linux-kernel - Re: [PATCH 4/9] cgroup: Print warning when /proc/cgroups is read on v2-only system

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Message-ID: <t35nwno7wwwq43psp7cumpqco3zmi5n5y2czh3m4nj72qw2udp@ha3g6qnwkzh7>
Date: Wed, 5 Mar 2025 11:17:22 +0100
From: Michal Koutný <mkoutny@...e.com>
To: Tejun Heo <tj@...nel.org>
Cc: cgroups@...r.kernel.org, linux-block@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Josef Bacik <josef@...icpanda.com>, Jens Axboe <axboe@...nel.dk>, 
	Johannes Weiner <hannes@...xchg.org>, Waiman Long <longman@...hat.com>
Subject: Re: [PATCH 4/9] cgroup: Print warning when /proc/cgroups is read on
 v2-only system

On Tue, Mar 04, 2025 at 06:55:02AM -1000, Tejun Heo <tj@...nel.org> wrote:
> I'm hoping that we could deprecate /proc/cgroups entirely. Maybe we can just
> warn whenever the file is accessed?

I added the guard with legacy systems (i.e. make this backportable) in
mind which start with no cgroupfs mounted at all and until they decide
to continue either v1 or v2 way, looking at /proc/cgroups is fine.
It should warn users that look at /proc/cgroups in cases when it bears
no valid information.

Michal

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