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Date: Tue, 1 Mar 2011 13:42:54 +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.
Message-ID: <20110301124254.GA29485@lst.de>
References: <20110228171956.05a84fb9@zephyr> <4D6BBB72.6040205@redhat.com>
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.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>


The only way to change the cache settings is from the guest.  Without
that we're guranteed to lose data when going from WCE=0 to WCE=1.

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.