bio_iter_len
if (bio_iter_len(bio, iter) > corrupt_bio_byte) {
corrupt_bio_byte -= bio_iter_len(bio, iter);
BUG_ON(cursor->resid < bio_iter_len(it->bio, it->iter));
BUG_ON(bytes > bio_iter_len(it->bio, it->iter));
BUG_ON(cursor->resid < bio_iter_len(it->bio, it->iter));