[PATCH bpf-next v2 10/15] selftests/bpf: Dump skb metadata on verification failure
From: Jakub Sitnicki <jakub@cloudflare.com>
Date: 2025-10-19 12:45:59
Also in:
bpf
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [selftests] (test runners & infrastructure), kernel selftest framework, the rest, xdp (express data path) · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Shuah Khan, Shuah Khan, Linus Torvalds, David S. Miller, Jakub Kicinski, Jesper Dangaard Brouer, John Fastabend
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> --- .../bpf/prog_tests/xdp_context_test_run.c | 28 +++++++++++++++++--- tools/testing/selftests/bpf/progs/test_xdp_meta.c | 30 +++++++++++++++++++--- 2 files changed, 51 insertions(+), 7 deletions(-)
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 93a1fbe6a4fd..a3de37942fa4 100644
--- 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 +171,25 @@ static int write_test_packet(int tap_fd) return 0; } +enum { + BPF_STDOUT = 1, + BPF_STDERR = 2, +}; + +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_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 +268,8 @@ 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 +334,8 @@ 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 +406,8 @@ 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 11288b20f56c..33480bcb8ec1 100644
--- a/tools/testing/selftests/bpf/progs/test_xdp_meta.c
+++ b/tools/testing/selftests/bpf/progs/test_xdp_meta.c@@ -18,6 +18,11 @@ * TC program then verifies if the passed metadata is correct. */ +enum { + BPF_STDOUT = 1, + BPF_STDERR = 2, +}; + bool test_pass; static const __u8 meta_want[META_SIZE] = {
@@ -27,6 +32,23 @@ 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_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_have[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 +58,7 @@ 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 +76,7 @@ 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 +114,7 @@ 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 +175,7 @@ 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;
--
2.43.0