/*
   * fs/fs-writeback.c
   *
   * Copyright (C) 2002, Linus Torvalds.
   *
   * Contains all the functions related to writing back and waiting
   * upon dirty inodes against superblocks, and writing back dirty
   * pages against inodes.  ie: data writeback.  Writeout of the
   * inode itself is not handled here.
   *

   * 10Apr2002	Andrew Morton

   *		Split out of fs/inode.c
   *		Additions for address_space-based writeback
   */
  
  #include <linux/kernel.h>

  #include <linux/module.h>

  #include <linux/spinlock.h>
  #include <linux/sched.h>
  #include <linux/fs.h>
  #include <linux/mm.h>

  #include <linux/kthread.h>
  #include <linux/freezer.h>

  #include <linux/writeback.h>
  #include <linux/blkdev.h>
  #include <linux/backing-dev.h>
  #include <linux/buffer_head.h>

  #include "internal.h"

  #define inode_to_bdi(inode)	((inode)->i_mapping->backing_dev_info)

  /*

   * We don't actually have pdflush, but this one is exported though /proc...
   */
  int nr_pdflush_threads;
  
  /*

   * Passed into wb_writeback(), essentially a subset of writeback_control
   */
  struct wb_writeback_args {
  	long nr_pages;
  	struct super_block *sb;
  	enum writeback_sync_modes sync_mode;

  	int for_kupdate:1;
  	int range_cyclic:1;
  	int for_background:1;

  };
  
  /*

   * Work items for the bdi_writeback threads

   */

  struct bdi_work {

  	struct list_head list;		/* pending work list */
  	struct rcu_head rcu_head;	/* for RCU free/clear of work */

  	unsigned long seen;		/* threads that have seen this work */
  	atomic_t pending;		/* number of threads still to do work */

  	struct wb_writeback_args args;	/* writeback arguments */

  	unsigned long state;		/* flag bits, see WS_* */

  };
  
  enum {
  	WS_USED_B = 0,
  	WS_ONSTACK_B,
  };
  
  #define WS_USED (1 << WS_USED_B)
  #define WS_ONSTACK (1 << WS_ONSTACK_B)
  
  static inline bool bdi_work_on_stack(struct bdi_work *work)
  {
  	return test_bit(WS_ONSTACK_B, &work->state);
  }
  
  static inline void bdi_work_init(struct bdi_work *work,

  				 struct wb_writeback_args *args)

  {
  	INIT_RCU_HEAD(&work->rcu_head);

  	work->args = *args;

  	work->state = WS_USED;
  }

  /**
   * writeback_in_progress - determine whether there is writeback in progress
   * @bdi: the device's backing_dev_info structure.
   *

   * Determine whether there is writeback waiting to be handled against a
   * backing device.

   */
  int writeback_in_progress(struct backing_dev_info *bdi)
  {

  	return !list_empty(&bdi->work_list);

  }

  static void bdi_work_clear(struct bdi_work *work)

  {

  	clear_bit(WS_USED_B, &work->state);
  	smp_mb__after_clear_bit();

  	/*
  	 * work can have disappeared at this point. bit waitq functions
  	 * should be able to tolerate this, provided bdi_sched_wait does
  	 * not dereference it's pointer argument.
  	*/

  	wake_up_bit(&work->state, WS_USED_B);

  }

  static void bdi_work_free(struct rcu_head *head)

  {

  	struct bdi_work *work = container_of(head, struct bdi_work, rcu_head);

  	if (!bdi_work_on_stack(work))
  		kfree(work);
  	else
  		bdi_work_clear(work);

  }

  static void wb_work_complete(struct bdi_work *work)

  {

  	const enum writeback_sync_modes sync_mode = work->args.sync_mode;

  	int onstack = bdi_work_on_stack(work);

  
  	/*

  	 * For allocated work, we can clear the done/seen bit right here.
  	 * For on-stack work, we need to postpone both the clear and free
  	 * to after the RCU grace period, since the stack could be invalidated
  	 * as soon as bdi_work_clear() has done the wakeup.

  	 */

  	if (!onstack)

  		bdi_work_clear(work);

  	if (sync_mode == WB_SYNC_NONE || onstack)

  		call_rcu(&work->rcu_head, bdi_work_free);
  }

  static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
  {

  	/*

  	 * The caller has retrieved the work arguments from this work,
  	 * drop our reference. If this is the last ref, delete and free it

  	 */

  	if (atomic_dec_and_test(&work->pending)) {
  		struct backing_dev_info *bdi = wb->bdi;

  		spin_lock(&bdi->wb_lock);
  		list_del_rcu(&work->list);
  		spin_unlock(&bdi->wb_lock);

  		wb_work_complete(work);
  	}
  }

  static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work)
  {

  	work->seen = bdi->wb_mask;
  	BUG_ON(!work->seen);
  	atomic_set(&work->pending, bdi->wb_cnt);
  	BUG_ON(!bdi->wb_cnt);

  	/*

  	 * list_add_tail_rcu() contains the necessary barriers to
  	 * make sure the above stores are seen before the item is
  	 * noticed on the list

