linux-kernel - Re: Attaching PID 0 to a cgroup

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Message-ID: <20080701105126.GA10403@linux.vnet.ibm.com>
Date:	Tue, 1 Jul 2008 16:21:26 +0530
From:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Paul Menage <menage@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Balbir Singh <balbir@...ibm.com>,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	lkml <linux-kernel@...r.kernel.org>, containers@...ts.osdl.org,
	Paul Jackson <pj@....com>
Subject: Re: Attaching PID 0 to a cgroup

On Tue, Jul 01, 2008 at 06:28:07PM +0800, Li Zefan wrote:
> CC: Paul Jackson <pj@....com>
> 
> Dhaval Giani wrote:
> > [put in the wrong alias for containers list correcting it.]
> > 
> > On Tue, Jul 01, 2008 at 03:15:45PM +0530, Dhaval Giani wrote:
> >> Hi Paul,
> >>
> >> Attaching PID 0 to a cgroup caused the current task to be attached to
> >> the cgroup. Looking at the code,
> >>
> 
> [...]
> 
> >>
> >> I was wondering, why this was done. It seems to be unexpected behavior.
> >> Wouldn't something like the following be a better response? (I've used
> >> EINVAL, but I can change it to ESRCH if that is better.)
> >>
> 
> Why is it unexpected? it follows the behavior of cpuset, so this patch will
> break backward compatibility of cpuset.

Ah, I was not aware of that. Thanks!

> 
> But it's better to document this.
> 

Yes please.

> -----------------------------------------
> 
> Document the following cgroup usage:
>  # echo 0 > /dev/cgroup/tasks
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>

Acked-by: Dhaval Giani <dhaval@...ux.vnet.ibm.com>

> ---
>  cgroups.txt |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Documentation/cgroups.txt b/Documentation/cgroups.txt
> index 824fc02..213f533 100644
> --- a/Documentation/cgroups.txt
> +++ b/Documentation/cgroups.txt
> @@ -390,6 +390,10 @@ If you have several tasks to attach, you have to do it one after another:
>  	...
>  # /bin/echo PIDn > tasks
> 
> +You can attach the current task by echoing 0:
> +
> +# /bin/echo 0 > tasks
> +
>  3. Kernel API
>  =============
> 
> 

-- 
regards,
Dhaval
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