selftests/bpf: ringbuf_multi: Test bpf_map__set_inner_map_fd

Test map__set_inner_map_fd() interaction with map-in-map
initialization. Use hashmap of maps just to make it different to
existing array of maps.
Signed-off-by: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210408061310.95877-9-yauheni.kaliuta@redhat.com

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

@@ -44,6 +44,7 @@ void test_ringbuf_multi(void)
 	struct ring_buffer *ringbuf = NULL;
 	int err;
 	int page_size = getpagesize();
+	int proto_fd = -1;
 
 	skel = test_ringbuf_multi__open();
 	if (CHECK(!skel, "skel_open", "skeleton open failed\n"))
@@ -61,10 +62,21 @@ void test_ringbuf_multi(void)
 	if (CHECK(err != 0, "bpf_map__set_max_entries", "bpf_map__set_max_entries failed\n"))
 		goto cleanup;
 
+	proto_fd = bpf_create_map(BPF_MAP_TYPE_RINGBUF, 0, 0, page_size, 0);
+	if (CHECK(proto_fd == -1, "bpf_create_map", "bpf_create_map failed\n"))
+		goto cleanup;
+
+	err = bpf_map__set_inner_map_fd(skel->maps.ringbuf_hash, proto_fd);
+	if (CHECK(err != 0, "bpf_map__set_inner_map_fd", "bpf_map__set_inner_map_fd failed\n"))
+		goto cleanup;
+
 	err = test_ringbuf_multi__load(skel);
 	if (CHECK(err != 0, "skel_load", "skeleton load failed\n"))
 		goto cleanup;
 
+	close(proto_fd);
+	proto_fd = -1;
+
 	/* only trigger BPF program for current process */
 	skel->bss->pid = getpid();
 
@@ -114,6 +126,8 @@ void test_ringbuf_multi(void)
 	      2L, skel->bss->total);
 
 cleanup:
+	if (proto_fd >= 0)
+		close(proto_fd);
 	ring_buffer__free(ringbuf);
 	test_ringbuf_multi__destroy(skel);
 }

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

@@ -30,6 +30,17 @@ struct {
 	},
 };
 
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH_OF_MAPS);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__array(values, struct ringbuf_map);
+} ringbuf_hash SEC(".maps") = {
+	.values = {
+		[0] = &ringbuf1,
+	},
+};
+
 /* inputs */
 int pid = 0;
 int target_ring = 0;