Re: [PATCH] update ctime and mtime for mmaped write

[Peter Staubach <staubach@redhat.com>]

Miklos Szeredi wrote:
> > > Take this example:
> > >
> > >     fd = open()
> > >     addr = mmap(.., fd)
> > >     write(fd, ...)
> > >     close(fd)
> > >     sleep(100)
> > >     msync(addr,...)
> > >     munmap(addr)
> > >
> > > The file times will be updated in write(), but with your patch, the
> > > bit in the mapping will also be set.
> > >
> > > Then in msync() the file times will be updated again, which is wrong,
> > > since the memory was _not_ modified through the mapping.
> > >       
> > This is correct.  I have updated my proposed patch to include the clearing
> > of AS_MCTIME in the routine which updates the mtime field.
> >     
>
> That doesn't really help.  Look at __generic_file_aio_write_nolock().
> file_update_time() is called before the data is written, so after the
> last write, there will be nothing to clear the flag.
>
> And even if fixed this case by moving the file_update_time() call to
> the end of the function, there's no guarantee, that some filesystem
> won't do something exotic and call set_page_dirty() indenpendently of
> write().  Good luck auditing all the set_page_dirty() calls ;)

Interesting.

No, I wouldn't want to get into worrying about set_page_dirty() calls.
Life is short and people have too much imagination...  :-)

   Thanx...

      ps

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/