code: func (d *Driver) CreateReadWrite(id, parent string, opts *graphdriver.CreateOpts) error {
  	if opts != nil && len(opts.StorageOpt) != 0 && !projectQuotaSupported {
  		return fmt.Errorf("--storage-opt is supported only for overlay over xfs with 'pquota' mount option")
  	}
  
  	if opts == nil {
  		opts = &graphdriver.CreateOpts{
  			StorageOpt: map[string]string{},
  		}
  	}
  
  	if _, ok := opts.StorageOpt["size"]; !ok {
  		if opts.StorageOpt == nil {
  			opts.StorageOpt = map[string]string{}
  		}
  		opts.StorageOpt["size"] = strconv.FormatUint(d.options.quota.Size, 10)
  	}
  
  	return d.create(id, parent, opts)
  }
docs: // CreateReadWrite creates a layer that is writable for use as a container
  // file system.