linux-kernel - Re: [RFC] fs, proc: Introduce the /proc/<pid>/map

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Message-ID: <20110824152222.GZ29452@sun>
Date:	Wed, 24 Aug 2011 19:22:22 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Zan Lynx <zlynx@....org>
Cc:	Nathan Lynch <ntl@...ox.com>, Oren Laadan <orenl@...columbia.edu>,
	Daniel Lezcano <dlezcano@...ibm.com>,
	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Glauber Costa <glommer@...allels.com>,
	containers@...ts.osdl.org, linux-kernel@...r.kernel.org,
	Pavel Emelyanov <xemul@...allels.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	LINUXFS-ML <linux-fsdevel@...r.kernel.org>,
	James Bottomley <jbottomley@...allels.com>
Subject: Re: [RFC] fs, proc: Introduce the /proc/<pid>/map_files/ directory v2

On Wed, Aug 24, 2011 at 09:05:21AM -0600, Zan Lynx wrote:
> On 8/24/2011 2:53 AM, Cyrill Gorcunov wrote:
> > From: Pavel Emelyanov <xemul@...allels.com>
> > 
> > This one behaves similarly to the /proc/<pid>/fd/ one - it contains symlinks
> > one for each mapping with file, the name of a symlink is vma->vm_start, the
> > target is the file. Opening a symlink results in a file that point exactly
> > to the same inode as them vma's one.
> > 
> > This thing is aimed to help checkpointing processes.
> > 
> > For example the ls -l of some arbitrary /proc/<pid>/map_files/
> > 
> >  | lr-x------ 1 cyrill cyrill 64 Aug  9 15:25 0x3d73a00000 -> /lib64/ld-2.5.so
> [snip]
> 
> Just curious: How do these symlinks work when the process reading a
> /proc file is in a chroot or a different namespace?
> 
> For example, a chroot environment might have independent copies of
> /lib64/ld-2.5.so and a bind mount of /proc. Does the symlink then point
> to the wrong file?

To be fair, I personally didn't tried such scenario but it should be
the same behaviour as for /proc/$pid/fd since data is taken from
a task pointed by pid. I'll check though, good question.

	Cyrill
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