Restore ext4_ext_walk_space().
Copy from rhel6.4 [2.6.32-358.23.2.el6] kernel.

Index: linux-2.6.32-431.3.1.el6.x86_64/fs/ext4/extents.c
===================================================================
--- linux-2.6.32-431.3.1.el6.x86_64.orig/fs/ext4/extents.c
+++ linux-2.6.32-431.3.1.el6.x86_64/fs/ext4/extents.c
@@ -4487,6 +4487,121 @@ static int ext4_xattr_fiemap(struct inod
 	return (error < 0 ? error : 0);
 }
 
+int ext4_ext_walk_space(struct inode *inode, ext4_lblk_t block,
+			ext4_lblk_t num, ext_prepare_callback func,
+			void *cbdata)
+{
+	struct ext4_ext_path *path = NULL;
+	struct ext4_ext_cache cbex;
+	struct ext4_extent *ex;
+	ext4_lblk_t next, start = 0, end = 0;
+	ext4_lblk_t last = block + num;
+	int depth, exists, err = 0;
+
+	BUG_ON(func == NULL);
+	BUG_ON(inode == NULL);
+
+	while (block < last && block != EXT_MAX_BLOCKS) {
+		num = last - block;
+		/* find extent for this block */
+		down_read(&EXT4_I(inode)->i_data_sem);
+		path = ext4_ext_find_extent(inode, block, path);
+		up_read(&EXT4_I(inode)->i_data_sem);
+		if (IS_ERR(path)) {
+			err = PTR_ERR(path);
+			path = NULL;
+			break;
+		}
+
+		depth = ext_depth(inode);
+		if (unlikely(path[depth].p_hdr == NULL)) {
+			EXT4_ERROR_INODE(inode, "path[%d].p_hdr == NULL", depth);
+			err = -EIO;
+			break;
+		}
+		ex = path[depth].p_ext;
+		next = ext4_ext_next_allocated_block(path);
+
+		exists = 0;
+		if (!ex) {
+			/* there is no extent yet, so try to allocate
+			 * all requested space */
+			start = block;
+			end = block + num;
+		} else if (le32_to_cpu(ex->ee_block) > block) {
+			/* need to allocate space before found extent */
+			start = block;
+			end = le32_to_cpu(ex->ee_block);
+			if (block + num < end)
+				end = block + num;
+		} else if (block >= le32_to_cpu(ex->ee_block)
+					+ ext4_ext_get_actual_len(ex)) {
+			/* need to allocate space after found extent */
+			start = block;
+			end = block + num;
+			if (end >= next)
+				end = next;
+		} else if (block >= le32_to_cpu(ex->ee_block)) {
+			/*
+			 * some part of requested space is covered
+			 * by found extent
+			 */
+			start = block;
+			end = le32_to_cpu(ex->ee_block)
+				+ ext4_ext_get_actual_len(ex);
+			if (block + num < end)
+				end = block + num;
+			exists = 1;
+		} else {
+			BUG();
+		}
+		BUG_ON(end <= start);
+
+		if (!exists) {
+			cbex.ec_block = start;
+			cbex.ec_len = end - start;
+			cbex.ec_start = 0;
+		} else {
+			cbex.ec_block = le32_to_cpu(ex->ee_block);
+			cbex.ec_len = ext4_ext_get_actual_len(ex);
+			cbex.ec_start = ext4_ext_pblock(ex);
+		}
+
+		if (unlikely(cbex.ec_len == 0)) {
+			EXT4_ERROR_INODE(inode, "cbex.ec_len == 0");
+			err = -EIO;
+			break;
+		}
+		err = func(inode, path, &cbex, ex, cbdata);
+		ext4_ext_drop_refs(path);
+
+		if (err < 0)
+			break;
+
+		if (err == EXT_REPEAT)
+			continue;
+		else if (err == EXT_BREAK) {
+			err = 0;
+			break;
+		}
+
+		if (ext_depth(inode) != depth) {
+			/* depth was changed. we have to realloc path */
+			kfree(path);
+			path = NULL;
+		}
+
+		block = cbex.ec_block + cbex.ec_len;
+	}
+
+	if (path) {
+		ext4_ext_drop_refs(path);
+		kfree(path);
+	}
+
+	return err;
+}
+
 /*
  * ext4_ext_punch_hole
  *
Index: linux-2.6.32-431.3.1.el6.x86_64/fs/ext4/ext4_extents.h
===================================================================
--- linux-2.6.32-431.3.1.el6.x86_64.orig/fs/ext4/ext4_extents.h
+++ linux-2.6.32-431.3.1.el6.x86_64/fs/ext4/ext4_extents.h
@@ -120,6 +120,19 @@ struct ext4_ext_path {
 	struct ext4_extent_header	*p_hdr;
 	struct buffer_head		*p_bh;
 };
+/*
+ * to be called by ext4_ext_walk_space()
+ * negative retcode - error
+ * positive retcode - signal for ext4_ext_walk_space(), see below
+ * callback must return valid extent (passed or newly created)
+ */
+typedef int (*ext_prepare_callback)(struct inode *, struct ext4_ext_path *,
+					struct ext4_ext_cache *,
+					struct ext4_extent *, void *);
+
+#define EXT_CONTINUE   0
+#define EXT_BREAK      1
+#define EXT_REPEAT     2
 
 /*
  * structure for external API
@@ -272,6 +285,9 @@ static inline void ext4_idx_store_pblock
 	ix->ei_leaf_hi = cpu_to_le16((unsigned long) ((pb >> 31) >> 1) &
 				     0xffff);
 }
+extern int ext4_ext_walk_space(struct inode *, ext4_lblk_t,
+			ext4_lblk_t, ext_prepare_callback,
+			void *);
 
 extern int ext4_ext_calc_metadata_amount(struct inode *inode,
 					 sector_t lblocks);