selftests/bpf: validate nulled-out struct_ops program is handled properly

Add a selftests validating that it's possible to have some struct_ops
callback set declaratively, then disable it (by setting to NULL)
programmatically. Libbpf should detect that such program should
not be loaded. Otherwise, it will unnecessarily fail the loading
when the host kernel does not have the type information.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240428030954.3918764-2-andrii@kernel.orgSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>

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

@@ -66,6 +66,7 @@ static void test_struct_ops_load(void)
 	 * auto-loading, or it will fail to load.
 	 */
 	bpf_program__set_autoload(skel->progs.test_2, false);
+	bpf_map__set_autocreate(skel->maps.testmod_zeroed, false);
 
 	err = struct_ops_module__load(skel);
 	if (!ASSERT_OK(err, "struct_ops_module_load"))
@@ -103,6 +104,10 @@ static void test_struct_ops_not_zeroed(void)
 	if (!ASSERT_OK_PTR(skel, "struct_ops_module_open"))
 		return;
 
+	skel->struct_ops.testmod_zeroed->zeroed = 0;
+	/* zeroed_op prog should be not loaded automatically now */
+	skel->struct_ops.testmod_zeroed->zeroed_op = NULL;
+
 	err = struct_ops_module__load(skel);
 	ASSERT_OK(err, "struct_ops_module_load");
 
@@ -118,6 +123,7 @@ static void test_struct_ops_not_zeroed(void)
 	 * value of "zeroed" is non-zero.
 	 */
 	skel->struct_ops.testmod_zeroed->zeroed = 0xdeadbeef;
+	skel->struct_ops.testmod_zeroed->zeroed_op = NULL;
 	err = struct_ops_module__load(skel);
 	ASSERT_ERR(err, "struct_ops_module_load_not_zeroed");
 
@@ -148,15 +154,23 @@ static void test_struct_ops_incompatible(void)
 {
 	struct struct_ops_module *skel;
 	struct bpf_link *link;
+	int err;
 
-	skel = struct_ops_module__open_and_load();
-	if (!ASSERT_OK_PTR(skel, "open_and_load"))
+	skel = struct_ops_module__open();
+	if (!ASSERT_OK_PTR(skel, "struct_ops_module_open"))
 		return;
 
+	bpf_map__set_autocreate(skel->maps.testmod_zeroed, false);
+
+	err = struct_ops_module__load(skel);
+	if (!ASSERT_OK(err, "skel_load"))
+		goto cleanup;
+
 	link = bpf_map__attach_struct_ops(skel->maps.testmod_incompatible);
 	if (ASSERT_OK_PTR(link, "attach_struct_ops"))
 		bpf_link__destroy(link);
 
+cleanup:
 	struct_ops_module__destroy(skel);
 }
 

tools/testing/selftests/bpf/progs/struct_ops_module.c

@@ -63,10 +63,17 @@ struct bpf_testmod_ops___zeroed {
 	int zeroed;
 };
 
+SEC("?struct_ops/test_3")
+int BPF_PROG(zeroed_op)
+{
+	return 1;
+}
+
 SEC(".struct_ops.link")
 struct bpf_testmod_ops___zeroed testmod_zeroed = {
 	.test_1 = (void *)test_1,
 	.test_2 = (void *)test_2_v2,
+	.zeroed_op = (void *)zeroed_op,
 };
 
 struct bpf_testmod_ops___incompatible {