linux-kernel - Re: [PATCH] cgroups: handle failure of cgroup_populate

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Message-ID: <4A1A6192.6050608@cn.fujitsu.com>
Date:	Mon, 25 May 2009 17:14:58 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>
CC:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Menage <menage@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	libcg-devel@...ts.sourceforge.net
Subject: Re: [PATCH] cgroups: handle failure of cgroup_populate_dir() at	mount/remount

Dhaval Giani wrote:
> On Fri, May 22, 2009 at 05:34:21PM +0900, KAMEZAWA Hiroyuki wrote:
>> On Fri, 22 May 2009 16:35:14 +0800
>> Li Zefan <lizf@...fujitsu.com> wrote:
>>
>>> KAMEZAWA Hiroyuki wrote:
>>>> On Fri, 22 May 2009 11:00:12 +0800
>>>> Li Zefan <lizf@...fujitsu.com> wrote:
>>>>
>>>>> Now we have 'stat' file in both memory and cpuacct subsystems. If we
>>>>> mount these 2 subsystems with option 'noprefix', the creation of 'stat'
>>>>> file for cpuacct will fail, but without any notificatin to the user.
>>>>>
>>>>> With this patch, we fail the mount/remount in this case.
>>>>>
>>>> Hm, shouldn't we allow "noprefix" to be effective only agaisnt cpuset ?
>>>> I think it's just for backward-compatibility of cpuset.
>>>> (I don't like the option at all.)
>>>>
>>> Yes, this mount option was introduced for cpuset. But it has been here for
>>> a long time and people may use it when mounting other cgroup subsystems,
>>> then is it OK to change to restrict its use within cpuset only?
>> Asking libcgroup people may be appropriate...added CC.
> 
> We just realized that we were not handling the noprefix usage in

I guess handling noprefix will increase complexity of libcgroup? since we
can't figure out which subsystem the file belongs to by looking at the
prefix of the file.

> libcgroup. From the pov of the library, the option should either not
> exist for any subsystem or for all of them. Anything else would mean
> having to add special cases.
> 

I don't see how to totally remove 'noprefix' while keep the backward 
compatibility of cpuset, so I think we have to reserve it, and fix
name collision caused by this option.

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