[PATCH 6/8] cgroups: Add res counter common ancestor searching

[Frederic Weisbecker <fweisbec@gmail.com>]

Add a new API to find the common ancestor between two resource
counters. This includes the passed resource counter themselves.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Paul Menage <menage@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Aditya Kali <adityakali@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
---
 include/linux/res_counter.h |    2 ++
 kernel/res_counter.c        |   19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 0 deletions(-)

diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
index 8c421ac..354ed30 100644
--- a/include/linux/res_counter.h
+++ b/include/linux/res_counter.h
@@ -139,6 +139,8 @@ void res_counter_uncharge_until(struct res_counter *counter, struct res_counter
 				unsigned long val);
 void res_counter_uncharge(struct res_counter *counter, unsigned long val);
 
+struct res_counter *res_counter_common_ancestor(struct res_counter *l, struct res_counter *r);
+
 /**
  * res_counter_margin - calculate chargeable space of a counter
  * @cnt: the counter
diff --git a/kernel/res_counter.c b/kernel/res_counter.c
index 3b48e64..725dfa6 100644
--- a/kernel/res_counter.c
+++ b/kernel/res_counter.c
@@ -102,6 +102,25 @@ void res_counter_uncharge(struct res_counter *counter, unsigned long val)
 	res_counter_uncharge_until(counter, NULL, val);
 }
 
+struct res_counter *
+res_counter_common_ancestor(struct res_counter *r1, struct res_counter *r2)
+{
+	struct res_counter *iter;
+
+	while (r1) {
+		iter = r2;
+		while (iter) {
+			if (iter == r1)
+				return iter;
+			iter = iter->parent;
+		}
+
+		r1 = r1->parent;
+	}
+
+	return NULL;
+}
+
 static inline unsigned long long *
 res_counter_member(struct res_counter *counter, int member)
 {
-- 
1.7.5.4