From owner-freebsd-hackers  Thu Jul 24 20:11:36 1997
Return-Path: <owner-freebsd-hackers>
Received: (from root@localhost)
          by hub.freebsd.org (8.8.5/8.8.5) id UAA10108
          for hackers-outgoing; Thu, 24 Jul 1997 20:11:36 -0700 (PDT)
Received: from itojun.csl.sony.co.jp (root@itojun.csl.sony.co.jp [133.138.1.134])
          by hub.freebsd.org (8.8.5/8.8.5) with ESMTP id UAA10102
          for <hackers@freebsd.org>; Thu, 24 Jul 1997 20:11:33 -0700 (PDT)
From: itojun@itojun.org
Received: from localhost (itojun@localhost [127.0.0.1]) by itojun.csl.sony.co.jp (8.8.5/3.3W3) with ESMTP id MAA16906 for <hackers@freebsd.org>; Fri, 25 Jul 1997 12:11:17 +0900 (JST)
To: hackers@freebsd.org
Subject: odd xxget() in some network drivers
X-Template-Reply-To: itojun@itojun.org
X-Template-Return-Receipt-To: itojun@itojun.org
X-PGP-Fingerprint: F8 24 B4 2C 8C 98 57 FD  90 5F B4 60 79 54 16 E2
X-Mailer: comp (MHng project) version 1997/04/30 02:23:09, by Jun-ichiro Itoh
MIME-Version: 1.0
Content-type: text/plain; charset=us-ascii
Content-transfer-encoding: 7bit
Content-ID: <top.869800277.16898@itojun.csl.sony.co.jp>
Date: Fri, 25 Jul 1997 12:11:17 +0900
Message-ID: <16903.869800277@itojun.csl.sony.co.jp>
Sender: owner-freebsd-hackers@freebsd.org
X-Loop: FreeBSD.org
Precedence: bulk

	If my memory is correct, it is assumed that network packets received
	by NICs should be placed into either:
	- single internal mbuf
	- two internal mbufs
	- multiple external mbufs
	(for ground information, see m_devget() in /sys/kern/uipc_mbuf.c
	or "TCP/IP illustrated vol.2" p42)
#	second case (two internal mbufs) can be omitted for simplicity
#	in current memory-rich environment, IMHO.

	However, there seems to be several drivers that does not meet this
	practice.  For example, /sys/dev/vx/if_vx.c will return the packet
	received in one of the following condition:
	- single internal mbuf (only if len % 4 == 0)
	- two internal mbufs (if len % 4 != 0)
		mbuf 1: m_len = len - (len % 4)
		mbuf 2: m_len = len % 4
	- three internal mbufs
		mbuf 1: m_len = MLEN
		mbuf 2: m_len = len - mlen - (len % 4)
		mbuf 3: m_len = len % 4
	- one external mbuf (only if len % 4 == 0)
	- two external mbufs
		mbuf 1: m_len = len - (len % 4)
		mbuf 2: m_len = len % 4
	- more than two external mbuf
		mbuf 1: m_len = MCLBYTES
		...
		mbuf n: m_len = len % 4
	I sent PR kernel/4020 but nobody seem to reply to this one.

	Questions:
	- could I apply the patch in kernel/4020 to the current source?
	  (who is the boss in /sys/dev/vx?)
	- could I make some check for other drivers, and apply patches if
	  necessery?

	Thanks.

Jun-ichiro Itoh