ocfs2: fill in the unused portion of the block with zeros by dio_zero…

…_block()

A simplified test case is (this case from Ryan):
1) dd if=/dev/zero of=/mnt/hello bs=512 count=1 oflag=direct;
2) truncate /mnt/hello -s 2097152
file 'hello' is not exist before test. After this command,
file 'hello' should be all zero. But 512~4096 is some random data.

Setting bh state to new when get a new block, if so,
direct_io_worker()->dio_zero_block() will fill-in the unused portion
of the block with zero.

Signed-off-by: Yiwen Jiang <[email protected]>
Reviewed-by: Joseph Qi <[email protected]>
Cc: Mark Fasheh <[email protected]>
Cc: Joel Becker <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

fs/ocfs2/aops.c

@@ -589,6 +589,7 @@ static int ocfs2_direct_IO_get_blocks(struct inode *inode, sector_t iblock,
 			ret = -EIO;
 			goto bail;
 		}
+		set_buffer_new(bh_result);
 		up_write(&OCFS2_I(inode)->ip_alloc_sem);
 	}