f2fs: issue cache flush on direct IO

Under direct IO path with O_(D)SYNC, it needs to set proper APPEND or UPDATE
flags, so taht f2fs_sync_file can make its data safe.
Acked-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -673,6 +673,9 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map,
 					err = reserve_new_block(&dn);
 			} else {
 				err = __allocate_data_block(&dn);
+				if (!err)
+					set_inode_flag(F2FS_I(inode),
+							FI_APPEND_WRITE);
 			}
 			if (err)
 				goto sync_out;
@@ -1685,8 +1688,12 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 	trace_f2fs_direct_IO_enter(inode, offset, count, iov_iter_rw(iter));
 
 	err = blockdev_direct_IO(iocb, inode, iter, offset, get_data_block_dio);
-	if (err < 0 && iov_iter_rw(iter) == WRITE)
-		f2fs_write_failed(mapping, offset + count);
+	if (iov_iter_rw(iter) == WRITE) {
+		if (err > 0)
+			set_inode_flag(F2FS_I(inode), FI_UPDATE_WRITE);
+		else if (err < 0)
+			f2fs_write_failed(mapping, offset + count);
+	}
 
 	trace_f2fs_direct_IO_exit(inode, offset, count, iov_iter_rw(iter), err);