text: /*
   * include/linux/backing-dev.h
   *
   * low-level device information and state which is propagated up through
   * to high-level code.
   */
  
  #ifndef _LINUX_BACKING_DEV_H
  #define _LINUX_BACKING_DEV_H
  
  #include <linux/percpu_counter.h>
  #include <linux/log2.h>
  #include <linux/proportions.h>
  #include <linux/kernel.h>
  #include <linux/fs.h>
  #include <linux/sched.h>
  #include <linux/timer.h>
  #include <linux/writeback.h>
  #include <asm/atomic.h>
  
  struct page;
  struct device;
  struct dentry;
  
  /*
   * Bits in backing_dev_info.state
   */
  enum bdi_state {
  	BDI_pending,		/* On its way to being activated */
  	BDI_wb_alloc,		/* Default embedded wb allocated */
  	BDI_async_congested,	/* The async (write) queue is getting full */
  	BDI_sync_congested,	/* The sync queue is getting full */
  	BDI_registered,		/* bdi_register() was done */
  	BDI_writeback_running,	/* Writeback is in progress */
  	BDI_unused,		/* Available bits start here */
  };
  
  typedef int (congested_fn)(void *, int);
  
  enum bdi_stat_item {
  	BDI_RECLAIMABLE,
  	BDI_WRITEBACK,
  	NR_BDI_STAT_ITEMS
  };
  
  #define BDI_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))
  
  struct bdi_writeback {
  	struct backing_dev_info *bdi;	/* our parent bdi */
  	unsigned int nr;
  
  	unsigned long last_old_flush;	/* last old data flush */
  	unsigned long last_active;	/* last time bdi thread was active */
  
  	struct task_struct *task;	/* writeback thread */
  	struct timer_list wakeup_timer; /* used for delayed bdi thread wakeup */
  	struct list_head b_dirty;	/* dirty inodes */
  	struct list_head b_io;		/* parked for writeback */
  	struct list_head b_more_io;	/* parked for more writeback */
  };
  
  struct backing_dev_info {
  	struct list_head bdi_list;
  	unsigned long ra_pages;	/* max readahead in PAGE_CACHE_SIZE units */
  	unsigned long state;	/* Always use atomic bitops on this */
  	unsigned int capabilities; /* Device capabilities */
  	congested_fn *congested_fn; /* Function pointer if device is md/dm */
  	void *congested_data;	/* Pointer to aux data for congested func */
  	void (*unplug_io_fn)(struct backing_dev_info *, struct page *);
  	void *unplug_io_data;
  
  	char *name;
  
  	struct percpu_counter bdi_stat[NR_BDI_STAT_ITEMS];
  
  	struct prop_local_percpu completions;
  	int dirty_exceeded;
  
  	unsigned int min_ratio;
  	unsigned int max_ratio, max_prop_frac;
  
  	struct bdi_writeback wb;  /* default writeback info for this bdi */
  	spinlock_t wb_lock;	  /* protects work_list */
  
  	struct list_head work_list;
  
  	struct device *dev;
  
  	struct timer_list laptop_mode_wb_timer;
  
  #ifdef CONFIG_DEBUG_FS
  	struct dentry *debug_dir;
  	struct dentry *debug_stats;
  #endif
  };
  
  int bdi_init(struct backing_dev_info *bdi);
  void bdi_destroy(struct backing_dev_info *bdi);
  
  int bdi_register(struct backing_dev_info *bdi, struct device *parent,
  		const char *fmt, ...);
  int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
  void bdi_unregister(struct backing_dev_info *bdi);
  int bdi_setup_and_register(struct backing_dev_info *, char *, unsigned int);
  void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages);
  void bdi_start_background_writeback(struct backing_dev_info *bdi);
  int bdi_writeback_thread(void *data);
  int bdi_has_dirty_io(struct backing_dev_info *bdi);
  void bdi_arm_supers_timer(void);
  void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi);
  
  extern spinlock_t bdi_lock;
  extern struct list_head bdi_list;
  
  static inline int wb_has_dirty_io(struct bdi_writeback *wb)
  {
  	return !list_empty(&wb->b_dirty) ||
  	       !list_empty(&wb->b_io) ||
  	       !list_empty(&wb->b_more_io);
  }
  
