Re: [RFC][PATCH] /proc/pid/maps doesn't match "ipcs -m" shmid

Badari Pulavarty
2007-06-07T17:01:09Z

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);