code: func (s *VolumesService) Unmount(ctx context.Context, vol *types.Volume, ref string) error {
  	v, err := s.vs.Get(ctx, vol.Name, opts.WithGetDriver(vol.Driver))
  	if err != nil {
  		if IsNotExist(err) {
  			err = errdefs.NotFound(err)
  		}
  		return err
  	}
  	return v.Unmount(ref)
  }
docs: // Unmount unmounts the volume.
  // Note that depending on the implementation, the volume may still be mounted due to other resources using it.
  //
  // The reference specified here should be the same reference specified during `Mount` and should be
  // unique for each mount/unmount pair.
  // See `Mount` documentation for an example.