SPACEMAP_OFF
(part_bmp_bytes + SPACEMAP_OFF + secsize - 1) /
freemap = (char *)cp + SPACEMAP_OFF;
cp = (uint8_t *)sbp + SPACEMAP_OFF;
part_bmp_sectors = (part_bmp_bytes + SPACEMAP_OFF + sectorsize - 1) /
(part_bmp_bytes + SPACEMAP_OFF + sectorsize - 1) &