Re: live migration between qemu-kvm 1.0 and 0.15

[Jan Kiszka <jan.kiszka@siemens.com>]

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.

Jan

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