Gleb Natapov wrote: > On Thu, Oct 08, 2009 at 06:42:07PM +0200, Avi Kivity wrote: > > On 10/08/2009 06:34 PM, Gleb Natapov wrote: > > >So suppose I have simple watchdog device that required to be poked every > > >second, otherwise it resets a computer. On migration we have to migrate > > >time elapsed since last poke, but if device doesn't expose it to > > >software in any way you are saying we can recreate is some other way? > > > > The time is exposed (you can measure it by poking the device and > The time yes, not its internal representation. What if one implementation > stores how much time passed and another how much time left. > One counts in wall clack another only when guest runs. etc... and > this is a device with only one write only register. In that case you can decide between calling it two different devices (which have the same guest-visible behaviour but are not interchangable), or calling them different implementations of one device - by adding a little more code to save state in a common format. (Although they may have to be different devices for qemu configuration, it's ok for them to have the same PCI IDs and for the guest not to know the difference) For your watchdog example, it's not hard to pick a saved state which works for both. ioapic will be harder to find a useful common saved state, and there might need to be an *optional hint* section (e.g. for selecting the next CPU to get an interrupt), but I think it would be worth it in this case. Being able to load a KVM image into TCG and vice versa is quite useful sometimes. E.g. I've had to do some OS installs using TCG at first, then switch to KVM later for performance. -- Jamie -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
