VHD_BLOCK_SIZE
imgsz = (rawsz + VHD_BLOCK_SIZE - 1) & ~(VHD_BLOCK_SIZE - 1);
bat_entries = imgsz / VHD_BLOCK_SIZE;
be32enc(&header.block_size, VHD_BLOCK_SIZE);
blkcnt = VHD_BLOCK_SIZE / secsz;
sector += (VHD_BLOCK_SIZE / VHD_SECTOR_SIZE) + 1;
blkcnt = VHD_BLOCK_SIZE / secsz;