[9fans] on board IP/TCP/UDP checksums

[9fans] on board IP/TCP/UDP checksums

[David Presotto]

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.