'Return a single extra spec item.'

def show(self, req, type_id, id):

    context = req.environ['cinder.context']
    authorize(context, action='show')
    self._check_type(context, type_id)
    specs = self._get_extra_specs(context, type_id)
    if (id in specs['extra_specs']):
        return {id: specs['extra_specs'][id]}
    else:
        raise exception.VolumeTypeExtraSpecsNotFound(volume_type_id=type_id, extra_specs_key=id)