  	 */

  	spin_lock(&bdi->wb_lock);
  	list_add_tail_rcu(&work->list, &bdi->work_list);
  	spin_unlock(&bdi->wb_lock);

  
  	/*
  	 * If the default thread isn't there, make sure we add it. When
  	 * it gets created and wakes up, we'll run this work.
  	 */
  	if (unlikely(list_empty_careful(&bdi->wb_list)))
  		wake_up_process(default_backing_dev_info.wb.task);
  	else {
  		struct bdi_writeback *wb = &bdi->wb;

  		if (wb->task)

  			wake_up_process(wb->task);

  	}

  }

  /*
   * Used for on-stack allocated work items. The caller needs to wait until
   * the wb threads have acked the work before it's safe to continue.
   */
  static void bdi_wait_on_work_clear(struct bdi_work *work)
  {
  	wait_on_bit(&work->state, WS_USED_B, bdi_sched_wait,
  		    TASK_UNINTERRUPTIBLE);
  }

  static void bdi_alloc_queue_work(struct backing_dev_info *bdi,

  				 struct wb_writeback_args *args)

  {

  	struct bdi_work *work;

  	/*
  	 * This is WB_SYNC_NONE writeback, so if allocation fails just
  	 * wakeup the thread for old dirty data writeback
  	 */

  	work = kmalloc(sizeof(*work), GFP_ATOMIC);

  	if (work) {

  		bdi_work_init(work, args);

  		bdi_queue_work(bdi, work);
  	} else {
  		struct bdi_writeback *wb = &bdi->wb;

  		if (wb->task)
  			wake_up_process(wb->task);
  	}

  }

  /**
   * bdi_sync_writeback - start and wait for writeback
   * @bdi: the backing device to write from
   * @sb: write inodes from this super_block
   *
   * Description:
   *   This does WB_SYNC_ALL data integrity writeback and waits for the
   *   IO to complete. Callers must hold the sb s_umount semaphore for
   *   reading, to avoid having the super disappear before we are done.
   */
  static void bdi_sync_writeback(struct backing_dev_info *bdi,
  			       struct super_block *sb)

  {

  	struct wb_writeback_args args = {
  		.sb		= sb,
  		.sync_mode	= WB_SYNC_ALL,
  		.nr_pages	= LONG_MAX,
  		.range_cyclic	= 0,
  	};
  	struct bdi_work work;

  	bdi_work_init(&work, &args);
  	work.state |= WS_ONSTACK;

  	bdi_queue_work(bdi, &work);
  	bdi_wait_on_work_clear(&work);
  }
  
  /**
   * bdi_start_writeback - start writeback
   * @bdi: the backing device to write from
   * @nr_pages: the number of pages to write
   *
   * Description:
   *   This does WB_SYNC_NONE opportunistic writeback. The IO is only
   *   started when this function returns, we make no guarentees on
   *   completion. Caller need not hold sb s_umount semaphore.
   *
   */

  void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
  			 long nr_pages)

  {
  	struct wb_writeback_args args = {

  		.sb		= sb,

  		.sync_mode	= WB_SYNC_NONE,
  		.nr_pages	= nr_pages,
  		.range_cyclic	= 1,
  	};

  	/*
  	 * We treat @nr_pages=0 as the special case to do background writeback,
  	 * ie. to sync pages until the background dirty threshold is reached.
  	 */
  	if (!nr_pages) {
  		args.nr_pages = LONG_MAX;
  		args.for_background = 1;
  	}

  	bdi_alloc_queue_work(bdi, &args);

  }
  
  /*

   * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
   * furthest end of its superblock's dirty-inode list.
   *
   * Before stamping the inode's ->dirtied_when, we check to see whether it is

   * already the most-recently-dirtied inode on the b_dirty list.  If that is

   * the case then the inode must have been redirtied while it was being written
   * out and we don't reset its dirtied_when.
   */
  static void redirty_tail(struct inode *inode)
  {

  	struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;

  	if (!list_empty(&wb->b_dirty)) {

  		struct inode *tail;

  		tail = list_entry(wb->b_dirty.next, struct inode, i_list);

  		if (time_before(inode->dirtied_when, tail->dirtied_when))

  			inode->dirtied_when = jiffies;
  	}

  	list_move(&inode->i_list, &wb->b_dirty);

  }
  
  /*

   * requeue inode for re-scanning after bdi->b_io list is exhausted.

   */

  static void requeue_io(struct inode *inode)

  {

  	struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
  
  	list_move(&inode->i_list, &wb->b_more_io);

  }

  static void inode_sync_complete(struct inode *inode)
  {
  	/*
  	 * Prevent speculative execution through spin_unlock(&inode_lock);
  	 */
  	smp_mb();
  	wake_up_bit(&inode->i_state, __I_SYNC);
  }

  static bool inode_dirtied_after(struct inode *inode, unsigned long t)
  {
  	bool ret = time_after(inode->dirtied_when, t);
  #ifndef CONFIG_64BIT
  	/*
  	 * For inodes being constantly redirtied, dirtied_when can get stuck.
  	 * It _appears_ to be in the future, but is actually in distant past.
  	 * This test is necessary to prevent such wrapped-around relative times

  	 * from permanently stopping the whole bdi writeback.

