linux-kernel - Re: cgroups(7): documenting /sys/kernel/cgroup files

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Message-ID: <CAKgNAkhDY09gauX-1Ut4SoL9DEoxj9wJ8SjS6h-Ntc90xeWi1A@mail.gmail.com>
Date:   Wed, 10 Jan 2018 18:31:20 +0100
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Roman Gushchin <guro@...com>, "Serge E. Hallyn" <serge@...lyn.com>,
        linux-man <linux-man@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>
Subject: Re: cgroups(7): documenting /sys/kernel/cgroup files

Hello Tejun,

On 10 January 2018 at 15:02, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Wed, Jan 10, 2018 at 04:44:14AM -0800, Roman Gushchin wrote:
>> cgroup.threads is not listed because it's not delegatable (doesn't have
>> CFTYPE_NS_DELEGATABLE flag set). I don't know if it was intended or just
>> an accident (I believe the latter).
>
> So, thread mode isn't delegatble.  Marking a cgroup as threaded turns
> that subtree threaded and join the parent's domain, so we can't allow
> delegation roots to be turned threaded - just like we can't mark the
> root cgroup threaded, and I'm not really not sure what it means to
> delegate a portion of threaded subtree.

So, I am confused. According to Documentation/cgroup-v2.txt,
cgoup.threads is delegated:

[[
Model of Delegation
~~~~~~~~~~~~~~~~~~~

A cgroup can be delegated in two ways.  First, to a less privileged
user by granting write access of the directory and its "cgroup.procs",
"cgroup.threads" and "cgroup.subtree_control" files to the user.
Second, if the "nsdelegate" mount option is set, automatically to a
cgroup namespace on namespace creation.
]]

So, is that a mistake in that text file?

Cheers,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/