code: func extendVmfsDatastore(ctx context.Context, s *object.HostDatastoreSystem, ds *object.Datastore, spec types.VmfsDatastoreExtendSpec) (*object.Datastore, error) {
  	req := types.ExtendVmfsDatastore{
  		This:      s.Reference(),
  		Datastore: ds.Reference(),
  		Spec:      spec,
  	}
  
  	res, err := methods.ExtendVmfsDatastore(ctx, s.Client(), &req)
  	if err != nil {
  		return nil, err
  	}
  
  	return object.NewDatastore(s.Client(), res.Returnval), nil
  }
docs: // extendVmfsDatastore is a stop-gap method that implements
  // ExtendVmfsDatastore. It will be removed once the higher level
  // HostDatastoreSystem object supports this method.