code: func (plugin *flexVolumePlugin) ConstructVolumeSpec(volumeName, mountPath string) (*volume.Spec, error) {
  	flexVolume := &api.Volume{
  		Name: volumeName,
  		VolumeSource: api.VolumeSource{
  			FlexVolume: &api.FlexVolumeSource{
  				Driver: plugin.driverName,
  			},
  		},
  	}
  	return volume.NewSpecFromVolume(flexVolume), nil
  }
docs: // ConstructVolumeSpec is part of the volume.AttachableVolumePlugin interface.