code: func (d *Daemon) containerExecIds() map[string]struct{} {
  	ids := map[string]struct{}{}
  	for _, c := range d.containers.List() {
  		for _, id := range c.ExecCommands.List() {
  			ids[id] = struct{}{}
  		}
  	}
  	return ids
  }
docs: // containerExecIds returns a list of all the current exec ids that are in use
  // and running inside a container.