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

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Message-Id: <20090527151640.52323b90.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 27 May 2009 15:16:40 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Paul Menage <menage@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>
Subject: Re: [PATCH] cgroups: handle failure of cgroup_populate_dir() at 
 mount/remount

On Wed, 27 May 2009 11:24:22 +0800
Li Zefan <lizf@...fujitsu.com> wrote:

> KAMEZAWA Hiroyuki wrote:
> > On Wed, 27 May 2009 09:07:31 +0800
> > Li Zefan <lizf@...fujitsu.com> wrote:
> > 
> >> Paul Menage wrote:
> >>> On Fri, May 22, 2009 at 1:25 AM, KAMEZAWA Hiroyuki
> >>> <kamezawa.hiroyu@...fujitsu.com> wrote:
> >>>> 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, exposing the "noprefix" option externally was one of the mistakes
> >>> I made when developing cgroups.
> >>>
> >>> It seems to me really unlikely that anyone is using "noprefix" for
> >> And "noprefix" is not documented in cgroups.txt, so I guess not
> >> many people know this option. Even libcgroup doesn't handle it.
> >>
> >>> anything other than implicitly when mounting the "cpuset" filesystem.
> >>> So I'd be inclined to just forbid it if we're mounting more than just
> >>> the cpuset subsystem. A bit of a nasty abstraction violation, but it
> >>> makes more sense overall. The only problem is that someone *might* be
> >>> using it - do we have any way to determine how, and how big do they
> >>> have to be before we care?
> >>>
> >> I think we can never know..
> > 
> > How about this method ?
> > 
> >  - add "noprefix" to "to-be-removed" list.
> >  - add "WARNING: noprefix option will be removed in 2.6.32 (or 2.6.31)" now
> >  - remove "noprefix" in 2.6.31-rc or later
> > 
> 
> I don't see how we can remove noprefix while reserve the compatibility of
> old cpuset..
> 
> As Paul Menage said, we can allow noprefix to be used only if we mount just
> cpuset subsystem:
> 
I have no objection.

-Kame


> (pseudo code)
> 
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -886,6 +886,11 @@ static int parse_cgroupfs_options(char *data,
>                 }
>         }
> 
> +
> +       if (test_bit(ROOT_NOPREFIX, &opts->flags) &&
> +           (opts->subsys_bits & ~cpuset_subsys_id) != 0)
> +               return -EINVAL;
> +
>         /* We can't have an empty hierarchy */
>         if (!opts->subsys_bits)
>                 return -EINVAL;
> 
> 

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