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Message-Id: <20251019-skb-meta-rx-path-v2-10-f9a58f3eb6d6@cloudflare.com>
Date: Sun, 19 Oct 2025 14:45:34 +0200
From: Jakub Sitnicki <jakub@...udflare.com>
To: bpf@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Daniel Borkmann <daniel@...earbox.net>,
John Fastabend <john.fastabend@...il.com>,
Stanislav Fomichev <sdf@...ichev.me>, Alexei Starovoitov <ast@...nel.org>,
Andrii Nakryiko <andrii@...nel.org>, Eduard Zingerman <eddyz87@...il.com>,
Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>,
KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>, Arthur Fabre <arthur@...hurfabre.com>,
netdev@...r.kernel.org, kernel-team@...udflare.com
Subject: [PATCH bpf-next v2 10/15] 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@...udflare.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
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