def fromFilesystemPath(cls, fsPath):
    """Instantiate a :class:`CeresNode` from the on-disk path of an existing node

    :params fsPath: The filesystem path of an existing node
    :returns: :class:`CeresNode`
    """
    dirPath = dirname(fsPath)

    while True:
      ceresDir = join(dirPath, '.ceres-tree')
      if isdir(ceresDir):
        tree = CeresTree(dirPath)
        nodePath = tree.getNodePath(fsPath)
        return cls(tree, nodePath, fsPath)

      dirPath = dirname(dirPath)

      if dirPath == '/':
        raise ValueError("the path '%s' is not in a ceres tree" % fsPath)