read_cgroup_id
if (read_cgroup_id(cgrp) < 0) {
if (cgrp && read_cgroup_id(cgrp) == 0)
if (read_cgroup_id(cgrp) < 0) {
if (!cgrp->id && read_cgroup_id(cgrp) < 0) {
int read_cgroup_id(struct cgroup *cgrp);