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

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Message-ID: <486A06B7.7020906@cn.fujitsu.com>
Date:	Tue, 01 Jul 2008 18:28:07 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Dhaval Giani <dhaval@...ux.vnet.ibm.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

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.

But it's better to document this.

-----------------------------------------

Document the following cgroup usage:
 # echo 0 > /dev/cgroup/tasks

Signed-off-by: Li Zefan <lizf@...fujitsu.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
 =============
 


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