include/linux/buffer_head.h - kernel/msm-5.4 - Gitiles

 /* SPDX-License-Identifier: GPL-2.0 */
 /*
  * include/linux/buffer_head.h
  *
  * Everything to do with buffer_heads.
  */

 #ifndef _LINUX_BUFFER_HEAD_H
 #define _LINUX_BUFFER_HEAD_H

 #include <linux/types.h>
 #include <linux/fs.h>
 #include <linux/linkage.h>
 #include <linux/pagemap.h>
 #include <linux/wait.h>
 #include <linux/atomic.h>

 #ifdef CONFIG_BLOCK

 enum bh_state_bits {
 	BH_Uptodate,	/* Contains valid data */
 	BH_Dirty,	/* Is dirty */
 	BH_Lock,	/* Is locked */
 	BH_Req,		/* Has been submitted for I/O */
 	BH_Uptodate_Lock,/* Used by the first bh in a page, to serialise
 			  * IO completion of other buffers in the page
 			  */

 	BH_Mapped,	/* Has a disk mapping */
 	BH_New,		/* Disk mapping was newly created by get_block */
 	BH_Async_Read,	/* Is under end_buffer_async_read I/O */
 	BH_Async_Write,	/* Is under end_buffer_async_write I/O */
 	BH_Delay,	/* Buffer is not yet allocated on disk */
 	BH_Boundary,	/* Block is followed by a discontiguity */
 	BH_Write_EIO,	/* I/O error on write */
 	BH_Unwritten,	/* Buffer is allocated on disk but not written */
 	BH_Quiet,	/* Buffer Error Prinks to be quiet */
 	BH_Meta,	/* Buffer contains metadata */
 	BH_Prio,	/* Buffer should be submitted with REQ_PRIO */
 	BH_Defer_Completion, /* Defer AIO completion to workqueue */

 	BH_PrivateStart,/* not a state bit, but the first bit available
 			 * for private allocation by other entities
 			 */
 };

 #define MAX_BUF_PER_PAGE (PAGE_SIZE / 512)

 struct page;
 struct buffer_head;
 struct address_space;
 typedef void (bh_end_io_t)(struct buffer_head *bh, int uptodate);

 /*
  * Historically, a buffer_head was used to map a single block
  * within a page, and of course as the unit of I/O through the
  * filesystem and block layers.  Nowadays the basic I/O unit
  * is the bio, and buffer_heads are used for extracting block
  * mappings (via a get_block_t call), for tracking state within
  * a page (via a page_mapping) and for wrapping bio submission
  * for backward compatibility reasons (e.g. submit_bh).
  */
 struct buffer_head {
 	unsigned long b_state;		/* buffer state bitmap (see above) */
 	struct buffer_head *b_this_page;/* circular list of page's buffers */
 	struct page *b_page;		/* the page this bh is mapped to */

 	sector_t b_blocknr;		/* start block number */
 	size_t b_size;			/* size of mapping */
 	char *b_data;			/* pointer to data within the page */

 	struct block_device *b_bdev;
 	bh_end_io_t *b_end_io;		/* I/O completion */
  	void *b_private;		/* reserved for b_end_io */
 	struct list_head b_assoc_buffers; /* associated with another mapping */
 	struct address_space *b_assoc_map;	/* mapping this buffer is
 						   associated with */
 	atomic_t b_count;		/* users using this buffer_head */
 };

 /*
  * macro tricks to expand the set_buffer_foo(), clear_buffer_foo()
  * and buffer_foo() functions.
  * To avoid reset buffer flags that are already set, because that causes
  * a costly cache line transition, check the flag first.
  */
 #define BUFFER_FNS(bit, name)						\
 static __always_inline void set_buffer_##name(struct buffer_head *bh)	\
 {									\
 	if (!test_bit(BH_##bit, &(bh)->b_state))			\
 		set_bit(BH_##bit, &(bh)->b_state);			\
 }									\
 static __always_inline void clear_buffer_##name(struct buffer_head *bh)	\
 {									\
 	clear_bit(BH_##bit, &(bh)->b_state);				\
 }									\
 static __always_inline int buffer_##name(const struct buffer_head *bh)	\
 {									\
 	return test_bit(BH_##bit, &(bh)->b_state);			\
 }

