[PATCH] ext3: disable O_DIRECT in journalled-data mode

We cannot sensibly support O_DIRECT reads or writes when all writes are
journalled.

This is because the VFS explicitly avoids syncing the file metadata during
O_DIRECT reads and writes.  ext3 with journalled data will leave pending
changes in memory and they will overwrite the results of O_DIRECT writes, and
O_DIRECT reads will not return the latest data.

Setting the a_op to null will cause opens and fcntl(F_SETFL) to return
-EINVAL if O_DIRECT is requested.

fs/ext3/inode.c

@@ -1644,7 +1644,6 @@ static struct address_space_operations ext3_journalled_aops = {
 	.bmap		= ext3_bmap,
 	.invalidatepage	= ext3_invalidatepage,
 	.releasepage	= ext3_releasepage,
-	.direct_IO	= ext3_direct_IO,
 };
 
 void ext3_set_aops(struct inode *inode)