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Date: Tue, 1 Mar 2011 13:50:36 +0100
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [Qemu-devel] [RFC][PATCH 0/2] Allow cache settings for block
	devices to be changed at runtime.
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To: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel <qemu-devel@nongnu.org>, Ananth Narayan <ananth@linux.vnet.ibm.com>, Prerna Saxena <prerna@linux.vnet.ibm.com>, Christoph Hellwig <hch@lst.de>

On Tue, Mar 01, 2011 at 12:48:34PM +0000, Stefan Hajnoczi wrote:
> On Tue, Mar 01, 2011 at 01:42:54PM +0100, Christoph Hellwig wrote:
> > I have patches to do that, and to allow changing O_DIRECT via a monitor
> > command, but to toggle O_SYNC via fcntl I first need to get a kernel
> > patch in as that's currently not allowed to be changed at runtime.
> 
> Great it sounds like you have already implemented the two cases (guest wce and
> host O_DIRECT) that we're talking about.

At least in theory.  And for Linux I can add setting/clearing of O_SYNC
via fcntl easily, but what do we do for other hosts?  I'm not sure
closing/reopening the backing file is easily feasible.