Re: 2.4.18 no timestamp update on modified mmapped files

From: Keith Owens (
Date: Tue Jun 11 2002 - 01:29:54 EST

On Mon, 10 Jun 2002 23:17:27 -0700,
Andrew Morton <> 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?
> 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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This archive was generated by hypermail 2b29 : Sat Jun 15 2002 - 22:00:21 EST