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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions
Date: Wed, 10 Jun 2009 17:46:03 +0100
References: <cover.1243253205.git.mst@redhat.com>
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Carsten Otte <cotte@de.ibm.com>, kvm@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, Blue Swirl <blauwirbel@gmail.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Avi Kivity <avi@redhat.com>

> > If you can't create an identical machine from scratch then I don't
> > consider snapshot/migration to be a useful feature. i.e. as soon as you
> > shutdown and restart the guest it is liable to break anyway.
>
> Why is liable to break?

A VM booted on an old version of qemu and migrated to a new version will 
behave differently to a the same VM booted on a new version of qemu.
I hope I don't need to explain why this is bad.

As previously discussed, any guest visible changes are liable to break a guest 
OS, particularly guests like Windows which deliberately break when run on 
"different" hardware. Personally I don't particularly care, but if we support 
live migration we also need to support "cold" migration - i.e. shutdown and 
restart.

>So once you load and image with MSIX capability off,
>it will stay off across guest restarts.

I'm assuming guest restart includes restarting qemu.

Paul