code: func (vm *volumeManager) getUnmountedVolumes(podName types.UniquePodName, expectedVolumes []string) []string {
  	mountedVolumes := sets.NewString()
  	for _, mountedVolume := range vm.actualStateOfWorld.GetMountedVolumesForPod(podName) {
  		mountedVolumes.Insert(mountedVolume.OuterVolumeSpecName)
  	}
  	return filterUnmountedVolumes(mountedVolumes, expectedVolumes)
  }
docs: // getUnmountedVolumes fetches the current list of mounted volumes from
  // the actual state of the world, and uses it to process the list of
  // expectedVolumes. It returns a list of unmounted volumes.