func (mr *Machiner) SetUp() (watcher.NotifyWatcher, error) {
	// Find which machine we're responsible for.
	m, err := mr.config.MachineAccessor.Machine(mr.config.Tag)
	if params.IsCodeNotFoundOrCodeUnauthorized(err) {
		return nil, worker.ErrTerminateAgent
	} else if err != nil {
		return nil, errors.Trace(err)
	}
	mr.machine = m

	if mr.config.ClearMachineAddressesOnStart {
		logger.Debugf("machine addresses ignored on start - resetting machine addresses")
		if err := m.SetMachineAddresses(nil); err != nil {
			return nil, errors.Annotate(err, "reseting machine addresses")
		}
	} else {
		// Set the addresses in state to the host's addresses.
		if err := setMachineAddresses(mr.config.Tag, m); err != nil {
			return nil, errors.Annotate(err, "setting machine addresses")
		}
	}

	// Mark the machine as started and log it.
	if err := m.SetStatus(status.Started, "", nil); err != nil {
		return nil, errors.Annotatef(err, "%s failed to set status started", mr.config.Tag)
	}
	logger.Infof("%q started", mr.config.Tag)

	return m.Watch()
}

// findUnknownInstances finds instances which are not associated with a machine.
func (task *provisionerTask) findUnknownInstances(stopping []instance.Instance) ([]instance.Instance, error) {
	// Make a copy of the instances we know about.
	instances := make(map[instance.Id]instance.Instance)
	for k, v := range task.instances {
		instances[k] = v
	}

	for _, m := range task.machines {
		instId, err := m.InstanceId()
		switch {
		case err == nil:
			delete(instances, instId)
		case params.IsCodeNotProvisioned(err):
		case params.IsCodeNotFoundOrCodeUnauthorized(err):
		default:
			return nil, err
		}
	}
	// Now remove all those instances that we are stopping already as we
	// know about those and don't want to include them in the unknown list.
	for _, inst := range stopping {
		delete(instances, inst.Id())
	}
	var unknown []instance.Instance
	for _, inst := range instances {
		unknown = append(unknown, inst)
	}
	return unknown, nil
}

func (mr *Machiner) Handle(_ <-chan struct{}) error {
	if err := mr.machine.Refresh(); params.IsCodeNotFoundOrCodeUnauthorized(err) {
		// NOTE(axw) we can distinguish between NotFound and CodeUnauthorized,
		// so we could call NotifyMachineDead here in case the agent failed to
		// call NotifyMachineDead directly after setting the machine Dead in
		// the first place. We're not doing that to be cautious: the machine
		// could be missing from state due to invalid global state.
		return worker.ErrTerminateAgent
	} else if err != nil {
		return err
	}

	life := mr.machine.Life()
	if life == params.Alive {
		observedConfig, err := getObservedNetworkConfig(networkingcommon.DefaultNetworkConfigSource())
		if err != nil {
			return errors.Annotate(err, "cannot discover observed network config")
		} else if len(observedConfig) == 0 {
			logger.Warningf("not updating network config: no observed config found to update")
		}
		if len(observedConfig) > 0 {
			if err := mr.machine.SetObservedNetworkConfig(observedConfig); err != nil {
				return errors.Annotate(err, "cannot update observed network config")
			}
		}
		logger.Debugf("observed network config updated")

		return nil
	}
	logger.Debugf("%q is now %s", mr.config.Tag, life)
	if err := mr.machine.SetStatus(status.Stopped, "", nil); err != nil {
		return errors.Annotatef(err, "%s failed to set status stopped", mr.config.Tag)
	}

