code: func ensureShared(path string, mountInfos []*dockermounts.Info) error {
  	sourceMount, optionalOpts, err := getSourceMount(path, mountInfos)
  	if err != nil {
  		return err
  	}
  
  	// Make sure source mount point is shared.
  	optsSplit := strings.Split(optionalOpts, " ")
  	for _, opt := range optsSplit {
  		if strings.HasPrefix(opt, "shared:") {
  			return nil
  		}
  	}
  
  	return fmt.Errorf("path %q is mounted on %q but it is not a shared mount", path, sourceMount)
  }
docs: // Ensure mount point on which path is mounted, is shared.