Feedback sought: can we drop cgroupv1 support soon?

[Lennart Poettering <lennart@xxxxxxxxxxxxxx>]

Heya!

It's currently a terrible mess having to support both cgroupsv1 and
cgroupsv2 in our codebase.

cgroupsv2 first entered the kernel in 2014, i.e. *eight* years ago
(kernel 3.16). We soon intend to raise the baseline for systemd to
kernel 4.3 (because we want to be able to rely on the existance of
ambient capabilities), but that also means, that all kernels we intend
to support have a well-enough working cgroupv2 implementation.

hence, i'd love to drop the cgroupv1 support from our tree entirely,
and simplify and modernize our codebase to go cgroupv2-only. Before we
do that I'd like to seek feedback on this though, given this is not
purely a thing between the kernel and systemd — this does leak into
some userspace, that operates on cgroups directly.

Specifically, legacy container infra (i.e. docker/moby) for the
longest time was cgroupsv1-only. But as I understand it has since been
updated, to cgroupsv2 too.

Hence my question: is there a strong community of people who insist on
using newest systemd while using legacy container infra? Anyone else
has a good reason to stick with cgroupsv1 but really wants newest
systemd?

The time where we'll drop cgroupv1 support *will* come eventually
either way, but what's still up for discussion is to determine
precisely when. hence, please let us know!

Thanks,

Lennart

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Lennart Poettering, Berlin