[PATCH bpf-next 11/13] selftests/bpf: Add tracing_multi bpf prog rollback test

[Leon Hwang <leon.hwang@linux.dev>]

When rollbacking, the prepared trampolines should be reverted.

In this test, the first bpf prog will be attached with the trampoline, and
the second bpf prog won't be attached because the bpf prog has been
attached by a fentry.multi prog, that causes the rollback procedure.

Assisted-by: Codex:gpt-5.5
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 tools/lib/bpf/libbpf.c                        |  2 +-
 tools/lib/bpf/libbpf_internal.h               |  1 +
 .../selftests/bpf/prog_tests/tracing_multi.c  | 61 +++++++++++++++++++
 3 files changed, 63 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index d698a64ff800..705f50a44410 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10629,7 +10629,7 @@ int libbpf_find_vmlinux_btf_id(const char *name,
 	return libbpf_err(err);
 }
 
-static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd, int token_fd)
+int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd, int token_fd)
 {
 	struct bpf_prog_info info;
 	__u32 info_len = sizeof(info);
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 7a74abb904f8..87a3828e9b8a 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -436,6 +436,7 @@ int btf_load_into_kernel(struct btf *btf,
 			 char *log_buf, size_t log_sz, __u32 log_level,
 			 int token_fd);
 struct btf *btf_load_from_kernel(__u32 id, struct btf *base_btf, int token_fd);
+int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd, int token_fd);
 
 struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf);
 void btf_get_kernel_prefix_kind(enum bpf_attach_type attach_type,
diff --git a/tools/testing/selftests/bpf/prog_tests/tracing_multi.c b/tools/testing/selftests/bpf/prog_tests/tracing_multi.c
index 070266a864d4..a4d9934ad1dc 100644
--- a/tools/testing/selftests/bpf/prog_tests/tracing_multi.c
+++ b/tools/testing/selftests/bpf/prog_tests/tracing_multi.c
@@ -377,6 +377,65 @@ static void test_cookies_bpf_prog(void)
 	__test_link_api_bpf_prog(true);
 }
 
+static void test_rollback_bpf_prog(void)
+{
+	int token_fd, prog_fd, fd = -1, pre_fd = -1;
+	LIBBPF_OPTS(bpf_link_create_opts, lopts);
+	struct tracing_multi_bpf *skel = NULL;
+	__u32 target_ids[2], ids[2];
+	int target_fds[2], fds[2];
+	int first, second;
+
+	skel = tracing_multi_bpf__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "tracing_multi_bpf__open_and_load"))
+		return;
+
+	token_fd = bpf_object__token_fd(skel->obj);
+	token_fd = token_fd < 0 ? 0 : token_fd;
+	target_fds[0] = bpf_program__fd(skel->progs.target_1);
+	target_fds[1] = bpf_program__fd(skel->progs.target_2);
+	target_ids[0] = libbpf_find_prog_btf_id("target_1", target_fds[0], token_fd);
+	if (!ASSERT_GT(target_ids[0], 0, "target_1_btf_id"))
+		goto cleanup;
+	target_ids[1] = libbpf_find_prog_btf_id("target_2", target_fds[1], token_fd);
+	if (!ASSERT_GT(target_ids[1], 0, "target_2_btf_id"))
+		goto cleanup;
+
+	first = target_fds[0] < target_fds[1] ? 0 : 1;
+	second = 1 - first;
+	fds[0] = target_fds[first];
+	fds[1] = target_fds[second];
+	ids[0] = target_ids[first];
+	ids[1] = target_ids[second];
+
+	prog_fd = bpf_program__fd(skel->progs.test_fentry);
+	lopts.tracing_multi.ids = &ids[1];
+	lopts.tracing_multi.fds = &fds[1];
+	lopts.tracing_multi.cnt = 1;
+	pre_fd = bpf_link_create(prog_fd, 0, BPF_TRACE_FENTRY_MULTI, &lopts);
+	if (!ASSERT_GE(pre_fd, 0, "pre_attach"))
+		goto cleanup;
+
+	lopts.tracing_multi.ids = ids;
+	lopts.tracing_multi.fds = fds;
+	lopts.tracing_multi.cnt = ARRAY_SIZE(ids);
+
+	fd = bpf_link_create(prog_fd, 0, BPF_TRACE_FENTRY_MULTI, &lopts);
+	if (!ASSERT_EQ(fd, -EBUSY, "bpf_link_create"))
+		goto cleanup;
+
+	if (run_bpf_target(skel->progs.target_1, first + 1, "rollback_target"))
+		goto cleanup;
+	ASSERT_EQ(skel->bss->test_result_fentry, 0, "test_result_fentry");
+
+cleanup:
+	if (fd >= 0)
+		close(fd);
+	if (pre_fd >= 0)
+		close(pre_fd);
+	tracing_multi_bpf__destroy(skel);
+}
+
 static void test_module_skel_api(void)
 {
 	struct tracing_multi_module *skel = NULL;
@@ -1219,4 +1278,6 @@ void test_tracing_multi_test(void)
 		test_attach_api_bpf_prog_fails();
 	if (test__start_subtest("cookies_bpf_prog"))
 		test_cookies_bpf_prog();
+	if (test__start_subtest("rollback_bpf_prog"))
+		test_rollback_bpf_prog();
 }
-- 
2.55.0