[PATCH] remove TTY_DONT_FLIP

Remove TTY_DONT_FLIP tty flag.  This flag was introduced in 2.1.X kernels
to prevent the N_TTY line discipline functions read_chan() and
n_tty_receive_buf() from running at the same time.  2.2.15 introduced
tty->read_lock to protect access to the N_TTY read buffer, which is the
only state requiring protection between these two functions.

The current TTY_DONT_FLIP implementation is broken for SMP, and is not
universally honored by drivers that send data directly to the line
discipline receive_buf function.

Because TTY_DONT_FLIP is not necessary, is broken in implementation, and is
not universally honored, it is removed.

Signed-off-by: Paul Fulghum <paulkf@microgate.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/char/pty.c

@@ -101,7 +101,7 @@ static void pty_unthrottle(struct tty_struct * tty)
  *
  * FIXME: Our pty_write method is called with our ldisc lock held but
  * not our partners. We can't just take the other one blindly without
- * risking deadlocks.  There is also the small matter of TTY_DONT_FLIP
+ * risking deadlocks.
  */
 static int pty_write(struct tty_struct * tty, const unsigned char *buf, int count)
 {