kern_preadv
error = kern_preadv(uap->fd, &auio, 0, &sysmsg->sysmsg_szresult);
error = kern_preadv(uap->fd, &auio, flags, &sysmsg->sysmsg_szresult);
error = kern_preadv(uap->fd, &auio, 0, &sysmsg->sysmsg_szresult);
error = kern_preadv(uap->fd, &auio, flags, &sysmsg->sysmsg_szresult);
int kern_preadv(int fd, struct uio *auio, int flags, size_t *res);