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 15:59:46 +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 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]

> > However, maybe it is possible to implement not via new syscall but
> > by implementation of new symlink in sysfs?  Then both ps-like tool and
> > CRIU-like tool is able to obtain the ns information by the same means.
> > Maybe sort of a symlink to a parent namespace or a process which is
> > inside of the parent namespace?  Then a process may identify IDs using
> > following steps:
> > 
> > 1) identify target NS by walking current procfs
> > 2) do setns(2)/chroot(2)
> > 3) look at procfs to identify target IDs in the target NS
> 
> Can you elaborate on this? Let's imagine we have picked two tasks with
> init_pid_ns' PIDs being 11 and 12 and we've found out using /proc/pid/ns/pid
> links that they both live in some non-init pid namespace.
> 
> Then we have to look at this ns' proc. It says that there are also two 
> tasks -- 2 and 3. How can we determine which pid is which?

Oh, right.  My idea is broken.

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