  	 */
  	ret = ret && time_before_eq(inode->dirtied_when, jiffies);
  #endif
  	return ret;
  }

  /*

   * Move expired dirty inodes from @delaying_queue to @dispatch_queue.
   */
  static void move_expired_inodes(struct list_head *delaying_queue,
  			       struct list_head *dispatch_queue,
  				unsigned long *older_than_this)
  {

  	LIST_HEAD(tmp);
  	struct list_head *pos, *node;

  	struct super_block *sb = NULL;

  	struct inode *inode;

  	int do_sb_sort = 0;

  	while (!list_empty(delaying_queue)) {

  		inode = list_entry(delaying_queue->prev, struct inode, i_list);

  		if (older_than_this &&

  		    inode_dirtied_after(inode, *older_than_this))

  			break;

  		if (sb && sb != inode->i_sb)
  			do_sb_sort = 1;
  		sb = inode->i_sb;

  		list_move(&inode->i_list, &tmp);
  	}

  	/* just one sb in list, splice to dispatch_queue and we're done */
  	if (!do_sb_sort) {
  		list_splice(&tmp, dispatch_queue);
  		return;
  	}

  	/* Move inodes from one superblock together */
  	while (!list_empty(&tmp)) {
  		inode = list_entry(tmp.prev, struct inode, i_list);
  		sb = inode->i_sb;
  		list_for_each_prev_safe(pos, node, &tmp) {
  			inode = list_entry(pos, struct inode, i_list);
  			if (inode->i_sb == sb)
  				list_move(&inode->i_list, dispatch_queue);
  		}

  	}
  }
  
  /*
   * Queue all expired dirty inodes for io, eldest first.
   */

  static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)

  {

  	list_splice_init(&wb->b_more_io, wb->b_io.prev);
  	move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);

  }

  static int write_inode(struct inode *inode, int sync)

  {

  	if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
  		return inode->i_sb->s_op->write_inode(inode, sync);
  	return 0;

  }

  /*

   * Wait for writeback on an inode to complete.
   */
  static void inode_wait_for_writeback(struct inode *inode)
  {
  	DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
  	wait_queue_head_t *wqh;
  
  	wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
  	do {
  		spin_unlock(&inode_lock);
  		__wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
  		spin_lock(&inode_lock);
  	} while (inode->i_state & I_SYNC);
  }
  
  /*
   * Write out an inode's dirty pages.  Called under inode_lock.  Either the
   * caller has ref on the inode (either via __iget or via syscall against an fd)
   * or the inode has I_WILL_FREE set (via generic_forget_inode)
   *

   * If `wait' is set, wait on the writeout.
   *
   * The whole writeout design is quite complex and fragile.  We want to avoid
   * starvation of particular inodes when others are being redirtied, prevent
   * livelocks, etc.
   *
   * Called under inode_lock.
   */
  static int

  writeback_single_inode(struct inode *inode, struct writeback_control *wbc)

  {

  	struct address_space *mapping = inode->i_mapping;

  	int wait = wbc->sync_mode == WB_SYNC_ALL;

  	unsigned dirty;

  	int ret;

  	if (!atomic_read(&inode->i_count))
  		WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
  	else
  		WARN_ON(inode->i_state & I_WILL_FREE);
  
  	if (inode->i_state & I_SYNC) {
  		/*
  		 * If this inode is locked for writeback and we are not doing

  		 * writeback-for-data-integrity, move it to b_more_io so that

  		 * writeback can proceed with the other inodes on s_io.
  		 *
  		 * We'll have another go at writing back this inode when we

  		 * completed a full scan of b_io.

  		 */
  		if (!wait) {
  			requeue_io(inode);
  			return 0;
  		}
  
  		/*
  		 * It's a data-integrity sync.  We must wait.
  		 */
  		inode_wait_for_writeback(inode);
  	}

  	BUG_ON(inode->i_state & I_SYNC);

  	/* Set I_SYNC, reset I_DIRTY */

  	dirty = inode->i_state & I_DIRTY;

  	inode->i_state |= I_SYNC;

  	inode->i_state &= ~I_DIRTY;
  
  	spin_unlock(&inode_lock);
  
  	ret = do_writepages(mapping, wbc);
  
  	/* Don't write the inode if only I_DIRTY_PAGES was set */
  	if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
  		int err = write_inode(inode, wait);
  		if (ret == 0)
  			ret = err;
  	}
  
  	if (wait) {
  		int err = filemap_fdatawait(mapping);
  		if (ret == 0)
  			ret = err;
  	}
  
  	spin_lock(&inode_lock);

  	inode->i_state &= ~I_SYNC;

  	if (!(inode->i_state & (I_FREEING | I_CLEAR))) {

  		if ((inode->i_state & I_DIRTY_PAGES) && wbc->for_kupdate) {

  			/*

  			 * More pages get dirtied by a fast dirtier.
  			 */
  			goto select_queue;
  		} else if (inode->i_state & I_DIRTY) {
  			/*
  			 * At least XFS will redirty the inode during the
  			 * writeback (delalloc) and on io completion (isize).

