linux-kernel - Re: [PATCH][RFC][BUG] updating the ctime and mtime time stamps in msync()

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Date:	Thu, 10 Jan 2008 13:53:59 +0300
From:	"Anton Salikhmetov" <salikhmetov@...il.com>
To:	"Jakob Oestergaard" <jakob@...hought.net>,
	"Anton Salikhmetov" <salikhmetov@...il.com>,
	"Rik van Riel" <riel@...hat.com>, Valdis.Kletnieks@...edu,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][RFC][BUG] updating the ctime and mtime time stamps in msync()

2008/1/10, Jakob Oestergaard <jakob@...hought.net>:
> On Thu, Jan 10, 2008 at 03:03:03AM +0300, Anton Salikhmetov wrote:
> ...
> > > I guess a third possible time (if we want to minimize the number of
> > > updates) would be when natural syncing of the file data to disk, by
> > > other things in the VM, would be about to clear the I_DIRTY_PAGES
> > > flag on the inode.  That way we do not need to remember any special
> > > "we already flushed all dirty data, but we have not updated the mtime
> > > and ctime yet" state.
> > >
> > > Does this sound reasonable?
> >
> > No, it doesn't. The msync() system call called with the MS_ASYNC flag
> > should (the POSIX standard requires that) update the st_ctime and
> > st_mtime stamps in the same manner as for the MS_SYNC flag. However,
> > the current implementation of msync() doesn't call the do_fsync()
> > function for the MS_ASYNC case. The msync() function may be called
> > with the MS_ASYNC flag before "natural syncing".
>
> If the update was done as Rik suggested, with the addition that msync()
> triggered an explicit sync of the inode data, then everything would be ok,
> right?

Indeed, if msync() is called with MS_SYNC an explicit sync is
triggered, and Rik's suggestion would work. However, the POSIX
standard requires a call to msync() with MS_ASYNC to update the
st_ctime and st_mtime stamps too. No explicit sync of the inode data
is triggered in the current implementation of msync(). Hence Rik's
suggestion would fail to satisfy POSIX in the latter case.

>
> --
>
>  / jakob
>
>
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