[PATCH bpf-next v2 2/2] selftests/bpf: open a pinned path of a struct_ops link.

[Kui-Feng Lee <thinker.li@gmail.com>]

Ensure that a pinned path of a struct_ops link can be opened to obtain a
file descriptor, which applications can then utilize to update the link.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
---
 .../selftests/bpf/bpf_testmod/bpf_testmod.c   |  6 ++
 .../bpf/prog_tests/test_struct_ops_module.c   | 56 +++++++++++++++++++
 2 files changed, 62 insertions(+)

diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
index 39ad96a18123..c4acd4ec630c 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
@@ -579,6 +579,11 @@ static void bpf_dummy_unreg(void *kdata)
 {
 }
 
+static int bpf_dummy_update(void *kdata, void *old_kdata)
+{
+	return bpf_dummy_reg(kdata);
+}
+
 static int bpf_testmod_test_1(void)
 {
 	return 0;
@@ -606,6 +611,7 @@ struct bpf_struct_ops bpf_bpf_testmod_ops = {
 	.init_member = bpf_testmod_ops_init_member,
 	.reg = bpf_dummy_reg,
 	.unreg = bpf_dummy_unreg,
+	.update = bpf_dummy_update,
 	.cfi_stubs = &__bpf_testmod_ops,
 	.name = "bpf_testmod_ops",
 	.owner = THIS_MODULE,
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 7cf2b9ddd3e1..47b965c4c3e1 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
@@ -160,6 +160,60 @@ static void test_struct_ops_incompatible(void)
 	struct_ops_module__destroy(skel);
 }
 
+/* Applications should be able to open a pinned path of a struct_ops link
+ * to get a file descriptor of the link and to update the link through the
+ * file descriptor.
+ */
+static void test_struct_ops_pinning_and_open(void)
+{
+	DECLARE_LIBBPF_OPTS(bpf_link_update_opts, opts);
+	struct struct_ops_module *skel;
+	int err, link_fd = -1, map_fd;
+	struct bpf_link *link;
+
+	/* Create and pin a struct_ops link */
+	skel = struct_ops_module__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "open_and_load"))
+		return;
+
+	link = bpf_map__attach_struct_ops(skel->maps.testmod_1);
+	if (!ASSERT_OK_PTR(link, "attach_struct_ops"))
+		goto cleanup;
+
+	err = bpf_link__pin(link, "/sys/fs/bpf/test_struct_ops_pinning");
+	if (!ASSERT_OK(err, "bpf_link__pin"))
+		goto cleanup;
+
+	/* Open the pinned path */
+	link_fd = open("/sys/fs/bpf/test_struct_ops_pinning", O_RDONLY);
+	bpf_link__unpin(link);
+	if (!ASSERT_GE(link_fd, 0, "open_pinned"))
+		goto cleanup;
+
+	skel->bss->test_1_result = 0;
+	skel->bss->test_2_result = 0;
+
+	map_fd = bpf_map__fd(skel->maps.testmod_1);
+	if (!ASSERT_GE(map_fd, 0, "map_fd"))
+		goto cleanup;
+
+	/* Update the link. test_1 and test_2 should be called again. */
+	err = bpf_link_update(link_fd, map_fd, &opts);
+	if (!ASSERT_OK(err, "bpf_link_update"))
+		goto cleanup;
+
+	/* Check if test_1 and test_2 have been called */
+	ASSERT_EQ(skel->bss->test_1_result, 0xdeadbeef,
+		  "bpf_link_update_test_1_result");
+	ASSERT_EQ(skel->bss->test_2_result, 5,
+		  "bpf_link_update_test_2_result");
+
+cleanup:
+	close(link_fd);
+	bpf_link__destroy(link);
+	struct_ops_module__destroy(skel);
+}
+
 void serial_test_struct_ops_module(void)
 {
 	if (test__start_subtest("test_struct_ops_load"))
@@ -168,5 +222,7 @@ void serial_test_struct_ops_module(void)
 		test_struct_ops_not_zeroed();
 	if (test__start_subtest("test_struct_ops_incompatible"))
 		test_struct_ops_incompatible();
+	if (test__start_subtest("test_struct_ops_pinning_and_open"))
+		test_struct_ops_pinning_and_open();
 }
 
-- 
2.34.1