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

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Message-ID: <47D0C76D.8050207@linux.vnet.ibm.com>
Date:	Fri, 07 Mar 2008 10:11:17 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	David Rientjes <rientjes@...gle.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

David Rientjes wrote:
> On Fri, 7 Mar 2008, Balbir Singh wrote:
> 
>> @@ -3010,3 +3020,16 @@ static void cgroup_release_agent(struct 
>>  	spin_unlock(&release_list_lock);
>>  	mutex_unlock(&cgroup_mutex);
>>  }
>> +
>> +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.

>> diff -puN Documentation/kernel-parameters.txt~cgroup_disable Documentation/kernel-parameters.txt
>> --- linux-2.6.25-rc4/Documentation/kernel-parameters.txt~cgroup_disable	2008-03-06 17:57:32.000000000 +0530
>> +++ linux-2.6.25-rc4-balbir/Documentation/kernel-parameters.txt	2008-03-06 18:00:32.000000000 +0530
>> @@ -383,6 +383,10 @@ and is between 256 and 4096 characters. 
>>  	ccw_timeout_log [S390]
>>  			See Documentation/s390/CommonIO for details.
>>  
>> +	cgroup_disable= [KNL] Enable disable a particular controller
>> +			Format: {name of the controller}
>> +			See /proc/cgroups for a list of compiled controllers
>> +
> 
> This works on multiple controllers, though, if they follow 
> cgroup_disable=, so the documentation and format should reflect that.

Absolutely! done.

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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