fs/xfs/xfs_buf.h - kernel/msm-4.19 - Gitiles

 /*
  * Copyright (c) 2000-2005 Silicon Graphics, Inc.
  * All Rights Reserved.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
  * published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it would be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write the Free Software Foundation,
  * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
 #ifndef __XFS_BUF_H__
 #define __XFS_BUF_H__

 #include <linux/list.h>
 #include <linux/types.h>
 #include <linux/spinlock.h>
 #include <linux/mm.h>
 #include <linux/fs.h>
 #include <linux/dax.h>
 #include <linux/buffer_head.h>
 #include <linux/uio.h>
 #include <linux/list_lru.h>

 /*
  *	Base types
  */

 #define XFS_BUF_DADDR_NULL	((xfs_daddr_t) (-1LL))

 typedef enum {
 	XBRW_READ = 1,			/* transfer into target memory */
 	XBRW_WRITE = 2,			/* transfer from target memory */
 	XBRW_ZERO = 3,			/* Zero target memory */
 } xfs_buf_rw_t;

 #define XBF_READ	 (1 << 0) /* buffer intended for reading from device */
 #define XBF_WRITE	 (1 << 1) /* buffer intended for writing to device */
 #define XBF_READ_AHEAD	 (1 << 2) /* asynchronous read-ahead */
 #define XBF_NO_IOACCT	 (1 << 3) /* bypass I/O accounting (non-LRU bufs) */
 #define XBF_ASYNC	 (1 << 4) /* initiator will not wait for completion */
 #define XBF_DONE	 (1 << 5) /* all pages in the buffer uptodate */
 #define XBF_STALE	 (1 << 6) /* buffer has been staled, do not find it */
 #define XBF_WRITE_FAIL	 (1 << 24)/* async writes have failed on this buffer */

 /* I/O hints for the BIO layer */
 #define XBF_SYNCIO	 (1 << 10)/* treat this buffer as synchronous I/O */
 #define XBF_FUA		 (1 << 11)/* force cache write through mode */
 #define XBF_FLUSH	 (1 << 12)/* flush the disk cache before a write */

 /* flags used only as arguments to access routines */
 #define XBF_TRYLOCK	 (1 << 16)/* lock requested, but do not wait */
 #define XBF_UNMAPPED	 (1 << 17)/* do not map the buffer */

 /* flags used only internally */
 #define _XBF_PAGES	 (1 << 20)/* backed by refcounted pages */
 #define _XBF_KMEM	 (1 << 21)/* backed by heap memory */
 #define _XBF_DELWRI_Q	 (1 << 22)/* buffer on a delwri queue */
 #define _XBF_COMPOUND	 (1 << 23)/* compound buffer */

 typedef unsigned int xfs_buf_flags_t;

 #define XFS_BUF_FLAGS \
 	{ XBF_READ,		"READ" }, \
 	{ XBF_WRITE,		"WRITE" }, \
 	{ XBF_READ_AHEAD,	"READ_AHEAD" }, \
 	{ XBF_NO_IOACCT,	"NO_IOACCT" }, \
 	{ XBF_ASYNC,		"ASYNC" }, \
 	{ XBF_DONE,		"DONE" }, \
 	{ XBF_STALE,		"STALE" }, \
 	{ XBF_WRITE_FAIL,	"WRITE_FAIL" }, \
 	{ XBF_SYNCIO,		"SYNCIO" }, \
 	{ XBF_FUA,		"FUA" }, \
 	{ XBF_FLUSH,		"FLUSH" }, \
 	{ XBF_TRYLOCK,		"TRYLOCK" },	/* should never be set */\
 	{ XBF_UNMAPPED,		"UNMAPPED" },	/* ditto */\
 	{ _XBF_PAGES,		"PAGES" }, \
 	{ _XBF_KMEM,		"KMEM" }, \
 	{ _XBF_DELWRI_Q,	"DELWRI_Q" }, \
 	{ _XBF_COMPOUND,	"COMPOUND" }


 /*
  * Internal state flags.
  */
 #define XFS_BSTATE_DISPOSE	 (1 << 0)	/* buffer being discarded */
 #define XFS_BSTATE_IN_FLIGHT	 (1 << 1)	/* I/O in flight */

