#include <linux/wait.h>
  #include <linux/backing-dev.h>
  #include <linux/fs.h>
  #include <linux/sched.h>
  #include <linux/module.h>

  #include <linux/writeback.h>
  #include <linux/device.h>
  
  
  static struct class *bdi_class;

  #ifdef CONFIG_DEBUG_FS
  #include <linux/debugfs.h>
  #include <linux/seq_file.h>
  
  static struct dentry *bdi_debug_root;
  
  static void bdi_debug_init(void)
  {
  	bdi_debug_root = debugfs_create_dir("bdi", NULL);
  }
  
  static int bdi_debug_stats_show(struct seq_file *m, void *v)
  {
  	struct backing_dev_info *bdi = m->private;

  	unsigned long background_thresh;
  	unsigned long dirty_thresh;
  	unsigned long bdi_thresh;

  
  	get_dirty_limits(&background_thresh, &dirty_thresh, &bdi_thresh, bdi);
  
  #define K(x) ((x) << (PAGE_SHIFT - 10))
  	seq_printf(m,
  		   "BdiWriteback:     %8lu kB
  "
  		   "BdiReclaimable:   %8lu kB
  "
  		   "BdiDirtyThresh:   %8lu kB
  "
  		   "DirtyThresh:      %8lu kB
  "
  		   "BackgroundThresh: %8lu kB
  ",
  		   (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
  		   (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
  		   K(bdi_thresh),
  		   K(dirty_thresh),
  		   K(background_thresh));
  #undef K
  
  	return 0;
  }
  
  static int bdi_debug_stats_open(struct inode *inode, struct file *file)
  {
  	return single_open(file, bdi_debug_stats_show, inode->i_private);
  }
  
  static const struct file_operations bdi_debug_stats_fops = {
  	.open		= bdi_debug_stats_open,
  	.read		= seq_read,
  	.llseek		= seq_lseek,
  	.release	= single_release,
  };
  
  static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
  {
  	bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
  	bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
  					       bdi, &bdi_debug_stats_fops);
  }
  
  static void bdi_debug_unregister(struct backing_dev_info *bdi)
  {
  	debugfs_remove(bdi->debug_stats);
  	debugfs_remove(bdi->debug_dir);
  }
  #else
  static inline void bdi_debug_init(void)
  {
  }
  static inline void bdi_debug_register(struct backing_dev_info *bdi,
  				      const char *name)
  {
  }
  static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
  {
  }
  #endif

  static ssize_t read_ahead_kb_store(struct device *dev,
  				  struct device_attribute *attr,
  				  const char *buf, size_t count)
  {
  	struct backing_dev_info *bdi = dev_get_drvdata(dev);
  	char *end;
  	unsigned long read_ahead_kb;
  	ssize_t ret = -EINVAL;
  
  	read_ahead_kb = simple_strtoul(buf, &end, 10);
  	if (*buf && (end[0] == '\0' || (end[0] == '
  ' && end[1] == '\0'))) {
  		bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
  		ret = count;
  	}
  	return ret;
  }
  
  #define K(pages) ((pages) << (PAGE_SHIFT - 10))
  
  #define BDI_SHOW(name, expr)						\
  static ssize_t name##_show(struct device *dev,				\
  			   struct device_attribute *attr, char *page)	\
  {									\
  	struct backing_dev_info *bdi = dev_get_drvdata(dev);		\
  									\
  	return snprintf(page, PAGE_SIZE-1, "%lld
  ", (long long)expr);	\
  }
  
  BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))

  static ssize_t min_ratio_store(struct device *dev,
  		struct device_attribute *attr, const char *buf, size_t count)
  {
  	struct backing_dev_info *bdi = dev_get_drvdata(dev);
  	char *end;
  	unsigned int ratio;
  	ssize_t ret = -EINVAL;
  
  	ratio = simple_strtoul(buf, &end, 10);
  	if (*buf && (end[0] == '\0' || (end[0] == '
  ' && end[1] == '\0'))) {
  		ret = bdi_set_min_ratio(bdi, ratio);
  		if (!ret)
  			ret = count;
  	}
  	return ret;
  }
  BDI_SHOW(min_ratio, bdi->min_ratio)

  static ssize_t max_ratio_store(struct device *dev,
  		struct device_attribute *attr, const char *buf, size_t count)
  {
  	struct backing_dev_info *bdi = dev_get_drvdata(dev);
  	char *end;
  	unsigned int ratio;
  	ssize_t ret = -EINVAL;
  
  	ratio = simple_strtoul(buf, &end, 10);
  	if (*buf && (end[0] == '\0' || (end[0] == '
  ' && end[1] == '\0'))) {
  		ret = bdi_set_max_ratio(bdi, ratio);
  		if (!ret)
  			ret = count;
  	}
  	return ret;
  }
  BDI_SHOW(max_ratio, bdi->max_ratio)

