ALIGNDOWN
new_size = ALIGNDOWN(start + offset + new_size,
new_size = ALIGNDOWN(last + offset + 1, alignment) -
new_lba = ALIGNDOWN(new_lba + offset, alignment) - offset;
size = ALIGNDOWN(size, alignment);
last = ALIGNDOWN(last + offset + 1, alignment) - 1;
a_lba = ALIGNDOWN(lba + offset, alignment);
len = ALIGNDOWN(last - a_first + 1, alignment);
size = ALIGNDOWN(last - start + 1, alignment);