From owner-freebsd-net@FreeBSD.ORG  Thu May 27 15:25:03 2010
Return-Path: <owner-freebsd-net@FreeBSD.ORG>
Delivered-To: freebsd-net@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id DDCF0106566C
	for <freebsd-net@freebsd.org>; Thu, 27 May 2010 15:25:03 +0000 (UTC)
	(envelope-from renmaosheng@gmail.com)
Received: from mail-vw0-f54.google.com (mail-vw0-f54.google.com
	[209.85.212.54])
	by mx1.freebsd.org (Postfix) with ESMTP id 8F36C8FC16
	for <freebsd-net@freebsd.org>; Thu, 27 May 2010 15:25:03 +0000 (UTC)
Received: by vws12 with SMTP id 12so75626vws.13
	for <freebsd-net@freebsd.org>; Thu, 27 May 2010 08:25:02 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma;
	h=domainkey-signature:mime-version:received:received:date:message-id
	:subject:from:to:content-type;
	bh=S2WOaGQdiGXVwP0hQQ/4quyFTqF7PcNfViK6KTqvQBI=;
	b=eR38pOKIH/M8oA7Z5IO4UY5zxuIb4hVP4iU7O8mXWugHIOClg740Z6+VswFpyHFX6Q
	fkrc/qCOVq7rPsrmEe+slNARJAB+08SfdfBFK9+L1LNaDQD9gmuuiUYKP1IQLeg7Bj/q
	vqKhiOqa4dpYaY6CZHkGTkfgNb5EuGr6IojTA=
DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma;
	h=mime-version:date:message-id:subject:from:to:content-type;
	b=scTt5anjIA5dPCMskXJNZzVR9ACaxPjiGSGwJkYAq+hZ5Mo/ym+0icY5O/j4no5H0l
	Jf3kSKrmFM3TKfiJJH57Y9kfNcc4b5Uh2weKMwL56o5Ct2Z34Dn0PyTXXmjw02FUMHzT
	Jkyf++eDtQjNr8UuS0s8zb5D+PTLDAiCFUM54=
MIME-Version: 1.0
Received: by 10.220.107.8 with SMTP id z8mr7570080vco.214.1274973902447; Thu, 
	27 May 2010 08:25:02 -0700 (PDT)
Received: by 10.220.85.80 with HTTP; Thu, 27 May 2010 08:25:02 -0700 (PDT)
Date: Thu, 27 May 2010 23:25:02 +0800
Message-ID: <AANLkTinXrwLlNSzbNRwpJZWMFqJpicMLFmo5EvmMucsY@mail.gmail.com>
From: ren maosheng <renmaosheng@gmail.com>
To: freebsd-net@freebsd.org
Content-Type: text/plain; charset=ISO-8859-1
X-Content-Filtered-By: Mailman/MimeDel 2.1.5
Subject: One question for tcp_input function
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: Thu, 27 May 2010 15:25:03 -0000

Hi folks,

I have a question about below source code when I study the stack:

 if (acked > so->so_snd.sb_cc) {
                        tp->snd_wnd -= so->so_snd.sb_cc;
====================>
                        sbdrop_locked(&so->so_snd, (int)so->so_snd.sb_cc);
                        ourfinisacked = 1;
                } else {
                        sbdrop_locked(&so->so_snd, acked);
                        tp->snd_wnd -= acked;
=====================>
                        ourfinisacked = 0;
                }

We reduce the snd_wnd by acked number, I investigate the RFC793 and didn't
find tcp will need to do this.

Could you please shed a light on this? Is there any reason freebsd stack
considering doing this?  Thanks a lot!

Best Regards,
Ren Maosheng