  			 */
  			redirty_tail(inode);
  		} else if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {

  			/*
  			 * We didn't write back all the pages.  nfs_writepages()
  			 * sometimes bales out without doing anything. Redirty

  			 * the inode; Move it from b_io onto b_more_io/b_dirty.

  			 */
  			/*
  			 * akpm: if the caller was the kupdate function we put

  			 * this inode at the head of b_dirty so it gets first

  			 * consideration.  Otherwise, move it to the tail, for
  			 * the reasons described there.  I'm not really sure
  			 * how much sense this makes.  Presumably I had a good
  			 * reasons for doing it this way, and I'd rather not
  			 * muck with it at present.

  			 */
  			if (wbc->for_kupdate) {
  				/*

  				 * For the kupdate function we move the inode

  				 * to b_more_io so it will get more writeout as

  				 * soon as the queue becomes uncongested.

  				 */
  				inode->i_state |= I_DIRTY_PAGES;

  select_queue:

  				if (wbc->nr_to_write <= 0) {
  					/*
  					 * slice used up: queue for next turn
  					 */
  					requeue_io(inode);
  				} else {
  					/*
  					 * somehow blocked: retry later
  					 */
  					redirty_tail(inode);
  				}

  			} else {
  				/*
  				 * Otherwise fully redirty the inode so that
  				 * other inodes on this superblock will get some
  				 * writeout.  Otherwise heavy writing to one
  				 * file would indefinitely suspend writeout of
  				 * all the other files.
  				 */
  				inode->i_state |= I_DIRTY_PAGES;

  				redirty_tail(inode);

  			}

  		} else if (atomic_read(&inode->i_count)) {
  			/*
  			 * The inode is clean, inuse
  			 */
  			list_move(&inode->i_list, &inode_in_use);
  		} else {
  			/*
  			 * The inode is clean, unused
  			 */
  			list_move(&inode->i_list, &inode_unused);

  		}
  	}

  	inode_sync_complete(inode);

  	return ret;
  }

  static void unpin_sb_for_writeback(struct super_block **psb)
  {
  	struct super_block *sb = *psb;
  
  	if (sb) {
  		up_read(&sb->s_umount);
  		put_super(sb);
  		*psb = NULL;
  	}
  }

  /*
   * For WB_SYNC_NONE writeback, the caller does not have the sb pinned
   * before calling writeback. So make sure that we do pin it, so it doesn't
   * go away while we are writing inodes from it.
   *
   * Returns 0 if the super was successfully pinned (or pinning wasn't needed),
   * 1 if we failed.
   */
  static int pin_sb_for_writeback(struct writeback_control *wbc,

  				struct inode *inode, struct super_block **psb)

  {
  	struct super_block *sb = inode->i_sb;
  
  	/*

  	 * If this sb is already pinned, nothing more to do. If not and
  	 * *psb is non-NULL, unpin the old one first
  	 */
  	if (sb == *psb)
  		return 0;
  	else if (*psb)
  		unpin_sb_for_writeback(psb);
  
  	/*

  	 * Caller must already hold the ref for this
  	 */
  	if (wbc->sync_mode == WB_SYNC_ALL) {
  		WARN_ON(!rwsem_is_locked(&sb->s_umount));
  		return 0;
  	}
  
  	spin_lock(&sb_lock);
  	sb->s_count++;
  	if (down_read_trylock(&sb->s_umount)) {
  		if (sb->s_root) {
  			spin_unlock(&sb_lock);

  			goto pinned;

  		}
  		/*
  		 * umounted, drop rwsem again and fall through to failure
  		 */
  		up_read(&sb->s_umount);
  	}
  
  	sb->s_count--;
  	spin_unlock(&sb_lock);
  	return 1;

  pinned:
  	*psb = sb;
  	return 0;

  }
  
  static void writeback_inodes_wb(struct bdi_writeback *wb,
  				struct writeback_control *wbc)

  {

  	struct super_block *sb = wbc->sb, *pin_sb = NULL;

  	const int is_blkdev_sb = sb_is_blkdev_sb(sb);

  	const unsigned long start = jiffies;	/* livelock avoidance */

  	spin_lock(&inode_lock);

  	if (!wbc->for_kupdate || list_empty(&wb->b_io))
  		queue_io(wb, wbc->older_than_this);

  	while (!list_empty(&wb->b_io)) {
  		struct inode *inode = list_entry(wb->b_io.prev,

  						struct inode, i_list);

  		long pages_skipped;