 /*
  * The xfs_buftarg contains 2 notions of "sector size" -
  *
  * 1) The metadata sector size, which is the minimum unit and
  *    alignment of IO which will be performed by metadata operations.
  * 2) The device logical sector size
  *
  * The first is specified at mkfs time, and is stored on-disk in the
  * superblock's sb_sectsize.
  *
  * The latter is derived from the underlying device, and controls direct IO
  * alignment constraints.
  */
 typedef struct xfs_buftarg {
 	dev_t			bt_dev;
 	struct block_device	*bt_bdev;
 	struct dax_device	*bt_daxdev;
 	struct xfs_mount	*bt_mount;
 	unsigned int		bt_meta_sectorsize;
 	size_t			bt_meta_sectormask;
 	size_t			bt_logical_sectorsize;
 	size_t			bt_logical_sectormask;

 	/* LRU control structures */
 	struct shrinker		bt_shrinker;
 	struct list_lru		bt_lru;

 	struct percpu_counter	bt_io_count;
 } xfs_buftarg_t;

 struct xfs_buf;
 typedef void (*xfs_buf_iodone_t)(struct xfs_buf *);


 #define XB_PAGES	2

 struct xfs_buf_map {
 	xfs_daddr_t		bm_bn;	/* block number for I/O */
 	int			bm_len;	/* size of I/O */
 };

 #define DEFINE_SINGLE_BUF_MAP(map, blkno, numblk) \
 	struct xfs_buf_map (map) = { .bm_bn = (blkno), .bm_len = (numblk) };

 struct xfs_buf_ops {
 	char *name;
 	void (*verify_read)(struct xfs_buf *);
 	void (*verify_write)(struct xfs_buf *);
 	xfs_failaddr_t (*verify_struct)(struct xfs_buf *bp);
 };

 typedef struct xfs_buf {
 	/*
 	 * first cacheline holds all the fields needed for an uncontended cache
 	 * hit to be fully processed. The semaphore straddles the cacheline
 	 * boundary, but the counter and lock sits on the first cacheline,
 	 * which is the only bit that is touched if we hit the semaphore
 	 * fast-path on locking.
 	 */
 	struct rhash_head	b_rhash_head;	/* pag buffer hash node */
 	xfs_daddr_t		b_bn;		/* block number of buffer */
 	int			b_length;	/* size of buffer in BBs */
 	atomic_t		b_hold;		/* reference count */
 	atomic_t		b_lru_ref;	/* lru reclaim ref count */
 	xfs_buf_flags_t		b_flags;	/* status flags */
 	struct semaphore	b_sema;		/* semaphore for lockables */

 	/*
 	 * concurrent access to b_lru and b_lru_flags are protected by
 	 * bt_lru_lock and not by b_sema
 	 */
 	struct list_head	b_lru;		/* lru list */
 	spinlock_t		b_lock;		/* internal state lock */
 	unsigned int		b_state;	/* internal state flags */
 	int			b_io_error;	/* internal IO error state */
 	wait_queue_head_t	b_waiters;	/* unpin waiters */
 	struct list_head	b_list;
 	struct xfs_perag	*b_pag;		/* contains rbtree root */
 	xfs_buftarg_t		*b_target;	/* buffer target (device) */
 	void			*b_addr;	/* virtual address of buffer */
 	struct work_struct	b_ioend_work;
 	struct workqueue_struct	*b_ioend_wq;	/* I/O completion wq */
 	xfs_buf_iodone_t	b_iodone;	/* I/O completion function */
 	struct completion	b_iowait;	/* queue for I/O waiters */
 	void			*b_log_item;
 	struct list_head	b_li_list;	/* Log items list head */
 	struct xfs_trans	*b_transp;
 	struct page		**b_pages;	/* array of page pointers */
 	struct page		*b_page_array[XB_PAGES]; /* inline pages */
 	struct xfs_buf_map	*b_maps;	/* compound buffer map */
 	struct xfs_buf_map	__b_map;	/* inline compound buffer map */
 	int			b_map_count;
 	int			b_io_length;	/* IO size in BBs */
 	atomic_t		b_pin_count;	/* pin count */
 	atomic_t		b_io_remaining;	/* #outstanding I/O requests */
 	unsigned int		b_page_count;	/* size of page array */
 	unsigned int		b_offset;	/* page offset in first page */
 	int			b_error;	/* error code on I/O */

