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Date: Thu, 07 Jun 2007 16:57:09 -0700 From: Badari Pulavarty <pbadari@...ibm.com> To: "Serge E. Hallyn" <serge@...lyn.com> CC: Andrew Morton <akpm@...ux-foundation.org>, Albert Cahalan <acahalan@...il.com>, lkml <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, ebiederm@...ssion.com, torvalds@...ux-foundation.org Subject: Re: [RFC][PATCH] /proc/pid/maps doesn't match "ipcs -m" shmid Serge E. Hallyn wrote: >Quoting Serge E. Hallyn (serge@...lyn.com): > >>Quoting Badari Pulavarty (pbadari@...ibm.com): >> >>>On Thu, 2007-06-07 at 15:37 -0500, Serge E. Hallyn wrote: >>> >>>>Quoting Badari Pulavarty (pbadari@...ibm.com): >>>> >>>>>On Thu, 2007-06-07 at 12:48 -0700, Andrew Morton wrote: >>>>> >>>>>>On Thu, 07 Jun 2007 10:06:37 -0700 >>>>>>Badari Pulavarty <pbadari@...ibm.com> wrote: >>>>>> >>>>>>>On Thu, 2007-06-07 at 12:43 -0400, Albert Cahalan wrote: >>>>>>> >>>>>>>>On 6/7/07, Badari Pulavarty <pbadari@...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? >>>>>> >>>>>Yes. Albert, please correct me if I am wrong. >>>>> >>>>It will, but could lead to two different inodes with the same i_ino, >>>>right? >>>> >>>Only if we generate same ID in two different namespaces. Is it currently >>>possible ? >>> >>Should be nothing stopping it. >> > >(just to be more certain, a quick test showed I can get id 0 for >different keys, and different ids for the same key 0xff, in different >ipc namespaces) > Funny. I played with it and decided that it can happen :) Thanks, Badari - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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