cgroup: Print message when /proc/cgroups is read on v2-only system

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As a followup to commits 6c2920926b ("cgroup: replace
unified-hierarchy.txt with a proper cgroup v2 documentation") and
ab03125268 ("cgroup: Show # of subsystem CSSes in cgroup.stat"),
add a runtime message to users who read status of controllers in
/proc/cgroups on v2-only system. The detection is based on a)
no controllers are attached to v1, b) default hierarchy is mounted (the
latter is for setups that never mount v2 but read /proc/cgroups upon
boot when controllers default to v2, so that this code may be backported
to older kernels).

Signed-off-by: Michal Koutný <mkoutny@suse.com>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

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Michal Koutný 2025-03-11 13:36:21 +01:00 • committed by Tejun Heo

parent 77bbb259db

commit a0ab145322

3 changed files with 9 additions and 1 deletions

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1

kernel/cgroup/cgroup-internal.h

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kernel/cgroup/cgroup-v1.c

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kernel/cgroup/cgroup.c

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