 	/*
 	 * async write failure retry count. Initialised to zero on the first
 	 * failure, then when it exceeds the maximum configured without a
 	 * success the write is considered to be failed permanently and the
 	 * iodone handler will take appropriate action.
 	 *
 	 * For retry timeouts, we record the jiffie of the first failure. This
 	 * means that we can change the retry timeout for buffers already under
 	 * I/O and thus avoid getting stuck in a retry loop with a long timeout.
 	 *
 	 * last_error is used to ensure that we are getting repeated errors, not
 	 * different errors. e.g. a block device might change ENOSPC to EIO when
 	 * a failure timeout occurs, so we want to re-initialise the error
 	 * retry behaviour appropriately when that happens.
 	 */
 	int			b_retries;
 	unsigned long		b_first_retry_time; /* in jiffies */
 	int			b_last_error;

 	const struct xfs_buf_ops	*b_ops;

 #ifdef XFS_BUF_LOCK_TRACKING
 	int			b_last_holder;
 #endif
 } xfs_buf_t;

 /* Finding and Reading Buffers */
 struct xfs_buf *_xfs_buf_find(struct xfs_buftarg *target,
 			      struct xfs_buf_map *map, int nmaps,
 			      xfs_buf_flags_t flags, struct xfs_buf *new_bp);

 static inline struct xfs_buf *
 xfs_incore(
 	struct xfs_buftarg	*target,
 	xfs_daddr_t		blkno,
 	size_t			numblks,
 	xfs_buf_flags_t		flags)
 {
 	DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
 	return _xfs_buf_find(target, &map, 1, flags, NULL);
 }

 struct xfs_buf *_xfs_buf_alloc(struct xfs_buftarg *target,
 			       struct xfs_buf_map *map, int nmaps,
 			       xfs_buf_flags_t flags);

 static inline struct xfs_buf *
 xfs_buf_alloc(
 	struct xfs_buftarg	*target,
 	xfs_daddr_t		blkno,
 	size_t			numblks,
 	xfs_buf_flags_t		flags)
 {
 	DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
 	return _xfs_buf_alloc(target, &map, 1, flags);
 }

 struct xfs_buf *xfs_buf_get_map(struct xfs_buftarg *target,
 			       struct xfs_buf_map *map, int nmaps,
 			       xfs_buf_flags_t flags);
 struct xfs_buf *xfs_buf_read_map(struct xfs_buftarg *target,
 			       struct xfs_buf_map *map, int nmaps,
 			       xfs_buf_flags_t flags,
 			       const struct xfs_buf_ops *ops);
 void xfs_buf_readahead_map(struct xfs_buftarg *target,
 			       struct xfs_buf_map *map, int nmaps,
 			       const struct xfs_buf_ops *ops);

 static inline struct xfs_buf *
 xfs_buf_get(
 	struct xfs_buftarg	*target,
 	xfs_daddr_t		blkno,
 	size_t			numblks,
 	xfs_buf_flags_t		flags)
 {
 	DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
 	return xfs_buf_get_map(target, &map, 1, flags);
 }

 static inline struct xfs_buf *
 xfs_buf_read(
 	struct xfs_buftarg	*target,
 	xfs_daddr_t		blkno,
 	size_t			numblks,
 	xfs_buf_flags_t		flags,
 	const struct xfs_buf_ops *ops)
 {
 	DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
 	return xfs_buf_read_map(target, &map, 1, flags, ops);
 }

 static inline void
 xfs_buf_readahead(
 	struct xfs_buftarg	*target,
 	xfs_daddr_t		blkno,
 	size_t			numblks,
 	const struct xfs_buf_ops *ops)
 {
 	DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
 	return xfs_buf_readahead_map(target, &map, 1, ops);
 }

 void xfs_buf_set_empty(struct xfs_buf *bp, size_t numblks);
 int xfs_buf_associate_memory(struct xfs_buf *bp, void *mem, size_t length);

 struct xfs_buf *xfs_buf_get_uncached(struct xfs_buftarg *target, size_t numblks,
 				int flags);
 int xfs_buf_read_uncached(struct xfs_buftarg *target, xfs_daddr_t daddr,
 			  size_t numblks, int flags, struct xfs_buf **bpp,
 			  const struct xfs_buf_ops *ops);
 void xfs_buf_hold(struct xfs_buf *bp);