	// Attempt to mark the machine Dead. If the machine still has units
	// assigned, or storage attached, this will fail with
	// CodeHasAssignedUnits or CodeMachineHasAttachedStorage respectively.
	// Once units or storage are removed, the watcher will trigger again
	// and we'll reattempt.
	if err := mr.machine.EnsureDead(); err != nil {
		if params.IsCodeHasAssignedUnits(err) {
			return nil
		}
		if params.IsCodeMachineHasAttachedStorage(err) {
			logger.Tracef("machine still has storage attached")
			return nil
		}
		return errors.Annotatef(err, "%s failed to set machine to dead", mr.config.Tag)
	}
	// Report on the machine's death. It is important that we do this after
	// the machine is Dead, because this is the mechanism we use to clean up
	// the machine (uninstall). If we were to report before marking the machine
	// as Dead, then we would risk uninstalling prematurely.
	if mr.config.NotifyMachineDead != nil {
		if err := mr.config.NotifyMachineDead(); err != nil {
			return errors.Annotate(err, "reporting machine death")
		}
	}
	return worker.ErrTerminateAgent
}

// NewActionRunner exists to satisfy the Factory interface.
func (f *factory) NewActionRunner(actionId string) (Runner, error) {
	ch, err := getCharm(f.paths.GetCharmDir())
	if err != nil {
		return nil, errors.Trace(err)
	}

	ok := names.IsValidAction(actionId)
	if !ok {
		return nil, &badActionError{actionId, "not valid actionId"}
	}
	tag := names.NewActionTag(actionId)
	action, err := f.state.Action(tag)
	if params.IsCodeNotFoundOrCodeUnauthorized(err) {
		return nil, ErrActionNotAvailable
	} else if params.IsCodeActionNotAvailable(err) {
		return nil, ErrActionNotAvailable
	} else if err != nil {
		return nil, errors.Trace(err)
	}

	name := action.Name()
	spec, ok := ch.Actions().ActionSpecs[name]
	if !ok {
		return nil, &badActionError{name, "not defined"}
	}
	params := action.Params()
	if err := spec.ValidateParams(params); err != nil {
		return nil, &badActionError{name, err.Error()}
	}

	actionData := newActionData(name, &tag, params)
	ctx, err := f.contextFactory.ActionContext(actionData)
	runner := NewRunner(ctx, f.paths)
	return runner, nil
}

// changed ensures that the named unit is deployed, recalled, or removed, as
// indicated by its state.
func (d *Deployer) changed(unitName string) error {
	unitTag := names.NewUnitTag(unitName)
	// Determine unit life state, and whether we're responsible for it.
	logger.Infof("checking unit %q", unitName)
	var life params.Life
	unit, err := d.st.Unit(unitTag)
	if params.IsCodeNotFoundOrCodeUnauthorized(err) {
		life = params.Dead
	} else if err != nil {
		return err
	} else {
		life = unit.Life()
	}
	// Deployed units must be removed if they're Dead, or if the deployer
	// is no longer responsible for them.
	if d.deployed.Contains(unitName) {
		if life == params.Dead {
			if err := d.recall(unitName); err != nil {
				return err
			}
		}
	}
	// The only units that should be deployed are those that (1) we are responsible
	// for and (2) are Alive -- if we're responsible for a Dying unit that is not
	// yet deployed, we should remove it immediately rather than undergo the hassle
	// of deploying a unit agent purely so it can set itself to Dead.
	if !d.deployed.Contains(unitName) {
		if life == params.Alive {
			return d.deploy(unit)
		} else if unit != nil {
			return d.remove(unit)
		}
	}
	return nil
}

func (mr *Machiner) Handle(_ <-chan struct{}) error {
	if err := mr.machine.Refresh(); params.IsCodeNotFoundOrCodeUnauthorized(err) {
		return worker.ErrTerminateAgent
	} else if err != nil {
		return err
	}
	life := mr.machine.Life()
	if life == params.Alive {
		return nil
	}
	logger.Debugf("%q is now %s", mr.tag, life)
	if err := mr.machine.SetStatus(params.StatusStopped, "", nil); err != nil {
		return errors.Annotatef(err, "%s failed to set status stopped", mr.tag)
	}

