On Wed, Jul 10, 2024 at 04:48:23PM -0300, Fabiano Rosas wrote: > Peter Xu <peterx@xxxxxxxxxx> writes: > > > On Wed, Jul 10, 2024 at 01:21:51PM -0300, Fabiano Rosas wrote: > >> It's not about trust, we simply don't support migrations other than > >> n->n+1 and (maybe) n->n-1. So QEMU from 2016 is certainly not included. > > > > Where does it come from? I thought we suppport that.. > > I'm taking that from: > > docs/devel/migration/main.rst: > "In general QEMU tries to maintain forward migration compatibility > (i.e. migrating from QEMU n->n+1) and there are users who benefit from > backward compatibility as well." > > But of course it doesn't say whether that comes with a transitive rule > allowing n->n+2 migrations. I'd say that "i.e." implies n->n+1 is not the only forward migration we would support. I _think_ we should support all forward migration as long as the machine type matches. > > > > > The same question would be: are we requesting an OpenStack cluster to > > always upgrade QEMU with +1 versions, otherwise migration will fail? > > Will an OpenStack cluster be using upstream QEMU? If not, then that's a It's an example to show what I meant! :) Nothing else. Definitely not saying that everyone should use an upstream released QEMU (but in reality, it's not a problem, I think, and I do feel like people use them, perhaps more with the stable releases). > question for the distro. In a very practical sense, we're not requesting > anything. We barely test n->n+1/n->n-1, even if we had a strong support > statement I wouldn't be confident saying migration from QEMU 2.7 -> QEMU > 9.1 should succeed. No matter what we test in CI, I don't think we should break that for >1 versions.. I hope 2.7->9.1 keeps working, otherwise I think it's legal to file a bug by anyone. For example, I randomly fetched a bug report: https://gitlab.com/qemu-project/qemu/-/issues/1937 QEMU version: 6.2 and 7.2.5 And I believe that's the common case even for upstream. If we don't do that right for upstream, it can be impossible tasks for downstream and for all of us to maintain. -- Peter Xu
