linux-kernel - Re: [PATCH] Add cgroup support for enabling controllers at boot time

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Date:	Thu, 6 Mar 2008 21:14:26 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
cc:	Paul Menage <menage@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelianov <xemul@...nvz.org>,
	Hugh Dickins <hugh@...itas.com>,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, taka@...inux.co.jp,
	linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH] Add cgroup support for enabling controllers at boot
 time

On Fri, 7 Mar 2008, Balbir Singh wrote:

> >> +static int __init cgroup_disable(char *str)
> >> +{
> >> +	int i;
> >> +	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
> >> +		struct cgroup_subsys *ss = subsys[i];
> >> +		if (!strcmp(str, ss->name)) {
> >> +			ss->disabled = 1;
> >> +			break;
> >> +		}
> >> +	}
> >> +}
> >> +__setup("cgroup_disable=", cgroup_disable);
> > 
> > This doesn't handle spaces very well, so isn't it possible for the name of 
> > a current or future cgroup subsystem to be specified after cgroup_disable= 
> > on the command line and have it disabled by accident?
> > 
> 
> How do you distinguish that from the user wanting to disable the controller on
> purpose? My understanding is that after parsing cgroup_disable=, the rest of the
> text is passed to cgroup_disable to process further. You'll find that all the
> __setup() code in the kernel is implemented this way.
> 

Since the command line is logically delimited by spaces, you can 
accidently disable a subsystem if its name appears in any of your kernel 
options following your cgroup_disable= option.  So if you're absolutely 
confident that it wouldn't happen (for instance, if there's no logical 
reason that a cgroup subsystem name should appear anywhere besides 
cgroup_disable on the command line), then there's no objection.
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