vhost-net: vhost-kernel: introduce vhost_net_virtqueue_reset()

Introduce vhost_virtqueue_reset(), which can reset the specific
virtqueue in the device. Then it will unmap vrings and the desc
of the virtqueue.

Here we do not reuse the vhost_net_stop_one() or vhost_dev_stop(),
because they work at queue pair level. We do not use
vhost_virtqueue_stop() because it may stop the device in the
backend.

This patch only considers the case of vhost-kernel, when
NetClientDriver is NET_CLIENT_DRIVER_TAP.

Furthermore, we do not need net->nc->info->poll() because
it enables userspace datapath and we want to stop all
datapaths for this reset virtqueue here.

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: <20221017092558.111082-10-xuanzhuo@linux.alibaba.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/net/vhost_net-stub.c

@@ -101,3 +101,9 @@ int vhost_net_set_mtu(struct vhost_net *net, uint16_t mtu)
 {
     return 0;
 }
+
+void vhost_net_virtqueue_reset(VirtIODevice *vdev, NetClientState *nc,
+                               int vq_index)
+{
+
+}

hw/net/vhost_net.c

@@ -531,3 +531,28 @@ int vhost_net_set_mtu(struct vhost_net *net, uint16_t mtu)
 
     return vhost_ops->vhost_net_set_mtu(&net->dev, mtu);
 }
+
+void vhost_net_virtqueue_reset(VirtIODevice *vdev, NetClientState *nc,
+                               int vq_index)
+{
+    VHostNetState *net = get_vhost_net(nc->peer);
+    const VhostOps *vhost_ops = net->dev.vhost_ops;
+    struct vhost_vring_file file = { .fd = -1 };
+    int idx;
+
+    /* should only be called after backend is connected */
+    assert(vhost_ops);
+
+    idx = vhost_ops->vhost_get_vq_index(&net->dev, vq_index);
+
+    if (net->nc->info->type == NET_CLIENT_DRIVER_TAP) {
+        file.index = idx;
+        int r = vhost_net_set_backend(&net->dev, &file);
+        assert(r >= 0);
+    }
+
+    vhost_virtqueue_stop(&net->dev,
+                         vdev,
+                         net->dev.vqs + idx,
+                         net->dev.vq_index + idx);
+}

include/net/vhost_net.h

@@ -48,4 +48,6 @@ uint64_t vhost_net_get_acked_features(VHostNetState *net);
 
 int vhost_net_set_mtu(struct vhost_net *net, uint16_t mtu);
 
+void vhost_net_virtqueue_reset(VirtIODevice *vdev, NetClientState *nc,
+                               int vq_index);
 #endif