linux-kernel - Re: [PATCH 3/3] pids: Make it possible to clone tasks with given pids

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Message-ID: <4EBC0B87.1030305@parallels.com>
Date:	Thu, 10 Nov 2011 21:36:07 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Glauber Costa <glommer@...allels.com>,
	Nathan Lynch <ntl@...ox.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Serge Hallyn <serue@...ibm.com>,
	Daniel Lezcano <dlezcano@...ibm.com>
Subject: Re: [PATCH 3/3] pids: Make it possible to clone tasks with given
 pids

On 11/10/2011 09:30 PM, Tejun Heo wrote:
> Hello, Pavel.
> 
>>  	for (i = ns->level; i >= 0; i--) {
>> -		nr = alloc_pidmap(tmp);
>> +		nr = 0;
>> +		if (unlikely(want_pids != NULL)) {
>> +			if (get_user(nr, want_pids)) {
>> +				nr = -EFAULT;
>> +				goto out_free;
>> +			}
>> +
>> +			if (nr != 0) {
>> +				want_pids++;
>> +				nr = set_pidmap(tmp, nr);
>> +			} else
>> +				want_pids = NULL; /* optimize above */
>> +		}
>> +		if (nr == 0)
>> +			nr = alloc_pidmap(tmp);
> 
> Hmmm... is it necessary to be able to replicate pids on all
> namespaces? 

Not for us (I mean OpenVZ). But since we should (in theory) be able to
recreate the nested set of namespaces it would be good if the API allows
for this from the very beginning.

> Also, isn't it a bit weird to be able to request PIDs in
> the namespaces which is beyond the task which requested cloning?

It is, but the last_pid != 0 check will abort this request with EPERM :)
Do you think some other behavior would be better?

> Thanks.

Thanks,
Pavel
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