code: func (l *linkIndex) parents(child *container.Container) map[string]*container.Container {
  	l.mu.Lock()
  
  	parents := make(map[string]*container.Container)
  	for parent, aliases := range l.childIdx[child] {
  		for alias := range aliases {
  			parents[alias] = parent
  		}
  	}
  
  	l.mu.Unlock()
  	return parents
  }
docs: // parents maps all the aliases->parent for the passed in child
  // aliases here are the aliases the parents use to refer to the child