 /* Releasing Buffers */
 extern void xfs_buf_free(xfs_buf_t *);
 extern void xfs_buf_rele(xfs_buf_t *);

 /* Locking and Unlocking Buffers */
 extern int xfs_buf_trylock(xfs_buf_t *);
 extern void xfs_buf_lock(xfs_buf_t *);
 extern void xfs_buf_unlock(xfs_buf_t *);
 #define xfs_buf_islocked(bp) \
 	((bp)->b_sema.count <= 0)

 /* Buffer Read and Write Routines */
 extern int xfs_bwrite(struct xfs_buf *bp);
 extern void xfs_buf_ioend(struct xfs_buf *bp);
 extern void __xfs_buf_ioerror(struct xfs_buf *bp, int error,
 		xfs_failaddr_t failaddr);
 #define xfs_buf_ioerror(bp, err) __xfs_buf_ioerror((bp), (err), __this_address)
 extern void xfs_buf_ioerror_alert(struct xfs_buf *, const char *func);
 extern void xfs_buf_submit(struct xfs_buf *bp);
 extern int xfs_buf_submit_wait(struct xfs_buf *bp);
 extern void xfs_buf_iomove(xfs_buf_t *, size_t, size_t, void *,
 				xfs_buf_rw_t);
 #define xfs_buf_zero(bp, off, len) \
 	    xfs_buf_iomove((bp), (off), (len), NULL, XBRW_ZERO)

 /* Buffer Utility Routines */
 extern void *xfs_buf_offset(struct xfs_buf *, size_t);
 extern void xfs_buf_stale(struct xfs_buf *bp);

 /* Delayed Write Buffer Routines */
 extern void xfs_buf_delwri_cancel(struct list_head *);
 extern bool xfs_buf_delwri_queue(struct xfs_buf *, struct list_head *);
 extern int xfs_buf_delwri_submit(struct list_head *);
 extern int xfs_buf_delwri_submit_nowait(struct list_head *);
 extern int xfs_buf_delwri_pushbuf(struct xfs_buf *, struct list_head *);

 /* Buffer Daemon Setup Routines */
 extern int xfs_buf_init(void);
 extern void xfs_buf_terminate(void);

 /*
  * These macros use the IO block map rather than b_bn. b_bn is now really
  * just for the buffer cache index for cached buffers. As IO does not use b_bn
  * anymore, uncached buffers do not use b_bn at all and hence must modify the IO
  * map directly. Uncached buffers are not allowed to be discontiguous, so this
  * is safe to do.
  *
  * In future, uncached buffers will pass the block number directly to the io
  * request function and hence these macros will go away at that point.
  */
 #define XFS_BUF_ADDR(bp)		((bp)->b_maps[0].bm_bn)
 #define XFS_BUF_SET_ADDR(bp, bno)	((bp)->b_maps[0].bm_bn = (xfs_daddr_t)(bno))

 void xfs_buf_set_ref(struct xfs_buf *bp, int lru_ref);

 static inline int xfs_buf_ispinned(struct xfs_buf *bp)
 {
 	return atomic_read(&bp->b_pin_count);
 }

 static inline void xfs_buf_relse(xfs_buf_t *bp)
 {
 	xfs_buf_unlock(bp);
 	xfs_buf_rele(bp);
 }

 static inline int
 xfs_buf_verify_cksum(struct xfs_buf *bp, unsigned long cksum_offset)
 {
 	return xfs_verify_cksum(bp->b_addr, BBTOB(bp->b_length),
 				cksum_offset);
 }

 static inline void
 xfs_buf_update_cksum(struct xfs_buf *bp, unsigned long cksum_offset)
 {
 	xfs_update_cksum(bp->b_addr, BBTOB(bp->b_length),
 			 cksum_offset);
 }

