xfs: refactor the ioend merging code

Introduce two nicely abstracted helper, which can be moved to the iomap
code later.  Also use list_first_entry_or_null to simplify the code a
bit.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_aops.c

@@ -116,6 +116,22 @@ xfs_destroy_ioend(
 	}
 }
 
+static void
+xfs_destroy_ioends(
+	struct xfs_ioend	*ioend,
+	int			error)
+{
+	struct list_head	tmp;
+
+	list_replace_init(&ioend->io_list, &tmp);
+	xfs_destroy_ioend(ioend, error);
+	while ((ioend = list_first_entry_or_null(&tmp, struct xfs_ioend,
+			io_list))) {
+		list_del_init(&ioend->io_list);
+		xfs_destroy_ioend(ioend, error);
+	}
+}
+
 /*
  * Fast and loose check if this write could update the on-disk inode size.
  */
@@ -230,7 +246,6 @@ STATIC void
 xfs_end_ioend(
 	struct xfs_ioend	*ioend)
 {
-	struct list_head	ioend_list;
 	struct xfs_inode	*ip = XFS_I(ioend->io_inode);
 	xfs_off_t		offset = ioend->io_offset;
 	size_t			size = ioend->io_size;
@@ -275,16 +290,7 @@ xfs_end_ioend(
 done:
 	if (ioend->io_append_trans)
 		error = xfs_setfilesize_ioend(ioend, error);
-	list_replace_init(&ioend->io_list, &ioend_list);
-	xfs_destroy_ioend(ioend, error);
-
-	while (!list_empty(&ioend_list)) {
-		ioend = list_first_entry(&ioend_list, struct xfs_ioend,
-				io_list);
-		list_del_init(&ioend->io_list);
-		xfs_destroy_ioend(ioend, error);
-	}
-
+	xfs_destroy_ioends(ioend, error);
 	memalloc_nofs_restore(nofs_flag);
 }
 
@@ -333,17 +339,18 @@ xfs_ioend_try_merge(
 	struct xfs_ioend	*ioend,
 	struct list_head	*more_ioends)
 {
-	struct xfs_ioend	*next_ioend;
+	struct xfs_ioend	*next;
+
+	INIT_LIST_HEAD(&ioend->io_list);
 
-	while (!list_empty(more_ioends)) {
-		next_ioend = list_first_entry(more_ioends, struct xfs_ioend,
-				io_list);
-		if (!xfs_ioend_can_merge(ioend, next_ioend))
+	while ((next = list_first_entry_or_null(more_ioends, struct xfs_ioend,
+			io_list))) {
+		if (!xfs_ioend_can_merge(ioend, next))
 			break;
-		list_move_tail(&next_ioend->io_list, &ioend->io_list);
-		ioend->io_size += next_ioend->io_size;
-		if (next_ioend->io_append_trans)
-			xfs_ioend_merge_append_transactions(ioend, next_ioend);
+		list_move_tail(&next->io_list, &ioend->io_list);
+		ioend->io_size += next->io_size;
+		if (next->io_append_trans)
+			xfs_ioend_merge_append_transactions(ioend, next);
 	}
 }
 
@@ -366,29 +373,33 @@ xfs_ioend_compare(
 	return 0;
 }
 
+static void
+xfs_sort_ioends(
+	struct list_head	*ioend_list)
+{
+	list_sort(NULL, ioend_list, xfs_ioend_compare);
+}
+
 /* Finish all pending io completions. */
 void
 xfs_end_io(
 	struct work_struct	*work)
 {
-	struct xfs_inode	*ip;
+	struct xfs_inode	*ip =
+		container_of(work, struct xfs_inode, i_ioend_work);
 	struct xfs_ioend	*ioend;
-	struct list_head	completion_list;
+	struct list_head	tmp;
 	unsigned long		flags;
 
-	ip = container_of(work, struct xfs_inode, i_ioend_work);
-
 	spin_lock_irqsave(&ip->i_ioend_lock, flags);
-	list_replace_init(&ip->i_ioend_list, &completion_list);
+	list_replace_init(&ip->i_ioend_list, &tmp);
 	spin_unlock_irqrestore(&ip->i_ioend_lock, flags);
 
-	list_sort(NULL, &completion_list, xfs_ioend_compare);
-
-	while (!list_empty(&completion_list)) {
-		ioend = list_first_entry(&completion_list, struct xfs_ioend,
-				io_list);
+	xfs_sort_ioends(&tmp);
+	while ((ioend = list_first_entry_or_null(&tmp, struct xfs_ioend,
+			io_list))) {
 		list_del_init(&ioend->io_list);
-		xfs_ioend_try_merge(ioend, &completion_list);
+		xfs_ioend_try_merge(ioend, &tmp);
 		xfs_end_ioend(ioend);
 	}
 }