On Thu, Oct 15, 2015 at 01:34:10PM +0530, Amit Shah wrote: > On (Thu) 15 Oct 2015 [08:36:49], Juan Quintela wrote: > > Amit Shah <amit.s...@redhat.com> wrote: > > > On (Wed) 14 Oct 2015 [17:12:44], Michael S. Tsirkin wrote: > > >> On Wed, Oct 14, 2015 at 03:21:15PM +0200, Juan Quintela wrote: > > >> > Amit Shah <amit.s...@redhat.com> wrote: > > >> > > We were announcing the dest host's IP as our new IP a bit too soon > > >> > > -- if > > >> > > there were errors detected after this announcement was done, the > > >> > > migration is failed and the VM could continue running on the src > > >> > > host -- > > >> > > causing problems later. > > >> > > > > >> > > Move around the qemu_announce_self() call so it's done just before > > >> > > the > > >> > > VM is runnable. > > >> > > > > >> > > Signed-off-by: Amit Shah <amit.s...@redhat.com> > > >> > > > >> > Reviewed-by: Juan Quintela <quint...@redhat.com> > > >> > > > >> > applied. > > >> > > > >> > I have the same question than Dave, but also agree that this is a > > >> > movement in the right direction. > > >> > > > >> > Why it is not only needed when we do a vm_start()? > > >> > > >> It's a complex question. We don't want to do this on each > > >> vmstop/vmcont. But maybe we want to, on the 1st vmstart after > > >> qemu is started. > > > > > > Why? When a guest starts, it will issue ARP requests and everything > > > will just work. We need this announce_self only to tell the switches > > > that the MAC belonging to the guest's IP has changed.. > > > > What happens if we stop a guest on one host and we start it on a > > different host? > > So the migration code doesn't get involved? IOW, we don't call > qemu_announce_self() at all? I'd say that's a corner case: we provide > live migration capability which sets up things fine; if people choose > to use something else, they have to do their own setup.
I agree it's not a big deal. Still, if someone is inclined to always announce self on first vm start, that would also be OK. > > If the communication is started from a different place, packets will go > > to old host, until some TCP timeout happens, right? > > Yes, packets from remote will keep going to the old host. If the old > host has since closed the qemu process, it will give tcp errors to the > remote, and the remote will in time shut down its sockets. Also, when > the VM sends out any packets, switches could adjust their tables and > send remote packets to the new host. Depends on how smart the > switches are. > > > Amit
