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Date: Tue, 1 Sep 2009 00:57:27 +0200
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [Qemu-devel] [PATCH 2/4] block: use fdatasync instead of fsync
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To: Jamie Lokier <jamie@shareable.org>
Cc: Christoph Hellwig <hch@lst.de>, qemu-devel@nongnu.org

On Mon, Aug 31, 2009 at 11:48:19PM +0100, Jamie Lokier wrote:
> > fdatasync is defined to provide that guarantee, and modulo the whole
> > clusterfuck around volatile write caches it does the right thing
> > thing on common Linux filesystems.
> 
> That's good to know.  I'm not sure about other hosts though.  It's
> specified to update the metadata, but I think I've encountered people
> saying it doesn't - specifically when extending a file, that it
> doesn't guarantee the file size is extended on some OSes.  But that
> might be an urban myth.

Those would be typical bugs for really naive implementations.  I'm
pretty sure those existed for a short time in a lot of places, but I
would be extremly surprised if they continued to exist for longer time
in any major operating system.