TTY_NO_WRITE_SPLIT
#if defined(TTY_NO_WRITE_SPLIT)
clear_bit(TTY_NO_WRITE_SPLIT, &tty->flags);
set_bit(TTY_NO_WRITE_SPLIT, &tty->flags);
if (test_bit(TTY_NO_WRITE_SPLIT, &tty->flags))
set_bit(TTY_NO_WRITE_SPLIT, &tty->flags);