an append file. A good example of this is when introducing a newer or older version of a recipe in another layer.

  • Updating Append Files:

    Since append (.bbappend) files generally only contain your customizations, they often do not need to be adjusted for new releases. However, if the append file is specific to a particular version of the recipe (i.e. its name does not use the % wildcard) and the version of the recipe to which it is appending has changed, then you will at a minimum need to rename the append file to match the name of the recipe file. A mismatch between an append file and its corresponding recipe file (.bb) will trigger an error during parsing.

    Depending on the type of customization the append file applies, other incompatibilities might occur when you upgrade. For example, if your append file applies a patch and the recipe to which it is appending is updated to a newer version, the patch might no longer apply. If this is the case and assuming the patch is still needed, you must modify the patch file so that it does apply.

Tip

You can list all append files used in your configuration by running:

bitbake-layers show-appends

  • Checking Image / SDK Changes:

    The buildhistory class can be used if you wish to check the impact of changes to images / SDKs across the migration (e.g. added/removed packages, added/removed files, size changes etc.). To do this, follow these steps:

    1. Enable buildhistory before the migration

    2. Run a pre-migration build

    3. Capture the buildhistory output (as specified by BUILDHISTORY_DIR) and ensure it is preserved for subsequent builds. How you would do this depends on how you are running your builds - if you are doing this all on one workstation in the same build directory you may not need to do anything other than not deleting the buildhistory output directory. For builds in a pipeline it may be more complicated.

    4. Set a tag in the buildhistory output (which is a git repository) before migration, to make the commit from the pre-migration build easy to find as you may end up running multiple builds during the migration.

    5. Perform the migration

    6. Run a build

    7. Check the output changes between the previously set tag and HEAD in the buildhistory output using git diff or buildhistory-diff.

    For more information on using buildhistory, see Maintaining Build Output Quality.