  		/*
  		 * super block given and doesn't match, skip this inode
  		 */
  		if (sb && sb != inode->i_sb) {
  			redirty_tail(inode);
  			continue;
  		}

  		if (!bdi_cap_writeback_dirty(wb->bdi)) {

  			redirty_tail(inode);

  			if (is_blkdev_sb) {

  				/*
  				 * Dirty memory-backed blockdev: the ramdisk
  				 * driver does this.  Skip just this inode
  				 */
  				continue;
  			}
  			/*
  			 * Dirty memory-backed inode against a filesystem other
  			 * than the kernel-internal bdev filesystem.  Skip the
  			 * entire superblock.
  			 */
  			break;
  		}

  		if (inode->i_state & (I_NEW | I_WILL_FREE)) {

  			requeue_io(inode);
  			continue;
  		}

  		if (wbc->nonblocking && bdi_write_congested(wb->bdi)) {

  			wbc->encountered_congestion = 1;

  			if (!is_blkdev_sb)

  				break;		/* Skip a congested fs */

  			requeue_io(inode);

  			continue;		/* Skip a congested blockdev */
  		}

  		/*
  		 * Was this inode dirtied after sync_sb_inodes was called?
  		 * This keeps sync from extra jobs and livelock.
  		 */
  		if (inode_dirtied_after(inode, start))

  			break;

  		if (pin_sb_for_writeback(wbc, inode, &pin_sb)) {

  			requeue_io(inode);
  			continue;
  		}

  		BUG_ON(inode->i_state & (I_FREEING | I_CLEAR));

  		__iget(inode);
  		pages_skipped = wbc->pages_skipped;

  		writeback_single_inode(inode, wbc);

  		if (wbc->pages_skipped != pages_skipped) {
  			/*
  			 * writeback is not making progress due to locked
  			 * buffers.  Skip this inode for now.
  			 */

  			redirty_tail(inode);

  		}
  		spin_unlock(&inode_lock);

  		iput(inode);

  		cond_resched();

  		spin_lock(&inode_lock);

  		if (wbc->nr_to_write <= 0) {
  			wbc->more_io = 1;

  			break;

  		}

  		if (!list_empty(&wb->b_more_io))

  			wbc->more_io = 1;

  	}

  	unpin_sb_for_writeback(&pin_sb);

  	spin_unlock(&inode_lock);
  	/* Leave any unwritten inodes on b_io */
  }

  void writeback_inodes_wbc(struct writeback_control *wbc)
  {
  	struct backing_dev_info *bdi = wbc->bdi;
  
  	writeback_inodes_wb(&bdi->wb, wbc);
  }

  /*

   * The maximum number of pages to writeout in a single bdi flush/kupdate
   * operation.  We do this so we don't hold I_SYNC against an inode for
   * enormous amounts of time, which would block a userspace task which has
   * been forced to throttle against that inode.  Also, the code reevaluates
   * the dirty each time it has written this many pages.
   */
  #define MAX_WRITEBACK_PAGES     1024
  
  static inline bool over_bground_thresh(void)
  {
  	unsigned long background_thresh, dirty_thresh;
  
  	get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
  
  	return (global_page_state(NR_FILE_DIRTY) +
  		global_page_state(NR_UNSTABLE_NFS) >= background_thresh);
  }
  
  /*
   * Explicit flushing or periodic writeback of "old" data.

   *

   * Define "old": the first time one of an inode's pages is dirtied, we mark the
   * dirtying-time in the inode's address_space.  So this periodic writeback code
   * just walks the superblock inode list, writing back any inodes which are
   * older than a specific point in time.

   *

   * Try to run once per dirty_writeback_interval.  But if a writeback event
   * takes longer than a dirty_writeback_interval interval, then leave a
   * one-second gap.

   *

   * older_than_this takes precedence over nr_to_write.  So we'll only write back
   * all dirty pages if they are all attached to "old" mappings.

   */

  static long wb_writeback(struct bdi_writeback *wb,
  			 struct wb_writeback_args *args)

  {

  	struct writeback_control wbc = {
  		.bdi			= wb->bdi,

  		.sb			= args->sb,
  		.sync_mode		= args->sync_mode,

  		.older_than_this	= NULL,

  		.for_kupdate		= args->for_kupdate,
  		.range_cyclic		= args->range_cyclic,

  	};
  	unsigned long oldest_jif;
  	long wrote = 0;

  	struct inode *inode;

  	if (wbc.for_kupdate) {
  		wbc.older_than_this = &oldest_jif;
  		oldest_jif = jiffies -
  				msecs_to_jiffies(dirty_expire_interval * 10);
  	}

  	if (!wbc.range_cyclic) {
  		wbc.range_start = 0;
  		wbc.range_end = LLONG_MAX;
  	}

  	for (;;) {
  		/*

  		 * Stop writeback when nr_pages has been consumed

  		 */

  		if (args->nr_pages <= 0)

  			break;

  		/*

  		 * For background writeout, stop when we are below the
  		 * background dirty threshold

  		 */

  		if (args->for_background && !over_bground_thresh())

  			break;

  		wbc.more_io = 0;
  		wbc.encountered_congestion = 0;
  		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
  		wbc.pages_skipped = 0;
  		writeback_inodes_wb(wb, &wbc);

  		args->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;

  		wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write;
  
  		/*

  		 * If we consumed everything, see if we have more

  		 */

  		if (wbc.nr_to_write <= 0)
  			continue;
  		/*
  		 * Didn't write everything and we don't have more IO, bail
  		 */
  		if (!wbc.more_io)

  			break;

