lba_read
d->lba_read = lba_read;
(*d->lba_read)(d, 0, 1, iobuf);
(*d->lba_read)(d, first + LABELSECTOR, 1, iobuf);
(*d->lba_read)(d, rf_offset + LABELSECTOR, 1, iobuf);
(*d->lba_read)(d, bno, size / 512, p);
static int lba_read(struct disk *, int64_t, int, void *);
int (*lba_read)(struct disk *, int64_t, int, void *);