code: func (p *csiPlugin) constructPVSourceSpec(volSpecName, driverName, volumeHandle string) *volume.Spec {
  	fsMode := api.PersistentVolumeFilesystem
  	pv := &api.PersistentVolume{
  		ObjectMeta: meta.ObjectMeta{
  			Name: volSpecName,
  		},
  		Spec: api.PersistentVolumeSpec{
  			PersistentVolumeSource: api.PersistentVolumeSource{
  				CSI: &api.CSIPersistentVolumeSource{
  					Driver:       driverName,
  					VolumeHandle: volumeHandle,
  				},
  			},
  			VolumeMode: &fsMode,
  		},
  	}
  	return volume.NewSpecFromPersistentVolume(pv, false)
  }
docs: //constructPVSourceSpec constructs volume.Spec with CSIPersistentVolumeSource