code: private INodeFileUnderConstruction unprotectedAddFile(long inodeId, String path,
        PermissionStatus permissions, short replication, long modificationTime,
        long atime, long preferredBlockSize, String clientName,
        String clientMachine) {
      INodeFileUnderConstruction newNode = new INodeFileUnderConstruction(
          inodeId, permissions, replication, preferredBlockSize, modificationTime,
          clientName, clientMachine, null);
      try {
        newNode = addNode(path, newNode, 0, false);
      } catch (IOException e) {
        return null;
      }
      return newNode;
    }
docs: Creates a {@link INodeFileUnderConstruction} and adds an empty file with no
  blocks to the FileSystem. No locks are taken while doing updates, the
  caller is expected to use the write lock.