 /*
  *	Handling of buftargs.
  */
 extern xfs_buftarg_t *xfs_alloc_buftarg(struct xfs_mount *,
 			struct block_device *, struct dax_device *);
 extern void xfs_free_buftarg(struct xfs_buftarg *);
 extern void xfs_wait_buftarg(xfs_buftarg_t *);
 extern int xfs_setsize_buftarg(xfs_buftarg_t *, unsigned int);

 #define xfs_getsize_buftarg(buftarg)	block_size((buftarg)->bt_bdev)
 #define xfs_readonly_buftarg(buftarg)	bdev_read_only((buftarg)->bt_bdev)

 #endif	/* __XFS_BUF_H__ */
	/*
	* Copyright (c) 2000-2005 Silicon Graphics, Inc.
	* All Rights Reserved.
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License as
	* published by the Free Software Foundation.
	*
	* This program is distributed in the hope that it would be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
	*/
	#ifndef __XFS_BUF_H__
	#define __XFS_BUF_H__

	#include <linux/list.h>
	#include <linux/types.h>
	#include <linux/spinlock.h>
	#include <linux/mm.h>
	#include <linux/fs.h>
	#include <linux/dax.h>
	#include <linux/buffer_head.h>
	#include <linux/uio.h>
	#include <linux/list_lru.h>

	/*
	* Base types
	*/

	#define XFS_BUF_DADDR_NULL ((xfs_daddr_t) (-1LL))

	typedef enum {
	XBRW_READ = 1, /* transfer into target memory */
	XBRW_WRITE = 2, /* transfer from target memory */
	XBRW_ZERO = 3, /* Zero target memory */
	} xfs_buf_rw_t;

	#define XBF_READ (1 << 0) /* buffer intended for reading from device */
	#define XBF_WRITE (1 << 1) /* buffer intended for writing to device */
	#define XBF_READ_AHEAD (1 << 2) /* asynchronous read-ahead */
	#define XBF_NO_IOACCT (1 << 3) /* bypass I/O accounting (non-LRU bufs) */
	#define XBF_ASYNC (1 << 4) /* initiator will not wait for completion */
	#define XBF_DONE (1 << 5) /* all pages in the buffer uptodate */
	#define XBF_STALE (1 << 6) /* buffer has been staled, do not find it */
	#define XBF_WRITE_FAIL (1 << 24)/* async writes have failed on this buffer */

	/* I/O hints for the BIO layer */
	#define XBF_SYNCIO (1 << 10)/* treat this buffer as synchronous I/O */
	#define XBF_FUA (1 << 11)/* force cache write through mode */
	#define XBF_FLUSH (1 << 12)/* flush the disk cache before a write */

	/* flags used only as arguments to access routines */
	#define XBF_TRYLOCK (1 << 16)/* lock requested, but do not wait */
	#define XBF_UNMAPPED (1 << 17)/* do not map the buffer */

	/* flags used only internally */
	#define _XBF_PAGES (1 << 20)/* backed by refcounted pages */
	#define _XBF_KMEM (1 << 21)/* backed by heap memory */
	#define _XBF_DELWRI_Q (1 << 22)/* buffer on a delwri queue */
	#define _XBF_COMPOUND (1 << 23)/* compound buffer */

	typedef unsigned int xfs_buf_flags_t;

	#define XFS_BUF_FLAGS \
	{ XBF_READ, "READ" }, \
	{ XBF_WRITE, "WRITE" }, \
	{ XBF_READ_AHEAD, "READ_AHEAD" }, \
	{ XBF_NO_IOACCT, "NO_IOACCT" }, \
	{ XBF_ASYNC, "ASYNC" }, \
	{ XBF_DONE, "DONE" }, \
	{ XBF_STALE, "STALE" }, \
	{ XBF_WRITE_FAIL, "WRITE_FAIL" }, \
	{ XBF_SYNCIO, "SYNCIO" }, \
	{ XBF_FUA, "FUA" }, \
	{ XBF_FLUSH, "FLUSH" }, \
	{ XBF_TRYLOCK, "TRYLOCK" }, /* should never be set */\
	{ XBF_UNMAPPED, "UNMAPPED" }, /* ditto */\
	{ _XBF_PAGES, "PAGES" }, \
	{ _XBF_KMEM, "KMEM" }, \
	{ _XBF_DELWRI_Q, "DELWRI_Q" }, \
	{ _XBF_COMPOUND, "COMPOUND" }


