diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index ec96f3a..9d4ba34 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -37,6 +37,11 @@ static int balance_node_right(struct btrfs_trans_handle *trans,
 			      struct extent_buffer *src_buf);
 static int del_ptr(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 		   struct btrfs_path *path, int level, int slot);
+static int setup_items_for_insert(struct btrfs_trans_handle *trans,
+			struct btrfs_root *root, struct btrfs_path *path,
+			struct btrfs_key *cpu_key, u32 *data_size,
+			u32 total_data, u32 total_size, int nr);
+
 
 struct btrfs_path *btrfs_alloc_path(void)
 {
@@ -2997,75 +3002,85 @@ again:
 	return ret;
 }
 
-/*
- * This function splits a single item into two items,
- * giving 'new_key' to the new item and splitting the
- * old one at split_offset (from the start of the item).
- *
- * The path may be released by this operation.  After
- * the split, the path is pointing to the old item.  The
- * new item is going to be in the same node as the old one.
- *
- * Note, the item being split must be smaller enough to live alone on
- * a tree block with room for one extra struct btrfs_item
- *
- * This allows us to split the item in place, keeping a lock on the
- * leaf the entire time.
- */
-int btrfs_split_item(struct btrfs_trans_handle *trans,
-		     struct btrfs_root *root,
-		     struct btrfs_path *path,
-		     struct btrfs_key *new_key,
-		     unsigned long split_offset)
+static noinline int setup_leaf_for_split(struct btrfs_trans_handle *trans,
+					 struct btrfs_root *root,
+					 struct btrfs_path *path, int ins_len)
 {
-	u32 item_size;
+	struct btrfs_key key;
 	struct extent_buffer *leaf;
-	struct btrfs_key orig_key;
-	struct btrfs_item *item;
-	struct btrfs_item *new_item;
-	int ret = 0;
-	int slot;
-	u32 nritems;
-	u32 orig_offset;
-	struct btrfs_disk_key disk_key;
-	char *buf;
+	struct btrfs_file_extent_item *fi;
+	u64 extent_len = 0;
+	u32 item_size;
+	int ret;
 
 	leaf = path->nodes[0];
-	btrfs_item_key_to_cpu(leaf, &orig_key, path->slots[0]);
-	if (btrfs_leaf_free_space(root, leaf) >= sizeof(struct btrfs_item))
-		goto split;
+	btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
+
+	BUG_ON(key.type != BTRFS_EXTENT_DATA_KEY &&
+	       key.type != BTRFS_EXTENT_CSUM_KEY);
+
+	if (btrfs_leaf_free_space(root, leaf) >= ins_len)
+		return 0;
 
 	item_size = btrfs_item_size_nr(leaf, path->slots[0]);
+	if (key.type == BTRFS_EXTENT_DATA_KEY) {
+		fi = btrfs_item_ptr(leaf, path->slots[0],
+				    struct btrfs_file_extent_item);
+		extent_len = btrfs_file_extent_num_bytes(leaf, fi);
+	}
 	btrfs_release_path(root, path);
 
-	path->search_for_split = 1;
 	path->keep_locks = 1;
-
-	ret = btrfs_search_slot(trans, root, &orig_key, path, 0, 1);
+	path->search_for_split = 1;
+	ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
 	path->search_for_split = 0;
+	if (ret < 0)
+		goto err;
 
+	ret = -EAGAIN;
+	leaf = path->nodes[0];
 	/* if our item isn't there or got smaller, return now */
-	if (ret != 0 || item_size != btrfs_item_size_nr(path->nodes[0],
-							path->slots[0])) {
-		path->keep_locks = 0;
-		return -EAGAIN;
+	if (ret > 0 || item_size != btrfs_item_size_nr(leaf, path->slots[0]))
+		goto err;
+
+	if (key.type == BTRFS_EXTENT_DATA_KEY) {
+		fi = btrfs_item_ptr(leaf, path->slots[0],
+				    struct btrfs_file_extent_item);
+		if (extent_len != btrfs_file_extent_num_bytes(leaf, fi))
+			goto err;
 	}
 
 	btrfs_set_path_blocking(path);
-	ret = split_leaf(trans, root, &orig_key, path,
-			 sizeof(struct btrfs_item), 1);
-	path->keep_locks = 0;
+	ret = split_leaf(trans, root, &key, path, ins_len, 1);
 	BUG_ON(ret);
 
+	path->keep_locks = 0;
 	btrfs_unlock_up_safe(path, 1);
+	return 0;
+err:
+	path->keep_locks = 0;
+	return ret;
+}
+
+static noinline int split_item(struct btrfs_trans_handle *trans,
+			       struct btrfs_root *root,
+			       struct btrfs_path *path,
+			       struct btrfs_key *new_key,
+			       unsigned long split_offset)
+{
+	struct extent_buffer *leaf;
+	struct btrfs_item *item;
+	struct btrfs_item *new_item;
+	int slot;
+	char *buf;
+	u32 nritems;
+	u32 item_size;
+	u32 orig_offset;
+	struct btrfs_disk_key disk_key;
+
 	leaf = path->nodes[0];
 	BUG_ON(btrfs_leaf_free_space(root, leaf) < sizeof(struct btrfs_item));
 