  		/*
  		 * Did we write something? Try for more
  		 */
  		if (wbc.nr_to_write < MAX_WRITEBACK_PAGES)
  			continue;
  		/*
  		 * Nothing written. Wait for some inode to
  		 * become available for writeback. Otherwise
  		 * we'll just busyloop.
  		 */
  		spin_lock(&inode_lock);
  		if (!list_empty(&wb->b_more_io))  {
  			inode = list_entry(wb->b_more_io.prev,
  						struct inode, i_list);
  			inode_wait_for_writeback(inode);

  		}

  		spin_unlock(&inode_lock);

  	}
  
  	return wrote;
  }
  
  /*
   * Return the next bdi_work struct that hasn't been processed by this

   * wb thread yet. ->seen is initially set for each thread that exists
   * for this device, when a thread first notices a piece of work it
   * clears its bit. Depending on writeback type, the thread will notify
   * completion on either receiving the work (WB_SYNC_NONE) or after
   * it is done (WB_SYNC_ALL).

   */
  static struct bdi_work *get_next_work_item(struct backing_dev_info *bdi,
  					   struct bdi_writeback *wb)
  {
  	struct bdi_work *work, *ret = NULL;
  
  	rcu_read_lock();
  
  	list_for_each_entry_rcu(work, &bdi->work_list, list) {

  		if (!test_bit(wb->nr, &work->seen))

  			continue;

  		clear_bit(wb->nr, &work->seen);

  
  		ret = work;
  		break;
  	}
  
  	rcu_read_unlock();
  	return ret;
  }
  
  static long wb_check_old_data_flush(struct bdi_writeback *wb)
  {
  	unsigned long expired;
  	long nr_pages;
  
  	expired = wb->last_old_flush +
  			msecs_to_jiffies(dirty_writeback_interval * 10);
  	if (time_before(jiffies, expired))
  		return 0;
  
  	wb->last_old_flush = jiffies;
  	nr_pages = global_page_state(NR_FILE_DIRTY) +
  			global_page_state(NR_UNSTABLE_NFS) +
  			(inodes_stat.nr_inodes - inodes_stat.nr_unused);

  	if (nr_pages) {
  		struct wb_writeback_args args = {
  			.nr_pages	= nr_pages,
  			.sync_mode	= WB_SYNC_NONE,
  			.for_kupdate	= 1,
  			.range_cyclic	= 1,
  		};
  
  		return wb_writeback(wb, &args);
  	}

  
  	return 0;
  }
  
  /*
   * Retrieve work items and do the writeback they describe
   */
  long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
  {
  	struct backing_dev_info *bdi = wb->bdi;
  	struct bdi_work *work;

  	long wrote = 0;

  
  	while ((work = get_next_work_item(bdi, wb)) != NULL) {

  		struct wb_writeback_args args = work->args;

  
  		/*
  		 * Override sync mode, in case we must wait for completion
  		 */
  		if (force_wait)

  			work->args.sync_mode = args.sync_mode = WB_SYNC_ALL;

  
  		/*
  		 * If this isn't a data integrity operation, just notify
  		 * that we have seen this work and we are now starting it.
  		 */

  		if (args.sync_mode == WB_SYNC_NONE)

  			wb_clear_pending(wb, work);

  		wrote += wb_writeback(wb, &args);

  
  		/*
  		 * This is a data integrity writeback, so only do the
  		 * notification when we have completed the work.
  		 */

  		if (args.sync_mode == WB_SYNC_ALL)

  			wb_clear_pending(wb, work);
  	}
  
  	/*
  	 * Check for periodic writeback, kupdated() style
  	 */
  	wrote += wb_check_old_data_flush(wb);
  
  	return wrote;
  }
  
  /*
   * Handle writeback of dirty data for the device backed by this bdi. Also
   * wakes up periodically and does kupdated style flushing.
   */
  int bdi_writeback_task(struct bdi_writeback *wb)
  {
  	unsigned long last_active = jiffies;
  	unsigned long wait_jiffies = -1UL;
  	long pages_written;
  
  	while (!kthread_should_stop()) {
  		pages_written = wb_do_writeback(wb, 0);
  
  		if (pages_written)
  			last_active = jiffies;
  		else if (wait_jiffies != -1UL) {
  			unsigned long max_idle;

  			/*

  			 * Longest period of inactivity that we tolerate. If we
  			 * see dirty data again later, the task will get
  			 * recreated automatically.

  			 */

  			max_idle = max(5UL * 60 * HZ, wait_jiffies);
  			if (time_after(jiffies, max_idle + last_active))
  				break;
  		}
  
  		wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);

  		schedule_timeout_interruptible(wait_jiffies);

  		try_to_freeze();
  	}
  
  	return 0;
  }
  
  /*

   * Schedule writeback for all backing devices. This does WB_SYNC_NONE
   * writeback, for integrity writeback see bdi_sync_writeback().