	/*
	* Internal state flags.
	*/
	#define XFS_BSTATE_DISPOSE (1 << 0) /* buffer being discarded */
	#define XFS_BSTATE_IN_FLIGHT (1 << 1) /* I/O in flight */

	/*
	* The xfs_buftarg contains 2 notions of "sector size" -
	*
	* 1) The metadata sector size, which is the minimum unit and
	* alignment of IO which will be performed by metadata operations.
	* 2) The device logical sector size
	*
	* The first is specified at mkfs time, and is stored on-disk in the
	* superblock's sb_sectsize.
	*
	* The latter is derived from the underlying device, and controls direct IO
	* alignment constraints.
	*/
	typedef struct xfs_buftarg {
	dev_t bt_dev;
	struct block_device *bt_bdev;
	struct dax_device *bt_daxdev;
	struct xfs_mount *bt_mount;
	unsigned int bt_meta_sectorsize;
	size_t bt_meta_sectormask;
	size_t bt_logical_sectorsize;
	size_t bt_logical_sectormask;

	/* LRU control structures */
	struct shrinker bt_shrinker;
	struct list_lru bt_lru;

	struct percpu_counter bt_io_count;
	} xfs_buftarg_t;

	struct xfs_buf;
	typedef void (xfs_buf_iodone_t)(struct xfs_buf );


	#define XB_PAGES 2

	struct xfs_buf_map {
	xfs_daddr_t bm_bn; /* block number for I/O */
	int bm_len; /* size of I/O */
	};

	#define DEFINE_SINGLE_BUF_MAP(map, blkno, numblk) \
	struct xfs_buf_map (map) = { .bm_bn = (blkno), .bm_len = (numblk) };

	struct xfs_buf_ops {
	char *name;
	void (verify_read)(struct xfs_buf );
	void (verify_write)(struct xfs_buf );
	xfs_failaddr_t (verify_struct)(struct xfs_buf bp);
	};

	typedef struct xfs_buf {
	/*
	* first cacheline holds all the fields needed for an uncontended cache
	* hit to be fully processed. The semaphore straddles the cacheline
	* boundary, but the counter and lock sits on the first cacheline,
	* which is the only bit that is touched if we hit the semaphore
	* fast-path on locking.
	*/
	struct rhash_head b_rhash_head; /* pag buffer hash node */
	xfs_daddr_t b_bn; /* block number of buffer */
	int b_length; /* size of buffer in BBs */
	atomic_t b_hold; /* reference count */
	atomic_t b_lru_ref; /* lru reclaim ref count */
	xfs_buf_flags_t b_flags; /* status flags */
	struct semaphore b_sema; /* semaphore for lockables */

	/*
	* concurrent access to b_lru and b_lru_flags are protected by
	* bt_lru_lock and not by b_sema
	*/
	struct list_head b_lru; /* lru list */
	spinlock_t b_lock; /* internal state lock */
	unsigned int b_state; /* internal state flags */
	int b_io_error; /* internal IO error state */
	wait_queue_head_t b_waiters; /* unpin waiters */
	struct list_head b_list;
	struct xfs_perag b_pag; / contains rbtree root */
	xfs_buftarg_t b_target; / buffer target (device) */
	void b_addr; / virtual address of buffer */
	struct work_struct b_ioend_work;
	struct workqueue_struct b_ioend_wq; / I/O completion wq */
	xfs_buf_iodone_t b_iodone; /* I/O completion function */
	struct completion b_iowait; /* queue for I/O waiters */
	void *b_log_item;
	struct list_head b_li_list; /* Log items list head */
	struct xfs_trans *b_transp;
	struct page *b_pages; / array of page pointers */
	struct page b_page_array[XB_PAGES]; / inline pages */
	struct xfs_buf_map b_maps; / compound buffer map */
	struct xfs_buf_map __b_map; /* inline compound buffer map */
	int b_map_count;
	int b_io_length; /* IO size in BBs */
	atomic_t b_pin_count; /* pin count */
	atomic_t b_io_remaining; /* #outstanding I/O requests */
	unsigned int b_page_count; /* size of page array */
	unsigned int b_offset; /* page offset in first page */
	int b_error; /* error code on I/O */

