func (s *backingSettings) updated(st *State, store *multiwatcher.Store, id interface{}) error {
	parentId, url, ok := backingEntityIdForSettingsKey(id.(string))
	if !ok {
		return nil
	}
	info0 := store.Get(parentId)
	switch info := info0.(type) {
	case nil:
		// The parent info doesn't exist. Ignore the status until it does.
		return nil
	case *params.ServiceInfo:
		// If we're seeing settings for the service with a different
		// charm URL, we ignore them - we will fetch
		// them again when the service charm changes.
		// By doing this we make sure that the settings in the
		// ServiceInfo are always consistent with the charm URL.
		if info.CharmURL != url {
			break
		}
		newInfo := *info
		cleanSettingsMap(*s)
		newInfo.Config = *s
		info0 = &newInfo
	default:
		return nil
	}
	store.Update(info0)
	return nil
}

func (svc *backingMachine) removed(st *State, store *multiwatcher.Store, id interface{}) error {
	store.Remove(params.EntityId{
		Kind: "machine",
		Id:   id,
	})
	return nil
}

func (svc *backingService) updated(st *State, store *multiwatcher.Store, id interface{}) error {
	if svc.CharmURL == nil {
		return errors.Errorf("charm url is nil")
	}
	env, err := st.Environment()
	if err != nil {
		return errors.Trace(err)
	}
	info := &params.ServiceInfo{
		Name:     svc.Name,
		Exposed:  svc.Exposed,
		CharmURL: svc.CharmURL.String(),
		OwnerTag: svc.fixOwnerTag(env),
		Life:     params.Life(svc.Life.String()),
		MinUnits: svc.MinUnits,
	}
	oldInfo := store.Get(info.EntityId())
	needConfig := false
	if oldInfo == nil {
		// We're adding the entry for the first time,
		// so fetch the associated child documents.
		c, err := readConstraints(st, serviceGlobalKey(svc.Name))
		if err != nil {
			return err
		}
		info.Constraints = c
		needConfig = true
	} else {
		// The entry already exists, so preserve the current status.
		oldInfo := oldInfo.(*params.ServiceInfo)
		info.Constraints = oldInfo.Constraints
		if info.CharmURL == oldInfo.CharmURL {
			// The charm URL remains the same - we can continue to
			// use the same config settings.
			info.Config = oldInfo.Config
		} else {
			// The charm URL has changed - we need to fetch the
			// settings from the new charm's settings doc.
			needConfig = true
		}
	}
	if needConfig {
		var err error
		info.Config, _, err = readSettingsDoc(st, serviceSettingsKey(svc.Name, svc.CharmURL))
		if err != nil {
			return err
		}
	}
	store.Update(info)
	return nil
}