ml_len
#define ml_len(_ml) ((_ml)->ml_len)
#define ml_empty(_ml) ((_ml)->ml_len == 0)
ml->ml_len = 0;
ml->ml_len++;
mla->ml_len += mlb->ml_len;
ml->ml_len--;
len = ml->ml_len;
#define mq_len(_mq) ml_len(&(_mq)->mq_list)
dropped = ml_len(ml);
u_int ml_len;