sll_next
p = sll_next(nextoff, p);
while (sll_next(nextoff, p))
p = sll_next(nextoff, p);
while (sll_next(nextoff, curr)) {
curr = sll_next(nextoff, curr);
*prev = sll_next(nextoff, curr);
curr = sll_next(nextoff, curr);
extern void *sll_next(long nextoff, void *item);