direct-io: Remove unused DIO_ASYNC_EXTEND flag

This flag was added by 60392573 ("direct-io: add flag to allow aio
writes beyond i_size") to support XFS. However, with the rework of
XFS' DIO's path to use iomap in acdda3aa ("xfs: use iomap_dio_rw")
it became redundant. So let's remove it.
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

fs/direct-io.c

@@ -1252,8 +1252,7 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 	 */
 	if (is_sync_kiocb(iocb))
 		dio->is_async = false;
-	else if (!(dio->flags & DIO_ASYNC_EXTEND) &&
-		 iov_iter_rw(iter) == WRITE && end > i_size_read(inode))
+	else if (iov_iter_rw(iter) == WRITE && end > i_size_read(inode))
 		dio->is_async = false;
 	else
 		dio->is_async = true;

include/linux/fs.h

@@ -2977,9 +2977,6 @@ enum {
 	/* filesystem does not support filling holes */
 	DIO_SKIP_HOLES	= 0x02,
 
-	/* filesystem can handle aio writes beyond i_size */
-	DIO_ASYNC_EXTEND = 0x04,
-
 	/* inode/fs/bdev does not need truncate protection */
 	DIO_SKIP_DIO_COUNT = 0x08,
 };