/*

   * Copyright (c) 2000-2002,2005 Silicon Graphics, Inc.

   * Copyright (c) 2008 Dave Chinner

   * All Rights Reserved.

   *

   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License as

   * published by the Free Software Foundation.
   *

   * This program is distributed in the hope that it would be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.

   *

   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write the Free Software Foundation,
   * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

   */

  #include "xfs.h"

  #include "xfs_fs.h"

  #include "xfs_types.h"

  #include "xfs_log.h"

  #include "xfs_inum.h"

  #include "xfs_trans.h"
  #include "xfs_sb.h"

  #include "xfs_ag.h"

  #include "xfs_mount.h"
  #include "xfs_trans_priv.h"

  #include "xfs_trace.h"

  #include "xfs_error.h"

  #ifdef DEBUG

  /*
   * Check that the list is sorted as it should be.
   */
  STATIC void
  xfs_ail_check(
  	struct xfs_ail	*ailp,
  	xfs_log_item_t	*lip)
  {
  	xfs_log_item_t	*prev_lip;
  
  	if (list_empty(&ailp->xa_ail))
  		return;
  
  	/*
  	 * Check the next and previous entries are valid.
  	 */
  	ASSERT((lip->li_flags & XFS_LI_IN_AIL) != 0);
  	prev_lip = list_entry(lip->li_ail.prev, xfs_log_item_t, li_ail);
  	if (&prev_lip->li_ail != &ailp->xa_ail)
  		ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0);
  
  	prev_lip = list_entry(lip->li_ail.next, xfs_log_item_t, li_ail);
  	if (&prev_lip->li_ail != &ailp->xa_ail)
  		ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) >= 0);
  
  
  #ifdef XFS_TRANS_DEBUG
  	/*
  	 * Walk the list checking lsn ordering, and that every entry has the
  	 * XFS_LI_IN_AIL flag set. This is really expensive, so only do it
  	 * when specifically debugging the transaction subsystem.
  	 */
  	prev_lip = list_entry(&ailp->xa_ail, xfs_log_item_t, li_ail);
  	list_for_each_entry(lip, &ailp->xa_ail, li_ail) {
  		if (&prev_lip->li_ail != &ailp->xa_ail)
  			ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0);
  		ASSERT((lip->li_flags & XFS_LI_IN_AIL) != 0);
  		prev_lip = lip;
  	}
  #endif /* XFS_TRANS_DEBUG */
  }
  #else /* !DEBUG */

  #define	xfs_ail_check(a,l)

  #endif /* DEBUG */

  /*
   * Return a pointer to the first item in the AIL.  If the AIL is empty, then
   * return NULL.
   */
  static xfs_log_item_t *
  xfs_ail_min(
  	struct xfs_ail  *ailp)
  {
  	if (list_empty(&ailp->xa_ail))
  		return NULL;
  
  	return list_first_entry(&ailp->xa_ail, xfs_log_item_t, li_ail);
  }

   /*
   * Return a pointer to the last item in the AIL.  If the AIL is empty, then
   * return NULL.
   */
  static xfs_log_item_t *
  xfs_ail_max(
  	struct xfs_ail  *ailp)
  {
  	if (list_empty(&ailp->xa_ail))
  		return NULL;
  
  	return list_entry(ailp->xa_ail.prev, xfs_log_item_t, li_ail);
  }

  /*
   * Return a pointer to the item which follows the given item in the AIL.  If
   * the given item is the last item in the list, then return NULL.
   */
  static xfs_log_item_t *
  xfs_ail_next(
  	struct xfs_ail  *ailp,
  	xfs_log_item_t  *lip)
  {
  	if (lip->li_ail.next == &ailp->xa_ail)
  		return NULL;
  
  	return list_first_entry(&lip->li_ail, xfs_log_item_t, li_ail);
  }

  
  /*

   * This is called by the log manager code to determine the LSN of the tail of
   * the log.  This is exactly the LSN of the first item in the AIL.  If the AIL
   * is empty, then this function returns 0.

   *

   * We need the AIL lock in order to get a coherent read of the lsn of the last
   * item in the AIL.

