selftests/bpf: Dump skb metadata on verification failure

Add diagnostic output when metadata verification fails to help with
troubleshooting test failures. Introduce a check_metadata() helper that
prints both expected and received metadata to the BPF program's stderr
stream on mismatch. The userspace test reads and dumps this stream on
failure.

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20251105-skb-meta-rx-path-v4-11-5ceb08a9b37b@cloudflare.com

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
index 93a1fbe6a4fdb7a94bbc04f6ff1887b07d0da537..db3027564261e324f3e2e9a9476faa6c38d307ff 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
@@ -171,6 +171,21 @@ static int write_test_packet(int tap_fd)
        return 0;
 }
 
+static void dump_err_stream(const struct bpf_program *prog)
+{
+       char buf[512];
+       int ret;
+
+       ret = 0;
+       do {
+               ret = bpf_prog_stream_read(bpf_program__fd(prog),
+                                          BPF_STREAM_STDERR, buf, sizeof(buf),
+                                          NULL);
+               if (ret > 0)
+                       fwrite(buf, sizeof(buf[0]), ret, stderr);
+       } while (ret > 0);
+}
+
 void test_xdp_context_veth(void)
 {
        LIBBPF_OPTS(bpf_tc_hook, tc_hook, .attach_point = BPF_TC_INGRESS);
@@ -249,7 +264,8 @@ void test_xdp_context_veth(void)
        if (!ASSERT_OK(ret, "send_test_packet"))
                goto close;
 
-       ASSERT_TRUE(skel->bss->test_pass, "test_pass");
+       if (!ASSERT_TRUE(skel->bss->test_pass, "test_pass"))
+               dump_err_stream(tc_prog);
 
 close:
        close_netns(nstoken);
@@ -314,7 +330,8 @@ static void test_tuntap(struct bpf_program *xdp_prog,
        if (!ASSERT_OK(ret, "write_test_packet"))
                goto close;
 
-       ASSERT_TRUE(*test_pass, "test_pass");
+       if (!ASSERT_TRUE(*test_pass, "test_pass"))
+               dump_err_stream(tc_prio_2_prog ? : tc_prio_1_prog);
 
 close:
        if (tap_fd >= 0)
@@ -385,7 +402,8 @@ static void test_tuntap_mirred(struct bpf_program *xdp_prog,
        if (!ASSERT_OK(ret, "write_test_packet"))
                goto close;
 
-       ASSERT_TRUE(*test_pass, "test_pass");
+       if (!ASSERT_TRUE(*test_pass, "test_pass"))
+               dump_err_stream(tc_prog);
 
 close:
        if (tap_fd >= 0)

diff --git a/tools/testing/selftests/bpf/progs/test_xdp_meta.c b/tools/testing/selftests/bpf/progs/test_xdp_meta.c
index 11288b20f56c731dfc88b88cbf8b4cc45db4f59b..3b137c4eed6cb6a2133e1b5d7d41aaadebd62b40 100644 (file)
--- a/tools/testing/selftests/bpf/progs/test_xdp_meta.c
+++ b/tools/testing/selftests/bpf/progs/test_xdp_meta.c
@@ -27,6 +27,23 @@ static const __u8 meta_want[META_SIZE] = {
        0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38,
 };
 
+static bool check_metadata(const char *file, int line, __u8 *meta_have)
+{
+       if (!__builtin_memcmp(meta_have, meta_want, META_SIZE))
+               return true;
+
+       bpf_stream_printk(BPF_STREAM_STDERR,
+                         "FAIL:%s:%d: metadata mismatch\n"
+                         "  have:\n    %pI6\n    %pI6\n"
+                         "  want:\n    %pI6\n    %pI6\n",
+                         file, line,
+                         &meta_have[0x00], &meta_have[0x10],
+                         &meta_want[0x00], &meta_want[0x10]);
+       return false;
+}
+
+#define check_metadata(meta_have) check_metadata(__FILE__, __LINE__, meta_have)
+
 SEC("tc")
 int ing_cls(struct __sk_buff *ctx)
 {
@@ -36,7 +53,7 @@ int ing_cls(struct __sk_buff *ctx)
        if (meta_have + META_SIZE > data)
                goto out;
 
-       if (__builtin_memcmp(meta_want, meta_have, META_SIZE))
+       if (!check_metadata(meta_have))
                goto out;
 
        test_pass = true;
@@ -54,7 +71,7 @@ int ing_cls_dynptr_read(struct __sk_buff *ctx)
        bpf_dynptr_from_skb_meta(ctx, 0, &meta);
        bpf_dynptr_read(meta_have, META_SIZE, &meta, 0, 0);
 
-       if (__builtin_memcmp(meta_want, meta_have, META_SIZE))
+       if (!check_metadata(meta_have))
                goto out;
 
        test_pass = true;
@@ -92,7 +109,7 @@ int ing_cls_dynptr_slice(struct __sk_buff *ctx)
        if (!meta_have)
                goto out;
 
-       if (__builtin_memcmp(meta_want, meta_have, META_SIZE))
+       if (!check_metadata(meta_have))
                goto out;
 
        test_pass = true;
@@ -153,7 +170,7 @@ int ing_cls_dynptr_offset_rd(struct __sk_buff *ctx)
                goto out;
        __builtin_memcpy(dst, src, chunk_len);
 
-       if (__builtin_memcmp(meta_want, meta_have, META_SIZE))
+       if (!check_metadata(meta_have))
                goto out;
 
        test_pass = true;