ext4: clean up the flags passed to __blockdev_direct_IO

For extent-based files, you can perform DIO to holes, as mentioned in
the comments in ext4_ext_direct_IO.  However, that function passes
DIO_SKIP_HOLES to __blockdev_direct_IO, which is *really* confusing to
the uninitiated reader.  The key, here, is that the get_block function
passed in, ext4_get_block_write, completely ignores the create flag
that is passed to it (the create flag is passed in from the direct I/O
code, which uses the DIO_SKIP_HOLES flag to determine whether or not
it should be cleared).

This is a long-winded way of saying that the DIO_SKIP_HOLES flag is
ultimately ignored.  So let's remove it.
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/inode.c

@@ -2941,7 +2941,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
 					 ext4_get_block_write,
 					 ext4_end_io_dio,
 					 NULL,
-					 DIO_LOCKING | DIO_SKIP_HOLES);
+					 DIO_LOCKING);
 		if (iocb->private)
 			EXT4_I(inode)->cur_aio_dio = NULL;
 		/*