Re: [PATCHv2 bpf-next] samples/bpf: add xdp program on egress for xdp_redirect_map

Current sample test xdp_redirect_map only count pkts on ingress. But we
can't know whether the pkts are redirected or dropped. So add a counter
on egress interface so we could know how many pkts are redirect in fact.

sample result:

$ ./xdp_redirect_map -X veth1 veth2
input: 5 output: 6
libbpf: elf: skipping unrecognized data section(9) .rodata.str1.16
libbpf: elf: skipping unrecognized data section(23) .eh_frame
libbpf: elf: skipping relo section(24) .rel.eh_frame for section(23) .eh_frame
in ifindex 5:          1 pkt/s, out ifindex 6:          1 pkt/s
in ifindex 5:          1 pkt/s, out ifindex 6:          1 pkt/s
in ifindex 5:          0 pkt/s, out ifindex 6:          0 pkt/s
in ifindex 5:         68 pkt/s, out ifindex 6:         68 pkt/s
in ifindex 5:         91 pkt/s, out ifindex 6:         91 pkt/s
in ifindex 5:         91 pkt/s, out ifindex 6:         91 pkt/s
in ifindex 5:         66 pkt/s, out ifindex 6:         66 pkt/s

Signed-off-by: Hangbin Liu <redacted>
---
v2:
a) use pkt counter instead of IP ttl modification on egress program
b) make the egress program selectable by option -X

---
  samples/bpf/xdp_redirect_map_kern.c |  26 +++--
  samples/bpf/xdp_redirect_map_user.c | 142 ++++++++++++++++++----------
  2 files changed, 113 insertions(+), 55 deletions(-)

diff --git a/samples/bpf/xdp_redirect_map_kern.c b/samples/bpf/xdp_redirect_map_kern.c
index 6489352ab7a4..fd6704a4f7e2 100644
--- a/samples/bpf/xdp_redirect_map_kern.c
+++ b/samples/bpf/xdp_redirect_map_kern.c

@@ -22,19 +22,19 @@
  struct {
  	__uint(type, BPF_MAP_TYPE_DEVMAP);
  	__uint(key_size, sizeof(int));
-	__uint(value_size, sizeof(int));
+	__uint(value_size, sizeof(struct bpf_devmap_val));
  	__uint(max_entries, 100);
  } tx_port SEC(".maps");
  
-/* Count RX packets, as XDP bpf_prog doesn't get direct TX-success
- * feedback.  Redirect TX errors can be caught via a tracepoint.
+/* Count RX/TX packets, use key 0 for rx pkt count, key 1 for tx
+ * pkt count.
   */
  struct {
  	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
  	__type(key, u32);
  	__type(value, long);
-	__uint(max_entries, 1);
-} rxcnt SEC(".maps");
+	__uint(max_entries, 2);
+} pktcnt SEC(".maps");
  
  static void swap_src_dst_mac(void *data)
  {

@@ -72,7 +72,7 @@ int xdp_redirect_map_prog(struct xdp_md *ctx)
  	vport = 0;
  
  	/* count packet in global counter */
-	value = bpf_map_lookup_elem(&rxcnt, &key);
+	value = bpf_map_lookup_elem(&pktcnt, &key);
  	if (value)
  		*value += 1;
  

@@ -82,6 +82,20 @@ int xdp_redirect_map_prog(struct xdp_md *ctx)
  	return bpf_redirect_map(&tx_port, vport, 0);
  }
  
+SEC("xdp_devmap/map_prog")
+int xdp_devmap_prog(struct xdp_md *ctx)
+{
+	long *value;
+	u32 key = 1;
+
+	/* count packet in global counter */
+	value = bpf_map_lookup_elem(&pktcnt, &key);
+	if (value)
+		*value += 1;
+
+	return XDP_PASS;
+}
+
  /* Redirect require an XDP bpf_prog loaded on the TX device */
  SEC("xdp_redirect_dummy")
  int xdp_redirect_dummy_prog(struct xdp_md *ctx)

diff --git a/samples/bpf/xdp_redirect_map_user.c b/samples/bpf/xdp_redirect_map_user.c
index 35e16dee613e..8bdec0865e1d 100644
--- a/samples/bpf/xdp_redirect_map_user.c
+++ b/samples/bpf/xdp_redirect_map_user.c

@@ -21,12 +21,13 @@
  
  static int ifindex_in;
  static int ifindex_out;
-static bool ifindex_out_xdp_dummy_attached = true;
+static bool ifindex_out_xdp_dummy_attached = false;
+static bool xdp_prog_attached = false;

  static __u32 prog_id;
  static __u32 dummy_prog_id;
  
  static __u32 xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST;
-static int rxcnt_map_fd;
+static int pktcnt_map_fd;
  
  static void int_exit(int sig)
  {

@@ -60,26 +61,46 @@ static void int_exit(int sig)
  	exit(0);
  }
  
-static void poll_stats(int interval, int ifindex)
+static void poll_stats(int interval, int if_ingress, int if_egress)
  {
  	unsigned int nr_cpus = bpf_num_possible_cpus();
-	__u64 values[nr_cpus], prev[nr_cpus];
+	__u64 values[nr_cpus], in_prev[nr_cpus], e_prev[nr_cpus];
+	__u64 sum;
+	__u32 key;
+	int i;
  
-	memset(prev, 0, sizeof(prev));
+	memset(in_prev, 0, sizeof(in_prev));
+	memset(e_prev, 0, sizeof(e_prev));
  
  	while (1) {
-		__u64 sum = 0;
-		__u32 key = 0;
-		int i;
+		sum = 0;
+		key = 0;
  
  		sleep(interval);
-		assert(bpf_map_lookup_elem(rxcnt_map_fd, &key, values) == 0);
-		for (i = 0; i < nr_cpus; i++)
-			sum += (values[i] - prev[i]);
-		if (sum)
-			printf("ifindex %i: %10llu pkt/s\n",
-			       ifindex, sum / interval);
-		memcpy(prev, values, sizeof(values));
+		if (bpf_map_lookup_elem(pktcnt_map_fd, &key, values) == 0) {