virtio-net: support queue reset

virtio-net and vhost-kernel implement queue reset.
Queued packets in the corresponding queue pair are flushed
or purged.

For virtio-net, userspace datapath will be disabled later in
__virtio_queue_reset(). It will set addr of vring to 0 and idx to 0.
Thus, virtio_net_receive() and virtio_net_flush_tx() will not receive
or send packets.

For vhost-net, the datapath will be disabled in vhost_net_virtqueue_reset().

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Kangjie Xu <kangjie.xu@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20221017092558.111082-13-xuanzhuo@linux.alibaba.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/net/virtio-net.c

@@ -546,6 +546,23 @@ static RxFilterInfo *virtio_net_query_rxfilter(NetClientState *nc)
     return info;
 }
 
+static void virtio_net_queue_reset(VirtIODevice *vdev, uint32_t queue_index)
+{
+    VirtIONet *n = VIRTIO_NET(vdev);
+    NetClientState *nc = qemu_get_subqueue(n->nic, vq2q(queue_index));
+
+    if (!nc->peer) {
+        return;
+    }
+
+    if (get_vhost_net(nc->peer) &&
+        nc->peer->info->type == NET_CLIENT_DRIVER_TAP) {
+        vhost_net_virtqueue_reset(vdev, nc, queue_index);
+    }
+
+    flush_or_purge_queued_packets(nc);
+}
+
 static void virtio_net_reset(VirtIODevice *vdev)
 {
     VirtIONet *n = VIRTIO_NET(vdev);
@@ -3827,6 +3844,7 @@ static void virtio_net_class_init(ObjectClass *klass, void *data)
     vdc->set_features = virtio_net_set_features;
     vdc->bad_features = virtio_net_bad_features;
     vdc->reset = virtio_net_reset;
+    vdc->queue_reset = virtio_net_queue_reset;
     vdc->set_status = virtio_net_set_status;
     vdc->guest_notifier_mask = virtio_net_guest_notifier_mask;
     vdc->guest_notifier_pending = virtio_net_guest_notifier_pending;