/*
   * 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 <asm/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_PrivateStart,/* not a state bit, but the first bit available
  			 * for private allocation by other entities
  			 */
  };
  
  #define MAX_BUF_PER_PAGE (PAGE_CACHE_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.
   */
  #define BUFFER_FNS(bit, name)						\
  static inline void set_buffer_##name(struct buffer_head *bh)		\
  {									\
  	set_bit(BH_##bit, &(bh)->b_state);				\
  }									\
  static inline void clear_buffer_##name(struct buffer_head *bh)		\
  {									\
  	clear_bit(BH_##bit, &(bh)->b_state);				\
  }									\
  static 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 inline int test_set_buffer_##name(struct buffer_head *bh)	\
  {									\
  	return test_and_set_bit(BH_##bit, &(bh)->b_state);		\
  }									\
  static 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)

  
  #define bh_offset(bh)		((unsigned long)(bh)->b_data & ~PAGE_MASK)
  #define touch_buffer(bh)	mark_page_accessed(bh->b_page)
  
  /* 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)
  
  /*
   * Declarations
   */

  void mark_buffer_dirty(struct buffer_head *bh);

  void init_buffer(struct buffer_head *, bh_end_io_t *, void *);
  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,
  		int 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 unmap_underlying_metadata(struct block_device *bdev, sector_t block);
  
  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(struct block_device *bdev, sector_t block,
  			unsigned size);

  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(struct block_device *, sector_t block, unsigned size);

  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, struct buffer_head * bh[]);
  int sync_dirty_buffer(struct buffer_head *bh);

  int __sync_dirty_buffer(struct buffer_head *bh, int rw);

  void write_dirty_buffer(struct buffer_head *bh, int rw);

  int submit_bh(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 long offset);

  int block_write_full_page(struct page *page, get_block_t *get_block,
  				struct writeback_control *wbc);

  int block_write_full_page_endio(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, read_descriptor_t *desc,
  				unsigned long from);

  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);

  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);

  void block_sync_page(struct page *);

  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)
  {
  	page_cache_get(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_dec();
          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(sb->s_bdev, block, sb->s_blocksize);
  }
  
  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(sb->s_bdev, block, sb->s_blocksize);
  }
  
  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);
  }

  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 */