Commit ae030e43 authored May 09, 2007 by Paul Fulghum Committed by Linus Torvalds May 09, 2007

tty_set_ldisc() receive_room fix

Fix tty_set_ldisc in tty_io.c so that tty->receive_room is only cleared if
actually changing line disciplines.

Without this fix a problem occurs when requesting the line discipline to
change to the same line discipline. In this case tty->receive_room is
cleared but ldisc->open() is not called to set tty->receive_room back to a
sane value. The result is that tty->receive_room is stuck at 0 preventing
the tty flip buffer from passing receive data to the line discipline.

For example: a switch from N_TTY to N_TTY followed by a select() call for
read input results in data never being received because tty->receive_room
is stuck at zero.

A switch from N_TTY to N_TTY followed by a read() call works because the
read() call itself sets tty->receive_room correctly (but select does not).

Previously (< 2.6.18) this was not a problem because the tty flip buffer
pushed data to the line discipline without regard for tty->receive room.

Signed-off-by: Paul Fulghum <paulkf@microgate.com>
Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 55c0d1f8

drivers/char/tty_io.c

+7 −7

Original line number	Diff line number	Diff line
		@@ -933,13 +933,6 @@ restart:
		if (ld == NULL)
		return -EINVAL;

		/*
		* No more input please, we are switching. The new ldisc
		* will update this value in the ldisc open function
		*/

		tty->receive_room = 0;

		/*
		* Problem: What do we do if this blocks ?
		*/
		@@ -951,6 +944,13 @@ restart:
		return 0;
		}

		/*
		* No more input please, we are switching. The new ldisc
		* will update this value in the ldisc open function
		*/

		tty->receive_room = 0;

		o_ldisc = tty->ldisc;
		o_tty = tty->link;

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