From: Li Zefan <lizefan@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
include/linux/cgroup.h | 1 +
kernel/cgroup.c | 20 ++++++++++++++++++++
2 files changed, 21 insertions(+)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 515927e..45aee0f 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -439,6 +439,7 @@ int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
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);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index d7dfa64..678a22c 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -276,6 +276,26 @@ inline int cgroup_is_removed(const struct cgroup *cgrp)
return test_bit(CGRP_REMOVED, &cgrp->flags);
}
+/**
+ * cgroup_is_descendant - test ancestry
+ * @cgrp: the cgroup to be tested
+ * @ancestor: possible ancestor of @cgrp
+ *
+ * Test whether @cgrp is a descendant of @ancestor. It also returns %true
+ * if @cgrp == @ancestor. This function is safe to call as long as @cgrp
+ * and @ancestor are accessible.
+ */
+bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor)
+{
+ while (cgrp) {
+ if (cgrp == ancestor)
+ return true;
+ cgrp = cgrp->parent;
+ }
+ return false;
+}
+EXPORT_SYMBOL_GPL(cgroup_is_descendant);
+
/* bits in struct cgroupfs_root flags field */
enum {
ROOT_NOPREFIX, /* mounted subsystems have no named prefix */
--
1.8.1.4
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