	// Attempt to mark the machine Dead. If the machine still has units
	// assigned, or storage attached, this will fail with
	// CodeHasAssignedUnits or CodeMachineHasAttachedStorage respectively.
	// Once units or storage are removed, the watcher will trigger again
	// and we'll reattempt.
	if err := mr.machine.EnsureDead(); err != nil {
		if params.IsCodeHasAssignedUnits(err) {
			return nil
		}
		if params.IsCodeMachineHasAttachedStorage(err) {
			logger.Tracef("machine still has storage attached")
			return nil
		}
		return errors.Annotatef(err, "%s failed to set machine to dead", mr.tag)
	}
	return worker.ErrTerminateAgent
}

// populateMachineMaps updates task.instances. Also updates
// task.machines map if a list of IDs is given.
func (task *provisionerTask) populateMachineMaps(ids []string) error {
	task.instances = make(map[instance.Id]instance.Instance)

	instances, err := task.broker.AllInstances()
	if err != nil {
		return errors.Annotate(err, "failed to get all instances from broker")
	}
	for _, i := range instances {
		task.instances[i.Id()] = i
	}

	// Update the machines map with new data for each of the machines in the
	// change list.
	// TODO(thumper): update for API server later to get all machines in one go.
	for _, id := range ids {
		machineTag := names.NewMachineTag(id)
		machine, err := task.machineGetter.Machine(machineTag)
		switch {
		case params.IsCodeNotFoundOrCodeUnauthorized(err):
			logger.Debugf("machine %q not found in state", id)
			delete(task.machines, id)
		case err == nil:
			task.machines[id] = machine
		default:
			return errors.Annotatef(err, "failed to get machine %v", id)
		}
	}
	return nil
}

// SetPassword is part of the ConnFacade interface.
func (facade *connFacade) SetPassword(entity names.Tag, password string) error {
	var results params.ErrorResults
	args := params.EntityPasswords{
		Changes: []params.EntityPassword{{
			Tag:      entity.String(),
			Password: password,
		}},
	}
	err := facade.caller.FacadeCall("SetPasswords", args, &results)
	if err != nil {
		return errors.Trace(err)
	}
	if len(results.Results) != 1 {
		return errors.Errorf("expected 1 result, got %d", len(results.Results))
	}
	if err := results.Results[0].Error; err != nil {
		if params.IsCodeDead(err) {
			return ErrDenied
		} else if params.IsCodeNotFoundOrCodeUnauthorized(err) {
			return ErrDenied
		}
		return errors.Trace(err)
	}
	return nil
}

// Life is part of the ConnFacade interface.
func (facade *connFacade) Life(entity names.Tag) (Life, error) {
	var results params.AgentGetEntitiesResults
	args := params.Entities{
		Entities: []params.Entity{{Tag: entity.String()}},
	}
	err := facade.caller.FacadeCall("GetEntities", args, &results)
	if err != nil {
		return "", errors.Trace(err)
	}
	if len(results.Entities) != 1 {
		return "", errors.Errorf("expected 1 result, got %d", len(results.Entities))
	}
	if err := results.Entities[0].Error; err != nil {
		if params.IsCodeNotFoundOrCodeUnauthorized(err) {
			return "", ErrDenied
		}
		return "", errors.Trace(err)
	}
	life := Life(results.Entities[0].Life)
	switch life {
	case Alive, Dying, Dead:
		return life, nil
	}
	return "", errors.Errorf("unknown life value %q", life)
}

// FailAction is part of the operation.Callbacks interface.
func (opc *operationCallbacks) FailAction(actionId, message string) error {
	if !names.IsValidAction(actionId) {
		return errors.Errorf("invalid action id %q", actionId)
	}
	tag := names.NewActionTag(actionId)
	err := opc.u.st.ActionFinish(tag, params.ActionFailed, nil, message)
	if params.IsCodeNotFoundOrCodeUnauthorized(err) {
		err = nil
	}
	return err
}