   */
  xfs_lsn_t

  xfs_ail_min_lsn(

  	struct xfs_ail	*ailp)

  {

  	xfs_lsn_t	lsn = 0;

  	xfs_log_item_t	*lip;

  	spin_lock(&ailp->xa_lock);

  	lip = xfs_ail_min(ailp);

  	if (lip)

  		lsn = lip->li_lsn;

  	spin_unlock(&ailp->xa_lock);

  
  	return lsn;
  }
  
  /*

   * Return the maximum lsn held in the AIL, or zero if the AIL is empty.
   */
  static xfs_lsn_t
  xfs_ail_max_lsn(
  	struct xfs_ail  *ailp)
  {
  	xfs_lsn_t       lsn = 0;
  	xfs_log_item_t  *lip;
  
  	spin_lock(&ailp->xa_lock);
  	lip = xfs_ail_max(ailp);
  	if (lip)
  		lsn = lip->li_lsn;
  	spin_unlock(&ailp->xa_lock);
  
  	return lsn;
  }
  
  /*

   * The cursor keeps track of where our current traversal is up to by tracking
   * the next item in the list for us. However, for this to be safe, removing an
   * object from the AIL needs to invalidate any cursor that points to it. hence
   * the traversal cursor needs to be linked to the struct xfs_ail so that
   * deletion can search all the active cursors for invalidation.

   */

  STATIC void

  xfs_trans_ail_cursor_init(
  	struct xfs_ail		*ailp,
  	struct xfs_ail_cursor	*cur)
  {
  	cur->item = NULL;

  	list_add_tail(&cur->list, &ailp->xa_cursors);

  }
  
  /*

   * Get the next item in the traversal and advance the cursor.  If the cursor
   * was invalidated (indicated by a lip of 1), restart the traversal.

   */

  struct xfs_log_item *

  xfs_trans_ail_cursor_next(
  	struct xfs_ail		*ailp,
  	struct xfs_ail_cursor	*cur)
  {
  	struct xfs_log_item	*lip = cur->item;
  
  	if ((__psint_t)lip & 1)
  		lip = xfs_ail_min(ailp);

  	if (lip)
  		cur->item = xfs_ail_next(ailp, lip);

  	return lip;
  }
  
  /*

   * When the traversal is complete, we need to remove the cursor from the list
   * of traversing cursors.

   */
  void
  xfs_trans_ail_cursor_done(
  	struct xfs_ail		*ailp,

  	struct xfs_ail_cursor	*cur)

  {

  	cur->item = NULL;
  	list_del_init(&cur->list);

  }
  
  /*

   * Invalidate any cursor that is pointing to this item. This is called when an
   * item is removed from the AIL. Any cursor pointing to this object is now
   * invalid and the traversal needs to be terminated so it doesn't reference a
   * freed object. We set the low bit of the cursor item pointer so we can
   * distinguish between an invalidation and the end of the list when getting the
   * next item from the cursor.

   */
  STATIC void
  xfs_trans_ail_cursor_clear(
  	struct xfs_ail		*ailp,
  	struct xfs_log_item	*lip)
  {
  	struct xfs_ail_cursor	*cur;

  	list_for_each_entry(cur, &ailp->xa_cursors, list) {

  		if (cur->item == lip)
  			cur->item = (struct xfs_log_item *)
  					((__psint_t)cur->item | 1);
  	}
  }
  
  /*

   * Find the first item in the AIL with the given @lsn by searching in ascending
   * LSN order and initialise the cursor to point to the next item for a
   * ascending traversal.  Pass a @lsn of zero to initialise the cursor to the
   * first item in the AIL. Returns NULL if the list is empty.

   */

  xfs_log_item_t *
  xfs_trans_ail_cursor_first(

  	struct xfs_ail		*ailp,
  	struct xfs_ail_cursor	*cur,
  	xfs_lsn_t		lsn)

  {

  	xfs_log_item_t		*lip;

  	xfs_trans_ail_cursor_init(ailp, cur);

  
  	if (lsn == 0) {
  		lip = xfs_ail_min(ailp);

  		goto out;

  	}

  	list_for_each_entry(lip, &ailp->xa_ail, li_ail) {

  		if (XFS_LSN_CMP(lip->li_lsn, lsn) >= 0)

  			goto out;

  	}

  	return NULL;

  out:

  	if (lip)
  		cur->item = xfs_ail_next(ailp, lip);

  	return lip;

