selftests/bpf: Test struct_ops bpf map auto-attach

Adding selftest to verify that struct_ops maps are auto attached by
bpf skeleton's `*__attach` function.

Signed-off-by: Mykyta Yatsenko <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

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

···
 		close(fd);
 }
 
+static void test_dctcp_autoattach_map(void)
+{
+	struct cb_opts cb_opts = {
+		.cc = "bpf_dctcp",
+	};
+	struct network_helper_opts opts = {
+		.post_socket_cb	= cc_cb,
+		.cb_opts	= &cb_opts,
+	};
+	struct bpf_dctcp *dctcp_skel;
+	struct bpf_link *link;
+
+	dctcp_skel = bpf_dctcp__open_and_load();
+	if (!ASSERT_OK_PTR(dctcp_skel, "bpf_dctcp__open_and_load"))
+		return;
+
+	bpf_map__set_autoattach(dctcp_skel->maps.dctcp, true);
+	bpf_map__set_autoattach(dctcp_skel->maps.dctcp_nouse, false);
+
+	if (!ASSERT_OK(bpf_dctcp__attach(dctcp_skel), "bpf_dctcp__attach"))
+		goto destroy;
+
+	/* struct_ops is auto-attached  */
+	link = dctcp_skel->links.dctcp;
+	if (!ASSERT_OK_PTR(link, "link"))
+		goto destroy;
+
+	do_test(&opts);
+
+destroy:
+	bpf_dctcp__destroy(dctcp_skel);
+}
+
 static char *err_str;
 static bool found;
 
···
 		test_tcp_ca_kfunc();
 	if (test__start_subtest("cc_cubic"))
 		test_cc_cubic();
+	if (test__start_subtest("dctcp_autoattach_map"))
+		test_dctcp_autoattach_map();
 }