func (w *RemoteStateWatcher) init(unitTag names.UnitTag) (err error) {
	// TODO(dfc) named return value is a time bomb
	// TODO(axw) move this logic.
	defer func() {
		if params.IsCodeNotFoundOrCodeUnauthorized(err) {
			err = worker.ErrTerminateAgent
		}
	}()
	if w.unit, err = w.st.Unit(unitTag); err != nil {
		return err
	}
	w.service, err = w.unit.Service()
	if err != nil {
		return err
	}
	return nil
}

func (w *RemoteStateWatcher) setUp(unitTag names.UnitTag) (err error) {
	// TODO(dfc) named return value is a time bomb
	// TODO(axw) move this logic.
	defer func() {
		cause := errors.Cause(err)
		if params.IsCodeNotFoundOrCodeUnauthorized(cause) {
			err = worker.ErrTerminateAgent
		}
	}()
	if w.unit, err = w.st.Unit(unitTag); err != nil {
		return errors.Trace(err)
	}
	w.service, err = w.unit.Application()
	if err != nil {
		return errors.Trace(err)
	}
	return nil
}

func (mr *Machiner) Handle() error {
	if err := mr.machine.Refresh(); params.IsCodeNotFoundOrCodeUnauthorized(err) {
		return worker.ErrTerminateAgent
	} else if err != nil {
		return err
	}
	if mr.machine.Life() == params.Alive {
		return nil
	}
	logger.Debugf("%q is now %s", mr.tag, mr.machine.Life())
	if err := mr.machine.SetStatus(params.StatusStopped, "", nil); err != nil {
		return fmt.Errorf("%s failed to set status stopped: %v", mr.tag, err)
	}

	// If the machine is Dying, it has no units,
	// and can be safely set to Dead.
	if err := mr.machine.EnsureDead(); err != nil {
		return fmt.Errorf("%s failed to set machine to dead: %v", mr.tag, err)
	}
	return worker.ErrTerminateAgent
}

// relationsChanged responds to service relation changes.
func (w *RemoteStateWatcher) relationsChanged(keys []string) error {
	w.mu.Lock()
	defer w.mu.Unlock()
	for _, key := range keys {
		relationTag := names.NewRelationTag(key)
		rel, err := w.st.Relation(relationTag)
		if params.IsCodeNotFoundOrCodeUnauthorized(err) {
			// If it's actually gone, this unit cannot have entered
			// scope, and therefore never needs to know about it.
			if ruw, ok := w.relations[relationTag]; ok {
				worker.Stop(ruw)
				delete(w.relations, relationTag)
				delete(w.current.Relations, ruw.relationId)
			}
		} else if err != nil {
			return errors.Trace(err)
		} else {
			if _, ok := w.relations[relationTag]; ok {
				relationSnapshot := w.current.Relations[rel.Id()]
				relationSnapshot.Life = rel.Life()
				w.current.Relations[rel.Id()] = relationSnapshot
				continue
			}
			ruw, err := w.st.WatchRelationUnits(relationTag, w.unit.Tag())
			if err != nil {
				return errors.Trace(err)
			}
			// Because of the delay before handing off responsibility to
			// newRelationUnitsWatcher below, add to our own catacomb to
			// ensure errors get picked up if they happen.
			if err := w.catacomb.Add(ruw); err != nil {
				return errors.Trace(err)
			}
			if err := w.watchRelationUnits(rel, relationTag, ruw); err != nil {
				return errors.Trace(err)
			}
		}
	}
	return nil
}

func (mr *Machiner) SetUp() (watcher.NotifyWatcher, error) {
	// Find which machine we're responsible for.
	m, err := mr.st.Machine(mr.tag)
	if params.IsCodeNotFoundOrCodeUnauthorized(err) {
		return nil, worker.ErrTerminateAgent
	} else if err != nil {
		return nil, err
	}
	mr.machine = m

	// Set the addresses in state to the host's addresses.
	if err := setMachineAddresses(mr.tag, m); err != nil {
		return nil, err
	}

