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, 10 insertions, 0 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 5e50ca1f5b47..f1b08d3cba55 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -29,6 +29,8 @@ static LIST_HEAD(blkio_list);
 struct blkio_cgroup blkio_root_cgroup = { .weight = 2*BLKIO_WEIGHT_DEFAULT };
 EXPORT_SYMBOL_GPL(blkio_root_cgroup);
 
+static struct blkio_policy_type *blkio_policy[BLKIO_NR_POLICIES];
+
 static struct cgroup_subsys_state *blkiocg_create(struct cgroup_subsys *,
                                                   struct cgroup *);
 static int blkiocg_can_attach(struct cgroup_subsys *, struct cgroup *,
@@ -1694,7 +1696,11 @@ static void blkiocg_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
 void blkio_policy_register(struct blkio_policy_type *blkiop)
 {
         spin_lock(&blkio_list_lock);
+
+        BUG_ON(blkio_policy[blkiop->plid]);
+        blkio_policy[blkiop->plid] = blkiop;
         list_add_tail(&blkiop->list, &blkio_list);
+
         spin_unlock(&blkio_list_lock);
 }
 EXPORT_SYMBOL_GPL(blkio_policy_register);
@@ -1702,7 +1708,11 @@ EXPORT_SYMBOL_GPL(blkio_policy_register);
 void blkio_policy_unregister(struct blkio_policy_type *blkiop)
 {
         spin_lock(&blkio_list_lock);
+
+        BUG_ON(blkio_policy[blkiop->plid] != blkiop);
+        blkio_policy[blkiop->plid] = NULL;
         list_del_init(&blkiop->list);
+
         spin_unlock(&blkio_list_lock);
 }
 EXPORT_SYMBOL_GPL(blkio_policy_unregister);