 /*
  * test_set_buffer_foo() and test_clear_buffer_foo()
  */
 #define TAS_BUFFER_FNS(bit, name)					\
 static __always_inline int test_set_buffer_##name(struct buffer_head *bh) \
 {									\
 	return test_and_set_bit(BH_##bit, &(bh)->b_state);		\
 }									\
 static __always_inline int test_clear_buffer_##name(struct buffer_head *bh) \
 {									\
 	return test_and_clear_bit(BH_##bit, &(bh)->b_state);		\
 }									\

 /*
  * Emit the buffer bitops functions.   Note that there are also functions
  * of the form "mark_buffer_foo()".  These are higher-level functions which
  * do something in addition to setting a b_state bit.
  */
 BUFFER_FNS(Uptodate, uptodate)
 BUFFER_FNS(Dirty, dirty)
 TAS_BUFFER_FNS(Dirty, dirty)
 BUFFER_FNS(Lock, locked)
 BUFFER_FNS(Req, req)
 TAS_BUFFER_FNS(Req, req)
 BUFFER_FNS(Mapped, mapped)
 BUFFER_FNS(New, new)
 BUFFER_FNS(Async_Read, async_read)
 BUFFER_FNS(Async_Write, async_write)
 BUFFER_FNS(Delay, delay)
 BUFFER_FNS(Boundary, boundary)
 BUFFER_FNS(Write_EIO, write_io_error)
 BUFFER_FNS(Unwritten, unwritten)
 BUFFER_FNS(Meta, meta)
 BUFFER_FNS(Prio, prio)
 BUFFER_FNS(Defer_Completion, defer_completion)

 #define bh_offset(bh)		((unsigned long)(bh)->b_data & ~PAGE_MASK)

 /* If we *know* page->private refers to buffer_heads */
 #define page_buffers(page)					\
 	({							\
 		BUG_ON(!PagePrivate(page));			\
 		((struct buffer_head *)page_private(page));	\
 	})
 #define page_has_buffers(page)	PagePrivate(page)

 void buffer_check_dirty_writeback(struct page *page,
 				     bool *dirty, bool *writeback);

 /*
  * Declarations
  */

 void mark_buffer_dirty(struct buffer_head *bh);
 void mark_buffer_write_io_error(struct buffer_head *bh);
 void touch_buffer(struct buffer_head *bh);
 void set_bh_page(struct buffer_head *bh,
 		struct page *page, unsigned long offset);
 int try_to_free_buffers(struct page *);
 struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
 		bool retry);
 void create_empty_buffers(struct page *, unsigned long,
 			unsigned long b_state);
 void end_buffer_read_sync(struct buffer_head *bh, int uptodate);
 void end_buffer_write_sync(struct buffer_head *bh, int uptodate);
 void end_buffer_async_write(struct buffer_head *bh, int uptodate);

 /* Things to do with buffers at mapping->private_list */
 void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode);
 int inode_has_buffers(struct inode *);
 void invalidate_inode_buffers(struct inode *);
 int remove_inode_buffers(struct inode *inode);
 int sync_mapping_buffers(struct address_space *mapping);
 void clean_bdev_aliases(struct block_device *bdev, sector_t block,
 			sector_t len);
 static inline void clean_bdev_bh_alias(struct buffer_head *bh)
 {
 	clean_bdev_aliases(bh->b_bdev, bh->b_blocknr, 1);
 }

