code: func (inode *Inode) fillXattrFromHead(resp *s3.HeadObjectOutput) {
  	inode.userMetadata = make(map[string][]byte)
  
  	if resp.ETag != nil {
  		inode.s3Metadata["etag"] = []byte(*resp.ETag)
  	}
  	if resp.StorageClass != nil {
  		inode.s3Metadata["storage-class"] = []byte(*resp.StorageClass)
  	} else {
  		inode.s3Metadata["storage-class"] = []byte("STANDARD")
  	}
  
  	for k, v := range resp.Metadata {
  		k = strings.ToLower(k)
  		value, err := url.PathUnescape(*v)
  		if err != nil {
  			value = *v
  		}
  		inode.userMetadata[k] = []byte(value)
  	}
  }
docs: // LOCKS_REQUIRED(inode.mu)