code: func ValidatePersistentVolumeUpdate(newPv, oldPv *api.PersistentVolume) field.ErrorList {
  	allErrs := field.ErrorList{}
  	allErrs = ValidatePersistentVolume(newPv)
  	newPv.Status = oldPv.Status
  	return allErrs
  }
docs: // ValidatePersistentVolumeUpdate tests to see if the update is legal for an end user to make.
  // newPv is updated with fields that cannot be changed.