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

Andrew Morton
2007-06-07T19:48:24Z

On Thu, 07 Jun 2007 10:06:37 -0700
Badari Pulavarty <pbadari@us.ibm.com> wrote:

> 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,

yup, we should put it back. The change was, afaik, accidental.

> here is the patch I originally suggested.

Confused. Will this one-liner fix all the userspace breakage to which
Albert refers?

> 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);