selftests/bpf: Extend sockopt tests to use BPF_LINK_CREATE

Run all existing test cases with the attachment created via
BPF_LINK_CREATE. Next commit will add extra test cases to verify
link_create attach_type enforcement.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240426231621.2716876-3-sdf@google.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

Author: fomichev

tools/testing/selftests/bpf/prog_tests/sockopt.c

@@ -1036,9 +1036,10 @@ static int call_getsockopt(bool use_io_uring, int fd, int level, int optname,
 	return getsockopt(fd, level, optname, optval, optlen);
 }
 
-static int run_test(int cgroup_fd, struct sockopt_test *test, bool use_io_uring)
+static int run_test(int cgroup_fd, struct sockopt_test *test, bool use_io_uring,
+		    bool use_link)
 {
-	int sock_fd, err, prog_fd;
+	int sock_fd, err, prog_fd, link_fd = -1;
 	void *optval = NULL;
 	int ret = 0;
 
@@ -1051,7 +1052,12 @@ static int run_test(int cgroup_fd, struct sockopt_test *test, bool use_io_uring)
 		return -1;
 	}
 
-	err = bpf_prog_attach(prog_fd, cgroup_fd, test->attach_type, 0);
+	if (use_link) {
+		err = bpf_link_create(prog_fd, cgroup_fd, test->attach_type, NULL);
+		link_fd = err;
+	} else {
+		err = bpf_prog_attach(prog_fd, cgroup_fd, test->attach_type, 0);
+	}
 	if (err < 0) {
 		if (test->error == DENY_ATTACH)
 			goto close_prog_fd;
@@ -1142,7 +1148,12 @@ static int run_test(int cgroup_fd, struct sockopt_test *test, bool use_io_uring)
 close_sock_fd:
 	close(sock_fd);
 detach_prog:
-	bpf_prog_detach2(prog_fd, cgroup_fd, test->attach_type);
+	if (use_link) {
+		if (link_fd >= 0)
+			close(link_fd);
+	} else {
+		bpf_prog_detach2(prog_fd, cgroup_fd, test->attach_type);
+	}
 close_prog_fd:
 	close(prog_fd);
 	return ret;
@@ -1160,10 +1171,12 @@ void test_sockopt(void)
 		if (!test__start_subtest(tests[i].descr))
 			continue;
 
-		ASSERT_OK(run_test(cgroup_fd, &tests[i], false),
+		ASSERT_OK(run_test(cgroup_fd, &tests[i], false, false),
+			  tests[i].descr);
+		ASSERT_OK(run_test(cgroup_fd, &tests[i], false, true),
 			  tests[i].descr);
 		if (tests[i].io_uring_support)
-			ASSERT_OK(run_test(cgroup_fd, &tests[i], true),
+			ASSERT_OK(run_test(cgroup_fd, &tests[i], true, false),
 				  tests[i].descr);
 	}