  static inline void __add_bdi_stat(struct backing_dev_info *bdi,
  		enum bdi_stat_item item, s64 amount)
  {
  	__percpu_counter_add(&bdi->bdi_stat[item], amount, BDI_STAT_BATCH);
  }
  
  static inline void __inc_bdi_stat(struct backing_dev_info *bdi,
  		enum bdi_stat_item item)
  {
  	__add_bdi_stat(bdi, item, 1);
  }
  
  static inline void inc_bdi_stat(struct backing_dev_info *bdi,
  		enum bdi_stat_item item)
  {
  	unsigned long flags;
  
  	local_irq_save(flags);
  	__inc_bdi_stat(bdi, item);
  	local_irq_restore(flags);
  }
  
  static inline void __dec_bdi_stat(struct backing_dev_info *bdi,
  		enum bdi_stat_item item)
  {
  	__add_bdi_stat(bdi, item, -1);
  }
  
  static inline void dec_bdi_stat(struct backing_dev_info *bdi,
  		enum bdi_stat_item item)
  {
  	unsigned long flags;
  
  	local_irq_save(flags);
  	__dec_bdi_stat(bdi, item);
  	local_irq_restore(flags);
  }
  
  static inline s64 bdi_stat(struct backing_dev_info *bdi,
  		enum bdi_stat_item item)
  {
  	return percpu_counter_read_positive(&bdi->bdi_stat[item]);
  }
  
  static inline s64 __bdi_stat_sum(struct backing_dev_info *bdi,
  		enum bdi_stat_item item)
  {
  	return percpu_counter_sum_positive(&bdi->bdi_stat[item]);
  }
  
  static inline s64 bdi_stat_sum(struct backing_dev_info *bdi,
  		enum bdi_stat_item item)
  {
  	s64 sum;
  	unsigned long flags;
  
  	local_irq_save(flags);
  	sum = __bdi_stat_sum(bdi, item);
  	local_irq_restore(flags);
  
  	return sum;
  }
  
  extern void bdi_writeout_inc(struct backing_dev_info *bdi);
  
  /*
   * maximal error of a stat counter.
   */
  static inline unsigned long bdi_stat_error(struct backing_dev_info *bdi)
  {
  #ifdef CONFIG_SMP
  	return nr_cpu_ids * BDI_STAT_BATCH;
  #else
  	return 1;
  #endif
  }
  
  int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio);
  int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
  
  /*
   * Flags in backing_dev_info::capability
   *
   * The first three flags control whether dirty pages will contribute to the
   * VM's accounting and whether writepages() should be called for dirty pages
   * (something that would not, for example, be appropriate for ramfs)
   *
   * WARNING: these flags are closely related and should not normally be
   * used separately.  The BDI_CAP_NO_ACCT_AND_WRITEBACK combines these
   * three flags into a single convenience macro.
   *
   * BDI_CAP_NO_ACCT_DIRTY:  Dirty pages shouldn't contribute to accounting
   * BDI_CAP_NO_WRITEBACK:   Don't write pages back
   * BDI_CAP_NO_ACCT_WB:     Don't automatically account writeback pages
   *
   * These flags let !MMU mmap() govern direct device mapping vs immediate
   * copying more easily for MAP_PRIVATE, especially for ROM filesystems.
   *
   * BDI_CAP_MAP_COPY:       Copy can be mapped (MAP_PRIVATE)
   * BDI_CAP_MAP_DIRECT:     Can be mapped directly (MAP_SHARED)
   * BDI_CAP_READ_MAP:       Can be mapped for reading
   * BDI_CAP_WRITE_MAP:      Can be mapped for writing
   * BDI_CAP_EXEC_MAP:       Can be mapped for execution
   *
   * BDI_CAP_SWAP_BACKED:    Count shmem/tmpfs objects as swap-backed.
   */
  #define BDI_CAP_NO_ACCT_DIRTY	0x00000001
  #define BDI_CAP_NO_WRITEBACK	0x00000002
  #define BDI_CAP_MAP_COPY	0x00000004
  #define BDI_CAP_MAP_DIRECT	0x00000008
  #define BDI_CAP_READ_MAP	0x00000010
  #define BDI_CAP_WRITE_MAP	0x00000020
  #define BDI_CAP_EXEC_MAP	0x00000040
  #define BDI_CAP_NO_ACCT_WB	0x00000080
  #define BDI_CAP_SWAP_BACKED	0x00000100
  
