docs: def volume_info(self, vol=None, type_filter=None):
  		'Get list of all volumes or info for the one specified.'
  		vols = yield self(join('volumes', vol))
  		if not isinstance(vols, list): vols = [vols]
  		if type_filter is not None:
  			vols = list(vol for vol in vols if vol['type'] == type_filter)
  		if vol is not None: defer.returnValue(vols[0] if vols else None)
  		defer.returnValue(vols)