blkcg_activate_policy
ret = blkcg_activate_policy(bfqd->queue->disk, &blkcg_policy_bfq);
EXPORT_SYMBOL_GPL(blkcg_activate_policy);
int blkcg_activate_policy(struct gendisk *disk, const struct blkcg_policy *pol);
ret = blkcg_activate_policy(disk, &blkcg_policy_iocost);
ret = blkcg_activate_policy(disk, &blkcg_policy_iolatency);
ret = blkcg_activate_policy(disk, &blkcg_policy_throtl);