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

…erly

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 be
loaded, even if host kernel doesn't have type information for it.

Signed-off-by: Andrii Nakryiko <andrii@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 {