Re: [PATCH net] veth: Avoid drop packets when xdp_redirect performs

In this context, if napi is not ready, we convert the xdp frame to a skb,
and then use veth_xmit() to deliver it to the peer veth.

Like the following case:
Even if veth1's napi cannot be used, the packet redirected from the NIC
will be transmitted to veth1 successfully:

NIC   ->   veth0----veth1
 |                   |
(XDP)             (no XDP)

Signed-off-by: Heng Qi <redacted>
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
 drivers/net/veth.c | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 466da01..e1f5561 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c

@@ -469,8 +469,42 @@ static int veth_xdp_xmit(struct net_device *dev, int n,
 	/* The napi pointer is set if NAPI is enabled, which ensures that
 	 * xdp_ring is initialized on receive side and the peer device is up.
 	 */
-	if (!rcu_access_pointer(rq->napi))
+	if (!rcu_access_pointer(rq->napi)) {
+		for (i = 0; i < n; i++) {
+			struct xdp_frame *xdpf = frames[i];
+			struct netdev_queue *txq = NULL;
+			struct sk_buff *skb;
+			int queue_mapping;
+			u16 mac_len;
+
+			skb = xdp_build_skb_from_frame(xdpf, dev);
+			if (unlikely(!skb)) {
+				ret = nxmit;
+				goto out;
+			}
+
+			/* We need to restore ETH header, because it is pulled
+			 * in eth_type_trans.
+			 */
+			mac_len = skb->data - skb_mac_header(skb);
+			skb_push(skb, mac_len);
+
+			nxmit++;
+
+			queue_mapping = skb_get_queue_mapping(skb);
+			txq = netdev_get_tx_queue(dev, netdev_cap_txqueue(dev, queue_mapping));
+			__netif_tx_lock(txq, smp_processor_id());
+			if (unlikely(veth_xmit(skb, dev) != NETDEV_TX_OK)) {
+				__netif_tx_unlock(txq);
+				ret = nxmit;
+				goto out;
+			}
+			__netif_tx_unlock(txq);