/*
   * include/linux/writeback.h
   */
  #ifndef WRITEBACK_H
  #define WRITEBACK_H
  
  #include <linux/sched.h>
  #include <linux/workqueue.h>
  #include <linux/fs.h>
  
  DECLARE_PER_CPU(int, dirty_throttle_leaks);
  
  /*
   * The 1/4 region under the global dirty thresh is for smooth dirty throttling:
   *
   *	(thresh - thresh/DIRTY_FULL_SCOPE, thresh)
   *
   * Further beyond, all dirtier tasks will enter a loop waiting (possibly long
   * time) for the dirty pages to drop, unless written enough pages.
   *
   * The global dirty threshold is normally equal to the global dirty limit,
   * except when the system suddenly allocates a lot of anonymous memory and
   * knocks down the global dirty threshold quickly, in which case the global
   * dirty limit will follow down slowly to prevent livelocking all dirtier tasks.
   */
  #define DIRTY_SCOPE		8
  #define DIRTY_FULL_SCOPE	(DIRTY_SCOPE / 2)
  
  struct backing_dev_info;
  
  /*
   * fs/fs-writeback.c
   */
  enum writeback_sync_modes {
  	WB_SYNC_NONE,	/* Don't wait on anything */
  	WB_SYNC_ALL,	/* Wait on every mapping */
  };
  
  /*
   * why some writeback work was initiated
   */
  enum wb_reason {
  	WB_REASON_BACKGROUND,
  	WB_REASON_TRY_TO_FREE_PAGES,
  	WB_REASON_SYNC,
  	WB_REASON_PERIODIC,
  	WB_REASON_LAPTOP_TIMER,
  	WB_REASON_FREE_MORE_MEM,
  	WB_REASON_FS_FREE_SPACE,
  	/*
  	 * There is no bdi forker thread any more and works are done
  	 * by emergency worker, however, this is TPs userland visible
  	 * and we'll be exposing exactly the same information,
  	 * so it has a mismatch name.
  	 */
  	WB_REASON_FORKER_THREAD,
  
  	WB_REASON_MAX,
  };
  
  /*
   * A control structure which tells the writeback code what to do.  These are
   * always on the stack, and hence need no locking.  They are always initialised
   * in a manner such that unspecified fields are set to zero.
   */
  struct writeback_control {
  	long nr_to_write;		/* Write this many pages, and decrement
  					   this for each page written */
  	long pages_skipped;		/* Pages which were not written */
  
  	/*
  	 * For a_ops->writepages(): if start or end are non-zero then this is
  	 * a hint that the filesystem need only write out the pages inside that
  	 * byterange.  The byte at `end' is included in the writeout request.
  	 */
  	loff_t range_start;
  	loff_t range_end;
  
  	enum writeback_sync_modes sync_mode;
  
  	unsigned for_kupdate:1;		/* A kupdate writeback */
  	unsigned for_background:1;	/* A background writeback */
  	unsigned tagged_writepages:1;	/* tag-and-write to avoid livelock */
  	unsigned for_reclaim:1;		/* Invoked from the page allocator */
  	unsigned range_cyclic:1;	/* range_start is cyclic */
  	unsigned for_sync:1;		/* sync(2) WB_SYNC_ALL writeback */
  };
  
  /*
   * fs/fs-writeback.c
   */	
  struct bdi_writeback;
  int inode_wait(void *);
  void writeback_inodes_sb(struct super_block *, enum wb_reason reason);
  void writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
  							enum wb_reason reason);
  int try_to_writeback_inodes_sb(struct super_block *, enum wb_reason reason);
  int try_to_writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
  				  enum wb_reason reason);
  void sync_inodes_sb(struct super_block *);
  void wakeup_flusher_threads(long nr_pages, enum wb_reason reason);
  void inode_wait_for_writeback(struct inode *inode);
  
  /* writeback.h requires fs.h; it, too, is not included from here. */
  static inline void wait_on_inode(struct inode *inode)
  {
  	might_sleep();
  	wait_on_bit(&inode->i_state, __I_NEW, inode_wait, TASK_UNINTERRUPTIBLE);
  }
  
  /*
   * mm/page-writeback.c
   */
  #ifdef CONFIG_BLOCK
  void laptop_io_completion(struct backing_dev_info *info);
  void laptop_sync_completion(void);
  void laptop_mode_sync(struct work_struct *work);
  void laptop_mode_timer_fn(unsigned long data);
  #else
  static inline void laptop_sync_completion(void) { }
  #endif
  void throttle_vm_writeout(gfp_t gfp_mask);
  bool zone_dirty_ok(struct zone *zone);
  
  extern unsigned long global_dirty_limit;
  
  /* These are exported to sysctl. */
  extern int dirty_background_ratio;
  extern unsigned long dirty_background_bytes;
  extern int vm_dirty_ratio;
  extern unsigned long vm_dirty_bytes;
  extern unsigned int dirty_writeback_interval;
  extern unsigned int dirty_expire_interval;
  extern int vm_highmem_is_dirtyable;
  extern int block_dump;
  extern int laptop_mode;
  
  extern int dirty_background_ratio_handler(struct ctl_table *table, int write,
  		void __user *buffer, size_t *lenp,
  		loff_t *ppos);
  extern int dirty_background_bytes_handler(struct ctl_table *table, int write,
  		void __user *buffer, size_t *lenp,
  		loff_t *ppos);
  extern int dirty_ratio_handler(struct ctl_table *table, int write,
  		void __user *buffer, size_t *lenp,
  		loff_t *ppos);
  extern int dirty_bytes_handler(struct ctl_table *table, int write,
  		void __user *buffer, size_t *lenp,
  		loff_t *ppos);
  
  struct ctl_table;
  int dirty_writeback_centisecs_handler(struct ctl_table *, int,
  				      void __user *, size_t *, loff_t *);
  
  void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty);
  unsigned long bdi_dirty_limit(struct backing_dev_info *bdi,
  			       unsigned long dirty);
  
  void __bdi_update_bandwidth(struct backing_dev_info *bdi,
  			    unsigned long thresh,
  			    unsigned long bg_thresh,
  			    unsigned long dirty,
  			    unsigned long bdi_thresh,
  			    unsigned long bdi_dirty,
  			    unsigned long start_time);
  
  void page_writeback_init(void);
  void balance_dirty_pages_ratelimited(struct address_space *mapping);
  
  typedef int (*writepage_t)(struct page *page, struct writeback_control *wbc,
  				void *data);
  
  int generic_writepages(struct address_space *mapping,
  		       struct writeback_control *wbc);
  void tag_pages_for_writeback(struct address_space *mapping,
  			     pgoff_t start, pgoff_t end);
  int write_cache_pages(struct address_space *mapping,
  		      struct writeback_control *wbc, writepage_t writepage,
  		      void *data);
  int do_writepages(struct address_space *mapping, struct writeback_control *wbc);
  void set_page_dirty_balance(struct page *page, int page_mkwrite);
  void writeback_set_ratelimit(void);
  void tag_pages_for_writeback(struct address_space *mapping,
  			     pgoff_t start, pgoff_t end);
  
  void account_page_redirty(struct page *page);
  
  #endif		/* WRITEBACK_H */