  }

  static struct xfs_log_item *
  __xfs_trans_ail_cursor_last(
  	struct xfs_ail		*ailp,
  	xfs_lsn_t		lsn)
  {
  	xfs_log_item_t		*lip;
  
  	list_for_each_entry_reverse(lip, &ailp->xa_ail, li_ail) {
  		if (XFS_LSN_CMP(lip->li_lsn, lsn) <= 0)
  			return lip;
  	}
  	return NULL;
  }
  
  /*

   * Find the last item in the AIL with the given @lsn by searching in descending
   * LSN order and initialise the cursor to point to that item.  If there is no
   * item with the value of @lsn, then it sets the cursor to the last item with an
   * LSN lower than @lsn.  Returns NULL if the list is empty.

   */
  struct xfs_log_item *
  xfs_trans_ail_cursor_last(
  	struct xfs_ail		*ailp,
  	struct xfs_ail_cursor	*cur,
  	xfs_lsn_t		lsn)
  {
  	xfs_trans_ail_cursor_init(ailp, cur);
  	cur->item = __xfs_trans_ail_cursor_last(ailp, lsn);
  	return cur->item;
  }
  
  /*

   * Splice the log item list into the AIL at the given LSN. We splice to the

   * tail of the given LSN to maintain insert order for push traversals. The
   * cursor is optional, allowing repeated updates to the same LSN to avoid

   * repeated traversals.  This should not be called with an empty list.

   */
  static void
  xfs_ail_splice(

  	struct xfs_ail		*ailp,
  	struct xfs_ail_cursor	*cur,
  	struct list_head	*list,
  	xfs_lsn_t		lsn)

  {

  	struct xfs_log_item	*lip;
  
  	ASSERT(!list_empty(list));

  	/*

  	 * Use the cursor to determine the insertion point if one is
  	 * provided.  If not, or if the one we got is not valid,
  	 * find the place in the AIL where the items belong.

  	 */

  	lip = cur ? cur->item : NULL;
  	if (!lip || (__psint_t) lip & 1)

  		lip = __xfs_trans_ail_cursor_last(ailp, lsn);

  	/*
  	 * If a cursor is provided, we know we're processing the AIL
  	 * in lsn order, and future items to be spliced in will
  	 * follow the last one being inserted now.  Update the
  	 * cursor to point to that last item, now while we have a
  	 * reliable pointer to it.
  	 */
  	if (cur)
  		cur->item = list_entry(list->prev, struct xfs_log_item, li_ail);

  	/*

  	 * Finally perform the splice.  Unless the AIL was empty,
  	 * lip points to the item in the AIL _after_ which the new
  	 * items should go.  If lip is null the AIL was empty, so
  	 * the new items go at the head of the AIL.

  	 */

  	if (lip)
  		list_splice(list, &lip->li_ail);
  	else
  		list_splice(list, &ailp->xa_ail);

  }
  
  /*
   * Delete the given item from the AIL.  Return a pointer to the item.
   */
  static void
  xfs_ail_delete(
  	struct xfs_ail  *ailp,
  	xfs_log_item_t  *lip)
  {
  	xfs_ail_check(ailp, lip);
  	list_del(&lip->li_ail);
  	xfs_trans_ail_cursor_clear(ailp, lip);
  }

  static long
  xfsaild_push(
  	struct xfs_ail		*ailp)

  {

  	xfs_mount_t		*mp = ailp->xa_mount;

  	struct xfs_ail_cursor	cur;

  	xfs_log_item_t		*lip;
  	xfs_lsn_t		lsn;

  	xfs_lsn_t		target;

  	long			tout = 10;

  	int			stuck = 0;
  	int			count = 0;
  	int			push_xfsbufd = 0;

  	/*
  	 * If last time we ran we encountered pinned items, force the log first
  	 * and wait for it before pushing again.
  	 */

  	spin_lock(&ailp->xa_lock);

  	if (ailp->xa_last_pushed_lsn == 0 && ailp->xa_log_flush &&
  	    !list_empty(&ailp->xa_ail)) {
  		ailp->xa_log_flush = 0;
  		spin_unlock(&ailp->xa_lock);
  		XFS_STATS_INC(xs_push_ail_flush);
  		xfs_log_force(mp, XFS_LOG_SYNC);
  		spin_lock(&ailp->xa_lock);
  	}

  	target = ailp->xa_target;

  	lip = xfs_trans_ail_cursor_first(ailp, &cur, ailp->xa_last_pushed_lsn);

  	if (!lip || XFS_FORCED_SHUTDOWN(mp)) {

  		/*

  		 * AIL is empty or our push has reached the end.

