code: func getVolumeSourceFromSpec(spec *volume.Spec) (interface{}, error) {
  	if spec.Volume != nil && spec.Volume.ScaleIO != nil {
  		return spec.Volume.ScaleIO, nil
  	}
  	if spec.PersistentVolume != nil &&
  		spec.PersistentVolume.Spec.ScaleIO != nil {
  		return spec.PersistentVolume.Spec.ScaleIO, nil
  	}
  
  	return nil, fmt.Errorf("ScaleIO not defined in spec")
  }
docs: // getVolumeSourceFromSpec safely extracts ScaleIOVolumeSource or ScaleIOPersistentVolumeSource from spec