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From: Keith Owens <kaos@ocs.com.au>
To: Andrew Morton <akpm@zip.com.au>
Cc: linux-kernel@vger.kernel.org
Subject: Re: 2.4.18 no timestamp update on modified mmapped files 
In-Reply-To: Your message of "Mon, 10 Jun 2002 23:17:27 MST."
             <3D0595F7.A21AE62B@zip.com.au> 
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Date: Tue, 11 Jun 2002 16:29:54 +1000
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On Mon, 10 Jun 2002 23:17:27 -0700, 
Andrew Morton <akpm@zip.com.au> wrote:
>Keith Owens wrote:
>> 
>> fd = open("foo", O_RDWR);
>> map = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
>> ... modify the mapped pages ...
>> munmap(map, size);
>> close(fd);
>> 
>> The timestamp on foo is not updated, even though the contents have
>> changed.  Adding msync(map, size, MS_[A]SYNC) before munmap makes no
>> difference.  2.4.19-pre10 has no obvious fixes for this problem.

>What do the standards say?
>
>http://www.opengroup.org/onlinepubs/007904975/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. If there is
>     no such call and if the underlying file is modified as a result of a write reference,
>     then these fields shall be marked for update at some time after the write reference.

That says nothing about a file where the only updates are via mmap.  My
file had grown to its final size so there were no more writes, only
pages being dirtied via mmap.

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