-split:
-	/*
-	 * make sure any changes to the path from split_leaf leave it
-	 * in a blocking state
-	 */
 	btrfs_set_path_blocking(path);
 
 	item = btrfs_item_nr(leaf, path->slots[0]);
@@ -3073,19 +3088,19 @@ split:
 	item_size = btrfs_item_size(leaf, item);
 
 	buf = kmalloc(item_size, GFP_NOFS);
+	if (!buf)
+		return -ENOMEM;
+
 	read_extent_buffer(leaf, buf, btrfs_item_ptr_offset(leaf,
 			    path->slots[0]), item_size);
-	slot = path->slots[0] + 1;
-	leaf = path->nodes[0];
 
+	slot = path->slots[0] + 1;
 	nritems = btrfs_header_nritems(leaf);
-
 	if (slot != nritems) {
 		/* shift the items */
 		memmove_extent_buffer(leaf, btrfs_item_nr_offset(slot + 1),
-			      btrfs_item_nr_offset(slot),
-			      (nritems - slot) * sizeof(struct btrfs_item));
-
+				btrfs_item_nr_offset(slot),
+				(nritems - slot) * sizeof(struct btrfs_item));
 	}
 
 	btrfs_cpu_key_to_disk(&disk_key, new_key);
@@ -3113,16 +3128,81 @@ split:
 			    item_size - split_offset);
 	btrfs_mark_buffer_dirty(leaf);
 
-	ret = 0;
-	if (btrfs_leaf_free_space(root, leaf) < 0) {
-		btrfs_print_leaf(root, leaf);
-		BUG();
-	}
+	BUG_ON(btrfs_leaf_free_space(root, leaf) < 0);
 	kfree(buf);
+	return 0;
+}
+
+/*
+ * This function splits a single item into two items,
+ * giving 'new_key' to the new item and splitting the
+ * old one at split_offset (from the start of the item).
+ *
+ * The path may be released by this operation.  After
+ * the split, the path is pointing to the old item.  The
+ * new item is going to be in the same node as the old one.
+ *
+ * Note, the item being split must be smaller enough to live alone on
+ * a tree block with room for one extra struct btrfs_item
+ *
+ * This allows us to split the item in place, keeping a lock on the
+ * leaf the entire time.
+ */
+int btrfs_split_item(struct btrfs_trans_handle *trans,
+		     struct btrfs_root *root,
+		     struct btrfs_path *path,
+		     struct btrfs_key *new_key,
+		     unsigned long split_offset)
+{
+	int ret;
+	ret = setup_leaf_for_split(trans, root, path,
+				   sizeof(struct btrfs_item));
+	if (ret)
+		return ret;
+
+	ret = split_item(trans, root, path, new_key, split_offset);
 	return ret;
 }
 
 /*
+ * This function duplicate a item, giving 'new_key' to the new item.
+ * It guarantees both items live in the same tree leaf and the new item
+ * is contiguous with the original item.
+ *
+ * This allows us to split file extent in place, keeping a lock on the
+ * leaf the entire time.
+ */
+int btrfs_duplicate_item(struct btrfs_trans_handle *trans,
+			 struct btrfs_root *root,
+			 struct btrfs_path *path,
+			 struct btrfs_key *new_key)
+{
+	struct extent_buffer *leaf;
+	int ret;
+	u32 item_size;
+
+	leaf = path->nodes[0];
+	item_size = btrfs_item_size_nr(leaf, path->slots[0]);
+	ret = setup_leaf_for_split(trans, root, path,
+				   item_size + sizeof(struct btrfs_item));
+	if (ret)
+		return ret;
+
+	path->slots[0]++;
+	ret = setup_items_for_insert(trans, root, path, new_key, &item_size,
+				     item_size, item_size +
+				     sizeof(struct btrfs_item), 1);
+	BUG_ON(ret);
+
+	leaf = path->nodes[0];
+	memcpy_extent_buffer(leaf,
+			     btrfs_item_ptr_offset(leaf, path->slots[0]),
+			     btrfs_item_ptr_offset(leaf, path->slots[0] - 1),
+			     item_size);
+	return 0;
+}
+
+/*
  * make the item pointed to by the path smaller.  new_size indicates
  * how small to make it, and from_end tells us if we just chop bytes
  * off the end of the item or if we shift the item to chop bytes off
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index e5dd628..33d9b13 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2089,6 +2089,10 @@ int btrfs_split_item(struct btrfs_trans_handle *trans,
 		     struct btrfs_path *path,
 		     struct btrfs_key *new_key,
 		     unsigned long split_offset);
+int btrfs_duplicate_item(struct btrfs_trans_handle *trans,
+			 struct btrfs_root *root,
+			 struct btrfs_path *path,
+			 struct btrfs_key *new_key);
 int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
 		      *root, struct btrfs_key *key, struct btrfs_path *p, int
 		      ins_len, int cow);
