linux-kernel - Re: [PATCH v2] /proc/pid/status: show all sets of pid according to ns

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Date:	Thu, 29 May 2014 14:02:06 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Richard Weinberger <richard@....at>
CC:	Vasily Kulikov <segoon@...nwall.com>,
	<containers@...ts.linux-foundation.org>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	<linux-kernel@...r.kernel.org>, Oleg Nesterov <oleg@...hat.com>,
	David Howells <dhowells@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v2] /proc/pid/status: show all sets of pid according to
 ns

On 05/29/2014 01:54 PM, Richard Weinberger wrote:
> Am 29.05.2014 11:41, schrieb Pavel Emelyanov:
>> On 05/29/2014 01:21 PM, Richard Weinberger wrote:
>>> Am 29.05.2014 11:07, schrieb Pavel Emelyanov:
>>>> On 05/29/2014 09:59 AM, Vasily Kulikov wrote:
>>>>> On Wed, May 28, 2014 at 23:27 +0400, Pavel Emelyanov wrote:
>>>>>> On 05/28/2014 10:28 PM, Vasily Kulikov wrote:
>>>>>>> On Wed, May 28, 2014 at 16:44 +0400, Pavel Emelyanov wrote:
>>>>>>> It will be simplier
>>>>>>> to parse the file -- if 'ns_ids' file contains some ID then this ID for
>>>>>>> every ns can be obtained regardless of the specific ID name (SID, PID,
>>>>>>> PGID, etc.).
>>>>>>
>>>>>> True, but given a task PID how to determine which pid namespaces it lives in
>>>>>> to get the idea of how PIDs map to each other? Maybe we need some explicit
>>>>>> API for converting (ID, NS1, NS2) into (ID)?
>>>>>
>>>>> AFAIU the idea of the patch is to add a new debugging information which
>>>>> can be trivially obtained via 'cat /proc/...':
>>>>
>>>> I agree, but this ability will be very useful by checkpoint-restore project
>>>> too and I'd really appreciate if the API we have for that would be scalable
>>>> enough. Per-task proc file works for me, but how about sid-s and pgid-s?
>>>
>>> What kind of information does CRIU need?
>>
>> We need to know what pid namespaces a task lives in and how pid, sid and
>> pgid look in all of them. A short example with pids only
> 
> So use case is to checkpoint/restore nested containers? :)

Yes, but there's one more scenario. AFAIK some applications create pid namespaces 
themselves, without starting what is typically called "a container" :) And when 
such an applications are run inside, well ... "more real" container (e.g. using
openvz, lxc or docker tools) we face this issue.

Thanks,
Pavel
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