code: func DropDisabledFields(pvcSpec, oldPVCSpec *core.PersistentVolumeClaimSpec) {
  	if !utilfeature.DefaultFeatureGate.Enabled(features.BlockVolume) && !volumeModeInUse(oldPVCSpec) {
  		pvcSpec.VolumeMode = nil
  	}
  	if !utilfeature.DefaultFeatureGate.Enabled(features.VolumeSnapshotDataSource) && !volumeSnapshotDataSourceInUse(oldPVCSpec) {
  		pvcSpec.DataSource = nil
  	}
  }
docs: // DropDisabledFields removes disabled fields from the pvc spec.
  // This should be called from PrepareForCreate/PrepareForUpdate for all resources containing a pvc spec.