linux-kernel - Re: mmap / mtime updates

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Date:	Thu, 11 Jan 2007 17:46:52 -0500
From:	Peter Staubach <staubach@...hat.com>
To:	Marek Michalkiewicz <marekm@...lek.gda.pl>
CC:	linux-kernel@...r.kernel.org
Subject: Re: mmap / mtime updates

Marek Michalkiewicz wrote:
> Hello,
>
> What is the current status of the bug where modifications to file
> contents made via mmap fail to update mtime of the file?
>
> This was discussed a few months ago in this thread:
>
> http://lkml.org/lkml/2006/5/17/138
>
> where patches have been posted, but it seems that no final solution
> has been agreed on and applied to the kernel tree.  Updating ctime
> and mtime appears to be required by the standard:
>
>   http://www.opengroup.org/onlinepubs/009695399/functions/mmap.html
>
>   The st_ctime and st_mtime fields of a file that is mapped with
>   MAP_SHARED and PROT_WRITE shall be marked for update at some point
>   in the interval between a write reference to the mapped region and
>   the next call to msync() with MS_ASYNC or MS_SYNC for that portion
>   of the file by any process.
>
> and failing to do it can lead to potential data loss as well, if
> modified files are not backed up (I'm seeing the problem with Samba
> tdb files not being backed up by rsnapshot, for example).

I am working on porting the patches to the current upstream kernel.
As soon as I complete this work, then I will repost the patch and
we'll see where things go then.

    Thanx...

       ps
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