A future systemd release will make non-/usr-merged systems incompatible with systemd: https://lists.freedesktop.org/archives/systemd-devel/2022-September/048352.html In theory, we can just make the systemd recipe require the usrmerge DISTRO_FEATURE and we're done. However, there are reports that systemd+usrmerge don't actually pass our QA. There's a hunch that this is just hardcoded paths in tests, but this hasn't been verified. We should also be able to run oe-selftest in this environment.
So far, dnf.DnfRepoTest.test_dnf_installroot_usrmerge is failing. This is most likely a test case issue, not a fundamental problem with usrmerge.
For anyone looking for it, in the "Announcements of Future Feature Removals" section of the draft systemd-252 release notes: * We intend to remove support for split-usr (/usr mounted separately during boot) and unmerged-usr (parallel directories /bin and /usr/bin, /lib and /usr/lib, etc). This will happen in the second half of 2023, in the first release that falls into that time window. For more details, see: https://lists.freedesktop.org/archives/systemd-devel/2022-September/048352.html https://github.com/systemd/systemd/releases/tag/v252-rc3
So far in my testing the problems are 1) dnf (this was a bug in the test, it's just broken) and 2) overlayfs (probably a bad assumption in the test too). Apart from that I think we're good to make systemd depend on usrmerge.
Patches sent to solve the dnf testimage failures.
Tests fixed in bb6ebb9956a42df3ed8681aec9aedf340b12f934. I think this is done.