cgroup: implement cgroup_is_descendant()
A couple controllers want to determine whether two cgroups are in
ancestor/descendant relationship. As it's more likely that the
descendant is the primary subject of interest and there are other
operations focusing on the descendants, let's ask is_descendent rather
than is_ancestor.
Implementation is trivial as the previous patch guarantees that all
ancestors of a cgroup stay accessible as long as the cgroup is
accessible.
tj: Removed depth optimization, renamed from cgroup_is_ancestor(),
rewrote descriptions.
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 92acf86..a2b9d4b 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -439,6 +439,7 @@
int cgroup_rm_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
int cgroup_is_removed(const struct cgroup *cgrp);
+bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor);
int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);