unimore/kernel-hacking-2024-linux-steffo
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tty_set_ldisc() receive_room fix

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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>
This commit is contained in:
Paul Fulghum 2007-05-09 02:33:38 -07:00 committed by Linus Torvalds
parent 55c0d1f83e
commit ae030e435f
1 changed files with 7 additions and 7 deletions
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14
drivers/char/tty_io.c
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@ -933,13 +933,6 @@ static int tty_set_ldisc(struct tty_struct *tty, int ldisc)
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 @@ static int tty_set_ldisc(struct tty_struct *tty, int ldisc)
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;