	/*
	* async write failure retry count. Initialised to zero on the first
	* failure, then when it exceeds the maximum configured without a
	* success the write is considered to be failed permanently and the
	* iodone handler will take appropriate action.
	*
	* For retry timeouts, we record the jiffie of the first failure. This
	* means that we can change the retry timeout for buffers already under
	* I/O and thus avoid getting stuck in a retry loop with a long timeout.
	*
	* last_error is used to ensure that we are getting repeated errors, not
	* different errors. e.g. a block device might change ENOSPC to EIO when
	* a failure timeout occurs, so we want to re-initialise the error
	* retry behaviour appropriately when that happens.
	*/
	int b_retries;
	unsigned long b_first_retry_time; /* in jiffies */
	int b_last_error;

	const struct xfs_buf_ops *b_ops;

	#ifdef XFS_BUF_LOCK_TRACKING
	int b_last_holder;
	#endif
	} xfs_buf_t;

	/* Finding and Reading Buffers */
	struct xfs_buf _xfs_buf_find(struct xfs_buftarg target,
	struct xfs_buf_map *map, int nmaps,
	xfs_buf_flags_t flags, struct xfs_buf *new_bp);

	static inline struct xfs_buf *
	xfs_incore(
	struct xfs_buftarg *target,
	xfs_daddr_t blkno,
	size_t numblks,
	xfs_buf_flags_t flags)
	{
	DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
	return _xfs_buf_find(target, &map, 1, flags, NULL);
	}

	struct xfs_buf _xfs_buf_alloc(struct xfs_buftarg target,
	struct xfs_buf_map *map, int nmaps,
	xfs_buf_flags_t flags);

	static inline struct xfs_buf *
	xfs_buf_alloc(
	struct xfs_buftarg *target,
	xfs_daddr_t blkno,
	size_t numblks,
	xfs_buf_flags_t flags)
	{
	DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
	return _xfs_buf_alloc(target, &map, 1, flags);
	}

	struct xfs_buf xfs_buf_get_map(struct xfs_buftarg target,
	struct xfs_buf_map *map, int nmaps,
	xfs_buf_flags_t flags);
	struct xfs_buf xfs_buf_read_map(struct xfs_buftarg target,
	struct xfs_buf_map *map, int nmaps,
	xfs_buf_flags_t flags,
	const struct xfs_buf_ops *ops);
	void xfs_buf_readahead_map(struct xfs_buftarg *target,
	struct xfs_buf_map *map, int nmaps,
	const struct xfs_buf_ops *ops);

	static inline struct xfs_buf *
	xfs_buf_get(
	struct xfs_buftarg *target,
	xfs_daddr_t blkno,
	size_t numblks,
	xfs_buf_flags_t flags)
	{
	DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
	return xfs_buf_get_map(target, &map, 1, flags);
	}

	static inline struct xfs_buf *
	xfs_buf_read(
	struct xfs_buftarg *target,
	xfs_daddr_t blkno,
	size_t numblks,
	xfs_buf_flags_t flags,
	const struct xfs_buf_ops *ops)
	{
	DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
	return xfs_buf_read_map(target, &map, 1, flags, ops);
	}

	static inline void
	xfs_buf_readahead(
	struct xfs_buftarg *target,
	xfs_daddr_t blkno,
	size_t numblks,
	const struct xfs_buf_ops *ops)
	{
	DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
	return xfs_buf_readahead_map(target, &map, 1, ops);
	}

	void xfs_buf_set_empty(struct xfs_buf *bp, size_t numblks);
	int xfs_buf_associate_memory(struct xfs_buf bp, void mem, size_t length);

	struct xfs_buf xfs_buf_get_uncached(struct xfs_buftarg target, size_t numblks,
	int flags);
	int xfs_buf_read_uncached(struct xfs_buftarg *target, xfs_daddr_t daddr,
	size_t numblks, int flags, struct xfs_buf **bpp,
	const struct xfs_buf_ops *ops);
	void xfs_buf_hold(struct xfs_buf *bp);

	/* Releasing Buffers */
	extern void xfs_buf_free(xfs_buf_t *);
	extern void xfs_buf_rele(xfs_buf_t *);

