netdev - [PATCH net] veth: Avoid drop packets when xdp

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Date:   Tue, 27 Sep 2022 16:30:13 +0800
From:   Heng Qi <hengqi@...ux.alibaba.com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: [PATCH net] veth: Avoid drop packets when xdp_redirect performs

In the current processing logic, when xdp_redirect occurs, it transmits
the xdp frame based on napi.

If napi of the peer veth is not ready, the veth will drop the packets.
This doesn't meet our expectations.

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 <hengqi@...ux.alibaba.com>
Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.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);
+		}
+
+		ret = nxmit;
 		goto out;
+	}
 
 	max_len = rcv->mtu + rcv->hard_header_len + VLAN_HLEN;
 
-- 
1.8.3.1