/*
	* Block io buffer header
	*/
struct buf
	{
	UCHAR		flags;	/* see below */
	UINT		dev;	/* device number */
	UINT		blk;	/* block number */
	UINT		count;	/* number of bytes to transfer */
	char*		data;	/* memory address */
	UCHAR		xmem;	/* extended address */
	struct buf *	forw;	/* for use by strategy routine */
	struct buf *	back;	/* for use by strategy routine */
	UINT		cyl;	/* for use by strategy routine */
	UCHAR		error;	/* error return */
	UINT		time;	/* "time" of last access */
	}
	blist[];

	/*
	 * flag bits
	 */
#define BWRITE	0000	/* mneumonic only */
#define ASYNC	0000	/* mneumonic only */
#define BREAD	0001	/* read the disk */
#define BBUSY	0002	/* busy -- do not access */
#define BSYNC	0004	/* syncronous io -- wait for completion */
#define BDELWRI 0010	/* write out before using */
#define BDONE	0020	/* io done -- data is valid */
#define BLOCK	0040	/* locked in core -- do not take */
#define BWANT	0100	/* wake up &buf on release */
#define BERROR	0200	/* error on last io transfer */

	/*
	 * xmem value
	 */
#define KERNEL	0	/* extended address of kernel memory */