  		 */

  		xfs_trans_ail_cursor_done(ailp, &cur);

  		spin_unlock(&ailp->xa_lock);

  		goto out_done;

  	}
  
  	XFS_STATS_INC(xs_push_ail);
  
  	/*
  	 * While the item we are looking at is below the given threshold

  	 * try to flush it out. We'd like not to stop until we've at least

  	 * tried to push on everything in the AIL with an LSN less than

  	 * the given threshold.
  	 *
  	 * However, we will stop after a certain number of pushes and wait
  	 * for a reduced timeout to fire before pushing further. This
  	 * prevents use from spinning when we can't do anything or there is
  	 * lots of contention on the AIL lists.

  	 */

  	lsn = lip->li_lsn;

  	while ((XFS_LSN_CMP(lip->li_lsn, target) <= 0)) {

  		int	lock_result;

  		/*

  		 * If we can lock the item without sleeping, unlock the AIL
  		 * lock and flush the item.  Then re-grab the AIL lock so we
  		 * can look for the next item on the AIL. List changes are
  		 * handled by the AIL lookup functions internally

  		 *

  		 * If we can't lock the item, either its holder will flush it
  		 * or it is already being flushed or it is being relogged.  In
  		 * any of these case it is being taken care of and we can just
  		 * skip to the next item in the list.

  		 */
  		lock_result = IOP_TRYLOCK(lip);

  		spin_unlock(&ailp->xa_lock);

  		switch (lock_result) {

  		case XFS_ITEM_SUCCESS:

  			XFS_STATS_INC(xs_push_ail_success);

  			trace_xfs_ail_push(lip);

  			IOP_PUSH(lip);

  			ailp->xa_last_pushed_lsn = lsn;

  			break;

  		case XFS_ITEM_PUSHBUF:

  			XFS_STATS_INC(xs_push_ail_pushbuf);

  			trace_xfs_ail_pushbuf(lip);

  
  			if (!IOP_PUSHBUF(lip)) {

  				trace_xfs_ail_pushbuf_pinned(lip);

  				stuck++;

  				ailp->xa_log_flush++;

  			} else {
  				ailp->xa_last_pushed_lsn = lsn;
  			}

  			push_xfsbufd = 1;

  			break;

  		case XFS_ITEM_PINNED:

  			XFS_STATS_INC(xs_push_ail_pinned);

  			trace_xfs_ail_pinned(lip);

  			stuck++;

  			ailp->xa_log_flush++;

  			break;

  		case XFS_ITEM_LOCKED:

  			XFS_STATS_INC(xs_push_ail_locked);

  			trace_xfs_ail_locked(lip);

  			stuck++;

  			break;

  		default:

  			ASSERT(0);
  			break;
  		}

  		spin_lock(&ailp->xa_lock);

  		/* should we bother continuing? */
  		if (XFS_FORCED_SHUTDOWN(mp))

  			break;

  		ASSERT(mp->m_log);
  
  		count++;

  		/*
  		 * Are there too many items we can't do anything with?
  		 * If we we are skipping too many items because we can't flush
  		 * them or they are already being flushed, we back off and
  		 * given them time to complete whatever operation is being
  		 * done. i.e. remove pressure from the AIL while we can't make
  		 * progress so traversals don't slow down further inserts and
  		 * removals to/from the AIL.
  		 *
  		 * The value of 100 is an arbitrary magic number based on
  		 * observation.
  		 */
  		if (stuck > 100)
  			break;

  		lip = xfs_trans_ail_cursor_next(ailp, &cur);

  		if (lip == NULL)
  			break;

  		lsn = lip->li_lsn;

  	}

  	xfs_trans_ail_cursor_done(ailp, &cur);

  	spin_unlock(&ailp->xa_lock);

  	if (push_xfsbufd) {
  		/* we've got delayed write buffers to flush */
  		wake_up_process(mp->m_ddev_targp->bt_task);
  	}

  	/* assume we have more work to do in a short while */

  out_done:

  	if (!count) {
  		/* We're past our target or empty, so idle */

  		ailp->xa_last_pushed_lsn = 0;

  		ailp->xa_log_flush = 0;

  		tout = 50;

