LN_PREV_LEN
LN_PREV_LEN(nextlinkp) + prevsize);
(void) memcpy(LN_PREV(prevlinkp), ptr, LN_PREV_LEN(prevlinkp));
prevsize = LN_PREV_LEN(dellinkp);
debug_print_key(fp, "prev", "", LN_PREV(linkp), LN_PREV_LEN(linkp));
linksize = LN_PREV_LEN(lastlinkp);