linux-kernel - Re: [PATCH 1/2] cgroup allow subsys to set default mode of its own file

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Message-Id: <20090227093835.8c7e6f23.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 27 Feb 2009 09:38:35 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Paul Menage <menage@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, lizf@...fujitsu.com,
	balbir@...ux.vnet.ibm.com
Subject: Re: [PATCH 1/2] cgroup allow subsys to set default mode of its own
  file

On Thu, 26 Feb 2009 16:28:11 -0800
Paul Menage <menage@...gle.com> wrote:

> On Thu, Feb 26, 2009 at 1:00 PM, Andrew Morton
> <akpm@...ux-foundation.org> wrote:
> > On Wed, 25 Feb 2009 16:35:55 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> >
> >>  When I wrote tools for maintain cgroup, I can't find which file is
> >>  writable intarfece or not via cgroup file systems. (finally, I did
> >>  dirty approach.)
> >>  IMHO, showing "this file is read-only" in explicit way is useful
> >>  for user-land (tools). In other story, a file whose name sounds read-only
> >>  may have "trigger" operation and support reseting. In this case,
> >>  "writable" is informative.
> >
> > Well, we have compatibility issues here.  If we make this change, and
> > people write tools which depend upon that change then those tools might
> > break when run upon older kernels.
> 
> I don't think that's too big a deal - a write can always fail at the
> whim of a cgroups subsystem, so this would just be a hint to a tool
> that it shouldn't even bother trying to write to the file. It should
> be able to handle a failure.
> 
> But I don't see why we can't figure out the mode automatically based
> on whether or not there's a write handler defined for the control
> file.
> 
That's because I wanted to allow -w------- or -w--w---- or some

Thanks,
-Kame



> Paul
> 

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