[RFC PATCH bpf-next v2 2/2] selftests/bpf: add tests for selective kmod BTF loading

Add test cases to verify the new ".kmod_btfs" section logic in libbpf.
The added test cases cover three main scenarios:

  - Valid module: targeting an existing kernel module BTF to ensure
    successful loading.
  - Non-existent module: targeting a fake or missing module, verifying
    that the process results in an expected failure.
  - Duplicates and unneeded: providing a mix of repeated and extra
    module names to ensure the parsing logic remains robust.

Signed-off-by: Fuyu Zhao <[email protected]>
---
 .../selftests/bpf/prog_tests/kmod_btfs.c      | 52 +++++++++++++++++++
 tools/testing/selftests/bpf/progs/kmod_btfs.c | 14 +++++
 .../selftests/bpf/progs/kmod_btfs_mix.c       | 15 ++++++
 .../selftests/bpf/progs/kmod_btfs_nonexist.c  | 18 +++++++
 4 files changed, 99 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/kmod_btfs.c
 create mode 100644 tools/testing/selftests/bpf/progs/kmod_btfs.c
 create mode 100644 tools/testing/selftests/bpf/progs/kmod_btfs_mix.c
 create mode 100644 tools/testing/selftests/bpf/progs/kmod_btfs_nonexist.c

diff --git a/tools/testing/selftests/bpf/prog_tests/kmod_btfs.c b/tools/testing/selftests/bpf/prog_tests/kmod_btfs.c
new file mode 100644
index 000000000000..d875fcce6681
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/kmod_btfs.c
@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include "kmod_btfs.skel.h"
+#include "kmod_btfs_nonexist.skel.h"
+#include "kmod_btfs_mix.skel.h"
+
+static void kmod_btfs_pass(void)
+{
+	struct kmod_btfs *kmod_btfs_skel;
+
+	kmod_btfs_skel = kmod_btfs__open_and_load();
+	if (!ASSERT_OK_PTR(kmod_btfs_skel, "kmod_btfs__open_and_load"))
+		return;
+
+	kmod_btfs__destroy(kmod_btfs_skel);
+}
+
+static void kmod_btfs_nonexist(void)
+{
+	struct kmod_btfs_nonexist *kmod_btfs_nonexist_skel;
+
+	kmod_btfs_nonexist_skel = kmod_btfs_nonexist__open_and_load();
+	ASSERT_NULL(kmod_btfs_nonexist_skel, "kmod_btfs_nonexist__open_and_load");
+}
+
+static void kmod_btfs_mix(void)
+{
+	struct kmod_btfs_mix *kmod_btfs_mix_skel;
+
+	kmod_btfs_mix_skel = kmod_btfs_mix__open_and_load();
+	if (!ASSERT_OK_PTR(kmod_btfs_mix_skel, "kmod_btfs_mix__open_and_load"))
+		return;
+
+	kmod_btfs_mix__destroy(kmod_btfs_mix_skel);
+}
+
+void test_kmod_btfs(void)
+{
+	if (!env.has_testmod) {
+		test__skip();
+		return;
+	}
+
+	if (test__start_subtest("kmod_btfs_pass"))
+		kmod_btfs_pass();
+
+	if (test__start_subtest("kmod_btfs_nonexist"))
+		kmod_btfs_nonexist();
+
+	if (test__start_subtest("kmod_btfs_mix"))
+		kmod_btfs_mix();
+}
diff --git a/tools/testing/selftests/bpf/progs/kmod_btfs.c b/tools/testing/selftests/bpf/progs/kmod_btfs.c
new file mode 100644
index 000000000000..8b986bc2e9ff
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/kmod_btfs.c
@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+
+SEC("fexit/bpf_testmod_loop_test")
+int test_kmod_btfs(void *ctx)
+{
+	return 0;
+}
+
+DEFINE_KMOD_BTFS(_needed_kmods) = { "bpf_testmod" };
+
+char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/kmod_btfs_mix.c b/tools/testing/selftests/bpf/progs/kmod_btfs_mix.c
new file mode 100644
index 000000000000..f445cf56ab16
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/kmod_btfs_mix.c
@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+
+SEC("fexit/bpf_testmod_loop_test")
+int test_kmod_btfs_mix(void *ctx)
+{
+	return 0;
+}
+
+/* mix of duplicated and unneeded modules */
+DEFINE_KMOD_BTFS(_needed_kmods) = { "bpf_testmod", "bpf_testmod", "bpf_test_no_cfi" };
+
+char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/kmod_btfs_nonexist.c b/tools/testing/selftests/bpf/progs/kmod_btfs_nonexist.c
new file mode 100644
index 000000000000..1638361e5732
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/kmod_btfs_nonexist.c
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+
+SEC("fexit/bpf_testmod_loop_test")
+int test_kmod_btfs_nonexist(void *ctx)
+{
+	return 0;
+}
+
+/*
+ * This should fail to load, because .kmod_btfs does not contain
+ * the needed module 'bpf_testmod'.
+ */
+DEFINE_KMOD_BTFS(_needed_kmods) = { "module_nonexist" };
+
+char _license[] SEC("license") = "GPL";
-- 
2.34.1