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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH] Change virtio-console to
	PCI_CLASS_SERIAL_OTHER
Date: Thu, 28 May 2009 14:22:51 +0100
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To: qemu-devel@nongnu.org
Cc: Mark McLoughlin <markmc@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, Dor Laor <dlaor@redhat.com>, ajax@redhat.com

> >>   - the device model cannot change or the guest OS will get confused
> >
> > IMHO think the only sane response is "don't do that". Trying to support
> > migration between different qemu versions just isn't worth the pain.
>
> It is very worth the pain.  I consider it a core requirement.

We disagree then. You're effectively requiring bug-compatibility.
This may be reasonable for a stable branch, but is not something I have any 
interest in across different release cycles. IMHO major VM upgrades should be 
considered the same as real hardware or firmware upgrades.

Paul