code: func (util *portworxVolumeUtil) UnmountVolume(u *portworxVolumeUnmounter, mountPath string) error {
  	driver, err := util.getLocalPortworxDriver(u.plugin.host)
  	if err != nil || driver == nil {
  		klog.Errorf("Failed to get portworx driver. Err: %v", err)
  		return err
  	}
  
  	err = driver.Unmount(u.volName, mountPath)
  	if err != nil {
  		klog.Errorf("Error unmounting Portworx Volume (%v) on Path (%v): %v", u.volName, mountPath, err)
  		return err
  	}
  	return nil
  }
docs: // UnmountVolume unmounts a Portworx Volume