code: func (p *csiPlugin) GetVolumeName(spec *volume.Spec) (string, error) {
  	csi, err := getPVSourceFromSpec(spec)
  	if err != nil {
  		klog.Error(log("plugin.GetVolumeName failed to extract volume source from spec: %v", err))
  		return "", err
  	}
  
  	// return driverName<separator>volumeHandle
  	return fmt.Sprintf("%s%s%s", csi.Driver, volNameSep, csi.VolumeHandle), nil
  }
docs: // GetvolumeName returns a concatenated string of CSIVolumeSource.Driver<volNameSe>CSIVolumeSource.VolumeHandle
  // That string value is used in Detach() to extract driver name and volumeName.