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Date: Mon, 11 Oct 2010 16:46:57 +0100
From: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Message-ID: <20101011154656.GE5439@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 05:39:01PM +0200, Avi Kivity wrote:
>  On 10/11/2010 05:30 PM, Stefan Hajnoczi wrote:
> >>
> >>  It was discussed before, but I don't think we came to a conclusion. Are
> >>  there any circumstances under which you don't want to set the
> >>  QED_CF_BACKING_FORMAT flag?
> >
> >I suggest the following:
> >
> >QED_CF_BACKING_FORMAT_RAW = 0x1
> >
> >When set, the backing file is a raw image and should not be probed for
> >its file format.  The default (unset) means that the backing image file
> >format may be probed.
> >
> >Now the backing_fmt_{offset,size} are no longer necessary.
> 
> Should it not be an incompatible option?  If the backing disk starts
> with a format magic, it will be probed by an older qemu,
> incorrectly.

Agreed, it should be a non-compat feature bit.

Stefan