   */

  static void bdi_writeback_all(struct super_block *sb, long nr_pages)

  {

  	struct wb_writeback_args args = {
  		.sb		= sb,
  		.nr_pages	= nr_pages,
  		.sync_mode	= WB_SYNC_NONE,
  	};

  	struct backing_dev_info *bdi;

  	rcu_read_lock();

  	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {

  		if (!bdi_has_dirty_io(bdi))
  			continue;

  		bdi_alloc_queue_work(bdi, &args);

  	}

  	rcu_read_unlock();

  }
  
  /*

   * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
   * the whole world.
   */
  void wakeup_flusher_threads(long nr_pages)
  {

  	if (nr_pages == 0)
  		nr_pages = global_page_state(NR_FILE_DIRTY) +
  				global_page_state(NR_UNSTABLE_NFS);

  	bdi_writeback_all(NULL, nr_pages);

  }
  
  static noinline void block_dump___mark_inode_dirty(struct inode *inode)
  {
  	if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
  		struct dentry *dentry;
  		const char *name = "?";
  
  		dentry = d_find_alias(inode);
  		if (dentry) {
  			spin_lock(&dentry->d_lock);
  			name = (const char *) dentry->d_name.name;
  		}
  		printk(KERN_DEBUG
  		       "%s(%d): dirtied inode %lu (%s) on %s
  ",
  		       current->comm, task_pid_nr(current), inode->i_ino,
  		       name, inode->i_sb->s_id);
  		if (dentry) {
  			spin_unlock(&dentry->d_lock);
  			dput(dentry);
  		}
  	}
  }
  
  /**
   *	__mark_inode_dirty -	internal function
   *	@inode: inode to mark
   *	@flags: what kind of dirty (i.e. I_DIRTY_SYNC)
   *	Mark an inode as dirty. Callers should use mark_inode_dirty or
   *  	mark_inode_dirty_sync.

   *

   * Put the inode on the super block's dirty list.
   *
   * CAREFUL! We mark it dirty unconditionally, but move it onto the
   * dirty list only if it is hashed or if it refers to a blockdev.
   * If it was not hashed, it will never be added to the dirty list
   * even if it is later hashed, as it will have been marked dirty already.
   *
   * In short, make sure you hash any inodes _before_ you start marking
   * them dirty.

   *

   * This function *must* be atomic for the I_DIRTY_PAGES case -
   * set_page_dirty() is called under spinlock in several places.

   *

   * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
   * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
   * the kernel-internal blockdev inode represents the dirtying time of the
   * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
   * page->mapping->host, so the page-dirtying time is recorded in the internal
   * blockdev inode.

   */

  void __mark_inode_dirty(struct inode *inode, int flags)

  {

  	struct super_block *sb = inode->i_sb;

  	/*
  	 * Don't do this for I_DIRTY_PAGES - that doesn't actually
  	 * dirty the inode itself
  	 */
  	if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
  		if (sb->s_op->dirty_inode)
  			sb->s_op->dirty_inode(inode);
  	}
  
  	/*
  	 * make sure that changes are seen by all cpus before we test i_state
  	 * -- mikulas
  	 */
  	smp_mb();
  
  	/* avoid the locking if we can */
  	if ((inode->i_state & flags) == flags)
  		return;
  
  	if (unlikely(block_dump))
  		block_dump___mark_inode_dirty(inode);
  
  	spin_lock(&inode_lock);
  	if ((inode->i_state & flags) != flags) {
  		const int was_dirty = inode->i_state & I_DIRTY;
  
  		inode->i_state |= flags;
  
  		/*
  		 * If the inode is being synced, just update its dirty state.
  		 * The unlocker will place the inode on the appropriate
  		 * superblock list, based upon its state.
  		 */
  		if (inode->i_state & I_SYNC)
  			goto out;
  
  		/*
  		 * Only add valid (hashed) inodes to the superblock's
  		 * dirty list.  Add blockdev inodes as well.
  		 */
  		if (!S_ISBLK(inode->i_mode)) {
  			if (hlist_unhashed(&inode->i_hash))
  				goto out;
  		}
  		if (inode->i_state & (I_FREEING|I_CLEAR))
  			goto out;
  
  		/*
  		 * If the inode was already on b_dirty/b_io/b_more_io, don't
  		 * reposition it (that would break b_dirty time-ordering).
  		 */
  		if (!was_dirty) {
  			struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;

  			struct backing_dev_info *bdi = wb->bdi;
  
  			if (bdi_cap_writeback_dirty(bdi) &&
  			    !test_bit(BDI_registered, &bdi->state)) {
  				WARN_ON(1);
  				printk(KERN_ERR "bdi-%s not registered
  ",
  								bdi->name);
  			}

  
  			inode->dirtied_when = jiffies;
  			list_move(&inode->i_list, &wb->b_dirty);

  		}

  	}

  out:
  	spin_unlock(&inode_lock);
  }
  EXPORT_SYMBOL(__mark_inode_dirty);
  
  /*
   * Write out a superblock's list of dirty inodes.  A wait will be performed
   * upon no inodes, all inodes or the final one, depending upon sync_mode.
   *
   * If older_than_this is non-NULL, then only write out inodes which
   * had their first dirtying at a time earlier than *older_than_this.
   *

