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Date: Wed, 24 Aug 2011 19:19:47 +0400
From: Pavel Emelyanov <xemul@parallels.com>
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To: Zan Lynx <zlynx@acm.org>
CC: Cyrill Gorcunov <gorcunov@gmail.com>, Nathan Lynch <ntl@pobox.com>,
        Oren Laadan <orenl@cs.columbia.edu>,
        Daniel Lezcano <dlezcano@fr.ibm.com>, Tejun Heo <tj@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Glauber Costa <glommer@parallels.com>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Serge Hallyn <serge.hallyn@canonical.com>,
        LINUXFS-ML <linux-fsdevel@vger.kernel.org>,
        James Bottomley <jbottomley@parallels.com>
Subject: Re: [RFC] fs, proc: Introduce the /proc/<pid>/map_files/ directory
 v2
References: <20110824085329.GL29452@sun> <4E551331.1010709@acm.org>
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On 08/24/2011 07:05 PM, Zan Lynx wrote:
> On 8/24/2011 2:53 AM, Cyrill Gorcunov wrote:
>> From: Pavel Emelyanov <xemul@parallels.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?

No and this is the trick - when you readlink it - it give you trash, but
when you open one - you get exactly the same file as the map points to.