On Tue, Jun 23, 2015 at 10:12:17AM +0800, Jason Wang wrote: > > > On 06/18/2015 11:16 PM, Thibaut Collet wrote: > > On Tue, Jun 16, 2015 at 10:05 AM, Jason Wang <jasow...@redhat.com> wrote: > >> > >> On 06/16/2015 03:24 PM, Thibaut Collet wrote: > >>> If my understanding is correct, on a resume operation, we have the > >>> following callback trace: > >>> 1. virtio_pci_restore function that calls all restore call back of > >>> virtio devices > >>> 2. virtnet_restore that calls try_fill_recv function for each virtual > >>> queues > >>> 3. try_fill_recv function kicks the virtual queue (through > >>> virtqueue_kick function) > >> Yes, but this happens only after pm resume not migration. Migration is > >> totally transparent to guest. > >> > > Hi Jason, > > > > After a deeper look in the migration code of QEMU a resume event is > > always sent when the live migration is finished. > > On a live migration we have the following callback trace: > > 1. The VM on the new host is set to the state RUN_STATE_INMIGRATE, the > > autostart boolean to 1 and calls the qemu_start_incoming_migration > > function (see function main of vl.c) > > ..... > > 2. call of process_incoming_migration function in > > migration/migration.c file whatever the way to do the live migration > > (tcp:, fd:, unix:, exec: ...) > > 3. call of process_incoming_migration_co function in migration/migration.c > > 4. call of vm_start function in vl.c (otherwise the migrated VM stay > > in the pause state, the autostart boolean is set to 1 by the main > > function in vl.c) > > 5. call of vm_start function that sets the VM is the RUN_STATE_RUNNING > > state. > > 6. call of qapi_event_send_resume function that ends a resume event to the > > VM > > AFAIK, this function sends resume event to qemu monitor not VM. > > > > > So when a live migration is ended: > > 1. a resume event is sent to the guest > > 2. On the reception of this resume event the virtual queue are kicked > > by the guest > > 3. Backend vhost user catches this kick and can emit a RARP to guest > > that does not support GUEST_ANNOUNCE > > > > This solution, as solution based on detection of DRIVER_OK status > > suggested by Michael, allows backend to send the RARP to legacy guest > > without involving QEMU and add ioctl to vhost-user. > > A question here is did vhost-user code pass status to the backend? If > not, how can userspace backend detect DRIVER_OK?
Sorry, I must have been unclear. vhost core calls VHOST_NET_SET_BACKEND on DRIVER_OK. Unfortunately vhost user currently translates it to VHOST_USER_NONE. As a work around, I think kicking ioeventfds once you get VHOST_NET_SET_BACKEND will work. > > > > Vhost user backend is free to implement one of this two solutions. > > > > The single drawback of these two solutions is useless RARP sending in > > some case (reboot, ...). These messages are harmless and probably not > > blocking for a "light" patch to support live migration with vhost > > user. > > > > If you agree > > > > 1. The first patch must be updated by: > > - removing the warning trace > > - setting the error trace inside a static bool flag to only > > print this once > > - removing the vhost_net_inject_rarp function (no more useful) > > 2. The second patch can be removed. Management of legacy guest for > > rarp sending can be done by modifications in backend without any > > change in QEMU. > > > > Best regards. > > > > Thibaut. > >
