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Date: Tue, 29 Jul 2014 04:16:30 +0000
From: Serge Hallyn <serge.hallyn@ubuntu.com>
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Subject: Re: [Qemu-devel] [PATCH] [RFC] Add machine type pc-1.0-qemu-kvm for
 live migrate compatibility with qemu-kvm
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To: Alex Bligh <alex@alex.org.uk>
Cc: Ryan Harper <ryan.harper@canonical.com>, Serge Hallyn <serge.hallyn@canonical.com>, "Michael S. Tsirkin" <mst@redhat.com>, Libvirt <libvir-list@redhat.com>, "quintela@redhat.com" <quintela@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Alexander Graf <agraf@suse.de>, Cole Robinson <crobinso@redhat.com>, Amit Shah <amit.shah@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Bruce Rogers <brogers@suse.com>, Andreas =?iso-8859-1?Q?F=E4rber?= <afaerber@suse.de>

Quoting Alex Bligh (alex@alex.org.uk):
> 
> On 22 Jul 2014, at 19:43, Alex Bligh <alex@alex.org.uk> wrote:
> 
> > Testing has been light to date (i.e.
> > can I migrate it inbound with -S without anything complaining).

thanks, Alex!

> 
> I've given this quite a bit more testing today.
> 
> It works fine qemu-kvm 1.0 -> qemu-2.0+patch (cirrus vga)
> It works fine qemu-2.0+patch -> qemu-2.0+patch (cirrus vga)
> It doesn't (yet) work qemu-2.0+patch -> qemu-kvm 1.0 (cirrus vga).
> 
> The reason for this is (at least) that I need to emulate the
> broken versioning of the mc146818rtc timer section, as writing
> it correctly confuses qemu-kvm 1.0. Therefore please don't bother
> testing migration back to 1.0 yet.

I don't think that is in any way a problem.  Is migrating to older
versions ever actually expected to work?  In either case I don't
think for this particular case it's a problem.

(The "how to handle this in libvirt" question is more interesting)

-serge