Re: [Qemu-devel] [PATCH v2] net: Add support of VIRTIO_NET_F_GUEST_ANNOUNCE for vhost-net/vhost-user

[Jason Wang <jasowang@redhat.com>]

On 06/08/2015 06:01 PM, Thibaut Collet wrote:
> Hi,
>
> I agree that my patch is OK only for recent drivers. To have a simple
> patch with only few modifications I do not implement a solution for
> old driver but I can be done later.
>

This makes sense.

> For legacy guest without VIRTIO_NET_F_GUEST_ANNOUNCE the problem is
> more complex. The RARP must be sent by the vhost client/backend. This
> component is outside QEMU (the reference implementation is
> snabbswitch: http://www.virtualopensystems.com/en/solutions/guides/snabbswitch-qemu/).
> To do that:
> - a receive function must be defined for the vhost user.
> - a message must be added between QEMU and vapp. This message will be
> sent only for old guest driver to avoid GARP duplication.
> - the added self_announce_disabled must be removed (decision to send
> or not the RARP is done later by the backend and not by the generic
> migration method)
>
> Do you agree with this solution ?
>
>

Sounds ok.

> Regards.
>
> On Mon, Jun 8, 2015 at 11:14 AM, Jason Wang <jasowang@redhat.com
> <mailto:jasowang@redhat.com>> wrote:
>
>
>
>     On 06/08/2015 04:21 PM, Thibaut Collet wrote:
>     > Hi,
>     >
>     > My understanding of gratuitous packet with virtio for any backend
>     > (vhost user or other):
>     > - When the VM is loaded (first start or migration) the virtio net
>     > interfaces are loaded ( virtio_net_load_device function in
>     > hw/net/virtio-net.c)
>     > - If the guest has the VIRTIO_NET_F_GUEST_ANNOUNCE capability,
>     request
>     > to send gratuitous packet is done.
>     >
>     > 1. To enable gratuitous packet through this mechanism I have
>     > added VIRTIO_NET_F_GUEST_ANNOUNCE capability to
>     hw/net/vhost_net.c. So
>     > host and guest can negotiate this feature when vhost-user is used.
>     >
>     > 2. self announce occurs in case of live migration. During a live
>     > migration a GARP is sent to all net backend through a queue
>     dedicated
>     > to the net backend.
>     >    But for vhost-user:
>     >        - this operation is not possible (vhost-user has no queue)
>     >        - it is already done with the previous mechanism.
>     >    Rather to define a queue to vhost user and notify twice the guest
>     > to send gratuitous packet I have disable GARP from self announce and
>     > use only the first mechanism for that.
>     >
>     > I have tested my modifications with guest that supports
>     > VIRTIO_NET_F_GUEST_ANNOUNCE and vhost-user on the host. After a live
>     > migration I have the GARP from the guest.
>
>     Yes, your patch works well for recent drivers. But the problem is
>     legacy
>     guest/driver without VIRTIO_NET_F_GUEST_ANNOUNCE. In this case there
>     will be no GARP sent after migration.
>
>     Thanks
>
>