On 07/07/2011 02:19 AM, Gerd Hoffmann wrote:
On 07/06/11 19:13, Anthony Liguori wrote:
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?
Well, in case of usb hid devices breaking the guest isn't that a big
issue for at least some guests because they manage to reset the device
and continue nevertheless ...
In a situation like this, I think our responsibility is to let the user
know that there could be a problem, and provide the ability to the user
to force the migration.
So for instance, you could have a "(qemu) migrate_ignore_section usb"
command or something like that.
But we shouldn't enable things that may sometimes work by default.
Regards,
Anthony Liguori
I think this is a case-by-case thing. In some cases we want break
migration because critical state is missing. In other cases we might
want allow it nevertheless.
cheers,
Gerd
