sb_bread512
bh = sb_bread512(sb, part_start + HFS_MDB_BLK, mdb);
bh = sb_bread512(sb, part_start + HFS_MDB_BLK, mdb);
bh = sb_bread512(sb, sect, mdb2);
bh = sb_bread512(sb, *part_start + HFS_PMAP_BLK + ++i, pm);
bh = sb_bread512(sb, *part_start + HFS_PMAP_BLK, data);