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Date: Mon, 11 Oct 2010 15:06:37 +0100
From: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Message-ID: <20101011140637.GC5439@stefan-thinkpad.transitives.com>
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Subject: [Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format
	specification
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To: Avi Kivity <avi@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, qemu-devel@nongnu.org, Christoph Hellwig <hch@lst.de>

On Mon, Oct 11, 2010 at 03:44:38PM +0200, Avi Kivity wrote:
>  On 10/11/2010 03:42 PM, Stefan Hajnoczi wrote:
> >>
> >>  A leak is acceptable (it won't grow; it's just an unused, incorrect
> >>  freelist), but data corruption is not.
> >
> >The alternative is for the freelist to be a non-compat feature bit.
> >That means older QEMU binaries cannot use a QED image that has enabled
> >the freelist.
> 
> For this one feature.  What about others?

Compat features that need to be in sync with the image state will either
require specific checks (e.g. checksum or shadow of the state) or they
need to be non-compat features and are not backwards compatible.

I'm not opposing autoclear feature bits themselves, they are a neat
idea.  However, they will initially have no users so is this something
we really want to carry?

Stefan