SGOFSET
#define VA_ROUNDDOWNTOSEG(va) ((int)(va) & ~SGOFSET)
baseoff = (u_int)base & SGOFSET;
i = (baseoff + len + SGOFSET) >> SGSHIFT;
baseoff = (u_int)base & SGOFSET;
i = (baseoff + len + SGOFSET) >> SGSHIFT;
zseg = (((p + NBPSG - 1) & ~SGOFSET) - KERNBASE) >> SGSHIFT;