This page should be used to keep track of items which should be added to the migration guide in the YP Reference Manual. It's a living document for the life of a development cycle and by M4 should represent a significant proportion of items that are worthy of note in the migration guide. Once the migration guide for a release has been completed the contents of this page should be cleared out.

2.5 Migration Guide items

kernel.bbclass now supports multiple kernel packages. If your kernel recipe/bbappend mentions packaging at all then you will need to replace "kernel" with "${KERNEL_PACKAGE_NAME}". For example if you disable automatic installation of the kernel image using RDEPENDS_kernel-base = "" then to avoid warnings you will now need to use RDEPENDS_${KERNEL_PACKAGE_NAME}-base = "" instead.
We removed the fetchall and checkuriall tasks, "bitbake X --runall=fetch" and "bitbake X --runall=checkuri" replace them. --runonly option added to bitbake which behaves like the older --runall option.
meson build system support has been added via meson.bbclass. Extra options defined via EXTRA_OEMESON. Ask AlexK for more details.
package postinst support has been reworked. On-target postinsts should be defined via pkg_postinst_ontarget(), explicit deferral via 'postinst_intercept defer_to_first_boot'. The relevant section in the yocto docs needs to be adjusted. Ask AlexK for more details.
The buildhistory class sets BUILDHISTORY_COMMIT to "1" by default, since this is the most sensible default. In the unlikely event that you were relying upon the default to not commit history to a git repository on every build, you'll now need to explicitly set BUILDHISTORY_COMMIT = "0" in your configuration.

FutureMigrationGuide