 void mark_buffer_async_write(struct buffer_head *bh);
 void __wait_on_buffer(struct buffer_head *);
 wait_queue_head_t *bh_waitq_head(struct buffer_head *bh);
 struct buffer_head *__find_get_block(struct block_device *bdev, sector_t block,
 			unsigned size);
 struct buffer_head *__getblk_gfp(struct block_device *bdev, sector_t block,
 				  unsigned size, gfp_t gfp);
 void __brelse(struct buffer_head *);
 void __bforget(struct buffer_head *);
 void __breadahead(struct block_device *, sector_t block, unsigned int size);
 struct buffer_head *__bread_gfp(struct block_device *,
 				sector_t block, unsigned size, gfp_t gfp);
 void invalidate_bh_lrus(void);
 struct buffer_head *alloc_buffer_head(gfp_t gfp_flags);
 void free_buffer_head(struct buffer_head * bh);
 void unlock_buffer(struct buffer_head *bh);
 void __lock_buffer(struct buffer_head *bh);
 void ll_rw_block(int, int, int, struct buffer_head * bh[]);
 int sync_dirty_buffer(struct buffer_head *bh);
 int __sync_dirty_buffer(struct buffer_head *bh, int op_flags);
 void write_dirty_buffer(struct buffer_head *bh, int op_flags);
 int submit_bh(int, int, struct buffer_head *);
 void write_boundary_block(struct block_device *bdev,
 			sector_t bblock, unsigned blocksize);
 int bh_uptodate_or_lock(struct buffer_head *bh);
 int bh_submit_read(struct buffer_head *bh);

 extern int buffer_heads_over_limit;

 /*
  * Generic address_space_operations implementations for buffer_head-backed
  * address_spaces.
  */
 void block_invalidatepage(struct page *page, unsigned int offset,
 			  unsigned int length);
 int block_write_full_page(struct page *page, get_block_t *get_block,
 				struct writeback_control *wbc);
 int __block_write_full_page(struct inode *inode, struct page *page,
 			get_block_t *get_block, struct writeback_control *wbc,
 			bh_end_io_t *handler);
 int block_read_full_page(struct page*, get_block_t*);
 int block_is_partially_uptodate(struct page *page, unsigned long from,
 				unsigned long count);
 int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
 		unsigned flags, struct page **pagep, get_block_t *get_block);
 int __block_write_begin(struct page *page, loff_t pos, unsigned len,
 		get_block_t *get_block);
 int block_write_end(struct file *, struct address_space *,
 				loff_t, unsigned, unsigned,
 				struct page *, void *);
 int generic_write_end(struct file *, struct address_space *,
 				loff_t, unsigned, unsigned,
 				struct page *, void *);
 void page_zero_new_buffers(struct page *page, unsigned from, unsigned to);
 void clean_page_buffers(struct page *page);
 int cont_write_begin(struct file *, struct address_space *, loff_t,
 			unsigned, unsigned, struct page **, void **,
 			get_block_t *, loff_t *);
 int generic_cont_expand_simple(struct inode *inode, loff_t size);
 int block_commit_write(struct page *page, unsigned from, unsigned to);
 int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 				get_block_t get_block);
 /* Convert errno to return value from ->page_mkwrite() call */
 static inline vm_fault_t block_page_mkwrite_return(int err)
 {
 	if (err == 0)
 		return VM_FAULT_LOCKED;
 	if (err == -EFAULT || err == -EAGAIN)
 		return VM_FAULT_NOPAGE;
 	if (err == -ENOMEM)
 		return VM_FAULT_OOM;
 	/* -ENOSPC, -EDQUOT, -EIO ... */
 	return VM_FAULT_SIGBUS;
 }
 sector_t generic_block_bmap(struct address_space *, sector_t, get_block_t *);
 int block_truncate_page(struct address_space *, loff_t, get_block_t *);
 int nobh_write_begin(struct address_space *, loff_t, unsigned, unsigned,
 				struct page **, void **, get_block_t*);
 int nobh_write_end(struct file *, struct address_space *,
 				loff_t, unsigned, unsigned,
 				struct page *, void *);
 int nobh_truncate_page(struct address_space *, loff_t, get_block_t *);
 int nobh_writepage(struct page *page, get_block_t *get_block,
                         struct writeback_control *wbc);

 void buffer_init(void);

