generic_file_direct_write(): make use of iov_iter_revert()

	ssize_t		written;

	size_t		write_len;

	pgoff_t		end;

	struct iov_iter data;

	write_len = iov_iter_count(from);

	end = (pos + write_len - 1) >> PAGE_SHIFT;

		}

	}

	data = *from;

	written = mapping->a_ops->direct_IO(iocb, &data);

	written = mapping->a_ops->direct_IO(iocb, from);

	/*

	 * Finally, try again to invalidate clean pages which might have been

	if (written > 0) {

		pos += written;

		iov_iter_advance(from, written);

		write_len -= written;

		if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {

			i_size_write(inode, pos);

			mark_inode_dirty(inode);

		}

		iocb->ki_pos = pos;

	}

	iov_iter_revert(from, write_len - iov_iter_count(from));

out:

	return written;

}