code: func (d *Driver) CreateReadWrite(id, parent string, opts *graphdriver.CreateOpts) error {
  	if opts != nil {
  		return d.create(id, parent, opts.MountLabel, false, opts.StorageOpt)
  	}
  	return d.create(id, parent, "", false, nil)
  }
docs: // CreateReadWrite creates a layer that is writable for use as a container
  // file system.