selftests/bpf: Test libbpf's ringbuf size fix up logic

Make sure we always excercise libbpf's ringbuf map size adjustment logic
by specifying non-zero size that's definitely not a page size multiple.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220509004148.1801791-10-andrii@kernel.org

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

@@ -50,18 +50,6 @@ void test_ringbuf_multi(void)
 	if (CHECK(!skel, "skel_open", "skeleton open failed\n"))
 		return;
 
-	err = bpf_map__set_max_entries(skel->maps.ringbuf1, page_size);
-	if (CHECK(err != 0, "bpf_map__set_max_entries", "bpf_map__set_max_entries failed\n"))
-		goto cleanup;
-
-	err = bpf_map__set_max_entries(skel->maps.ringbuf2, page_size);
-	if (CHECK(err != 0, "bpf_map__set_max_entries", "bpf_map__set_max_entries failed\n"))
-		goto cleanup;
-
-	err = bpf_map__set_max_entries(bpf_map__inner_map(skel->maps.ringbuf_arr), page_size);
-	if (CHECK(err != 0, "bpf_map__set_max_entries", "bpf_map__set_max_entries failed\n"))
-		goto cleanup;
-
 	proto_fd = bpf_map_create(BPF_MAP_TYPE_RINGBUF, NULL, 0, 0, page_size, NULL);
 	if (CHECK(proto_fd < 0, "bpf_map_create", "bpf_map_create failed\n"))
 		goto cleanup;

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

@@ -15,6 +15,8 @@ struct sample {
 
 struct ringbuf_map {
 	__uint(type, BPF_MAP_TYPE_RINGBUF);
+	/* libbpf will adjust to valid page size */
+	__uint(max_entries, 1000);
 } ringbuf1 SEC(".maps"),
   ringbuf2 SEC(".maps");