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Date: Wed, 25 Nov 2009 14:42:25 +0100
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] Re: Live migration protocol, device features,	ABIs
	and other beasts
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: dlaor@redhat.com, qemu-devel <qemu-devel@nongnu.org>, Juan Quintela <quintela@redhat.com>

>>   And this is also the trivial part to describe: I want a
>> machine like the one in qemu-0.11.
>
> Yes, but there might be a ton of reasons to want a
> machine like the one in qemu 0.11.
> The need to migrate to old qemu is very rare,
> it is a completely separate decision
> one might take long after starting qemu,

Doesn't work.  If you have a qemu 0.11 machine, a virtio nic and your 
guest uses MSI-X you simply can't migrate to qemu 0.10.  End of story.

If you want to be able to migrate to 0.10 you have to start in 0.10 
compat mode with MSI-X disabled.  So IMHO it does makes sense to tie the 
savevm format to -M pc-<version>.

cheers,
   Gerd