[PATCH bpf 2/2] selftests/bpf: Test private struct_ops bitfield rejection

[Mingpei CAO <caomingpei@gmail.com>]

Add an optional all-zero private bitfield to the struct_ops test. Verify
that libbpf returns -ENOTSUP and emits the bitfield diagnostic.

Keep the existing all-zero scalar test as the compatibility control.

Assisted-by: LLM
Signed-off-by: Mingpei CAO <caomingpei@gmail.com>
---
 .../bpf/prog_tests/test_struct_ops_module.c   | 31 +++++++++++++++++++
 .../selftests/bpf/progs/struct_ops_module.c   |  7 +++++
 2 files changed, 38 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c
index 75a0dea511b3f..517e5abe67c0c 100644
--- a/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c
+++ b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c
@@ -150,6 +150,35 @@ static void test_struct_ops_not_zeroed(void)
 	struct_ops_module__destroy(skel);
 }
 
+static void test_struct_ops_private_bitfield(void)
+{
+	struct struct_ops_module *skel;
+	char *log = NULL;
+	int err;
+
+	skel = struct_ops_module__open();
+	if (!ASSERT_OK_PTR(skel, "struct_ops_module_open_private_bitfield"))
+		return;
+
+	bpf_map__set_autocreate(skel->maps.testmod_zeroed, false);
+	err = bpf_map__set_autocreate(skel->maps.testmod_private_bitfield, true);
+	if (!ASSERT_OK(err, "enable_private_bitfield_map"))
+		goto cleanup;
+
+	if (start_libbpf_log_capture())
+		goto cleanup;
+	err = struct_ops_module__load(skel);
+	log = stop_libbpf_log_capture();
+	ASSERT_EQ(err, -ENOTSUP, "struct_ops_module_load_private_bitfield");
+	ASSERT_HAS_SUBSTR(log,
+			  "bitfield private_bitfield is not supported",
+			  "private_bitfield_rejection_log");
+
+cleanup:
+	free(log);
+	struct_ops_module__destroy(skel);
+}
+
 /* The signature of an implementation might not match the signature of the
  * function pointer prototype defined in the BPF program. This mismatch
  * should be allowed as long as the behavior of the operator program
@@ -304,6 +333,8 @@ void serial_test_struct_ops_module(void)
 		test_struct_ops_load();
 	if (test__start_subtest("struct_ops_not_zeroed"))
 		test_struct_ops_not_zeroed();
+	if (test__start_subtest("struct_ops_private_bitfield"))
+		test_struct_ops_private_bitfield();
 	if (test__start_subtest("struct_ops_incompatible"))
 		test_struct_ops_incompatible();
 	if (test__start_subtest("struct_ops_null_out_cb"))
diff --git a/tools/testing/selftests/bpf/progs/struct_ops_module.c b/tools/testing/selftests/bpf/progs/struct_ops_module.c
index 71c420c3a5a6c..423caf78f4207 100644
--- a/tools/testing/selftests/bpf/progs/struct_ops_module.c
+++ b/tools/testing/selftests/bpf/progs/struct_ops_module.c
@@ -76,6 +76,13 @@ struct bpf_testmod_ops___zeroed testmod_zeroed = {
 	.zeroed_op = (void *)zeroed_op,
 };
 
+struct bpf_testmod_ops___private_bitfield {
+	unsigned int private_bitfield:31;
+};
+
+SEC("?.struct_ops.link")
+struct bpf_testmod_ops___private_bitfield testmod_private_bitfield;
+
 struct bpf_testmod_ops___incompatible {
 	int (*test_1)(void);
 	void (*test_2)(int *a);
-- 
2.43.0