	// Mark the machine as started and log it.
	if err := m.SetStatus(params.StatusStarted, "", nil); err != nil {
		return nil, fmt.Errorf("%s failed to set status started: %v", mr.tag, err)
	}
	logger.Infof("%q started", mr.tag)

	return m.Watch()
}

// relationsChanged responds to service relation changes.
func (w *RemoteStateWatcher) relationsChanged(keys []string) error {
	w.mu.Lock()
	defer w.mu.Unlock()
	for _, key := range keys {
		relationTag := names.NewRelationTag(key)
		rel, err := w.st.Relation(relationTag)
		if params.IsCodeNotFoundOrCodeUnauthorized(err) {
			// If it's actually gone, this unit cannot have entered
			// scope, and therefore never needs to know about it.
			if ruw, ok := w.relations[relationTag]; ok {
				if err := ruw.Stop(); err != nil {
					return errors.Trace(err)
				}
				delete(w.relations, relationTag)
				delete(w.current.Relations, ruw.relationId)
			}
		} else if err != nil {
			return err
		} else {
			if _, ok := w.relations[relationTag]; ok {
				relationSnapshot := w.current.Relations[rel.Id()]
				relationSnapshot.Life = rel.Life()
				w.current.Relations[rel.Id()] = relationSnapshot
				continue
			}
			in, err := w.st.WatchRelationUnits(relationTag, w.unit.Tag())
			if err != nil {
				return errors.Trace(err)
			}
			if err := w.watchRelationUnits(rel, relationTag, in); err != nil {
				watcher.Stop(in, &w.tomb)
				return errors.Trace(err)
			}
		}
	}
	return nil
}

func (f *filter) loop(unitTag names.UnitTag) (err error) {
	// TODO(dfc) named return value is a time bomb
	defer func() {
		if params.IsCodeNotFoundOrCodeUnauthorized(err) {
			err = worker.ErrTerminateAgent
		}
	}()
	if f.unit, err = f.st.Unit(unitTag); err != nil {
		return err
	}
	if err = f.unitChanged(); err != nil {
		return err
	}
	if err = f.meterStatusChanged(); err != nil {
		return err
	}
	f.service, err = f.unit.Service()
	if err != nil {
		return err
	}
	if err = f.serviceChanged(); err != nil {
		return err
	}
	unitw, err := f.unit.Watch()
	if err != nil {
		return err
	}
	defer f.maybeStopWatcher(unitw)
	servicew, err := f.service.Watch()
	if err != nil {
		return err
	}
	defer f.maybeStopWatcher(servicew)
	// configw and relationsw can get restarted, so we need to use
	// their eventual values in the defer calls.
	var configw apiwatcher.NotifyWatcher
	var configChanges <-chan struct{}
	curl, err := f.unit.CharmURL()
	if err == nil {
		configw, err = f.unit.WatchConfigSettings()
		if err != nil {
			return err
		}
		configChanges = configw.Changes()
		f.upgradeFrom.url = curl
	} else if err != uniter.ErrNoCharmURLSet {
		filterLogger.Errorf("unit charm: %v", err)
		return err
	}
	defer f.maybeStopWatcher(configw)
	actionsw, err := f.unit.WatchActionNotifications()
	if err != nil {
		return err
	}
	f.actionsPending = make([]string, 0)
	defer f.maybeStopWatcher(actionsw)
	relationsw, err := f.service.WatchRelations()
	if err != nil {
		return err
	}
	defer f.maybeStopWatcher(relationsw)
	meterStatusw, err := f.unit.WatchMeterStatus()
	if err != nil {
		return err
	}
	defer f.maybeStopWatcher(meterStatusw)
	addressesw, err := f.unit.WatchAddresses()
	if err != nil {
		return err
	}
	defer watcher.Stop(addressesw, &f.tomb)
	storagew, err := f.unit.WatchStorage()
	if err != nil {
		return err
	}
	defer watcher.Stop(storagew, &f.tomb)
	leaderSettingsw, err := f.st.LeadershipSettings.WatchLeadershipSettings(f.service.Tag().Id())
	if err != nil {
		return err
	}
	defer watcher.Stop(leaderSettingsw, &f.tomb)

