linux-kernel - Re: [PATCH] clone.2: Document CLONE_INTO

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Date:   Tue, 21 Apr 2020 16:30:46 +0200
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:     Christian Brauner <christian@...uner.io>
Cc:     "open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Linux API <linux-api@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        linux-man <linux-man@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] clone.2: Document CLONE_INTO_CGROUP

Hi Christian,

Ping!

Cheers,

Michael

On Fri, 10 Apr 2020 at 22:18, Michael Kerrisk (man-pages)
<mtk.manpages@...il.com> wrote:
>
> Hi Christian,
>
> Thank you for writing this!
>
> On 4/10/20 12:41 PM, Christian Brauner wrote:
> > From: Christian Brauner <christian.brauner@...ntu.com>
> >
> > Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
> > ---
> >  man2/clone.2 | 20 ++++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> >
> > diff --git a/man2/clone.2 b/man2/clone.2
> > index 39cec4c86..8d9aa9f99 100644
> > --- a/man2/clone.2
> > +++ b/man2/clone.2
> > @@ -197,6 +197,7 @@ struct clone_args {
> >      u64 tls;          /* Location of new TLS */
> >      u64 set_tid;      /* Pointer to a \fIpid_t\fP array */
> >      u64 set_tid_size; /* Number of elements in \fIset_tid\fP */
> > +    u64 cgroup;       /* Target cgroup file descriptor for the child process */
> >  };
> >  .EE
> >  .in
> > @@ -448,6 +449,25 @@ Specifying this flag together with
> >  .B CLONE_SIGHAND
> >  is nonsensical and disallowed.
> >  .TP
> > +.BR CLONE_INTO_CGROUP " (since Linux 5.7)"
> > +.\" commit ef2c41cf38a7559bbf91af42d5b6a4429db8fc68
> > +By default, the child process will belong to the same cgroup as its parent.
>
> s/belong to/be placed in/
>
> s/cgroup/version 2 cgroup/
>
> > +If this flag is specified the child process will be created in a
> > +different cgroup than its parent.
> > +
> > +When using
> > +.RB clone3 ()
> > +the target cgroup can be specified by setting the
> > +.I cl_args.cgroup
> > +member to the file descriptor of the target cgroup. The cgroup file
>
> We need to say something about how this file descriptor is
> obtained. Is it by opening a directory in the v2 cgroup hierarchy?
> With what flags? O_RDONLY? or is O_PATH also possible? Yes, these
> are some rhetorical questions (I read your nice commit message);
> these things need to be explicit in the manual page though.
>
> Also, your commit message mentions a nice list of use cases.
> I think it would be well worth capturing those in a paragraph
> in the manual page text.
>
> > +descriptor must refer to a cgroup in a cgroup v2 hierarchy
> > +(see
> > +.BR cgroup (2)).
>
> s/cgroup/cgroups/
> s/2/7/
>
> > +
> > +Note that all usual cgroup v2 process migration restrictions apply. See
> > +.BR cgroup (2)
>
> s/cgroup/cgroups/
> s/2/7/
>
> Thanks,
>
> Michael
>
> --
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Linux/UNIX System Programming Training: http://man7.org/training/



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