[RFC][PATCH 08/11] blkiocg async: Function to search blkcg from css ID

[Munehiro Ikeda <m-ikeda@ds.jp.nec.com>]

iotrack stores css ID of blkcg in page_cgroup.  The blkcg is what
the process which dirtied the page belongs to.
This patch introduces a function to search blkcg from the recorded
ID.

Signed-off-by: Munehiro "Muuhh" Ikeda <m-ikeda@ds.jp.nec.com>
---
 block/blk-cgroup.c |   13 +++++++++++++
 block/blk-cgroup.h |    1 +
 2 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index a680964..0756910 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -408,6 +408,19 @@ struct blkio_group *blkiocg_lookup_group(struct blkio_cgroup *blkcg, void *key)
 }
 EXPORT_SYMBOL_GPL(blkiocg_lookup_group);
 
+/* called under rcu_read_lock(). */
+struct blkio_cgroup *blkiocg_id_to_blkcg(unsigned short id)
+{
+	struct cgroup_subsys_state *css;
+
+	css = css_lookup(&blkio_subsys, id);
+	if (!css)
+		return NULL;
+
+	return container_of(css, struct blkio_cgroup, css);
+}
+EXPORT_SYMBOL_GPL(blkiocg_id_to_blkcg);
+
 #define SHOW_FUNCTION(__VAR)						\
 static u64 blkiocg_##__VAR##_read(struct cgroup *cgroup,		\
 				       struct cftype *cftype)		\
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 2b866ec..75c73bd 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -216,6 +216,7 @@ extern void blkiocg_add_blkio_group(struct blkio_cgroup *blkcg,
 extern int blkiocg_del_blkio_group(struct blkio_group *blkg);
 extern struct blkio_group *blkiocg_lookup_group(struct blkio_cgroup *blkcg,
 						void *key);
+extern struct blkio_cgroup *blkiocg_id_to_blkcg(unsigned short id);
 void blkiocg_update_timeslice_used(struct blkio_group *blkg,
 					unsigned long time);
 void blkiocg_update_dispatch_stats(struct blkio_group *blkg, uint64_t bytes,
-- 
1.6.2.5