bpf: local_storage memory usage

A new helper is introduced to calculate local_storage map memory usage.
Currently the dynamically allocated elements are not counted, since it
will take runtime overhead in the element update or delete path. So
let's put it aside currently, and implement it in the future if the user
really needs it.
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Link: https://lore.kernel.org/r/20230305124615.12358-14-laoar.shao@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/local_storage.c

@@ -446,6 +446,12 @@ static void cgroup_storage_seq_show_elem(struct bpf_map *map, void *key,
 	rcu_read_unlock();
 }
 
+static u64 cgroup_storage_map_usage(const struct bpf_map *map)
+{
+	/* Currently the dynamically allocated elements are not counted. */
+	return sizeof(struct bpf_cgroup_storage_map);
+}
+
 BTF_ID_LIST_SINGLE(cgroup_storage_map_btf_ids, struct,
 		   bpf_cgroup_storage_map)
 const struct bpf_map_ops cgroup_storage_map_ops = {
@@ -457,6 +463,7 @@ const struct bpf_map_ops cgroup_storage_map_ops = {
 	.map_delete_elem = cgroup_storage_delete_elem,
 	.map_check_btf = cgroup_storage_check_btf,
 	.map_seq_show_elem = cgroup_storage_seq_show_elem,
+	.map_mem_usage = cgroup_storage_map_usage,
 	.map_btf_id = &cgroup_storage_map_btf_ids[0],
 };