selftests/bpf: Test autocreate behavior for struct_ops maps

Check that bpf_map__set_autocreate() can be used to disable automatic
creation for struct_ops maps.
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240306104529.6453-8-eddyz87@gmail.com

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

+// SPDX-License-Identifier: GPL-2.0
+
+#include <test_progs.h>
+#include "struct_ops_autocreate.skel.h"
+
+static void cant_load_full_object(void)
+{
+	struct struct_ops_autocreate *skel;
+	char *log = NULL;
+	int err;
+
+	skel = struct_ops_autocreate__open();
+	if (!ASSERT_OK_PTR(skel, "struct_ops_autocreate__open"))
+		return;
+
+	if (start_libbpf_log_capture())
+		goto cleanup;
+	/* The testmod_2 map BTF type (struct bpf_testmod_ops___v2) doesn't
+	 * match the BTF of the actual struct bpf_testmod_ops defined in the
+	 * kernel, so we should fail to load it if we don't disable autocreate
+	 * for that map.
+	 */
+	err = struct_ops_autocreate__load(skel);
+	log = stop_libbpf_log_capture();
+	if (!ASSERT_ERR(err, "struct_ops_autocreate__load"))
+		goto cleanup;
+
+	ASSERT_HAS_SUBSTR(log, "libbpf: struct_ops init_kern", "init_kern message");
+	ASSERT_EQ(err, -ENOTSUP, "errno should be ENOTSUP");
+
+cleanup:
+	free(log);
+	struct_ops_autocreate__destroy(skel);
+}
+
+static void can_load_partial_object(void)
+{
+	struct struct_ops_autocreate *skel;
+	struct bpf_link *link = NULL;
+	int err;
+
+	skel = struct_ops_autocreate__open();
+	if (!ASSERT_OK_PTR(skel, "struct_ops_autocreate__open_opts"))
+		return;
+
+	err = bpf_program__set_autoload(skel->progs.test_2, false);
+	if (!ASSERT_OK(err, "bpf_program__set_autoload"))
+		goto cleanup;
+
+	err = bpf_map__set_autocreate(skel->maps.testmod_2, false);
+	if (!ASSERT_OK(err, "bpf_map__set_autocreate"))
+		goto cleanup;
+
+	err = struct_ops_autocreate__load(skel);
+	if (ASSERT_OK(err, "struct_ops_autocreate__load"))
+		goto cleanup;
+
+	link = bpf_map__attach_struct_ops(skel->maps.testmod_1);
+	if (!ASSERT_OK_PTR(link, "bpf_map__attach_struct_ops"))
+		goto cleanup;
+
+	/* test_1() would be called from bpf_dummy_reg2() in bpf_testmod.c */
+	ASSERT_EQ(skel->bss->test_1_result, 42, "test_1_result");
+
+cleanup:
+	bpf_link__destroy(link);
+	struct_ops_autocreate__destroy(skel);
+}
+
+void test_struct_ops_autocreate(void)
+{
+	if (test__start_subtest("cant_load_full_object"))
+		cant_load_full_object();
+	if (test__start_subtest("can_load_partial_object"))
+		can_load_partial_object();
+}

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

+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+int test_1_result = 0;
+
+SEC("struct_ops/test_1")
+int BPF_PROG(test_1)
+{
+	test_1_result = 42;
+	return 0;
+}
+
+SEC("struct_ops/test_1")
+int BPF_PROG(test_2)
+{
+	return 0;
+}
+
+struct bpf_testmod_ops___v1 {
+	int (*test_1)(void);
+};
+
+struct bpf_testmod_ops___v2 {
+	int (*test_1)(void);
+	int (*does_not_exist)(void);
+};
+
+SEC(".struct_ops.link")
+struct bpf_testmod_ops___v1 testmod_1 = {
+	.test_1 = (void *)test_1
+};
+
+SEC(".struct_ops.link")
+struct bpf_testmod_ops___v2 testmod_2 = {
+	.test_1 = (void *)test_1,
+	.does_not_exist = (void *)test_2
+};