Re: [Qemu-devel] migration: new sections and backward compatibility.

[Anthony Liguori]

On 07/06/2011 11:04 AM, Gerd Hoffmann wrote:
> Hi folks,
>
> We'll need to figure a sane way to handle migration to older versions
> with new sections, i.e. devices which used to not save state before do now.
>
> We already have one case in tree: usb. qemu 0.14 saves state for usb-hid
> devices and the usb-hub, whereas qemu 0.13 and older don't. You can't
> migrate a vm with a usb-tablet from 0.14 to 0.13 because of that even if
> you use -M pc-0.13.

Because if you did migrate, you would actively break the guest during 
migration.  So why is this a problem?

This comes up a lot.  We shouldn't enable migration if we know the guest 
is going to break during migration.  That's a feature, not a bug.

Regards,

Anthony Liguori