   * If `bdi' is non-zero then we're being asked to writeback a specific queue.
   * This function assumes that the blockdev superblock's inodes are backed by
   * a variety of queues, so all inodes are searched.  For other superblocks,
   * assume that all inodes are backed by the same queue.
   *
   * The inodes to be written are parked on bdi->b_io.  They are moved back onto
   * bdi->b_dirty as they are selected for writing.  This way, none can be missed
   * on the writer throttling path, and we get decent balancing between many
   * throttled threads: we don't want them all piling up on inode_sync_wait.
   */

  static void wait_sb_inodes(struct super_block *sb)

  {
  	struct inode *inode, *old_inode = NULL;
  
  	/*
  	 * We need to be protected against the filesystem going from
  	 * r/o to r/w or vice versa.
  	 */

  	WARN_ON(!rwsem_is_locked(&sb->s_umount));

  
  	spin_lock(&inode_lock);
  
  	/*
  	 * Data integrity sync. Must wait for all pages under writeback,
  	 * because there may have been pages dirtied before our sync
  	 * call, but which had writeout started before we write it out.
  	 * In which case, the inode may not be on the dirty list, but
  	 * we still have to wait for that writeout.
  	 */

  	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {

  		struct address_space *mapping;
  
  		if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE|I_NEW))
  			continue;
  		mapping = inode->i_mapping;
  		if (mapping->nrpages == 0)
  			continue;
  		__iget(inode);
  		spin_unlock(&inode_lock);
  		/*
  		 * We hold a reference to 'inode' so it couldn't have
  		 * been removed from s_inodes list while we dropped the
  		 * inode_lock.  We cannot iput the inode now as we can
  		 * be holding the last reference and we cannot iput it
  		 * under inode_lock. So we keep the reference and iput
  		 * it later.
  		 */
  		iput(old_inode);
  		old_inode = inode;
  
  		filemap_fdatawait(mapping);
  
  		cond_resched();
  
  		spin_lock(&inode_lock);
  	}
  	spin_unlock(&inode_lock);
  	iput(old_inode);

  }

  /**
   * writeback_inodes_sb	-	writeback dirty inodes from given super_block
   * @sb: the superblock

   *

   * Start writeback on some inodes on this super_block. No guarantees are made
   * on how many (if any) will be written, and this function does not wait
   * for IO completion of submitted IO. The number of pages submitted is
   * returned.

   */

  void writeback_inodes_sb(struct super_block *sb)

  {

  	unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
  	unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
  	long nr_to_write;

  	nr_to_write = nr_dirty + nr_unstable +

  			(inodes_stat.nr_inodes - inodes_stat.nr_unused);

  	bdi_start_writeback(sb->s_bdi, sb, nr_to_write);

  }
  EXPORT_SYMBOL(writeback_inodes_sb);
  
  /**
   * sync_inodes_sb	-	sync sb inode pages
   * @sb: the superblock
   *
   * This function writes and waits on any dirty inode belonging to this
   * super_block. The number of pages synced is returned.
   */

  void sync_inodes_sb(struct super_block *sb)

  {

  	bdi_sync_writeback(sb->s_bdi, sb);
  	wait_sb_inodes(sb);

  }

  EXPORT_SYMBOL(sync_inodes_sb);

  /**

   * write_inode_now	-	write an inode to disk
   * @inode: inode to write to disk
   * @sync: whether the write should be synchronous or not
   *
   * This function commits an inode to disk immediately if it is dirty. This is
   * primarily needed by knfsd.

   *

   * The caller must either have a ref on the inode or must have set I_WILL_FREE.

   */

  int write_inode_now(struct inode *inode, int sync)
  {
  	int ret;
  	struct writeback_control wbc = {
  		.nr_to_write = LONG_MAX,

  		.sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,

  		.range_start = 0,
  		.range_end = LLONG_MAX,

  	};
  
  	if (!mapping_cap_writeback_dirty(inode->i_mapping))

  		wbc.nr_to_write = 0;

  
  	might_sleep();
  	spin_lock(&inode_lock);

  	ret = writeback_single_inode(inode, &wbc);

  	spin_unlock(&inode_lock);
  	if (sync)

  		inode_sync_wait(inode);

  	return ret;
  }
  EXPORT_SYMBOL(write_inode_now);
  
  /**
   * sync_inode - write an inode and its pages to disk.
   * @inode: the inode to sync
   * @wbc: controls the writeback mode
   *
   * sync_inode() will write an inode and its pages to disk.  It will also
   * correctly update the inode on its superblock's dirty inode lists and will
   * update inode->i_state.
   *
   * The caller must have a ref on the inode.
   */
  int sync_inode(struct inode *inode, struct writeback_control *wbc)
  {
  	int ret;
  
  	spin_lock(&inode_lock);

  	ret = writeback_single_inode(inode, wbc);

  	spin_unlock(&inode_lock);
  	return ret;
  }
  EXPORT_SYMBOL(sync_inode);