From: Dave Chinner <david@fromorbit.com>
Subject: Re: e4defrag modifies folder's mtime.
Date: Wed, 4 Jan 2012 18:43:57 +1100
Message-ID: <20120104074357.GC17026@dastard>
References: <4F00BE34.1080006@gmail.com>
 <20120103203443.GC30502@thunk.org>
 <20120104045318.GA17026@dastard>
 <20120104052718.GB13438@thunk.org>
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Cc: Thomas Lindroth <thomas.lindroth@gmail.com>,
	linux-ext4@vger.kernel.org
To: Ted Ts'o <tytso@mit.edu>
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In-Reply-To: <20120104052718.GB13438@thunk.org>
Sender: linux-ext4-owner@vger.kernel.org

On Wed, Jan 04, 2012 at 12:27:18AM -0500, Ted Ts'o wrote:
> On Wed, Jan 04, 2012 at 03:53:18PM +1100, Dave Chinner wrote:
> > 
> > xfs_fsr doesn't use these donor files to avoid mtime updates - it
> > uses invisible IO (i.e. O_NOATIME|O_NOCMTIME) to do that.
> 
> O_NOCMTIME doesn't exist yet.  From include/linux/fs.h:
> 
> /*
>  * Don't update ctime and mtime.
>  *
>  * Currently a special hack for the XFS open_by_handle ioctl, but we'll
>  * hopefully graduate it to a proper O_CMTIME flag supported by open(2) soon.
>  */
> #define FMODE_NOCMTIME		((__force fmode_t)0x800)
> 
> I'd have to check, but it wouldn't surprise me if glibc is filtering
> out all fcntl flags it doesn't understand, so for now, this is an
> XFS-only special...

Sounds to me like e2defrag needs it, so perhaps it should finally
be made a proper open flag like the comment says rather than
inventing some other way of solving the problem....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com