  	} else if (XFS_LSN_CMP(lsn, target) >= 0) {
  		/*
  		 * We reached the target so wait a bit longer for I/O to
  		 * complete and remove pushed items from the AIL before we
  		 * start the next scan from the start of the AIL.
  		 */

  		tout = 50;

  		ailp->xa_last_pushed_lsn = 0;

  	} else if ((stuck * 100) / count > 90) {

  		/*
  		 * Either there is a lot of contention on the AIL or we
  		 * are stuck due to operations in progress. "Stuck" in this
  		 * case is defined as >90% of the items we tried to push
  		 * were stuck.
  		 *
  		 * Backoff a bit more to allow some I/O to complete before

  		 * restarting from the start of the AIL. This prevents us
  		 * from spinning on the same items, and if they are pinned will
  		 * all the restart to issue a log force to unpin the stuck
  		 * items.

  		 */

  		tout = 20;

  		ailp->xa_last_pushed_lsn = 0;

  	}

  	return tout;
  }
  
  static int
  xfsaild(
  	void		*data)
  {
  	struct xfs_ail	*ailp = data;
  	long		tout = 0;	/* milliseconds */
  
  	while (!kthread_should_stop()) {
  		if (tout && tout <= 20)
  			__set_current_state(TASK_KILLABLE);
  		else
  			__set_current_state(TASK_INTERRUPTIBLE);
  		schedule_timeout(tout ?
  				 msecs_to_jiffies(tout) : MAX_SCHEDULE_TIMEOUT);
  
  		try_to_freeze();
  
  		tout = xfsaild_push(ailp);
  	}
  
  	return 0;

  }

  /*
   * This routine is called to move the tail of the AIL forward.  It does this by
   * trying to flush items in the AIL whose lsns are below the given
   * threshold_lsn.
   *
   * The push is run asynchronously in a workqueue, which means the caller needs
   * to handle waiting on the async flush for space to become available.
   * We don't want to interrupt any push that is in progress, hence we only queue
   * work if we set the pushing bit approriately.
   *
   * We do this unlocked - we only need to know whether there is anything in the
   * AIL at the time we are called. We don't need to access the contents of
   * any of the objects, so the lock is not needed.
   */
  void

  xfs_ail_push(

  	struct xfs_ail	*ailp,
  	xfs_lsn_t	threshold_lsn)
  {
  	xfs_log_item_t	*lip;
  
  	lip = xfs_ail_min(ailp);
  	if (!lip || XFS_FORCED_SHUTDOWN(ailp->xa_mount) ||
  	    XFS_LSN_CMP(threshold_lsn, ailp->xa_target) <= 0)
  		return;
  
  	/*
  	 * Ensure that the new target is noticed in push code before it clears
  	 * the XFS_AIL_PUSHING_BIT.
  	 */
  	smp_wmb();

  	xfs_trans_ail_copy_lsn(ailp, &ailp->xa_target, &threshold_lsn);

  	smp_wmb();
  
  	wake_up_process(ailp->xa_task);

  }

  
  /*

   * Push out all items in the AIL immediately
   */
  void
  xfs_ail_push_all(
  	struct xfs_ail  *ailp)
  {
  	xfs_lsn_t       threshold_lsn = xfs_ail_max_lsn(ailp);
  
  	if (threshold_lsn)
  		xfs_ail_push(ailp, threshold_lsn);
  }
  
  /*

   * This is to be called when an item is unlocked that may have
   * been in the AIL.  It will wake up the first member of the AIL
   * wait list if this item's unlocking might allow it to progress.
   * If the item is in the AIL, then we need to get the AIL lock
   * while doing our checking so we don't race with someone going
   * to sleep waiting for this event in xfs_trans_push_ail().
   */
  void
  xfs_trans_unlocked_item(

  	struct xfs_ail	*ailp,

  	xfs_log_item_t	*lip)
  {
  	xfs_log_item_t	*min_lip;
  
  	/*
  	 * If we're forcibly shutting down, we may have
  	 * unlocked log items arbitrarily. The last thing
  	 * we want to do is to move the tail of the log
  	 * over some potentially valid data.
  	 */
  	if (!(lip->li_flags & XFS_LI_IN_AIL) ||

