kqueue_register
static int kqueue_register(struct kqueue *kq, struct kevent *kev,
error = kqueue_register(kq, kevp, td, M_WAITOK);
error = kqueue_register(kq, kev, td, mflag);
error = kqueue_register(kq, &kev, NULL, M_NOWAIT);
error = kqueue_register(kq, &kev, NULL, M_NOWAIT);