bpf: reuseport_array memory usage

A new helper is introduced to calculate reuseport_array memory usage.

The result as follows,
- before
14: reuseport_sockarray  name count_map  flags 0x0
        key 4B  value 8B  max_entries 65536  memlock 1048576B

- after
14: reuseport_sockarray  name count_map  flags 0x0
        key 4B  value 8B  max_entries 65536  memlock 524544B
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Link: https://lore.kernel.org/r/20230305124615.12358-7-laoar.shao@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/reuseport_array.c

@@ -335,6 +335,13 @@ static int reuseport_array_get_next_key(struct bpf_map *map, void *key,
 	return 0;
 }
 
+static u64 reuseport_array_mem_usage(const struct bpf_map *map)
+{
+	struct reuseport_array *array;
+
+	return struct_size(array, ptrs, map->max_entries);
+}
+
 BTF_ID_LIST_SINGLE(reuseport_array_map_btf_ids, struct, reuseport_array)
 const struct bpf_map_ops reuseport_array_ops = {
 	.map_meta_equal = bpf_map_meta_equal,
@@ -344,5 +351,6 @@ const struct bpf_map_ops reuseport_array_ops = {
 	.map_lookup_elem = reuseport_array_lookup_elem,
 	.map_get_next_key = reuseport_array_get_next_key,
 	.map_delete_elem = reuseport_array_delete_elem,
+	.map_mem_usage = reuseport_array_mem_usage,
 	.map_btf_id = &reuseport_array_map_btf_ids[0],
 };