unix の top の kqread とはなにか？

  PID USERNAME    THR PRI NICE   SIZE    RES STATE    TIME   WCPU COMMAND
  744 squid         1   4    0  7868K  3384K kqread  18:20  0.00% squid

/*
 * Scan, Update kn_data (if not ONESHOT), and copyout triggered events.
 * We treat KN_MARKER knotes as if they are INFLUX.
 */
static int
kqueue_scan(struct kqueue *kq, int maxevents, struct kevent_copyops *k_ops,
	const struct timespec *tsp, struct kevent *keva, struct thread *td)
{
	struct kevent *kevp;
	struct timeval atv, rtv, ttv;
	struct knote *kn, *marker;
	int count, timeout, nkev, error;
	int haskqglobal;

	省略

start:
        kevp = keva;
        if (kq->kq_count == 0) {
                if (timeout < 0) {
                        error = EWOULDBLOCK;
                } else {
                        kq->kq_state |= KQ_SLEEP;
                        error = msleep(kq, &kq->kq_lock, PSOCK | PCATCH,
                            "kqread", timeout);
                }
                if (error == 0)
                        goto retry;
                /* don't restart after signals... */
                if (error == ERESTART)
                        error = EINTR;
                else if (error == EWOULDBLOCK)
                        error = 0;
                goto done;
        }

	...