blkio: Some debugging aids for CFQ

o Some debugging aids for CFQ.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/Kconfig

@@ -90,6 +90,15 @@ config BLK_CGROUP
 	control disk bandwidth allocation (proportional time slice allocation)
 	to such task groups.
 
+config DEBUG_BLK_CGROUP
+	bool
+	depends on BLK_CGROUP
+	default n
+	---help---
+	Enable some debugging help. Currently it stores the cgroup path
+	in the blk group which can be used by cfq for tracing various
+	group related activity.
+
 endif # BLOCK
 
 config BLOCK_COMPAT