maxcls
howmany((RESFTE + maxcls(fat)) * (fat / BPN),
(u_int64_t) (maxcls(fat) + 1) * bpb.bpbSecPerClust) <=
x2 = howmany((RESFTE + MIN(x, maxcls(fat))) * (fat / BPN),
if (cls > maxcls(fat)) {
cls = maxcls(fat);