  #define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
  
  static struct device_attribute bdi_dev_attrs[] = {
  	__ATTR_RW(read_ahead_kb),

  	__ATTR_RW(min_ratio),

  	__ATTR_RW(max_ratio),

  	__ATTR_NULL,
  };
  
  static __init int bdi_class_init(void)
  {
  	bdi_class = class_create(THIS_MODULE, "bdi");
  	bdi_class->dev_attrs = bdi_dev_attrs;

  	bdi_debug_init();

  	return 0;
  }

  postcore_initcall(bdi_class_init);

  
  int bdi_register(struct backing_dev_info *bdi, struct device *parent,
  		const char *fmt, ...)
  {

  	va_list args;
  	int ret = 0;
  	struct device *dev;

  	if (bdi->dev)	/* The driver needs to use separate queues per device */

  		goto exit;

  	va_start(args, fmt);

  	dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);

  	va_end(args);

  	if (IS_ERR(dev)) {
  		ret = PTR_ERR(dev);
  		goto exit;
  	}
  
  	bdi->dev = dev;

  	bdi_debug_register(bdi, dev_name(dev));

  
  exit:

  	return ret;
  }
  EXPORT_SYMBOL(bdi_register);
  
  int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
  {
  	return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
  }
  EXPORT_SYMBOL(bdi_register_dev);
  
  void bdi_unregister(struct backing_dev_info *bdi)
  {
  	if (bdi->dev) {

  		bdi_debug_unregister(bdi);

  		device_unregister(bdi->dev);
  		bdi->dev = NULL;
  	}
  }
  EXPORT_SYMBOL(bdi_unregister);

  int bdi_init(struct backing_dev_info *bdi)
  {

  	int i;

  	int err;

  	bdi->dev = NULL;

  	bdi->min_ratio = 0;

  	bdi->max_ratio = 100;
  	bdi->max_prop_frac = PROP_FRAC_BASE;

  	for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {

  		err = percpu_counter_init(&bdi->bdi_stat[i], 0);

  		if (err)
  			goto err;
  	}
  
  	bdi->dirty_exceeded = 0;
  	err = prop_local_init_percpu(&bdi->completions);
  
  	if (err) {
  err:

  		while (i--)

  			percpu_counter_destroy(&bdi->bdi_stat[i]);

  	}
  
  	return err;
  }
  EXPORT_SYMBOL(bdi_init);
  
  void bdi_destroy(struct backing_dev_info *bdi)
  {
  	int i;

  	bdi_unregister(bdi);

  	for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
  		percpu_counter_destroy(&bdi->bdi_stat[i]);

  
  	prop_local_destroy_percpu(&bdi->completions);

  }
  EXPORT_SYMBOL(bdi_destroy);

  static wait_queue_head_t congestion_wqh[2] = {
  		__WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
  		__WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
  	};
  
  
  void clear_bdi_congested(struct backing_dev_info *bdi, int rw)
  {
  	enum bdi_state bit;
  	wait_queue_head_t *wqh = &congestion_wqh[rw];
  
  	bit = (rw == WRITE) ? BDI_write_congested : BDI_read_congested;
  	clear_bit(bit, &bdi->state);
  	smp_mb__after_clear_bit();
  	if (waitqueue_active(wqh))
  		wake_up(wqh);
  }
  EXPORT_SYMBOL(clear_bdi_congested);
  
  void set_bdi_congested(struct backing_dev_info *bdi, int rw)
  {
  	enum bdi_state bit;
  
  	bit = (rw == WRITE) ? BDI_write_congested : BDI_read_congested;
  	set_bit(bit, &bdi->state);
  }
  EXPORT_SYMBOL(set_bdi_congested);
  
  /**
   * congestion_wait - wait for a backing_dev to become uncongested
   * @rw: READ or WRITE
   * @timeout: timeout in jiffies
   *
   * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
   * write congestion.  If no backing_devs are congested then just wait for the
   * next write to be completed.
   */
  long congestion_wait(int rw, long timeout)
  {
  	long ret;
  	DEFINE_WAIT(wait);
  	wait_queue_head_t *wqh = &congestion_wqh[rw];
  
  	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
  	ret = io_schedule_timeout(timeout);
  	finish_wait(wqh, &wait);
  	return ret;
  }
  EXPORT_SYMBOL(congestion_wait);