journal: Set +C if we create /var/log/journal

[DaanDeMeyer]

systemd-journal-flush.service runs before systemd-tmpfiles-setup.service so we can't rely on tmpfiles setting +C for us, so let's make journald set it itself if it creates /var/log/journal itself.

[github-actions]

Important

An -rc1 tag has been created and a release is being prepared, so please note that PRs introducing new features and APIs will be held back until the new version has been released.

[poettering]

hmm, this is quite problematic, since people might want to turn this off, which is via tmpfiles, but hard if encoded in C.

the fix seems rather to run the flush code after tmpfiles?

[DaanDeMeyer]

@poettering You seem to have different thoughts according to 74055aa

journalctl: add new --flush command and make use of it in systemd-journal-flush.service

This new command will ask the journal daemon to flush all log data
stored in /run to /var, and wait for it to complete. This is useful, so
that in case of Storage=persistent we can order systemd-tmpfiles-setup
afterwards, to ensure any possibly newly created directory in /var/log
gets proper access mode and owners.

[poettering]

hmm, i think we have a problem and can't really apply it before and after, can we?

hmpf. fucking btrfs.

it could be so easy if nocow was something one could turn off/on later.

btw, i think there's an issue somewhere about this already, we should probably link this up here.

I guess we should just bite the bullet and either add a journald.conf knob for this, or an env var that journald reads, to give people control, and then simply hack this up in C code, and drop the nocow flag handling in tmpfiles.