virtio-net: support queue_enable

Support queue_enable in vhost-kernel scenario. It can be called when
a vq reset operation has been performed and the vq is restared.

It should be noted that we can restart the vq when the vhost has
already started. When launching a new vhost device, the vhost is not
started and all vqs are not initalized until VIRTIO_PCI_COMMON_STATUS
is written. Thus, we should use vhost_started to differentiate the
two cases: vq reset and device start.

Currently it only supports vhost-kernel.

Signed-off-by: Kangjie Xu <kangjie.xu@linux.alibaba.com>
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20221017092558.111082-14-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

@@ -563,6 +563,26 @@ static void virtio_net_queue_reset(VirtIODevice *vdev, uint32_t queue_index)
     flush_or_purge_queued_packets(nc);
 }
 
+static void virtio_net_queue_enable(VirtIODevice *vdev, uint32_t queue_index)
+{
+    VirtIONet *n = VIRTIO_NET(vdev);
+    NetClientState *nc = qemu_get_subqueue(n->nic, vq2q(queue_index));
+    int r;
+
+    if (!nc->peer || !vdev->vhost_started) {
+        return;
+    }
+
+    if (get_vhost_net(nc->peer) &&
+        nc->peer->info->type == NET_CLIENT_DRIVER_TAP) {
+        r = vhost_net_virtqueue_restart(vdev, nc, queue_index);
+        if (r < 0) {
+            error_report("unable to restart vhost net virtqueue: %d, "
+                            "when resetting the queue", queue_index);
+        }
+    }
+}
+
 static void virtio_net_reset(VirtIODevice *vdev)
 {
     VirtIONet *n = VIRTIO_NET(vdev);
@@ -3845,6 +3865,7 @@ static void virtio_net_class_init(ObjectClass *klass, void *data)
     vdc->bad_features = virtio_net_bad_features;
     vdc->reset = virtio_net_reset;
     vdc->queue_reset = virtio_net_queue_reset;
+    vdc->queue_enable = virtio_net_queue_enable;
     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;