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Date: Wed, 25 Nov 2009 15:42:20 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [Qemu-devel] Re: Live migration protocol, device features,
	ABIs and other beasts
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To: Gerd Hoffmann <kraxel@redhat.com>
Cc: dlaor@redhat.com, qemu-devel <qemu-devel@nongnu.org>, Juan Quintela <quintela@redhat.com>

On Wed, Nov 25, 2009 at 02:42:25PM +0100, Gerd Hoffmann wrote:
>>>   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

MSI-X is an orthogonal issue, let's not mix it in.
Maybe you are using e1000, or maybe you
disabled MSI-X with a flag.

-- 
MST