linux-kernel - Re: [PATCH] kdesu broken

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Date:	Mon, 27 Jul 2009 22:42:20 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Ray Lee <ray-lk@...rabbit.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] kdesu broken

I'd favour we go with this which passes t1, expect, emacs and a corrected
t3

(test t3 is buggy as it has no \n and leaves the tty in line by line mode
so its typing a long line at the pty but never hits return to finish the
input)


It's theoretically imperfect in the case where you write a vast amount of
output in one go, the tty is blocked the other end and then you close.
However in practice that doesn't happen because with tty->low_latency = 1
we run the pty received n_tty ldisc code in our context so each write
fires through the entire n_tty ldisc and does flow control synchronously.

It needs re-addressing but its simple which at this point wins over
everything else and its one people tested before we tried to fix the hard
corner cases

commit aaf9da79c95a32fc5286fb851632baf09dc6134b
Author: Alan Cox <alan@...ux.intel.com>
Date:   Mon Jul 27 22:17:51 2009 +0100

    pty: quickfix for the pty ENXIO timing problems
    
    This also makes close stall in the normal case which is apparently needed
    to fix emacs
    
    Signed-off-by: Alan Cox <alan@...ux.intel.com>

diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index 6e6942c..3850a68 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -52,6 +52,7 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
 		return;
 	tty->link->packet = 0;
 	set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
+	tty_flip_buffer_push(tty->link);
 	wake_up_interruptible(&tty->link->read_wait);
 	wake_up_interruptible(&tty->link->write_wait);
 	if (tty->driver->subtype == PTY_TYPE_MASTER) {
@@ -207,6 +208,7 @@ static int pty_open(struct tty_struct *tty, struct file *filp)
 	clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
 	set_bit(TTY_THROTTLED, &tty->flags);
 	retval = 0;
+	tty->low_latency = 1;
 out:
 	return retval;
 }
--
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