 /*
  * inline definitions
  */

 static inline void attach_page_buffers(struct page *page,
 		struct buffer_head *head)
 {
 	get_page(page);
 	SetPagePrivate(page);
 	set_page_private(page, (unsigned long)head);
 }

 static inline void get_bh(struct buffer_head *bh)
 {
         atomic_inc(&bh->b_count);
 }

 static inline void put_bh(struct buffer_head *bh)
 {
         smp_mb__before_atomic();
         atomic_dec(&bh->b_count);
 }

 static inline void brelse(struct buffer_head *bh)
 {
 	if (bh)
 		__brelse(bh);
 }

 static inline void bforget(struct buffer_head *bh)
 {
 	if (bh)
 		__bforget(bh);
 }

 static inline struct buffer_head *
 sb_bread(struct super_block *sb, sector_t block)
 {
 	return __bread_gfp(sb->s_bdev, block, sb->s_blocksize, __GFP_MOVABLE);
 }

 static inline struct buffer_head *
 sb_bread_unmovable(struct super_block *sb, sector_t block)
 {
 	return __bread_gfp(sb->s_bdev, block, sb->s_blocksize, 0);
 }

 static inline void
 sb_breadahead(struct super_block *sb, sector_t block)
 {
 	__breadahead(sb->s_bdev, block, sb->s_blocksize);
 }

 static inline struct buffer_head *
 sb_getblk(struct super_block *sb, sector_t block)
 {
 	return __getblk_gfp(sb->s_bdev, block, sb->s_blocksize, __GFP_MOVABLE);
 }


 static inline struct buffer_head *
 sb_getblk_gfp(struct super_block *sb, sector_t block, gfp_t gfp)
 {
 	return __getblk_gfp(sb->s_bdev, block, sb->s_blocksize, gfp);
 }

 static inline struct buffer_head *
 sb_find_get_block(struct super_block *sb, sector_t block)
 {
 	return __find_get_block(sb->s_bdev, block, sb->s_blocksize);
 }

 static inline void
 map_bh(struct buffer_head *bh, struct super_block *sb, sector_t block)
 {
 	set_buffer_mapped(bh);
 	bh->b_bdev = sb->s_bdev;
 	bh->b_blocknr = block;
 	bh->b_size = sb->s_blocksize;
 }

 static inline void wait_on_buffer(struct buffer_head *bh)
 {
 	might_sleep();
 	if (buffer_locked(bh))
 		__wait_on_buffer(bh);
 }

 static inline int trylock_buffer(struct buffer_head *bh)
 {
 	return likely(!test_and_set_bit_lock(BH_Lock, &bh->b_state));
 }

 static inline void lock_buffer(struct buffer_head *bh)
 {
 	might_sleep();
 	if (!trylock_buffer(bh))
 		__lock_buffer(bh);
 }

 static inline struct buffer_head *getblk_unmovable(struct block_device *bdev,
 						   sector_t block,
 						   unsigned size)
 {
 	return __getblk_gfp(bdev, block, size, 0);
 }

 static inline struct buffer_head *__getblk(struct block_device *bdev,
 					   sector_t block,
 					   unsigned size)
 {
 	return __getblk_gfp(bdev, block, size, __GFP_MOVABLE);
 }

 /**
  *  __bread() - reads a specified block and returns the bh
  *  @bdev: the block_device to read from
  *  @block: number of block
  *  @size: size (in bytes) to read
  *
  *  Reads a specified block, and returns buffer head that contains it.
  *  The page cache is allocated from movable area so that it can be migrated.
  *  It returns NULL if the block was unreadable.
  */
 static inline struct buffer_head *
 __bread(struct block_device *bdev, sector_t block, unsigned size)
 {
 	return __bread_gfp(bdev, block, size, __GFP_MOVABLE);
 }

 extern int __set_page_dirty_buffers(struct page *page);

 #else /* CONFIG_BLOCK */

 static inline void buffer_init(void) {}
 static inline int try_to_free_buffers(struct page *page) { return 1; }
 static inline int inode_has_buffers(struct inode *inode) { return 0; }
 static inline void invalidate_inode_buffers(struct inode *inode) {}
 static inline int remove_inode_buffers(struct inode *inode) { return 1; }
 static inline int sync_mapping_buffers(struct address_space *mapping) { return 0; }

