On 2012-03-29 17:23, Anthony Liguori wrote: > On 03/27/2012 12:42 PM, Jan Kiszka wrote: >> On 2012-03-27 18:49, Anthony Liguori wrote: >>> On 03/27/2012 11:46 AM, Avi Kivity wrote: >>>> On 03/27/2012 06:39 PM, Anthony Liguori wrote: >>>>> >>>>> So, since we're approaching 1.1, we should really discuss release >>>>> criteria for 1.1 with respect to live migration. I'd prefer to avoid >>>>> surprises in this release. >>>> >>>> Agree strongly. >>>> >>>>> >>>>> My expectation is that migration works from: >>>>> >>>>> qemu-1.0 -M 1.0 => qemu-1.1 -M 1.1 >>>> >>>> Why do you expect that? Maybe you meant -M 1.0 at the end? >>> >>> Sorry, I did mean -M 1.0. >>> >>>> >>>>> qemu-1.1 -M 1.0<= qemu-1.1 -M 1.0 >>>>> >>>>> I would expect that migration works from: >>>>> >>>>> qemu-0.15 -M 0.15 => qemu-1.1 -M 0.15 >>>>> >>>> >>>> Ack. >>>> >>>>> I'm okay if this fails gracefully: >>>>> >>>>> qemu-1.1 -M 0.15<= qemu-0.15 -M 0.15 >>>> >>>> RHEL has more stringent requirements (going back to its heavily patched >>>> 0.12). I think we should have the infrastructure that allow one to add >>>> the hacks to make this work, even if we don't actually do the compat >>>> work for the release (I think it's fine for qemu to support just one >>>> version going back; and unreasonable to require it to go as far back as >>>> RHEL). >>> >>> This is reasonable to me. >> >> Here is a draft to get things written in the old format. Totally >> untested and likely borken (written in a hurry). I'll split up if it >> works fine. > > I don't really like this as a matter of principle. > > Knowingly migrating when the result may be a broken guest is a bug, it's not a > feature. > > It's one thing if we're changing formats for other reasons, but if we're > changing the format to send what's effectively broken migration state, then > that's an evil thing to do. > > Subsections are the compromise. We send a subsection when we think migration > can work and fail gracefully when it can't. Presumably there's a reason we're > not using subsections here. In this case (instance ID), it's actually not about a bug fix but a consolidation of the vmstate format. So I think it's an exception, though I don't like the code changes it requires as well. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- 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
