selftests/bpf: Improve inner_map test coverage.

Check that hash and array inner maps are properly initialized.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211201181040.23337-14-alexei.starovoitov@gmail.com

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

@@ -334,9 +334,11 @@ static inline int check_lpm_trie(void)
 	return 1;
 }
 
+#define INNER_MAX_ENTRIES 1234
+
 struct inner_map {
 	__uint(type, BPF_MAP_TYPE_ARRAY);
-	__uint(max_entries, 1);
+	__uint(max_entries, INNER_MAX_ENTRIES);
 	__type(key, __u32);
 	__type(value, __u32);
 } inner_map SEC(".maps");
@@ -348,7 +350,7 @@ struct {
 	__type(value, __u32);
 	__array(values, struct {
 		__uint(type, BPF_MAP_TYPE_ARRAY);
-		__uint(max_entries, 1);
+		__uint(max_entries, INNER_MAX_ENTRIES);
 		__type(key, __u32);
 		__type(value, __u32);
 	});
@@ -360,8 +362,13 @@ static inline int check_array_of_maps(void)
 {
 	struct bpf_array *array_of_maps = (struct bpf_array *)&m_array_of_maps;
 	struct bpf_map *map = (struct bpf_map *)&m_array_of_maps;
+	struct bpf_array *inner_map;
+	int key = 0;
 
 	VERIFY(check_default(&array_of_maps->map, map));
+	inner_map = bpf_map_lookup_elem(array_of_maps, &key);
+	VERIFY(inner_map != 0);
+	VERIFY(inner_map->map.max_entries == INNER_MAX_ENTRIES);
 
 	return 1;
 }
@@ -382,8 +389,13 @@ static inline int check_hash_of_maps(void)
 {
 	struct bpf_htab *hash_of_maps = (struct bpf_htab *)&m_hash_of_maps;
 	struct bpf_map *map = (struct bpf_map *)&m_hash_of_maps;
+	struct bpf_htab *inner_map;
+	int key = 2;
 
 	VERIFY(check_default(&hash_of_maps->map, map));
+	inner_map = bpf_map_lookup_elem(hash_of_maps, &key);
+	VERIFY(inner_map != 0);
+	VERIFY(inner_map->map.max_entries == INNER_MAX_ENTRIES);
 
 	return 1;
 }