 #endif /* CONFIG_BLOCK */
 #endif /* _LINUX_BUFFER_HEAD_H */
	/* SPDX-License-Identifier: GPL-2.0 */
	/*
	* include/linux/buffer_head.h
	*
	* Everything to do with buffer_heads.
	*/

	#ifndef _LINUX_BUFFER_HEAD_H
	#define _LINUX_BUFFER_HEAD_H

	#include <linux/types.h>
	#include <linux/fs.h>
	#include <linux/linkage.h>
	#include <linux/pagemap.h>
	#include <linux/wait.h>
	#include <linux/atomic.h>

	#ifdef CONFIG_BLOCK

	enum bh_state_bits {
	BH_Uptodate, /* Contains valid data */
	BH_Dirty, /* Is dirty */
	BH_Lock, /* Is locked */
	BH_Req, /* Has been submitted for I/O */
	BH_Uptodate_Lock,/* Used by the first bh in a page, to serialise
	* IO completion of other buffers in the page
	*/

	BH_Mapped, /* Has a disk mapping */
	BH_New, /* Disk mapping was newly created by get_block */
	BH_Async_Read, /* Is under end_buffer_async_read I/O */
	BH_Async_Write, /* Is under end_buffer_async_write I/O */
	BH_Delay, /* Buffer is not yet allocated on disk */
	BH_Boundary, /* Block is followed by a discontiguity */
	BH_Write_EIO, /* I/O error on write */
	BH_Unwritten, /* Buffer is allocated on disk but not written */
	BH_Quiet, /* Buffer Error Prinks to be quiet */
	BH_Meta, /* Buffer contains metadata */
	BH_Prio, /* Buffer should be submitted with REQ_PRIO */
	BH_Defer_Completion, /* Defer AIO completion to workqueue */

	BH_PrivateStart,/* not a state bit, but the first bit available
	* for private allocation by other entities
	*/
	};

	#define MAX_BUF_PER_PAGE (PAGE_SIZE / 512)

	struct page;
	struct buffer_head;
	struct address_space;
	typedef void (bh_end_io_t)(struct buffer_head *bh, int uptodate);

	/*
	* Historically, a buffer_head was used to map a single block
	* within a page, and of course as the unit of I/O through the
	* filesystem and block layers. Nowadays the basic I/O unit
	* is the bio, and buffer_heads are used for extracting block
	* mappings (via a get_block_t call), for tracking state within
	* a page (via a page_mapping) and for wrapping bio submission
	* for backward compatibility reasons (e.g. submit_bh).
	*/
	struct buffer_head {
	unsigned long b_state; /* buffer state bitmap (see above) */
	struct buffer_head b_this_page;/ circular list of page's buffers */
	struct page b_page; / the page this bh is mapped to */

	sector_t b_blocknr; /* start block number */
	size_t b_size; /* size of mapping */
	char b_data; / pointer to data within the page */

	struct block_device *b_bdev;
	bh_end_io_t b_end_io; / I/O completion */
	void b_private; / reserved for b_end_io */
	struct list_head b_assoc_buffers; /* associated with another mapping */
	struct address_space b_assoc_map; / mapping this buffer is
	associated with */
	atomic_t b_count; /* users using this buffer_head */
	};

	/*
	* macro tricks to expand the set_buffer_foo(), clear_buffer_foo()
	* and buffer_foo() functions.
	* To avoid reset buffer flags that are already set, because that causes
	* a costly cache line transition, check the flag first.
	*/
	#define BUFFER_FNS(bit, name) \
	static __always_inline void set_buffer_##name(struct buffer_head *bh) \
	{ \
	if (!test_bit(BH_##bit, &(bh)->b_state)) \
	set_bit(BH_##bit, &(bh)->b_state); \
	} \
	static __always_inline void clear_buffer_##name(struct buffer_head *bh) \
	{ \
	clear_bit(BH_##bit, &(bh)->b_state); \
	} \
	static __always_inline int buffer_##name(const struct buffer_head *bh) \
	{ \
	return test_bit(BH_##bit, &(bh)->b_state); \
	}

