[Qemu-devel] vhost_user and VIRTIO_NET_F_GUEST_ANNOUNCE

[Pavel Fedin]

 Hello!

 I am currently testing this patchset 
(http://dpdk.org/ml/archives/dev/2015-December/029193.html), and I've got a 
question.
 After the migration the guest has to announce its MAC address for the network 
to work. Guest OS can do it itself, or qemu can send
VHOST_USER_SEND_RARP to the vhost device. The problem arises because:
 1. DPDK currently does not implement VHOST_USER_SEND_RARP
 2. DPDK does not announce VIRTIO_NET_F_GUEST_ANNOUNCE feature, therefore qemu 
does not propagate it to the guest, and the quest
does not activate own announcing.

 The question is: why do we expect vhost-user to return 
VIRTIO_NET_F_GUEST_ANNOUNCE ? Does the device really need to have some
explicit support for it? As far as I can understand, there's no special 
handling to be done, the guest just sends GARP and that's
it. So why doesn't qemu turn on this feature by itself?

Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia