blkcg: implement blkio_policy_type->cftypes

Add blkiop->cftypes which is added and removed together with the
policy.  This will be used to move conf/stat handling to the policies.

Signed-off-by: Tejun Heo <tj@kernel.org>

block/blk-cgroup.c

@@ -1538,6 +1538,9 @@ void blkio_policy_register(struct blkio_policy_type *blkiop)
 	list_for_each_entry(q, &all_q_list, all_q_node)
 		update_root_blkg_pd(q, blkiop->plid);
 	blkcg_bypass_end();
+
+	if (blkiop->cftypes)
+		WARN_ON(cgroup_add_cftypes(&blkio_subsys, blkiop->cftypes));
 }
 EXPORT_SYMBOL_GPL(blkio_policy_register);
 
@@ -1545,6 +1548,9 @@ void blkio_policy_unregister(struct blkio_policy_type *blkiop)
 {
 	struct request_queue *q;
 
+	if (blkiop->cftypes)
+		cgroup_rm_cftypes(&blkio_subsys, blkiop->cftypes);
+
 	blkcg_bypass_start();
 	spin_lock(&blkio_list_lock);
 

block/blk-cgroup.h

@@ -181,6 +181,7 @@ struct blkio_policy_type {
 	struct blkio_policy_ops ops;
 	enum blkio_policy_id plid;
 	size_t pdata_size;		/* policy specific private data size */
+	struct cftype *cftypes;		/* cgroup files for the policy */
 };
 
 extern int blkcg_init_queue(struct request_queue *q);