selftests/bpf: attach struct_ops maps before test prog runs

In test_loader based tests to bpf_map__attach_struct_ops()
before call to bpf_prog_test_run_opts() in order to trigger
bpf_struct_ops->reg() callbacks on kernel side.
This allows to use __retval macro for struct_ops tests.

Signed-off-by: Eduard Zingerman <[e-mail]>
Signed-off-by: Martin KaFai Lau <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/testing/selftests/bpf/test_loader.c

···
 {
 	struct test_subspec *subspec = unpriv ? &spec->unpriv : &spec->priv;
 	struct bpf_program *tprog = NULL, *tprog_iter;
+	struct bpf_link *link, *links[32] = {};
 	struct test_spec *spec_iter;
 	struct cap_state caps = {};
 	struct bpf_object *tobj;
 	struct bpf_map *map;
 	int retval, err, i;
+	int links_cnt = 0;
 	bool should_load;
 
 	if (!test__start_subtest(subspec->name))
···
 		if (restore_capabilities(&caps))
 			goto tobj_cleanup;
 
+		/* Do bpf_map__attach_struct_ops() for each struct_ops map.
+		 * This should trigger bpf_struct_ops->reg callback on kernel side.
+		 */
+		bpf_object__for_each_map(map, tobj) {
+			if (!bpf_map__autocreate(map) ||
+			    bpf_map__type(map) != BPF_MAP_TYPE_STRUCT_OPS)
+				continue;
+			if (links_cnt >= ARRAY_SIZE(links)) {
+				PRINT_FAIL("too many struct_ops maps");
+				goto tobj_cleanup;
+			}
+			link = bpf_map__attach_struct_ops(map);
+			if (!link) {
+				PRINT_FAIL("bpf_map__attach_struct_ops failed for map %s: err=%d\n",
+					   bpf_map__name(map), err);
+				goto tobj_cleanup;
+			}
+			links[links_cnt++] = link;
+		}
+
 		if (tester->pre_execution_cb) {
 			err = tester->pre_execution_cb(tobj);
 			if (err) {
···
 			PRINT_FAIL("Unexpected retval: %d != %d\n", retval, subspec->retval);
 			goto tobj_cleanup;
 		}
+		/* redo bpf_map__attach_struct_ops for each test */
+		while (links_cnt > 0)
+			bpf_link__destroy(links[--links_cnt]);
 	}
 
 tobj_cleanup:
+	while (links_cnt > 0)
+		bpf_link__destroy(links[--links_cnt]);
 	bpf_object__close(tobj);
 subtest_cleanup:
 	test__end_subtest();