On 09/01/2008, Anton Salikhmetov <salikhmetov@gmail.com> wrote:
quoted text
> 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.


...
quoted text
> 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.


quoted text
> 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.

quoted text
> 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.

...
quoted text
> > 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>
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