[PATCH RFC net-next 2/4] xdp: return status from generic_xdp_tx()

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

Once veth will start to use __do_xdp_generic(), this will be helpful for
correct stats values being incremented - otherwise we would not have a
knowledge whether XDP_TX succeeded or not. With this being implemented we
will only bump xdp_tx stat when actual transmission happened.

Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
---
 include/linux/netdevice.h |  2 +-
 kernel/bpf/devmap.c       |  2 +-
 net/core/dev.c            | 11 +++++++++--
 net/core/filter.c         |  2 +-
 4 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 47417b2d48a4..473b18b0bb63 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -4255,7 +4255,7 @@ static inline void dev_consume_skb_any(struct sk_buff *skb)
 
 u32 bpf_prog_run_generic_xdp(struct sk_buff *skb, struct xdp_buff *xdp,
 			     const struct bpf_prog *xdp_prog);
-void generic_xdp_tx(struct sk_buff *skb, const struct bpf_prog *xdp_prog);
+int generic_xdp_tx(struct sk_buff *skb, const struct bpf_prog *xdp_prog);
 int do_xdp_generic(const struct bpf_prog *xdp_prog, struct sk_buff **pskb);
 int netif_rx(struct sk_buff *skb);
 int __netif_rx(struct sk_buff *skb);
diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index 3d619d01088e..b7a4a0266345 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -714,7 +714,7 @@ int dev_map_generic_redirect(struct bpf_dtab_netdev *dst, struct sk_buff *skb,
 		return 0;
 
 	skb->dev = dst->dev;
-	generic_xdp_tx(skb, xdp_prog);
+	(void)generic_xdp_tx(skb, xdp_prog);
 
 	return 0;
 }
diff --git a/net/core/dev.c b/net/core/dev.c
index 6cc2a5bed20f..09012cdea376 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5628,11 +5628,12 @@ static u32 netif_receive_generic_xdp(struct sk_buff **pskb,
  * and DDOS attacks will be more effective. In-driver-XDP use dedicated TX
  * queues, so they do not have this starvation issue.
  */
-void generic_xdp_tx(struct sk_buff *skb, const struct bpf_prog *xdp_prog)
+int generic_xdp_tx(struct sk_buff *skb, const struct bpf_prog *xdp_prog)
 {
 	struct net_device *dev = skb->dev;
 	struct netdev_queue *txq;
 	bool free_skb = true;
+	int err = -ENETDOWN;
 	int cpu, rc;
 
 	txq = netdev_core_pick_tx(dev, skb, NULL);
@@ -5640,8 +5641,12 @@ void generic_xdp_tx(struct sk_buff *skb, const struct bpf_prog *xdp_prog)
 	HARD_TX_LOCK(dev, txq, cpu);
 	if (!netif_xmit_frozen_or_drv_stopped(txq)) {
 		rc = netdev_start_xmit(skb, dev, txq, 0);
-		if (dev_xmit_complete(rc))
+		if (dev_xmit_complete(rc)) {
 			free_skb = false;
+			err = 0;
+		} else {
+			err = -EBUSY;
+		}
 	}
 	HARD_TX_UNLOCK(dev, txq);
 	if (free_skb) {
@@ -5649,6 +5654,8 @@ void generic_xdp_tx(struct sk_buff *skb, const struct bpf_prog *xdp_prog)
 		dev_core_stats_tx_dropped_inc(dev);
 		kfree_skb(skb);
 	}
+
+	return err;
 }
 
 static DEFINE_STATIC_KEY_FALSE(generic_xdp_needed_key);
diff --git a/net/core/filter.c b/net/core/filter.c
index bf9c37b27646..d6d14e0a1e35 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4619,7 +4619,7 @@ int xdp_do_generic_redirect(struct net_device *dev, struct sk_buff *skb,
 
 		skb->dev = fwd;
 		_trace_xdp_redirect(dev, xdp_prog, ri->tgt_index);
-		generic_xdp_tx(skb, xdp_prog);
+		(void)generic_xdp_tx(skb, xdp_prog);
 		return 0;
 	}
 
-- 
2.43.0