typedef struct RingBuf {	uchar	owner;	uchar	unused;	ushort	len;	uchar	pkt[sizeof(Etherpkt)];} RingBuf; enum {	Host		= 0,		/* buffer owned by host */	Interface	= 1,		/* buffer owned by card */ 	Nrb		= 32,		/* default number of receive buffers */	Ntb		= 8,		/* default number of transmit buffers */}; typedef struct Ether Ether;struct Ether {	ISAConf;			/* hardware info */	int	ctlrno;	int	state;			/* 0: unfound, 1: found, 2: attaching */	int	tbdf; 	void	(*attach)(Ether*);	/* filled in by reset routine */	void	(*transmit)(Ether*);	void	(*interrupt)(Ureg*, void*);	void	(*detach)(Ether*);	void	*ctlr; 	ushort	nrb;			/* number of software receive buffers */	ushort	ntb;			/* number of software transmit buffers */	RingBuf *rb;			/* software receive buffers */	RingBuf *tb;			/* software transmit buffers */ 	ushort	rh;			/* first receive buffer belonging to host */	ushort	ri;			/* first receive buffer belonging to card */	 	ushort	th;			/* first transmit buffer belonging to host */		ushort	ti;			/* first transmit buffer belonging to card */	int	tbusy;			/* transmitter is busy */	int	mbps;			/* zero means link down */	}; void etherrloop(Ether*, Etherpkt*, long);void addethercard(char*, int(*)(Ether*));void	toringbuf(Ether*, void*, int);Block	*fromringbuf(Ether*); #define NEXT(x, l)	(((x)+1)%(l))#define PREV(x, l)	(((x) == 0) ? (l)-1: (x)-1)