linux-kernel - Re: Large pastes into readline enabled programs causes breakage from v2.6.31 onwards

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Date:	Sat, 17 Aug 2013 17:28:53 +0200
From:	Pavel Machek <pavel@....cz>
To:	Maximiliano Curia <maxy@...ian.org>
Cc:	Peter Hurley <peter@...leysoftware.com>,
	Margarita Manterola <margamanterola@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: Large pastes into readline enabled programs causes breakage
 from v2.6.31 onwards

Hi!

> > n_tty_set_room() in drivers/tty/n_tty.c (3.10 mainline)
> 
> > From n_tty_set_room():
> 
> > 	/*
> > 	 * If we are doing input canonicalization, and there are no
> > 	 * pending newlines, let characters through without limit, so
> > 	 * that erase characters will be handled.  Other excess
> > 	 * characters will be beeped.
> > 	 */
> > 	if (left <= 0)
> > 		left = ldata->icanon && !ldata->canon_data;
> > 	old_left = tty->receive_room;
> > 	tty->receive_room = left;
> 
> I took a long look at this code and thought about how it could be made to work
> for readline's case and also for the canonical readers.  I came up with this
> simple patch:
> 
> diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
> index 4bf0fc0..2ba7f4e 100644
> --- a/drivers/tty/n_tty.c
> +++ b/drivers/tty/n_tty.c
> @@ -149,7 +149,8 @@ static int set_room(struct tty_struct *tty)
>          * characters will be beeped.
>          */
>         if (left <= 0)
> -               left = ldata->icanon && !ldata->canon_data;
> +               if (waitqueue_active(&tty->read_wait))
> +                       left = ldata->icanon && !ldata->canon_data;
>         old_left = tty->receive_room;
>         tty->receive_room = left;
> 
> This is of course just an idea, but I tested this and it worked correctly for
> the cases I was testing.
> 
> The effect of this patch is that when there is a canonical reader waiting for
> input, it maintains the previous behavior, but when there's no reader (like
> when readline is changing modes), it blocks and doesn't lose any characters.
> 
> Another approach would be to recalculate the size of canon_data when the mode
> is changed, but this would probably be much more invasive, and awfully less
> efficient since it would imply going through the buffer.
> 
> What do you think? Is the proposed solution, or something along those lines,
> acceptable?
> 
> If there are other cases that need to be taken into account and that I
> currently don't know about, please let me know.

Was this applied? You may want to cc rjw... it is a regression, it is
not pretty, and it is something I blieve I hit but thought it was some
kind of "X weirdness".

Thanks,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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