# File lib/ec2/right_ec2_ebs.rb, line 301
    def modify_snapshot_attribute_create_volume_permission_add_groups(snapshot_id, *user_group)
      user_group.flatten!
      user_group = ['all'] if user_group.blank?
      modify_snapshot_attribute(snapshot_id, 'createVolumePermission', 'add', :user_group => user_group )
    end