From owner-freebsd-net@FreeBSD.ORG  Thu Jun  5 15:13:08 2008
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 91474106566C
	for <freebsd-net@freebsd.org>; Thu,  5 Jun 2008 15:13:08 +0000 (UTC)
	(envelope-from marc.loerner@hob.de)
Received: from mailgate.hob.de (mailgate.hob.de [212.185.199.3])
	by mx1.freebsd.org (Postfix) with ESMTP id 58EAA8FC21
	for <freebsd-net@freebsd.org>; Thu,  5 Jun 2008 15:13:08 +0000 (UTC)
	(envelope-from marc.loerner@hob.de)
Received: from imap.hob.de (mail2.hob.de [172.25.1.102])
	by mailgate.hob.de (Postfix) with ESMTP id 7592B520015
	for <freebsd-net@freebsd.org>; Thu,  5 Jun 2008 17:13:06 +0200 (CEST)
Received: from [172.22.0.190] (linux03.hob.de [172.22.0.190])
	by imap.hob.de (Postfix on SuSE eMail Server 2.0) with ESMTP id
	0F674FD269
	for <freebsd-net@freebsd.org>; Thu,  5 Jun 2008 17:13:06 +0200 (CEST)
From: Marc =?iso-8859-1?q?L=F6rner?= <marc.loerner@hob.de>
Organization: hob
To: freebsd-net@freebsd.org
Date: Thu, 5 Jun 2008 17:12:47 +0200
User-Agent: KMail/1.6.2
MIME-Version: 1.0
Content-Disposition: inline
Content-Type: text/plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Message-Id: <200806051712.47048.marc.loerner@hob.de>
Subject: Probable Bug in tcp.h
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, 05 Jun 2008 15:13:08 -0000

Hello,
I probably found a bug in declaration of "struct tcphdr"!

struct tcphdr {
	u_short	th_sport;		/* source port */
	u_short	th_dport;		/* destination port */
	tcp_seq	th_seq;			/* sequence number */
	tcp_seq	th_ack;			/* acknowledgement number */
#if BYTE_ORDER == LITTLE_ENDIAN
	u_int	th_x2:4,		/* (unused) */						<---here
		th_off:4;		/* data offset */						<---
#endif
#if BYTE_ORDER == BIG_ENDIAN
	u_int	th_off:4,		/* data offset */
		th_x2:4;		/* (unused) */
#endif
	u_char	th_flags;

First of all I have the problam of misalignment of th_off. Because in this way 
always 4 bytes are read and the the bits of th_off are replaced. Then the 4 
bytes are written back. 

But should (th_x and th_off) not only be 1 byte in whole -> only read and 
write 1 byte?

I think if this was changed, my misalignment problems would go away!

I'll appreciate any thoughts on this!

Regards,
Marc

P.S.: Please cc me because I'm not on the list!