	/*
	* test_set_buffer_foo() and test_clear_buffer_foo()
	*/
	#define TAS_BUFFER_FNS(bit, name) \
	static __always_inline int test_set_buffer_##name(struct buffer_head *bh) \
	{ \
	return test_and_set_bit(BH_##bit, &(bh)->b_state); \
	} \
	static __always_inline int test_clear_buffer_##name(struct buffer_head *bh) \
	{ \
	return test_and_clear_bit(BH_##bit, &(bh)->b_state); \
	} \

	/*
	* Emit the buffer bitops functions. Note that there are also functions
	* of the form "mark_buffer_foo()". These are higher-level functions which
	* do something in addition to setting a b_state bit.
	*/
	BUFFER_FNS(Uptodate, uptodate)
	BUFFER_FNS(Dirty, dirty)
	TAS_BUFFER_FNS(Dirty, dirty)
	BUFFER_FNS(Lock, locked)
	BUFFER_FNS(Req, req)
	TAS_BUFFER_FNS(Req, req)
	BUFFER_FNS(Mapped, mapped)
	BUFFER_FNS(New, new)
	BUFFER_FNS(Async_Read, async_read)
	BUFFER_FNS(Async_Write, async_write)
	BUFFER_FNS(Delay, delay)
	BUFFER_FNS(Boundary, boundary)
	BUFFER_FNS(Write_EIO, write_io_error)
	BUFFER_FNS(Unwritten, unwritten)
	BUFFER_FNS(Meta, meta)
	BUFFER_FNS(Prio, prio)
	BUFFER_FNS(Defer_Completion, defer_completion)

	#define bh_offset(bh) ((unsigned long)(bh)->b_data & ~PAGE_MASK)

	/* If we know page->private refers to buffer_heads */
	#define page_buffers(page) \
	({ \
	BUG_ON(!PagePrivate(page)); \
	((struct buffer_head *)page_private(page)); \
	})
	#define page_has_buffers(page) PagePrivate(page)

	void buffer_check_dirty_writeback(struct page *page,
	bool dirty, bool writeback);

	/*
	* Declarations
	*/

	void mark_buffer_dirty(struct buffer_head *bh);
	void mark_buffer_write_io_error(struct buffer_head *bh);
	void touch_buffer(struct buffer_head *bh);
	void set_bh_page(struct buffer_head *bh,
	struct page *page, unsigned long offset);
	int try_to_free_buffers(struct page *);
	struct buffer_head alloc_page_buffers(struct page page, unsigned long size,
	bool retry);
	void create_empty_buffers(struct page *, unsigned long,
	unsigned long b_state);
	void end_buffer_read_sync(struct buffer_head *bh, int uptodate);
	void end_buffer_write_sync(struct buffer_head *bh, int uptodate);
	void end_buffer_async_write(struct buffer_head *bh, int uptodate);

	/* Things to do with buffers at mapping->private_list */
	void mark_buffer_dirty_inode(struct buffer_head bh, struct inode inode);
	int inode_has_buffers(struct inode *);
	void invalidate_inode_buffers(struct inode *);
	int remove_inode_buffers(struct inode *inode);
	int sync_mapping_buffers(struct address_space *mapping);
	void clean_bdev_aliases(struct block_device *bdev, sector_t block,
	sector_t len);
	static inline void clean_bdev_bh_alias(struct buffer_head *bh)
	{
	clean_bdev_aliases(bh->b_bdev, bh->b_blocknr, 1);
	}

