On 1/23/2018 2:33 AM, Jason Wang wrote:

On 2018年01月12日 13:58, Sridhar Samudrala wrote:

quoted

  static netdev_tx_t start_xmit(struct sk_buff *skb, struct 
net_device *dev)
  {
      struct virtnet_info *vi = netdev_priv(dev);
      int qnum = skb_get_queue_mapping(skb);
      struct send_queue *sq = &vi->sq[qnum];
+    struct net_device *vf_netdev;
      int err;
      struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
      bool kick = !skb->xmit_more;
      bool use_napi = sq->napi.weight;
  +    /* If VF is present and up then redirect packets
+     * called with rcu_read_lock_bh
+     */
+    vf_netdev = rcu_dereference_bh(vi->vf_netdev);
+    if (vf_netdev && netif_running(vf_netdev) &&
+        !netpoll_tx_running(dev) &&
+        is_unicast_ether_addr(eth_hdr(skb)->h_dest))
+        return virtnet_vf_xmit(dev, vf_netdev, skb);
+

A question here.

If I read the code correctly, all features were validated against 
virtio instead VF before transmitting. This assumes VF's feature is a 
superset of virtio, does this really work? Do we need to sanitize the 
feature before joining? (e.g at last NETIF_R_GSO_ROBUST needs to be 
removed).

Actually, virtnet_vf_xmit() calls dev_queue_xmit() after updating 
skb->dev to vf netdev.
So the features get validated against VF features and the right tx queue 
is selected
before the real transmit.

Thanks
Sridhar