Add tests to verify the new logs in link_create and xdp link_create,
including a log reported via extack when fail to create an xdp link.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 .../selftests/bpf/prog_tests/xdp_link.c       | 101 ++++++++++++++++++
 1 file changed, 101 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_link.c b/tools/testing/selftests/bpf/prog_tests/xdp_link.c
index e7e9f3c22edf..18c1f1039d4e 100644
--- a/tools/testing/selftests/bpf/prog_tests/xdp_link.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_link.c
@@ -150,3 +150,104 @@ void serial_test_xdp_link(void)
 	test_xdp_link__destroy(skel1);
 	test_xdp_link__destroy(skel2);
 }
+
+static void test_link_create(int prog_fd, int ifindex, enum bpf_attach_type attach_type,
+			     struct bpf_link_create_opts *opts, int exp_err, const char *msg)
+{
+	char log_buf[128] = {};
+	int fd;
+	LIBBPF_OPTS(bpf_log_opts, log_opts,
+		    .buf = log_buf,
+		    .size = sizeof(log_buf),
+		    .level = 1,
+	);
+
+	fd = bpf_link_create_log(prog_fd, ifindex, attach_type, opts, &log_opts);
+	if (!ASSERT_LT(fd, 0, "bpf_link_create_log")) {
+		close(fd);
+		return;
+	}
+
+	ASSERT_EQ(fd, exp_err, "fd");
+	ASSERT_STREQ(log_buf, msg, "log_buf");
+	ASSERT_EQ(log_opts.true_size, strlen(msg) + 1, "log_size");
+}
+
+static void test_link_create_invalid_prog_fd(void)
+{
+	const char *msg = "Invalid prog_fd.\n";
+
+	test_link_create(-1, IFINDEX_LO, BPF_XDP, NULL, -EBADF, msg);
+}
+
+static void test_link_create_invalid_prog_type(void)
+{
+	const struct bpf_insn insns[] = {
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	const char *msg = "Invalid prog type.\n";
+	int prog_fd;
+
+	prog_fd = bpf_prog_load(BPF_PROG_TYPE_LIRC_MODE2, NULL, "GPL", insns,
+				ARRAY_SIZE(insns), NULL);
+	if (!ASSERT_GE(prog_fd, 0, "bpf_prog_load"))
+		return;
+
+	test_link_create(prog_fd, 0, BPF_LIRC_MODE2, NULL, -EINVAL, msg);
+
+	close(prog_fd);
+}
+
+static void test_link_create_attach(int ifindex, enum bpf_attach_type attach_type,
+				    struct bpf_link_create_opts *opts, const char *msg)
+{
+	struct test_xdp_link *skel;
+
+	skel = test_xdp_link__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "test_xdp_link__open_and_load"))
+		return;
+
+	test_link_create(bpf_program__fd(skel->progs.xdp_handler), ifindex, attach_type, opts,
+			 -EINVAL, msg);
+
+	test_xdp_link__destroy(skel);
+}
+
+static void test_link_create_invalid_attach_type(void)
+{
+	const char *msg = "Invalid attach_type.\n";
+
+	test_link_create_attach(IFINDEX_LO, BPF_CGROUP_INET_INGRESS, NULL, msg);
+}
+
+static void test_link_create_xdp_invalid_target_ifindex(void)
+{
+	const char *msg = "Invalid target_ifindex.\n";
+
+	test_link_create_attach(0, BPF_XDP, NULL, msg);
+}
+
+static void test_link_create_xdp_extack(void)
+{
+	const char *msg = "Invalid XDP flags for BPF link attachment\n";
+	LIBBPF_OPTS(bpf_link_create_opts, opts,
+		    .flags = XDP_FLAGS_REPLACE,
+	);
+
+	test_link_create_attach(IFINDEX_LO, BPF_XDP, &opts, msg);
+}
+
+void test_link_create_log(void)
+{
+	if (test__start_subtest("invalid_prog_fd"))
+		test_link_create_invalid_prog_fd();
+	if (test__start_subtest("invalid_prog_type"))
+		test_link_create_invalid_prog_type();
+	if (test__start_subtest("invalid_attach_type"))
+		test_link_create_invalid_attach_type();
+	if (test__start_subtest("xdp/invalid_target_ifindex"))
+		test_link_create_xdp_invalid_target_ifindex();
+	if (test__start_subtest("xdp/extack"))
+		test_link_create_xdp_extack();
+}
-- 
2.55.0