On Tue, Nov 21, 2017 at 01:16:12AM +0100, Paolo Bonzini wrote: > On 20/11/2017 21:44, Michael S. Tsirkin wrote: > > Live migrations is supposed to be migrating guest writeable state too. > > If you mean migrating RO fields like size, then > > I don't think it's a good idea to reuse SET_CONFIG for that. > > SET_CONFIG should obey exactly the virtio semantics. > > > > And I agree, it should say that slave must treat it as a write, > > and get config as a read according to virtio semantics. > > > > If someone needs to pass configuration from qemu to > > slave, let's add specific messages with precisely defined semantics. > > Fair enough, but I'd add nevertheless a 32-bit flags field to both > GET_CONFIG and SET_CONFIG, and document that the slave MUST check that > it is zero and otherwise fail. > > Paolo
We generally just use protocol feature bits for extensions. But I have no problem with reserved padding if desired which seems to be what's described here. -- MST
