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

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Message-ID: <20140531060713.GA5315@cachalot>
Date:	Sat, 31 May 2014 10:07:13 +0400
From:	Vasily Kulikov <segoon@...nwall.com>
To:	Pavel Emelyanov <xemul@...allels.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 Thu, May 29, 2014 at 16:53 +0400, Pavel Emelyanov wrote:
> 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.

Hm, right.

What about the following solution: export global process ID (PID in
init ns) which is visible inside of any namespace.  Then you can compare
numbers regardless in what namespace you are.

-- 
Vasily Kulikov
http://www.openwall.com - bringing security into open computing environments
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