From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: O_DIRECT and barriers
Date: Sun, 23 Aug 2009 22:42:33 -0400
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To: Theodore Tso <tytso@mit.edu>,
	Christoph Hellwig <hch@infradead.org>,
	Jamie Lokier <jamie@shareable.org>,
	Jens Axboe <jens.axboe@oracle.com>,
	linux-fsdevel@vger.kernel.org, linux-scsi
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On Fri, Aug 21, 2009 at 10:11:37PM -0400, Theodore Tso wrote:
> Yeah, I guess we can only do that if the filesystem guarantees
> coherence between the page cache and O_DIRECT reads; it's been a long
> while since I've studied that code, so I'm not sure whether all
> filesystems that support O_DIRECT provide this coherency (since I
> thought it was provided in the generic O_DIRECT routines, isn't it?)
> or not.

It's provided in the generic code, yes (or at least appears to).  

Note that xfstests has quite a few tests exercising it.