Subject: Re: [RFC][PATCH] /proc/pid/maps doesn't match "ipcs -m" shmid
From: Badari Pulavarty <pbadari@us.ibm.com>
To: Albert Cahalan <acahalan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
       lkml <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>,
       ebiederm@xmission.com, torvalds@linux-foundation.org
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Date: Thu, 07 Jun 2007 10:06:37 -0700
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On Thu, 2007-06-07 at 12:43 -0400, Albert Cahalan wrote:
> On 6/7/07, Badari Pulavarty <pbadari@us.ibm.com> wrote:
> 
> > BTW, I agree with Eric that its would be nice to use shmid as part
> > of name instead of forcing to be as inode number. It should be
> > possible for pmap to workout shmid from "key" or name. Isn't it ?
> 
> It is not at all nice.
> 
> 1. it's incompatible ABI breakage
> 2. where will you put the key then, in the inode? :-)

Nope. Currently "key" is part of the name (but its not unique).

> 
> Changing to "SYSVID%d" is no good either. Look, people
> are ***parsing*** this stuff in /proc. The /proc filesystem
> is not some random sandbox to be playing in.
> 
> Before you go messing with it, note that the device number
> also matters. (it's per-boot dynamic, but that's OK)
> That's how one knows that /SYSV00000000 is not just
> a regular file; sadly these didn't get a non-/ prefix.
> (and no you can't fix that now; it's way too late)
> 
> Next time you feel like breaking an ABI, mind putting
> "LET'S BREAK AN ABI!" in the subject of your email?

I am not breaking ABI. Its already broken in the current
mainline. I am trying to fix it by putting back the ino#
as shmid. Eric had a suggestion that, instead of depending
on the inode# to be shmid, we could embed shmid into name
(instead of "key" which is currently not unique).

> BTW, I suspect this kind of thing also breaks:
> a. fuser, lsof, and other resource usage display tools
> b. various obscure emulators (similar to valgrind)

If you strongly feel that "old" behaviour needs to be retained, 
here is the patch I originally suggested.

Thanks,
Badari

"ino#" in /proc/pid/maps used to match "ipcs -m" output for shared 
memory (shmid). It was useful in debugging, but its changed recently. 
This patch sets inode number to shared memory id to match /proc/pid/maps.

Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>

Index: linux-2.6.22-rc4/ipc/shm.c
===================================================================
--- linux-2.6.22-rc4.orig/ipc/shm.c	2007-06-04 17:57:25.000000000 -0700
+++ linux-2.6.22-rc4/ipc/shm.c	2007-06-06 08:23:57.000000000 -0700
@@ -397,6 +397,7 @@ static int newseg (struct ipc_namespace 
 	shp->shm_nattch = 0;
 	shp->id = shm_buildid(ns, id, shp->shm_perm.seq);
 	shp->shm_file = file;
+	file->f_dentry->d_inode->i_ino = shp->id;
 
 	ns->shm_tot += numpages;
 	shm_unlock(shp);


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