[Merge] ~enr0n/ubuntu/+source/systemd:ubuntu-kinetic into ~ubuntu-core-dev/ubuntu/+source/systemd:ubuntu-kinetic

[Lukas Märdian]

Review: Approve

Thank you, Nick. This looks good to me. Please remember to mention a test build/PPA (and potential autopkgtest) of your changes for next time. I think I found a test build in your PPA for now: https://launchpad.net/~enr0n/+archive/ubuntu/systemd-251/+packages

I am a bit reluctant about adding even more /etc/writable workarounds for Ubuntu Core, but I understand that we need this now. Last time, I asked the snapd team to come up with a more sustainable solution for this issue (LP: #1953172) but I think nothing came out of this up to now.. (Thanks for also mentioning this bug in the patch headers!)

Medium term, I think we should probably move that "writable_filename()" function to a more global place inside systemd (maybe some utils file inside libsystemd, that is available to all components applying this workaround? Or a new "ubuntu-quirks.h" header that we include from all those modules?) – I'm not sure if such place exists, but it might be cleaner than copying the same static function into all those modules. We could then consolidate the 3 patches into a single, smaller one:
- debian/patches/debian/UBUNTU-Support-system-image-read-only-etc.patch
- debian/patches/debian/UBUNTU-Fix-timezone-setting-on-read-only-etc.patch
- debian/patches/lp1981042-core-firstboot-workaround-timezone-issues-caused-by-Ubunt.patch

=> But this shall not block this upload.

Long term, I still hope we (or the snapd team) get somewhere with LP: #1953172
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https://code.launchpad.net/~enr0n/ubuntu/+source/systemd/+git/systemd/+merge/427302
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