	// Ignore external requests for leader settings behaviour until we see the first change.
	var discardLeaderSettings <-chan struct{}
	var wantLeaderSettings <-chan bool
	// By default we send all leaderSettings onwards.
	sendLeaderSettings := true

	// Config events cannot be meaningfully discarded until one is available;
	// once we receive the initial config and address changes, we unblock
	// discard requests by setting this channel to its namesake on f.
	var discardConfig chan struct{}
	var seenConfigChange bool
	var seenAddressChange bool
	maybePrepareConfigEvent := func() {
		if !seenAddressChange {
			filterLogger.Debugf("no address change seen yet, skipping config event")
			return
		}
		if !seenConfigChange {
//.........这里部分代码省略.........

// Update is part of the Relations interface.
func (r *relations) Update(ids []int) error {
	for _, id := range ids {
		if relationer, found := r.relationers[id]; found {
			rel := relationer.ru.Relation()
			if err := rel.Refresh(); err != nil {
				return errors.Annotatef(err, "cannot update relation %q", rel)
			}
			if rel.Life() == params.Dying {
				if err := r.setDying(id); err != nil {
					return errors.Trace(err)
				}
			}
			continue
		}
		// Relations that are not alive are simply skipped, because they
		// were not previously known anyway.
		rel, err := r.st.RelationById(id)
		if err != nil {
			if params.IsCodeNotFoundOrCodeUnauthorized(err) {
				continue
			}
			return errors.Trace(err)
		}
		if rel.Life() != params.Alive {
			continue
		}
		// Make sure we ignore relations not implemented by the unit's charm.
		ch, err := corecharm.ReadCharmDir(r.charmDir)
		if err != nil {
			return errors.Trace(err)
		}
		if ep, err := rel.Endpoint(); err != nil {
			return errors.Trace(err)
		} else if !ep.ImplementedBy(ch) {
			logger.Warningf("skipping relation with unknown endpoint %q", ep.Name)
			continue
		}
		dir, err := relation.ReadStateDir(r.relationsDir, id)
		if err != nil {
			return errors.Trace(err)
		}
		err = r.add(rel, dir)
		if err == nil {
			r.relationers[id].StartHooks()
			continue
		}
		e := dir.Remove()
		if !params.IsCodeCannotEnterScope(err) {
			return errors.Trace(err)
		}
		if e != nil {
			return errors.Trace(e)
		}
	}
	if ok, err := r.unit.IsPrincipal(); err != nil {
		return errors.Trace(err)
	} else if ok {
		return nil
	}
	// If no Alive relations remain between a subordinate unit's service
	// and its principal's service, the subordinate must become Dying.
	for _, relationer := range r.relationers {
		scope := relationer.ru.Endpoint().Scope
		if scope == corecharm.ScopeContainer && !relationer.dying {
			return nil
		}
	}
	return r.unit.Destroy()
}

