samples/bpf: xdp_monitor also record xdp_exception tracepoint

Also monitor the tracepoint xdp_exception.  This tracepoint is usually
invoked by the drivers.  Programs themselves can activate this by
returning XDP_ABORTED, which will drop the packet but also trigger the
tracepoint.  This is useful for distinguishing intentional (XDP_DROP)
vs. ebpf-program error cases that cased a drop (XDP_ABORTED).

Drivers also use this tracepoint for reporting on XDP actions that are
unknown to the specific driver.  This can help the user to detect if a
driver e.g. doesn't implement XDP_REDIRECT yet.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 37 insertions, 1 deletions

diff --git a/samples/bpf/xdp_monitor_kern.c b/samples/bpf/xdp_monitor_kern.c
index cc7e19d2ad76..2fe2f761a0d0 100644
--- a/samples/bpf/xdp_monitor_kern.c
+++ b/samples/bpf/xdp_monitor_kern.c
@@ -13,6 +13,14 @@ struct bpf_map_def SEC("maps") redirect_err_cnt = {
 	/* TODO: have entries for all possible errno's */
 };
 
+#define XDP_UNKNOWN	XDP_REDIRECT + 1
+struct bpf_map_def SEC("maps") exception_cnt = {
+	.type		= BPF_MAP_TYPE_PERCPU_ARRAY,
+	.key_size	= sizeof(u32),
+	.value_size	= sizeof(u64),
+	.max_entries	= XDP_UNKNOWN + 1,
+};
+
 /* Tracepoint format: /sys/kernel/debug/tracing/events/xdp/xdp_redirect/format
  * Code in:                kernel/include/trace/events/xdp.h
  */
@@ -44,7 +52,7 @@ int xdp_redirect_collect_stat(struct xdp_redirect_ctx *ctx)
 
 	cnt  = bpf_map_lookup_elem(&redirect_err_cnt, &key);
 	if (!cnt)
-		return 0;
+		return 1;
 	*cnt += 1;
 
 	return 0; /* Indicate event was filtered (no further processing)*/
@@ -82,3 +90,31 @@ int trace_xdp_redirect_map(struct xdp_redirect_ctx *ctx)
 {
 	return xdp_redirect_collect_stat(ctx);
 }
+
+/* Tracepoint format: /sys/kernel/debug/tracing/events/xdp/xdp_exception/format
+ * Code in:                kernel/include/trace/events/xdp.h
+ */
+struct xdp_exception_ctx {
+	u64 __pad;	// First 8 bytes are not accessible by bpf code
+	int prog_id;	//	offset:8;  size:4; signed:1;
+	u32 act;	//	offset:12; size:4; signed:0;
+	int ifindex;	//	offset:16; size:4; signed:1;
+};
+
+SEC("tracepoint/xdp/xdp_exception")
+int trace_xdp_exception(struct xdp_exception_ctx *ctx)
+{
+	u64 *cnt;;
+	u32 key;
+
+	key = ctx->act;
+	if (key > XDP_REDIRECT)
+		key = XDP_UNKNOWN;
+
+	cnt = bpf_map_lookup_elem(&exception_cnt, &key);
+	if (!cnt)
+		return 1;
+	*cnt += 1;
+
+	return 0;
+}