selftest/bpf: Add map_in_maps with BPF_MAP_TYPE_PERF_EVENT_ARRAY values

Check that bpf_object__load() successfully creates map_in_maps
with BPF_MAP_TYPE_PERF_EVENT_ARRAY values.
These changes cover fix in the previous patch
"libbpf: Apply map_set_def_max_entries() for inner_maps on creation".

A command line output is:
- w/o fix
$ sudo ./test_maps
libbpf: map 'mim_array_pe': failed to create inner map: -22
libbpf: map 'mim_array_pe': failed to create: Invalid argument(-22)
libbpf: failed to load object './test_map_in_map.bpf.o'
Failed to load test prog

- with fix
$ sudo ./test_maps
...
test_maps: OK, 0 SKIPPED

Fixes: 646f02ffdd49 ("libbpf: Add BTF-defined map-in-map support")
Signed-off-by: Andrey Grafin <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Acked-by: Yonghong Song <[e-mail]>
Acked-by: Hou Tao <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

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

···
 	__type(value, __u32);
 } mim_hash SEC(".maps");
 
+/* The following three maps are used to test
+ * perf_event_array map can be an inner
+ * map of hash/array_of_maps.
+ */
+struct perf_event_array {
+	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
+	__type(key, __u32);
+	__type(value, __u32);
+} inner_map0 SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY_OF_MAPS);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__array(values, struct perf_event_array);
+} mim_array_pe SEC(".maps") = {
+	.values = {&inner_map0}};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH_OF_MAPS);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__array(values, struct perf_event_array);
+} mim_hash_pe SEC(".maps") = {
+	.values = {&inner_map0}};
+
 SEC("xdp")
 int xdp_mimtest0(struct xdp_md *ctx)
 {

tools/testing/selftests/bpf/test_maps.c

···
 		goto out_map_in_map;
 	}
 
-	bpf_object__load(obj);
+	err = bpf_object__load(obj);
+	if (err) {
+		printf("Failed to load test prog\n");
+		goto out_map_in_map;
+	}
 
 	map = bpf_object__find_map_by_name(obj, "mim_array");
 	if (!map) {