f2fs: still write data if preallocate only partial blocks

If there is not enough space left, f2fs_preallocate_blocks may only
preallocte partial blocks. As a result, the write operation fails
but i_blocks is not 0.  To avoid this, f2fs should write data in
non-preallocation way and write as many data as the size of i_blocks.
Signed-off-by: Sheng Yong <shengyong1@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -862,8 +862,14 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
 		if (err)
 			return err;
 	}
-	if (!f2fs_has_inline_data(inode))
-		return f2fs_map_blocks(inode, &map, 1, F2FS_GET_BLOCK_PRE_AIO);
+	if (!f2fs_has_inline_data(inode)) {
+		err = f2fs_map_blocks(inode, &map, 1, F2FS_GET_BLOCK_PRE_AIO);
+		if (map.m_len > 0 && err == -ENOSPC) {
+			set_inode_flag(inode, FI_NO_PREALLOC);
+			err = 0;
+		}
+		return err;
+	}
 	return err;
 }