void test() {
    printk("%s: nbuckets = %llu, bucket_size = %u.\n", __func__, dc->sb.nbuckets, dc->sb.bucket_size);
    printk("%s: bdev_nr_sectors = %lu.\n", __func__, bdev_sectors(dc->bdev));
    SET_KEY_OFFSET(k, bio->bi_iter.bi_sector);
    bio_sectors(bio);
}