TTY_ON
rv |= TTY_ON;
tty.ty_status &= ~TTY_ON;
tty.ty_status |= TTY_ON;
rv |= TTY_ON;
if ((typ->ty_status & TTY_ON) == 0 ||
if ((typ->ty_status & TTY_ON) == 0 ||
if ((tty->ty_status & TTY_ON) == 0)