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From: "Jesper Juhl" <jesper.juhl@gmail.com>
To: "Anton Salikhmetov" <salikhmetov@gmail.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, joe@evalesco.com
Subject: Re: [PATCH][RFC][BUG] updating the ctime and mtime time stamps in msync()
Date: Wed, 9 Jan 2008 15:41:11 +0100	[thread overview]
Message-ID: <9a8748490801090641s41a06c1era3764091f135567d@mail.gmail.com> (raw)
In-Reply-To: <4df4ef0c0801090332y345ccb67se98409edc65fd6bf@mail.gmail.com>

On 09/01/2008, Anton Salikhmetov <salikhmetov@gmail.com> wrote:
> Since no reaction in LKML was recieved for this message it seemed
> logical to suggest closing the bug #2645 as "WONTFIX":
>
> http://bugzilla.kernel.org/show_bug.cgi?id=2645#c15
>
> However, the reporter of the bug, Jacob Oestergaard, insisted the
> solution to be resubmitted once more:
>

Good idea. The bug is real and should be fixed IMHO.


...
> This bug causes backup systems to *miss* changed files.
>
> This bug does cause data loss in common real-world deployments (I gave an
> example with a database when posting the bug, but this affects the data from
> all mmap using applications with common backup systems).
>
Not just backup systems, but any application that relies on mtime
being correctly updated will be bitten by this.


> Silent exclusion from backups is very very nasty.
>
Agreed.

In fact if mtime is not reliable (which it is not) one could argue
that we might as well not update it at all, ever. But I think we can
all agree that just fixing it (as your patch does) is a lot better.

> Please comment on my solution or commit it if it's acceptable in its
> present form.
>
I've only looked briefly at your patch but it seems resonable. I'll
try to do some testing with it later.

Thank you for working on this long standing bug.

...
> > I would like to propose my solution for the bug #2645 from the kernel bug tracker:
> >
> > http://bugzilla.kernel.org/show_bug.cgi?id=2645
> >
> > The Open Group defines the behavior of the mmap() function as follows.
> >
> > 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.
> >
> > The above citation was taken from the following link:
> >
> > http://www.opengroup.org/onlinepubs/009695399/functions/mmap.html
> >
...

I agree that our current behaviour is certainly not what the standard
(sensibly) requires.


-- 
Jesper Juhl <jesper.juhl@gmail.com>
Don't top-post  http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please      http://www.expita.com/nomime.html

  parent reply	other threads:[~2008-01-09 14:41 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-07 17:54 Anton Salikhmetov
2008-01-09 11:32 ` Anton Salikhmetov
2008-01-09 11:47   ` Jakob Oestergaard
2008-01-09 12:22   ` Jakob Oestergaard
2008-01-09 14:41   ` Jesper Juhl [this message]
2008-01-09 15:31     ` Anton Salikhmetov
2008-01-09 21:28   ` Peter Staubach
2008-01-09 20:50 ` Rik van Riel
2008-01-09 21:01   ` Klaus S. Madsen
2008-01-09 21:06   ` Valdis.Kletnieks
2008-01-09 22:06     ` Rik van Riel
2008-01-09 22:19       ` Peter Staubach
2008-01-09 22:33       ` Jakob Oestergaard
2008-01-09 23:41         ` Rik van Riel
2008-01-10  0:03           ` Anton Salikhmetov
2008-01-10  8:51             ` Jakob Oestergaard
2008-01-10 10:53               ` Anton Salikhmetov
2008-01-10 15:45                 ` Rik van Riel
2008-01-10 15:56                   ` Anton Salikhmetov
2008-01-10 16:07                     ` Rik van Riel
2008-01-10 16:40                       ` Anton Salikhmetov
2008-01-10 16:52                         ` Peter Staubach
2008-01-10 16:46                       ` Peter Staubach
2008-01-10 20:48           ` Valdis.Kletnieks
2008-01-10  0:48       ` Anton Salikhmetov
2008-01-10  0:40   ` Anton Salikhmetov
2008-01-09 21:18 ` Peter Staubach

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