void WaitForInput()
{
  fd_set readable;
  int t, tmax;

  FD_ZERO(&readable);
  FD_SET(&readable,0);
  tmax = t = Lbarton->ttypty->master_pty();
  FD_SET(&readable,t);
  t = Lcarl->ttypty->master_pty();
  if (t > tmax)
    tmax = t;
  FD_SET(&readable,t);
  return select(tmax+1,&readable,(fd_set *)0,(fd_set *)0,(struct timeval *)0);
}