func (r *relations) update(remote map[int]remotestate.RelationSnapshot) error {
	for id, relationSnapshot := range remote {
		if _, found := r.relationers[id]; found {
			// We've seen this relation before. The only changes
			// we care about are to the lifecycle state, and to
			// the member settings versions. We handle differences
			// in settings in nextRelationHook.
			if relationSnapshot.Life == params.Dying {
				if err := r.setDying(id); err != nil {
					return errors.Trace(err)
				}
			}
			continue
		}
		// Relations that are not alive are simply skipped, because they
		// were not previously known anyway.
		if relationSnapshot.Life != params.Alive {
			continue
		}
		rel, err := r.st.RelationById(id)
		if err != nil {
			if params.IsCodeNotFoundOrCodeUnauthorized(err) {
				continue
			}
			return errors.Trace(err)
		}
		// Make sure we ignore relations not implemented by the unit's charm.
		ch, err := corecharm.ReadCharmDir(r.charmDir)
		if err != nil {
			return errors.Trace(err)
		}
		if ep, err := rel.Endpoint(); err != nil {
			return errors.Trace(err)
		} else if !ep.ImplementedBy(ch) {
			logger.Warningf("skipping relation with unknown endpoint %q", ep.Name)
			continue
		}
		dir, err := ReadStateDir(r.relationsDir, id)
		if err != nil {
			return errors.Trace(err)
		}
		addErr := r.add(rel, dir)
		if addErr == nil {
			continue
		}
		removeErr := dir.Remove()
		if !params.IsCodeCannotEnterScope(addErr) {
			return errors.Trace(addErr)
		}
		if removeErr != nil {
			return errors.Trace(removeErr)
		}
	}
	if ok, err := r.unit.IsPrincipal(); err != nil {
		return errors.Trace(err)
	} else if ok {
		return nil
	}
	// If no Alive relations remain between a subordinate unit's service
	// and its principal's service, the subordinate must become Dying.
	for _, relationer := range r.relationers {
		scope := relationer.ru.Endpoint().Scope
		if scope == corecharm.ScopeContainer && !relationer.dying {
			return nil
		}
	}
	return r.unit.Destroy()
}

func (f *filter) loop(unitTag string) (err error) {
	// TODO(dfc) named return value is a time bomb
	defer func() {
		if params.IsCodeNotFoundOrCodeUnauthorized(err) {
			err = worker.ErrTerminateAgent
		}
	}()
	tag, err := names.ParseUnitTag(unitTag)
	if err != nil {
		return err
	}
	if f.unit, err = f.st.Unit(tag); err != nil {
		return err
	}
	if err = f.unitChanged(); err != nil {
		return err
	}
	f.service, err = f.unit.Service()
	if err != nil {
		return err
	}
	if err = f.serviceChanged(); err != nil {
		return err
	}
	unitw, err := f.unit.Watch()
	if err != nil {
		return err
	}
	defer f.maybeStopWatcher(unitw)
	servicew, err := f.service.Watch()
	if err != nil {
		return err
	}
	defer f.maybeStopWatcher(servicew)
	// configw and relationsw can get restarted, so we need to use
	// their eventual values in the defer calls.
	var configw apiwatcher.NotifyWatcher
	var configChanges <-chan struct{}
	curl, err := f.unit.CharmURL()
	if err == nil {
		configw, err = f.unit.WatchConfigSettings()
		if err != nil {
			return err
		}
		configChanges = configw.Changes()
		f.upgradeFrom.url = curl
	} else if err != uniter.ErrNoCharmURLSet {
		filterLogger.Errorf("unit charm: %v", err)
		return err
	}
	defer func() {
		if configw != nil {
			watcher.Stop(configw, &f.tomb)
		}
	}()
	actionsw, err := f.unit.WatchActions()
	if err != nil {
		return err
	}
	f.actionsPending = make([]string, 0)
	defer func() {
		if actionsw != nil {
			watcher.Stop(actionsw, &f.tomb)
		}
	}()
	relationsw, err := f.service.WatchRelations()
	if err != nil {
		return err
	}
	defer func() {
		if relationsw != nil {
			watcher.Stop(relationsw, &f.tomb)
		}
	}()
	var addressChanges <-chan struct{}
	addressesw, err := f.unit.WatchAddresses()
	if err != nil {
		return err
	}
	defer watcher.Stop(addressesw, &f.tomb)

	// Config events cannot be meaningfully discarded until one is available;
	// once we receive the initial change, we unblock discard requests by
	// setting this channel to its namesake on f.
	var discardConfig chan struct{}
	for {
		var ok bool
		select {
		case <-f.tomb.Dying():
			return tomb.ErrDying

		// Handle watcher changes.
		case _, ok = <-unitw.Changes():
			filterLogger.Debugf("got unit change")
			if !ok {
				return watcher.MustErr(unitw)
			}
			if err = f.unitChanged(); err != nil {
				return err
			}
//.........这里部分代码省略.........