linux-kernel - Re: xterm loses data (pty regression)

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Date:	Mon, 10 Aug 2009 11:07:20 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ray Lee <ray-lk@...rabbit.org>
cc:	Artur Skawina <art.08.09@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: xterm loses data (pty regression)



On Mon, 10 Aug 2009, Linus Torvalds wrote:
> 
> On Mon, 10 Aug 2009, Ray Lee wrote:
> > On Mon, Aug 10, 2009 at 8:29 AM, Artur Skawina <art.08.09@...il.com> wrote:
> > >
> > > First noticed it after upgrading to v2.6.31-rc5-246-g90bc1a6, still happens
> > > in rc5-381-g7b2aa03.
> > > If i press ^S in an xterm the output stops as expected, but after a ^Q i see
> > > only the newly written data, everything in between is lost. 
> 
> Yup, I can confirm that. 
> 
> > > > for i in `seq 1 111`; do echo $i; sleep 1; done
> 
> (Do ^S/^Q, see data loss)
> 
> Will take a look asap, thanks. Although I bet it's the same old commit 
> (d945cb9cc: "pty: Rework the pty layer to use the normal buffering logic") 
> again.

I think it's really this trivial.

That pty commit removed the checking for tty->stopped in 
pty_write_buffer() for no clear reason. And when it did that, it broke all 
the pausing logic in drivers/char/n_tty.c.

Can you confirm?

		Linus

---
 drivers/char/pty.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index 6e6942c..d083c73 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -144,6 +144,8 @@ static int pty_write(struct tty_struct *tty, const unsigned char *buf,
 
 static int pty_write_room(struct tty_struct *tty)
 {
+	if (tty->stopped)
+		return 0;
 	return pty_space(tty->link);
 }
 
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