LN_NEXT_LEN
nextsize = LN_NEXT_LEN(newlinkp);
diff = nextsize - LN_NEXT_LEN(prevlinkp);
nextsize = LN_NEXT_LEN(dellinkp);
debug_print_key(fp, "next", "", LN_NEXT(linkp), LN_NEXT_LEN(linkp));
nextsize = LN_NEXT_LEN(new_linkp);