From owner-freebsd-net@FreeBSD.ORG  Mon Jun 25 16:52:56 2007
Return-Path: <owner-freebsd-net@FreeBSD.ORG>
X-Original-To: freebsd-net@freebsd.org
Delivered-To: freebsd-net@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52])
	by hub.freebsd.org (Postfix) with ESMTP id 7977016A400
	for <freebsd-net@freebsd.org>; Mon, 25 Jun 2007 16:52:56 +0000 (UTC)
	(envelope-from brde@optusnet.com.au)
Received: from mail08.syd.optusnet.com.au (mail08.syd.optusnet.com.au
	[211.29.132.189])
	by mx1.freebsd.org (Postfix) with ESMTP id 0172013C469
	for <freebsd-net@freebsd.org>; Mon, 25 Jun 2007 16:52:55 +0000 (UTC)
	(envelope-from brde@optusnet.com.au)
Received: from besplex.bde.org (c220-239-235-248.carlnfd3.nsw.optusnet.com.au
	[220.239.235.248])
	by mail08.syd.optusnet.com.au (8.13.1/8.13.1) with ESMTP id
	l5PGqjcL014450
	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO);
	Tue, 26 Jun 2007 02:52:50 +1000
Date: Tue, 26 Jun 2007 02:52:45 +1000 (EST)
From: Bruce Evans <brde@optusnet.com.au>
X-X-Sender: bde@besplex.bde.org
To: Julian Elischer <julian@elischer.org>
In-Reply-To: <467C727D.4060703@elischer.org>
Message-ID: <20070626023944.M82078@besplex.bde.org>
References: <467C727D.4060703@elischer.org>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
Cc: FreeBSD Net <freebsd-net@freebsd.org>
Subject: Re: [6.x] problem with AIO, non-blocking sockets on freebSD and IE7
 on windows.
X-BeenThere: freebsd-net@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Networking and TCP/IP with FreeBSD <freebsd-net.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-net>,
	<mailto:freebsd-net-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-net>
List-Post: <mailto:freebsd-net@freebsd.org>
List-Help: <mailto:freebsd-net-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-net>,
	<mailto:freebsd-net-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 25 Jun 2007 16:52:56 -0000

On Fri, 22 Jun 2007, Julian Elischer wrote:

> If one has an event-driven process that accepts tcp connections, one needs to 
> set eh non-blocking socket option and use kqueue or similar to schedule work.
>
> This is ok for data transfers, however when it comes to the close() call 
> there is a problem.  The problem in in the following code in so_close()
>
>
>               if (so->so_options & SO_LINGER) {
>                       if ((so->so_state & SS_ISDISCONNECTING) &&
>                           (so->so_state & SS_NBIO))
>                               goto drop;
> ...
> drop:
>  [ continues on to destroy socket ]
>
>
> because SS_NBIO is set, the socket acts as if SO_LINGER was set, with a 
> timeout of 0.
> the result of this, is the following behaviour:

[ patckets in flight get lost ]

This seems to be the correct behaviour.  The application doesn't care
about its data and/or wants to close the descriptor without blocking,
so it doesn't turn off the blocking flag and/or wait for i/o to complete
(so that it can see if the i/o actually worked) before calling close().

I implemented this behaviour for tty drivers in FreeBSD.  Old BSD tty
drivers didn't check the nonblocking flag and didn't have a timeout,
so close() on tty devices tended to hang forever (normally at long
weekends) even for closes that should have been nonblocking.

Bruce