Re: [Qemu-devel] live migration between qemu-kvm 1.0 and 0.15

[Avi Kivity]

On 03/27/2012 11:55 AM, Jan Kiszka wrote:
> On 2012-03-27 10:55, Vasilis Liaskovitis wrote:
> > Hi,
> > 
> > is live migration between qemu-kvm stable-0.15 and stable-1.0 trees 
> > possible?
> > When I live migrate a VM from 1.0 to 0.15, the destination side 0.15 
> > qemu-kvm
> > exits with:
> > (qemu) Unknown savevm section or instance 'i8259' 0
> > 
> > That's expected, since commit "i8259:convert to qdev" 
> > 747c70af78f7088f182c87e683bdf847beead1e4
> > introduces the i8259 device in the qdev tree.
> > 
> > The other direction (live migrate from 0.15.1 to 1.0.0) seems to work fine.
> > Are any other issues expected in this direction?
> > 
> > The vmstate for i8259 has not changed between these trees afaict. If the
> > qdev-ified i8259 is reverted from stable-1.0 tree (to restore live-migration
> > compatibility between the versions), would you expect problems?
>
> The legacy instance IDs used in old versions are not written out by
> newer ones. They are just accepted on reading to allow moving forward.
> There are more devices in the tree that used those instance IDs, not
> only the i8259. Reverting the qdev conversion may reactivate backward
> migratability for 1.0->0.15 (unless there are others as well). But that
> will definitely be over after 1.1 as inrevertible code depends on the
> qdev conversion.

Is this true even for -M pc-0.15?

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