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 16:53:01 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Vasily Kulikov <segoon@...nwall.com>
CC:	Richard Weinberger <richard.weinberger@...il.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 03:59 PM, Vasily Kulikov wrote:
> On Thu, May 29, 2014 at 15:31 +0400, Pavel Emelyanov wrote:
>> On 05/29/2014 03:12 PM, Vasily Kulikov wrote:
>>> On Thu, May 29, 2014 at 13:07 +0400, Pavel Emelyanov wrote:
>>>> On 05/29/2014 09:59 AM, Vasily Kulikov wrote:
>>>>> On Wed, May 28, 2014 at 23:27 +0400, Pavel Emelyanov wrote:
>>>>> ] We need a direct method of getting the pid inside containers.
>>>>> ] If some issues occurred inside container guest, host user
>>>>> ] could not know which process is in trouble just by guest pid:
>>>>> ] the users of container guest only knew the pid inside containers.
>>>>> ] This will bring obstacle for trouble shooting.
>>>>>
>>>>> A new syscall might complicate trouble shooting by admin.
>>>>
>>>> Pure syscall -- yes. What if we teach the ps and top utilities to show additional
>>>> info? I think that would help.
>>>
>>> I like the idea with low level non-shell API which can be used by
>>> utility like ps (or implementation of a new tool to work with complex
>>> namespace hierarchies).  It should fit for troublesooting.  Then there
>>> should be no reason to implement two different APIs for observation from
>>> shell via FS and from applications.
>>
>> Maybe we can reuse the existing kcmp() system call? We would have to store
>> the collected pid values in some hash/tree anyway, and kcmp() provides us
>> good comparing function for doing this.
>>
>> Like we can call kcmp(pid1, pid2, KCMP_PID, nsfd1, nsfd2) which will mean
>> "Are tasks with pid1 in namespace pointed by nsfd1 and with pid2 in namespace
>> nsfd2 the same?"
>>
>> What do you think?
> 
> kcmp() is not needed, just compare inode numbers:
> 
>     # ls -il /proc/{43,self}/ns/mnt
>     208182 lrwxrwxrwx 1 root root 0 мая   29 15:52 /proc/43/ns/mnt -> mnt:[4026531856]
>     216556 lrwxrwxrwx 1 root root 0 мая   29 15:57 /proc/self/ns/mnt -> mnt:[4026531840]

But that's for comparing the namespaces, while I'm proposing the kcmp to
check for PIDs.

Thanks,
Pavel
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