xdp: add trace event for xdp redirect

This adds a trace event for xdp redirect which may help when debugging
XDP programs that use redirect bpf commands.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -2232,7 +2232,7 @@ static struct sk_buff *ixgbe_run_xdp(struct ixgbe_adapter *adapter,
 		result = ixgbe_xmit_xdp_ring(adapter, xdp);
 		break;
 	case XDP_REDIRECT:
-		err = xdp_do_redirect(adapter->netdev, xdp);
+		err = xdp_do_redirect(adapter->netdev, xdp, xdp_prog);
 		if (!err)
 			result = IXGBE_XDP_TX;
 		else

include/linux/filter.h

@@ -713,7 +713,9 @@ struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
 				       const struct bpf_insn *patch, u32 len);
 
 int xdp_do_generic_redirect(struct net_device *dev, struct sk_buff *skb);
-int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp);
+int xdp_do_redirect(struct net_device *dev,
+		    struct xdp_buff *xdp,
+		    struct bpf_prog *prog);
 
 void bpf_warn_invalid_xdp_action(u32 act);
 void bpf_warn_invalid_xdp_redirect(u32 ifindex);

include/trace/events/xdp.h

@@ -12,7 +12,8 @@
 	FN(ABORTED)		\
 	FN(DROP)		\
 	FN(PASS)		\
-	FN(TX)
+	FN(TX)			\
+	FN(REDIRECT)
 
 #define __XDP_ACT_TP_FN(x)	\
 	TRACE_DEFINE_ENUM(XDP_##x);
@@ -48,6 +49,34 @@ TRACE_EVENT(xdp_exception,
 		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB))
 );
 
+TRACE_EVENT(xdp_redirect,
+
+	TP_PROTO(const struct net_device *from,
+		 const struct net_device *to,
+		 const struct bpf_prog *xdp, u32 act),
+
+	TP_ARGS(from, to, xdp, act),
+
+	TP_STRUCT__entry(
+		__string(name_from, from->name)
+		__string(name_to, to->name)
+		__array(u8, prog_tag, 8)
+		__field(u32, act)
+	),
+
+	TP_fast_assign(
+		BUILD_BUG_ON(sizeof(__entry->prog_tag) != sizeof(xdp->tag));
+		memcpy(__entry->prog_tag, xdp->tag, sizeof(xdp->tag));
+		__assign_str(name_from, from->name);
+		__assign_str(name_to, to->name);
+		__entry->act = act;
+	),
+
+	TP_printk("prog=%s from=%s to=%s action=%s",
+		  __print_hex_str(__entry->prog_tag, 8),
+		  __get_str(name_from), __get_str(name_to),
+		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB))
+);
 #endif /* _TRACE_XDP_H */
 
 #include <trace/define_trace.h>

net/core/filter.c

@@ -55,6 +55,7 @@
 #include <net/sock_reuseport.h>
 #include <net/busy_poll.h>
 #include <net/tcp.h>
+#include <linux/bpf_trace.h>
 
 /**
  *	sk_filter_trim_cap - run a packet through a socket filter
@@ -2422,18 +2423,22 @@ static int __bpf_tx_xdp(struct net_device *dev, struct xdp_buff *xdp)
 	return -EOPNOTSUPP;
 }
 
-int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp)
+int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
+		    struct bpf_prog *xdp_prog)
 {
 	struct redirect_info *ri = this_cpu_ptr(&redirect_info);
+	struct net_device *fwd;
 
-	dev = dev_get_by_index_rcu(dev_net(dev), ri->ifindex);
+	fwd = dev_get_by_index_rcu(dev_net(dev), ri->ifindex);
 	ri->ifindex = 0;
-	if (unlikely(!dev)) {
+	if (unlikely(!fwd)) {
 		bpf_warn_invalid_xdp_redirect(ri->ifindex);
 		return -EINVAL;
 	}
 
-	return __bpf_tx_xdp(dev, xdp);
+	trace_xdp_redirect(dev, fwd, xdp_prog, XDP_REDIRECT);
+
+	return __bpf_tx_xdp(fwd, xdp);
 }
 EXPORT_SYMBOL_GPL(xdp_do_redirect);