xdp/trace: extend tracepoint in devmap with an err

Extending tracepoint xdp:xdp_devmap_xmit in devmap with an err code
allow people to easier identify the reason behind the ndo_xdp_xmit
call to a given driver is failing.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/trace/events/xdp.h

@@ -234,9 +234,9 @@ TRACE_EVENT(xdp_devmap_xmit,
 	TP_PROTO(const struct bpf_map *map, u32 map_index,
 		 int sent, int drops,
 		 const struct net_device *from_dev,
-		 const struct net_device *to_dev),
+		 const struct net_device *to_dev, int err),
 
-	TP_ARGS(map, map_index, sent, drops, from_dev, to_dev),
+	TP_ARGS(map, map_index, sent, drops, from_dev, to_dev, err),
 
 	TP_STRUCT__entry(
 		__field(int, map_id)
@@ -246,6 +246,7 @@ TRACE_EVENT(xdp_devmap_xmit,
 		__field(int, sent)
 		__field(int, from_ifindex)
 		__field(int, to_ifindex)
+		__field(int, err)
 	),
 
 	TP_fast_assign(
@@ -256,16 +257,17 @@ TRACE_EVENT(xdp_devmap_xmit,
 		__entry->sent		= sent;
 		__entry->from_ifindex	= from_dev->ifindex;
 		__entry->to_ifindex	= to_dev->ifindex;
+		__entry->err		= err;
 	),
 
 	TP_printk("ndo_xdp_xmit"
 		  " map_id=%d map_index=%d action=%s"
 		  " sent=%d drops=%d"
-		  " from_ifindex=%d to_ifindex=%d",
+		  " from_ifindex=%d to_ifindex=%d err=%d",
 		  __entry->map_id, __entry->map_index,
 		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB),
 		  __entry->sent, __entry->drops,
-		  __entry->from_ifindex, __entry->to_ifindex)
+		  __entry->from_ifindex, __entry->to_ifindex, __entry->err)
 );
 
 #endif /* _TRACE_XDP_H */

kernel/bpf/devmap.c

@@ -220,7 +220,7 @@ static int bq_xmit_all(struct bpf_dtab_netdev *obj,
 			 struct xdp_bulk_queue *bq)
 {
 	struct net_device *dev = obj->dev;
-	int sent = 0, drops = 0;
+	int sent = 0, drops = 0, err = 0;
 	int i;
 
 	if (unlikely(!bq->count))
@@ -234,6 +234,7 @@ static int bq_xmit_all(struct bpf_dtab_netdev *obj,
 
 	sent = dev->netdev_ops->ndo_xdp_xmit(dev, bq->count, bq->q);
 	if (sent < 0) {
+		err = sent;
 		sent = 0;
 		goto error;
 	}
@@ -242,7 +243,7 @@ static int bq_xmit_all(struct bpf_dtab_netdev *obj,
 	bq->count = 0;
 
 	trace_xdp_devmap_xmit(&obj->dtab->map, obj->bit,
-			      sent, drops, bq->dev_rx, dev);
+			      sent, drops, bq->dev_rx, dev, err);
 	bq->dev_rx = NULL;
 	return 0;
 error: