[PATCH 2/2]Fix return value of splitting extents for dio write over fallocate

[Mingming <cmm@us.ibm.com>]

ext4: Fix return value of splitting extents for dio write over fallocate 

To prepare direct IO write, we need to split the unwritten extents before
submit the IO. In case of there is no need to split at all, ext4_split_unwritten_extents()
was incorrectly returns 0 instead of the size of uninitalized extents. This bug
caused the buffer remains unmapped, thus mislead VFS direct IO falling back to buffered IO.

Signed-off-by: Mingming Cao <cmm@us.ibm.com>
---
 fs/ext4/extents.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Index: linux-2.6.31-rc4/fs/ext4/extents.c
===================================================================
--- linux-2.6.31-rc4.orig/fs/ext4/extents.c
+++ linux-2.6.31-rc4/fs/ext4/extents.c
@@ -2788,6 +2788,8 @@ fix_extent_len:
  * into three uninitialized extent(at most). After IO complete, the part
  * being filled will be convert to initialized by the end_io callback function
  * via ext4_convert_unwritten_extents().
+ *
+ * Returns the size of unitialized extent to be writen, on success.
  */
 static int ext4_split_unwritten_extents(handle_t *handle,
 					struct inode *inode,
@@ -2829,7 +2831,7 @@ static int ext4_split_unwritten_extents(
  	 * uninitialized extent
  	 */
  	if (allocated <= max_blocks)
-		return ret;
+		return allocated;
 
 	err = ext4_ext_get_access(handle, inode, path + depth);
 	if (err)