code: func (n *mutDir) maybeAddChild(name string, permanode *search.DescribedPermanode,
  	child mutFileOrDir) {
  	if current, ok := n.children[name]; !ok ||
  		current.permanodeString() != child.permanodeString() {
  
  		child.xattr().load(permanode)
  		n.children[name] = child
  	}
  }
docs: // maybeAddChild adds a child directory to this mutable directory
  // unless it already has one with this name and permanode.