systemd-networkd is DefaultDependencies=no and thus can run on early boot. This means that it is possible that networkd starts before tmpfiles. Adding an ordering with tmpfiles makes networkd order after local-fs.target, which is probably undesirable.

Indeed the s390x autopkgtest has plenty of errors because networkd is started too early:

Jun 29 16:08:05 autopkgtest-lxc-gokrjz systemd-networkd[7617]: dummy0: Failed to save link data to /run/systemd/netif/links/60: No such file or directory
Jun 29 16:08:05 autopkgtest-lxc-gokrjz systemd-networkd[7617]: test_eth42: Failed to save link data to /run/systemd/netif/links/58: No such file or directory
Jun 29 16:08:05 autopkgtest-lxc-gokrjz systemd-networkd[7617]: eth0: Failed to save link data to /run/systemd/netif/links/215321: No such file or directory
Jun 29 16:08:05 autopkgtest-lxc-gokrjz systemd-networkd[7617]: lo: Failed to save link data to /run/systemd/netif/links/1: No such file or directory

And many more such messages.

While I sympasize with the goal, I am not this can be really done for early-boot services like resolved and networkd.

It might be possible to make this work with RuntimeDirectory= though, that definitely deserves some looking into, but tmpfiles can't really work, afaics. RuntimeDirectory= as it is designed right now is not a great fit either, but I think we could relatively easily make it one. Specifically, /run/network and friends are supposed to survive restarts of networkd (as we use them to serialize state). Maybe we could tweak RuntimeDirectory= a bit, bit adding some single-character modifier or so, which would permit configuring a directory that is created on first service start if missing but is not automatically removed. Maybe a syntax like this:

RuntimeDirectory=!/run/foobar

i.e. using ! is indicator character, that the dir is supposed to stay. Using a single character isn't pretty, but it's kinda what we have been using for a number of cases already, for example we prefix ExecStart= with - to ignore the exit status of the command, and so on.

Does that make sense?

Maybe we could tweak RuntimeDirectory= a bit, bit adding some single-character modifier or so, which would permit configuring a directory that is created on first service start if missing but is not automatically removed

This is #6087 . TBH I prefer the RuntimeDirectoryPreserve= approach over single-character prefix, as it is more self-documenting.

Yupp, #6087 appears like the right way out for this. It would be excellent if this PR could be reworked to implement that, so that we can reduce the priviliged code in resolved+networkd but also not require tmpfiles

Thanks for the feedback. I'll look into it.

I have pushed an alternative version of this PR as #6393.

Closing this one in favour of #6393