  	    XFS_FORCED_SHUTDOWN(ailp->xa_mount)) {

  		return;
  	}
  
  	/*
  	 * This is the one case where we can call into xfs_ail_min()
  	 * without holding the AIL lock because we only care about the
  	 * case where we are at the tail of the AIL.  If the object isn't
  	 * at the tail, it doesn't matter what result we get back.  This
  	 * is slightly racy because since we were just unlocked, we could
  	 * go to sleep between the call to xfs_ail_min and the call to
  	 * xfs_log_move_tail, have someone else lock us, commit to us disk,
  	 * move us out of the tail of the AIL, and then we wake up.  However,
  	 * the call to xfs_log_move_tail() doesn't do anything if there's
  	 * not enough free space to wake people up so we're safe calling it.
  	 */

  	min_lip = xfs_ail_min(ailp);

  
  	if (min_lip == lip)

  		xfs_log_move_tail(ailp->xa_mount, 1);

  }	/* xfs_trans_unlocked_item */

  /*

   * xfs_trans_ail_update - bulk AIL insertion operation.
   *
   * @xfs_trans_ail_update takes an array of log items that all need to be
   * positioned at the same LSN in the AIL. If an item is not in the AIL, it will
   * be added.  Otherwise, it will be repositioned  by removing it and re-adding
   * it to the AIL. If we move the first item in the AIL, update the log tail to
   * match the new minimum LSN in the AIL.
   *
   * This function takes the AIL lock once to execute the update operations on
   * all the items in the array, and as such should not be called with the AIL
   * lock held. As a result, once we have the AIL lock, we need to check each log
   * item LSN to confirm it needs to be moved forward in the AIL.
   *
   * To optimise the insert operation, we delete all the items from the AIL in
   * the first pass, moving them into a temporary list, then splice the temporary
   * list into the correct position in the AIL. This avoids needing to do an
   * insert operation on every item.
   *
   * This function must be called with the AIL lock held.  The lock is dropped
   * before returning.
   */
  void
  xfs_trans_ail_update_bulk(
  	struct xfs_ail		*ailp,

  	struct xfs_ail_cursor	*cur,

  	struct xfs_log_item	**log_items,
  	int			nr_items,
  	xfs_lsn_t		lsn) __releases(ailp->xa_lock)
  {
  	xfs_log_item_t		*mlip;
  	xfs_lsn_t		tail_lsn;
  	int			mlip_changed = 0;
  	int			i;
  	LIST_HEAD(tmp);

  	ASSERT(nr_items > 0);		/* Not required, but true. */

  	mlip = xfs_ail_min(ailp);
  
  	for (i = 0; i < nr_items; i++) {
  		struct xfs_log_item *lip = log_items[i];
  		if (lip->li_flags & XFS_LI_IN_AIL) {
  			/* check if we really need to move the item */
  			if (XFS_LSN_CMP(lsn, lip->li_lsn) <= 0)
  				continue;
  
  			xfs_ail_delete(ailp, lip);
  			if (mlip == lip)
  				mlip_changed = 1;
  		} else {
  			lip->li_flags |= XFS_LI_IN_AIL;
  		}
  		lip->li_lsn = lsn;
  		list_add(&lip->li_ail, &tmp);
  	}

  	if (!list_empty(&tmp))
  		xfs_ail_splice(ailp, cur, &tmp, lsn);

  
  	if (!mlip_changed) {
  		spin_unlock(&ailp->xa_lock);
  		return;
  	}
  
  	/*
  	 * It is not safe to access mlip after the AIL lock is dropped, so we
  	 * must get a copy of li_lsn before we do so.  This is especially
  	 * important on 32-bit platforms where accessing and updating 64-bit
  	 * values like li_lsn is not atomic.
  	 */
  	mlip = xfs_ail_min(ailp);
  	tail_lsn = mlip->li_lsn;
  	spin_unlock(&ailp->xa_lock);
  	xfs_log_move_tail(ailp->xa_mount, tail_lsn);
  }
  