	void mark_buffer_async_write(struct buffer_head *bh);
	void __wait_on_buffer(struct buffer_head *);
	wait_queue_head_t bh_waitq_head(struct buffer_head bh);
	struct buffer_head __find_get_block(struct block_device bdev, sector_t block,
	unsigned size);
	struct buffer_head __getblk_gfp(struct block_device bdev, sector_t block,
	unsigned size, gfp_t gfp);
	void __brelse(struct buffer_head *);
	void __bforget(struct buffer_head *);
	void __breadahead(struct block_device *, sector_t block, unsigned int size);
	struct buffer_head __bread_gfp(struct block_device ,
	sector_t block, unsigned size, gfp_t gfp);
	void invalidate_bh_lrus(void);
	struct buffer_head *alloc_buffer_head(gfp_t gfp_flags);
	void free_buffer_head(struct buffer_head * bh);
	void unlock_buffer(struct buffer_head *bh);
	void __lock_buffer(struct buffer_head *bh);
	void ll_rw_block(int, int, int, struct buffer_head * bh[]);
	int sync_dirty_buffer(struct buffer_head *bh);
	int __sync_dirty_buffer(struct buffer_head *bh, int op_flags);
	void write_dirty_buffer(struct buffer_head *bh, int op_flags);
	int submit_bh(int, int, struct buffer_head *);
	void write_boundary_block(struct block_device *bdev,
	sector_t bblock, unsigned blocksize);
	int bh_uptodate_or_lock(struct buffer_head *bh);
	int bh_submit_read(struct buffer_head *bh);

	extern int buffer_heads_over_limit;

	/*
	* Generic address_space_operations implementations for buffer_head-backed
	* address_spaces.
	*/
	void block_invalidatepage(struct page *page, unsigned int offset,
	unsigned int length);
	int block_write_full_page(struct page page, get_block_t get_block,
	struct writeback_control *wbc);
	int __block_write_full_page(struct inode inode, struct page page,
	get_block_t get_block, struct writeback_control wbc,
	bh_end_io_t *handler);
	int block_read_full_page(struct page, get_block_t);
	int block_is_partially_uptodate(struct page *page, unsigned long from,
	unsigned long count);
	int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
	unsigned flags, struct page *pagep, get_block_t get_block);
	int __block_write_begin(struct page *page, loff_t pos, unsigned len,
	get_block_t *get_block);
	int block_write_end(struct file , struct address_space ,
	loff_t, unsigned, unsigned,
	struct page , void );
	int generic_write_end(struct file , struct address_space ,
	loff_t, unsigned, unsigned,
	struct page , void );
	void page_zero_new_buffers(struct page *page, unsigned from, unsigned to);
	void clean_page_buffers(struct page *page);
	int cont_write_begin(struct file , struct address_space , loff_t,
	unsigned, unsigned, struct page , void ,
	get_block_t , loff_t );
	int generic_cont_expand_simple(struct inode *inode, loff_t size);
	int block_commit_write(struct page *page, unsigned from, unsigned to);
	int block_page_mkwrite(struct vm_area_struct vma, struct vm_fault vmf,
	get_block_t get_block);
	/* Convert errno to return value from ->page_mkwrite() call */
	static inline vm_fault_t block_page_mkwrite_return(int err)
	{
	if (err == 0)
	return VM_FAULT_LOCKED;
	if (err == -EFAULT \|\| err == -EAGAIN)
	return VM_FAULT_NOPAGE;
	if (err == -ENOMEM)
	return VM_FAULT_OOM;
	/* -ENOSPC, -EDQUOT, -EIO ... */
	return VM_FAULT_SIGBUS;
	}
	sector_t generic_block_bmap(struct address_space , sector_t, get_block_t );
	int block_truncate_page(struct address_space , loff_t, get_block_t );
	int nobh_write_begin(struct address_space *, loff_t, unsigned, unsigned,
	struct page , void , get_block_t*);
	int nobh_write_end(struct file , struct address_space ,
	loff_t, unsigned, unsigned,
	struct page , void );
	int nobh_truncate_page(struct address_space , loff_t, get_block_t );
	int nobh_writepage(struct page page, get_block_t get_block,
	struct writeback_control *wbc);

	void buffer_init(void);