	/* Locking and Unlocking Buffers */
	extern int xfs_buf_trylock(xfs_buf_t *);
	extern void xfs_buf_lock(xfs_buf_t *);
	extern void xfs_buf_unlock(xfs_buf_t *);
	#define xfs_buf_islocked(bp) \
	((bp)->b_sema.count <= 0)

	/* Buffer Read and Write Routines */
	extern int xfs_bwrite(struct xfs_buf *bp);
	extern void xfs_buf_ioend(struct xfs_buf *bp);
	extern void __xfs_buf_ioerror(struct xfs_buf *bp, int error,
	xfs_failaddr_t failaddr);
	#define xfs_buf_ioerror(bp, err) __xfs_buf_ioerror((bp), (err), __this_address)
	extern void xfs_buf_ioerror_alert(struct xfs_buf , const char func);
	extern void xfs_buf_submit(struct xfs_buf *bp);
	extern int xfs_buf_submit_wait(struct xfs_buf *bp);
	extern void xfs_buf_iomove(xfs_buf_t , size_t, size_t, void ,
	xfs_buf_rw_t);
	#define xfs_buf_zero(bp, off, len) \
	xfs_buf_iomove((bp), (off), (len), NULL, XBRW_ZERO)

	/* Buffer Utility Routines */
	extern void xfs_buf_offset(struct xfs_buf , size_t);
	extern void xfs_buf_stale(struct xfs_buf *bp);

	/* Delayed Write Buffer Routines */
	extern void xfs_buf_delwri_cancel(struct list_head *);
	extern bool xfs_buf_delwri_queue(struct xfs_buf , struct list_head );
	extern int xfs_buf_delwri_submit(struct list_head *);
	extern int xfs_buf_delwri_submit_nowait(struct list_head *);
	extern int xfs_buf_delwri_pushbuf(struct xfs_buf , struct list_head );

	/* Buffer Daemon Setup Routines */
	extern int xfs_buf_init(void);
	extern void xfs_buf_terminate(void);

	/*
	* These macros use the IO block map rather than b_bn. b_bn is now really
	* just for the buffer cache index for cached buffers. As IO does not use b_bn
	* anymore, uncached buffers do not use b_bn at all and hence must modify the IO
	* map directly. Uncached buffers are not allowed to be discontiguous, so this
	* is safe to do.
	*
	* In future, uncached buffers will pass the block number directly to the io
	* request function and hence these macros will go away at that point.
	*/
	#define XFS_BUF_ADDR(bp) ((bp)->b_maps[0].bm_bn)
	#define XFS_BUF_SET_ADDR(bp, bno) ((bp)->b_maps[0].bm_bn = (xfs_daddr_t)(bno))

	void xfs_buf_set_ref(struct xfs_buf *bp, int lru_ref);

	static inline int xfs_buf_ispinned(struct xfs_buf *bp)
	{
	return atomic_read(&bp->b_pin_count);
	}

	static inline void xfs_buf_relse(xfs_buf_t *bp)
	{
	xfs_buf_unlock(bp);
	xfs_buf_rele(bp);
	}

	static inline int
	xfs_buf_verify_cksum(struct xfs_buf *bp, unsigned long cksum_offset)
	{
	return xfs_verify_cksum(bp->b_addr, BBTOB(bp->b_length),
	cksum_offset);
	}

	static inline void
	xfs_buf_update_cksum(struct xfs_buf *bp, unsigned long cksum_offset)
	{
	xfs_update_cksum(bp->b_addr, BBTOB(bp->b_length),
	cksum_offset);
	}

	/*
	* Handling of buftargs.
	*/
	extern xfs_buftarg_t xfs_alloc_buftarg(struct xfs_mount ,
	struct block_device , struct dax_device );
	extern void xfs_free_buftarg(struct xfs_buftarg *);
	extern void xfs_wait_buftarg(xfs_buftarg_t *);
	extern int xfs_setsize_buftarg(xfs_buftarg_t *, unsigned int);

	#define xfs_getsize_buftarg(buftarg) block_size((buftarg)->bt_bdev)
	#define xfs_readonly_buftarg(buftarg) bdev_read_only((buftarg)->bt_bdev)

	#endif /* __XFS_BUF_H__ */