From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <eceef8dd5c85cd19f9741588f4d6b726@plan9.bell-labs.com>
From: David Presotto <presotto@closedmind.org>
To: 9fans@cse.psu.edu
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Subject: [9fans] on board IP/TCP/UDP checksums
Date: Wed, 12 Feb 2003 13:54:20 -0500
Topicbox-Message-UUID: 59a896d4-eacb-11e9-9e20-41e7f4b1d025

Anyone out there know the details of checksum calculations on
various ether chips/cards?  Jmk and I are currently sticking in
support for hardware checksuming on the intel 82543gc.  We
created flags in the Block header that mean 'do IP and/or
UDP and/or TCP checksum for this packet' outbound to the
interface and mean 'IP and/or UDP and/or TCP checksum
already done' for incoming packets.  We also added a ushort
that can be used to carry the whole packet checksum
so that we can support v6:


/* flag values */
enum
{
	BINTR	=	(1<<0),
	BFREE	=	(1<<1),
	Bipck	=	(1<<2),		/* ip checksum */
	Budpck	=	(1<<3),		/* udp checksum */
	Btcpck	=	(1<<4),		/* tcp checksum */
	Bpktck	=	(1<<5),		/* packet checksum */
};

struct Block
{
	Block*	next;
	Block*	list;
	uchar*	rp;			/* first unconsumed byte */
	uchar*	wp;			/* first empty byte */
	uchar*	lim;			/* 1 past the end of the buffer */
	uchar*	base;			/* start of the buffer */
	void	(*free)(Block*);
	ushort	flag;
	ushort	checksum;		/* IP checksum of complete packet (minus media header) */
};

I'm wondering if this will be sufficient for other chips/cards but
know nothing about them and would appreciate any elucidation from the
community.