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

From: Miklos Szeredi
Date: Thu Feb 22 2007 - 15:44:33 EST

> > 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 ;)

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