blkcg: add blkio_policy[] array and allow one policy per policy ID

Block cgroup policies are maintained in a linked list and,
theoretically, multiple policies sharing the same policy ID are
allowed.

This patch temporarily restricts one policy per plid and adds
blkio_policy[] array which indexes registered policy types by plid.
Both the restriction and blkio_policy[] array are transitional and
will be removed once API cleanup is complete.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 2 insertions, 0 deletions

diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 41c960b99c57..562fa55d97b1 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -19,6 +19,8 @@
 enum blkio_policy_id {
         BLKIO_POLICY_PROP = 0,          /* Proportional Bandwidth division */
         BLKIO_POLICY_THROTL,            /* Throttling */
+
+        BLKIO_NR_POLICIES,
 };
 
 /* Max limits for throttle policy */