virtio_net: support rx queue resize

This patch implements the resize function of the rx queues.
Based on this function, it is possible to modify the ring num of the
queue.

Includes fixup:

virtio_net: fix for stuck when change rx ring size with dev down

When dev is set to DOWN state, napi has been disabled, if we modify the
ring size at this time, we should not call napi_disable() again, which
will cause stuck.

And all operations are under the protection of rtnl_lock, so there is no
need to consider concurrency issues.

Message-Id: <20220801063902.129329-41-xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20220811080258.79398-2-xuanzhuo@linux.alibaba.com>
Reported-by: Kangjie Xu <kangjie.xu@linux.alibaba.com>
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/net/virtio_net.c

@@ -284,6 +284,8 @@ struct padded_vnet_hdr {
 	char padding[12];
 };
 
+static void virtnet_rq_free_unused_buf(struct virtqueue *vq, void *buf);
+
 static bool is_xdp_frame(void *ptr)
 {
 	return (unsigned long)ptr & VIRTIO_XDP_FLAG;
@@ -1872,6 +1874,29 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
 	return NETDEV_TX_OK;
 }
 
+static int virtnet_rx_resize(struct virtnet_info *vi,
+			     struct receive_queue *rq, u32 ring_num)
+{
+	bool running = netif_running(vi->dev);
+	int err, qindex;
+
+	qindex = rq - vi->rq;
+
+	if (running)
+		napi_disable(&rq->napi);
+
+	err = virtqueue_resize(rq->vq, ring_num, virtnet_rq_free_unused_buf);
+	if (err)
+		netdev_err(vi->dev, "resize rx fail: rx queue index: %d err: %d\n", qindex, err);
+
+	if (!try_fill_recv(vi, rq, GFP_KERNEL))
+		schedule_delayed_work(&vi->refill, 0);
+
+	if (running)
+		virtnet_napi_enable(rq->vq, &rq->napi);
+	return err;
+}
+
 /*
  * Send command via the control virtqueue and check status.  Commands
  * supported by the hypervisor, as indicated by feature bits, should