/*
 * Copyright (c) 1986 Regents of the University of California.
 * All rights reserved.  The Berkeley software License Agreement
 * specifies the terms and conditions for redistribution.
 *
 *	@(#)buf.h	1.4 (2.11BSD GTE) 1996/9/13
 */

/*
 * The header for buffers in the buffer pool and otherwise used
 * to describe a block i/o request is given here.
 *
 * Each buffer in the pool is usually doubly linked into 2 lists:
 * hashed into a chain by <dev,blkno> so it can be located in the cache,
 * and (usually) on (one of several) queues.  These lists are circular and
 * doubly linked for easy removal.
 *
 * There are currently two queues for buffers:
 * 	one for buffers containing ``useful'' information (the cache)
 *	one for buffers containing ``non-useful'' information
 *		(and empty buffers, pushed onto the front)
 * These queues contain the buffers which are available for
 * reallocation, are kept in lru order.  When not on one of these queues,
 * the buffers are ``checked out'' to drivers which use the available list
 * pointers to keep track of them in their i/o active queues.
 */

/*
 * Bufhd structures used at the head of the hashed buffer queues.
 * We only need three words for these, so this abbreviated
 * definition saves some space.
 */
struct bufhd
{
	short	b_flags;		/* see defines below */
	struct	buf *b_forw, *b_back;	/* fwd/bkwd pointer in chain */
};
struct buf
{
	short	b_flags;		/* see defines below */
	struct	buf *b_forw, *b_back;	/* hash chain (2 way street) */
	struct	buf *av_forw, *av_back;	/* position on free list if not BUSY */
#define	b_actf	av_forw			/* alternate names for driver queue */
#define	b_actl	av_back			/*    head - isn't history wonderful */
	u_short	b_bcount;		/* transfer count */
#define	b_active b_bcount		/* driver queue head: drive active */
	char	b_error;		/* returned after I/O */
	char	b_xmem;			/* high order core address */
	dev_t	b_dev;			/* major+minor device name */
	union {
	    caddr_t b_addr;		/* low order core address */
	} b_un;
	daddr_t	b_blkno;		/* block # on device */
	u_short	b_resid;		/* words not transferred after error */
#define	b_cylin b_resid			/* disksort */
#define	b_errcnt b_resid		/* while i/o in progress: # retries */
};

/*
 * We never use BQ_LOCKED or BQ_EMPTY, but if you want the 4.X block I/O
 * code to drop in, you have to have BQ_AGE and BQ_LRU *after* the first
 * queue, and it only costs 6 bytes of data space.
 */
#define	BQUEUES		3		/* number of free buffer queues */

#define	BQ_LOCKED	0		/* super-blocks &c */
#define	BQ_LRU		1		/* lru, useful buffers */
#define	BQ_AGE		2		/* rubbish */
#define	BQ_EMPTY	3		/* buffer headers with no memory */

/* Flags to low-level allocation routines. */
#define B_CLRBUF	0x01	/* Request allocated buffer be cleared. */
#define B_SYNC		0x02	/* Do all allocations synchronously. */

#define	bawrite(bp)	{(bp)->b_flags |= B_ASYNC; bwrite(bp);}
#define	bfree(bp)	(bp)->b_bcount = 0
#define	bftopaddr(bp)	((u_int)(bp)->b_un.b_addr >> 6 | (bp)->b_xmem << 10)

#if defined(KERNEL) && !defined(SUPERVISOR)
#define	BUFHSZ	16	/* must be power of 2 */
#define	BUFHASH(dev,blkno)	((struct buf *)&bufhash[((long)(dev) + blkno) & ((long)(BUFHSZ - 1))])
extern struct	buf buf[];		/* the buffer pool itself */
extern int	nbuf;			/* number of buffer headers */
extern struct	bufhd bufhash[];	/* heads of hash lists */
extern struct	buf bfreelist[];	/* heads of available lists */

struct	buf *balloc();
struct	buf *getblk();
struct	buf *geteblk();
struct	buf *getnewbuf();
struct	buf *bread();
struct	buf *breada();
#endif

/*
 * These flags are kept in b_flags.
 */
#define	B_WRITE		0x00000		/* non-read pseudo-flag */
#define	B_READ		0x00001		/* read when I/O occurs */
#define	B_DONE		0x00002		/* transaction finished */
#define	B_ERROR		0x00004		/* transaction aborted */
#define	B_BUSY		0x00008		/* not on av_forw/back list */
#define	B_PHYS		0x00010		/* physical IO */
#define	B_MAP		0x00020		/* alloc UNIBUS */
#define	B_WANTED 	0x00040		/* issue wakeup when BUSY goes off */
#define	B_AGE		0x00080		/* delayed write for correct aging */
#define	B_ASYNC		0x00100		/* don't wait for I/O completion */
#define	B_DELWRI 	0x00200		/* write at exit of avail list */
#define	B_TAPE 		0x00400		/* this is a magtape (no bdwrite) */
#define	B_INVAL		0x00800		/* does not contain valid info */
#define	B_BAD		0x01000		/* bad block revectoring in progress */
#define	B_LOCKED	0x02000		/* locked in core (not reusable) */
#define	B_UBAREMAP	0x04000		/* addr UNIBUS virtual, not physical */
#define	B_RAMREMAP	0x08000		/* remapped into ramdisk */

/*
 * Insq/Remq for the buffer hash lists.
 */
#define	bremhash(bp) { \
	(bp)->b_back->b_forw = (bp)->b_forw; \
	(bp)->b_forw->b_back = (bp)->b_back; \
}
#define	binshash(bp, dp) { \
	(bp)->b_forw = (dp)->b_forw; \
	(bp)->b_back = (dp); \
	(dp)->b_forw->b_back = (bp); \
	(dp)->b_forw = (bp); \
}

/*
 * Insq/Remq for the buffer free lists.
 */
#define	bremfree(bp) { \
	(bp)->av_back->av_forw = (bp)->av_forw; \
	(bp)->av_forw->av_back = (bp)->av_back; \
}
#define	binsheadfree(bp, dp) { \
	(dp)->av_forw->av_back = (bp); \
	(bp)->av_forw = (dp)->av_forw; \
	(dp)->av_forw = (bp); \
	(bp)->av_back = (dp); \
}
#define	binstailfree(bp, dp) { \
	(dp)->av_back->av_forw = (bp); \
	(bp)->av_back = (dp)->av_back; \
	(dp)->av_back = (bp); \
	(bp)->av_forw = (dp); \
}

/*
 * Take a buffer off the free list it's on and
 * mark it as being use (B_BUSY) by a device.
 */
#define	notavail(bp) { \
	register int x = splbio(); \
	bremfree(bp); \
	(bp)->b_flags |= B_BUSY; \
	splx(x); \
}

#define	iodone	biodone
#define	iowait	biowait