[PATCH 4/4 v2] Fix direct IO return values over fullfilled fallocate space

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

ext4: Fix direct IO return values over fullfilled fallocate space 

To prepare direct IO write, we need to split the unwritten extents before
submit the IO. In case of no split needs at all, ext4_split_unwritten_extents()
was incorrectly returns 0 instead of the size of uninitialized extents. This bug
caused wrong return value sent back to VFS code when it gets called from async
IO path, leads to falling back to buffered IO.

Signed-off-by: Mingming Cao <cmm@us.ibm.com>
---
 fs/ext4/extents.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

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 uninitialized extent to be written, on success.
  */
 static int ext4_split_unwritten_extents(handle_t *handle,
 					struct inode *inode,
@@ -2805,7 +2807,6 @@ static int ext4_split_unwritten_extents(
 	unsigned int allocated, ee_len, depth;
 	ext4_fsblk_t newblock;
 	int err = 0;
-	int ret = 0;
 
 	ext_debug("ext4_split_unwritten_extents: inode %lu,"
 		  "iblock %llu, max_blocks %u\n", inode->i_ino,
@@ -2827,8 +2828,8 @@ static int ext4_split_unwritten_extents(
  	 * the size of extent to write, there is no need to split
  	 * uninitialized extent
  	 */
- 	if (allocated <= max_blocks)
-		return ret;
+ 	if (iblock == ee_block && allocated <= max_blocks)
+		return allocated;
 
 	err = ext4_ext_get_access(handle, inode, path + depth);
 	if (err)