TTY_WAITBG
tty->flags &= ~TTY_WAITBG;
if ((tty->flags & (TTY_WAITFG|TTY_WAITBG) ||
tty->flags &= ~(TTY_WAITBG|TTY_WAITFG);
tty->flags |= (TTY_WAITBG|TTY_WAITFG);
tty->flags |= (TTY_WAITBG|TTY_WAITFG);