	/*
	* inline definitions
	*/

	static inline void attach_page_buffers(struct page *page,
	struct buffer_head *head)
	{
	get_page(page);
	SetPagePrivate(page);
	set_page_private(page, (unsigned long)head);
	}

	static inline void get_bh(struct buffer_head *bh)
	{
	atomic_inc(&bh->b_count);
	}

	static inline void put_bh(struct buffer_head *bh)
	{
	smp_mb__before_atomic();
	atomic_dec(&bh->b_count);
	}

	static inline void brelse(struct buffer_head *bh)
	{
	if (bh)
	__brelse(bh);
	}

	static inline void bforget(struct buffer_head *bh)
	{
	if (bh)
	__bforget(bh);
	}

	static inline struct buffer_head *
	sb_bread(struct super_block *sb, sector_t block)
	{
	return __bread_gfp(sb->s_bdev, block, sb->s_blocksize, __GFP_MOVABLE);
	}

	static inline struct buffer_head *
	sb_bread_unmovable(struct super_block *sb, sector_t block)
	{
	return __bread_gfp(sb->s_bdev, block, sb->s_blocksize, 0);
	}

	static inline void
	sb_breadahead(struct super_block *sb, sector_t block)
	{
	__breadahead(sb->s_bdev, block, sb->s_blocksize);
	}

	static inline struct buffer_head *
	sb_getblk(struct super_block *sb, sector_t block)
	{
	return __getblk_gfp(sb->s_bdev, block, sb->s_blocksize, __GFP_MOVABLE);
	}


	static inline struct buffer_head *
	sb_getblk_gfp(struct super_block *sb, sector_t block, gfp_t gfp)
	{
	return __getblk_gfp(sb->s_bdev, block, sb->s_blocksize, gfp);
	}

	static inline struct buffer_head *
	sb_find_get_block(struct super_block *sb, sector_t block)
	{
	return __find_get_block(sb->s_bdev, block, sb->s_blocksize);
	}

	static inline void
	map_bh(struct buffer_head bh, struct super_block sb, sector_t block)
	{
	set_buffer_mapped(bh);
	bh->b_bdev = sb->s_bdev;
	bh->b_blocknr = block;
	bh->b_size = sb->s_blocksize;
	}

	static inline void wait_on_buffer(struct buffer_head *bh)
	{
	might_sleep();
	if (buffer_locked(bh))
	__wait_on_buffer(bh);
	}

	static inline int trylock_buffer(struct buffer_head *bh)
	{
	return likely(!test_and_set_bit_lock(BH_Lock, &bh->b_state));
	}

	static inline void lock_buffer(struct buffer_head *bh)
	{
	might_sleep();
	if (!trylock_buffer(bh))
	__lock_buffer(bh);
	}

	static inline struct buffer_head getblk_unmovable(struct block_device bdev,
	sector_t block,
	unsigned size)
	{
	return __getblk_gfp(bdev, block, size, 0);
	}

	static inline struct buffer_head __getblk(struct block_device bdev,
	sector_t block,
	unsigned size)
	{
	return __getblk_gfp(bdev, block, size, __GFP_MOVABLE);
	}

	/**
	* __bread() - reads a specified block and returns the bh
	* @bdev: the block_device to read from
	* @block: number of block
	* @size: size (in bytes) to read
	*
	* Reads a specified block, and returns buffer head that contains it.
	* The page cache is allocated from movable area so that it can be migrated.
	* It returns NULL if the block was unreadable.
	*/
	static inline struct buffer_head *
	__bread(struct block_device *bdev, sector_t block, unsigned size)
	{
	return __bread_gfp(bdev, block, size, __GFP_MOVABLE);
	}

	extern int __set_page_dirty_buffers(struct page *page);

	#else /* CONFIG_BLOCK */

	static inline void buffer_init(void) {}
	static inline int try_to_free_buffers(struct page *page) { return 1; }
	static inline int inode_has_buffers(struct inode *inode) { return 0; }
	static inline void invalidate_inode_buffers(struct inode *inode) {}
	static inline int remove_inode_buffers(struct inode *inode) { return 1; }
	static inline int sync_mapping_buffers(struct address_space *mapping) { return 0; }

	#endif /* CONFIG_BLOCK */
	#endif /* _LINUX_BUFFER_HEAD_H */