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Date: Fri, 8 Apr 2011 17:08:53 -0400
From: Christoph Hellwig <hch@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Steve Rago <sar@nec-labs.com>, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] Allow O_SYNC to be set by fcntl(F_SETFL)
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On Fri, Apr 08, 2011 at 10:56:02AM -0700, Andrew Morton wrote:
> Because it's inconsistent.  An O_SYNC fd never has outstanding writeout. 
> Except for in this one new and special time window between a setfl()
> and the next write().

It might actually have outstanding writes for as long as it eventually
takes the writeback code to push them out.  O_SYNC only does a range
writeout for the area that was written.