  #define BDI_CAP_VMFLAGS \
  	(BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP)
  
  #define BDI_CAP_NO_ACCT_AND_WRITEBACK \
  	(BDI_CAP_NO_WRITEBACK | BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_ACCT_WB)
  
  #if defined(VM_MAYREAD) && \
  	(BDI_CAP_READ_MAP != VM_MAYREAD || \
  	 BDI_CAP_WRITE_MAP != VM_MAYWRITE || \
  	 BDI_CAP_EXEC_MAP != VM_MAYEXEC)
  #error please change backing_dev_info::capabilities flags
  #endif
  
  extern struct backing_dev_info default_backing_dev_info;
  extern struct backing_dev_info noop_backing_dev_info;
  void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page);
  
  int writeback_in_progress(struct backing_dev_info *bdi);
  
  static inline int bdi_congested(struct backing_dev_info *bdi, int bdi_bits)
  {
  	if (bdi->congested_fn)
  		return bdi->congested_fn(bdi->congested_data, bdi_bits);
  	return (bdi->state & bdi_bits);
  }
  
  static inline int bdi_read_congested(struct backing_dev_info *bdi)
  {
  	return bdi_congested(bdi, 1 << BDI_sync_congested);
  }
  
  static inline int bdi_write_congested(struct backing_dev_info *bdi)
  {
  	return bdi_congested(bdi, 1 << BDI_async_congested);
  }
  
  static inline int bdi_rw_congested(struct backing_dev_info *bdi)
  {
  	return bdi_congested(bdi, (1 << BDI_sync_congested) |
  				  (1 << BDI_async_congested));
  }
  
  enum {
  	BLK_RW_ASYNC	= 0,
  	BLK_RW_SYNC	= 1,
  };
  
  void clear_bdi_congested(struct backing_dev_info *bdi, int sync);
  void set_bdi_congested(struct backing_dev_info *bdi, int sync);
  long congestion_wait(int sync, long timeout);
  
  
  static inline bool bdi_cap_writeback_dirty(struct backing_dev_info *bdi)
  {
  	return !(bdi->capabilities & BDI_CAP_NO_WRITEBACK);
  }
  
  static inline bool bdi_cap_account_dirty(struct backing_dev_info *bdi)
  {
  	return !(bdi->capabilities & BDI_CAP_NO_ACCT_DIRTY);
  }
  
  static inline bool bdi_cap_account_writeback(struct backing_dev_info *bdi)
  {
  	/* Paranoia: BDI_CAP_NO_WRITEBACK implies BDI_CAP_NO_ACCT_WB */
  	return !(bdi->capabilities & (BDI_CAP_NO_ACCT_WB |
  				      BDI_CAP_NO_WRITEBACK));
  }
  
  static inline bool bdi_cap_swap_backed(struct backing_dev_info *bdi)
  {
  	return bdi->capabilities & BDI_CAP_SWAP_BACKED;
  }
  
  static inline bool bdi_cap_flush_forker(struct backing_dev_info *bdi)
  {
  	return bdi == &default_backing_dev_info;
  }
  
  static inline bool mapping_cap_writeback_dirty(struct address_space *mapping)
  {
  	return bdi_cap_writeback_dirty(mapping->backing_dev_info);
  }
  
  static inline bool mapping_cap_account_dirty(struct address_space *mapping)
  {
  	return bdi_cap_account_dirty(mapping->backing_dev_info);
  }
  
  static inline bool mapping_cap_swap_backed(struct address_space *mapping)
  {
  	return bdi_cap_swap_backed(mapping->backing_dev_info);
  }
  
  static inline int bdi_sched_wait(void *word)
  {
  	schedule();
  	return 0;
  }
  
  static inline void blk_run_backing_dev(struct backing_dev_info *bdi,
  				       struct page *page)
  {
  	if (bdi && bdi->unplug_io_fn)
  		bdi->unplug_io_fn(bdi, page);
  }
  
  static inline void blk_run_address_space(struct address_space *mapping)
  {
  	if (mapping)
  		blk_run_backing_dev(mapping->backing_dev_info, NULL);
  }
  
  #endif		/* _LINUX_BACKING_DEV_H */
  