  /*

   * xfs_trans_ail_delete_bulk - remove multiple log items from the AIL
   *
   * @xfs_trans_ail_delete_bulk takes an array of log items that all need to
   * removed from the AIL. The caller is already holding the AIL lock, and done
   * all the checks necessary to ensure the items passed in via @log_items are
   * ready for deletion. This includes checking that the items are in the AIL.
   *
   * For each log item to be removed, unlink it  from the AIL, clear the IN_AIL
   * flag from the item and reset the item's lsn to 0. If we remove the first
   * item in the AIL, update the log tail to match the new minimum LSN in the
   * AIL.
   *
   * This function will not drop the AIL lock until all items are removed from
   * the AIL to minimise the amount of lock traffic on the AIL. This does not
   * greatly increase the AIL hold time, but does significantly reduce the amount
   * of traffic on the lock, especially during IO completion.
   *
   * This function must be called with the AIL lock held.  The lock is dropped
   * before returning.
   */
  void
  xfs_trans_ail_delete_bulk(
  	struct xfs_ail		*ailp,
  	struct xfs_log_item	**log_items,
  	int			nr_items) __releases(ailp->xa_lock)
  {
  	xfs_log_item_t		*mlip;
  	xfs_lsn_t		tail_lsn;
  	int			mlip_changed = 0;
  	int			i;
  
  	mlip = xfs_ail_min(ailp);
  
  	for (i = 0; i < nr_items; i++) {
  		struct xfs_log_item *lip = log_items[i];
  		if (!(lip->li_flags & XFS_LI_IN_AIL)) {
  			struct xfs_mount	*mp = ailp->xa_mount;
  
  			spin_unlock(&ailp->xa_lock);
  			if (!XFS_FORCED_SHUTDOWN(mp)) {

  				xfs_alert_tag(mp, XFS_PTAG_AILDELETE,

  		"%s: attempting to delete a log item that is not in the AIL",
  						__func__);
  				xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
  			}
  			return;
  		}
  
  		xfs_ail_delete(ailp, lip);
  		lip->li_flags &= ~XFS_LI_IN_AIL;
  		lip->li_lsn = 0;
  		if (mlip == lip)
  			mlip_changed = 1;
  	}
  
  	if (!mlip_changed) {
  		spin_unlock(&ailp->xa_lock);
  		return;
  	}
  
  	/*
  	 * It is not safe to access mlip after the AIL lock is dropped, so we
  	 * must get a copy of li_lsn before we do so.  This is especially
  	 * important on 32-bit platforms where accessing and updating 64-bit
  	 * values like li_lsn is not atomic. It is possible we've emptied the
  	 * AIL here, so if that is the case, pass an LSN of 0 to the tail move.
  	 */
  	mlip = xfs_ail_min(ailp);
  	tail_lsn = mlip ? mlip->li_lsn : 0;
  	spin_unlock(&ailp->xa_lock);
  	xfs_log_move_tail(ailp->xa_mount, tail_lsn);
  }

  /*

   * The active item list (AIL) is a doubly linked list of log
   * items sorted by ascending lsn.  The base of the list is
   * a forw/back pointer pair embedded in the xfs mount structure.
   * The base is initialized with both pointers pointing to the
   * base.  This case always needs to be distinguished, because
   * the base has no lsn to look at.  We almost always insert
   * at the end of the list, so on inserts we search from the
   * end of the list to find where the new item belongs.
   */
  
  /*
   * Initialize the doubly linked list to point only to itself.
   */

  int

  xfs_trans_ail_init(
  	xfs_mount_t	*mp)
  {

  	struct xfs_ail	*ailp;
  
  	ailp = kmem_zalloc(sizeof(struct xfs_ail), KM_MAYFAIL);
  	if (!ailp)
  		return ENOMEM;
  
  	ailp->xa_mount = mp;
  	INIT_LIST_HEAD(&ailp->xa_ail);

  	INIT_LIST_HEAD(&ailp->xa_cursors);

  	spin_lock_init(&ailp->xa_lock);

  
  	ailp->xa_task = kthread_run(xfsaild, ailp, "xfsaild/%s",
  			ailp->xa_mount->m_fsname);
  	if (IS_ERR(ailp->xa_task))
  		goto out_free_ailp;

  	mp->m_ail = ailp;
  	return 0;

  
  out_free_ailp:
  	kmem_free(ailp);
  	return ENOMEM;

  }
  
  void
  xfs_trans_ail_destroy(
  	xfs_mount_t	*mp)
  {

  	struct xfs_ail	*ailp = mp->m_ail;

  	kthread_stop(ailp->xa_task);

  	kmem_free(ailp);

  }