blkg_conf_prep
ret = blkg_conf_prep(blkcg, &blkcg_policy_bfq, &ctx);
EXPORT_SYMBOL_GPL(blkg_conf_prep);
int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
ret = blkg_conf_prep(blkcg, &blkcg_policy_iocost, &ctx);
ret = blkg_conf_prep(blkcg, &blkcg_policy_iolatency, &ctx);
ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, &ctx);
ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, &ctx);