func isCompatibleWithVers(vers map[string]*version.Versions, local types.ID, minV, maxV *semver.Version) bool {
	var ok bool
	for id, v := range vers {
		// ignore comparison with local version
		if id == local.String() {
			continue
		}
		if v == nil {
			continue
		}
		clusterv, err := semver.NewVersion(v.Cluster)
		if err != nil {
			plog.Errorf("cannot understand the cluster version of member %s (%v)", id, err)
			continue
		}
		if clusterv.LessThan(*minV) {
			plog.Warningf("the running cluster version(%v) is lower than the minimal cluster version(%v) supported", clusterv.String(), minV.String())
			return false
		}
		if maxV.LessThan(*clusterv) {
			plog.Warningf("the running cluster version(%v) is higher than the maximum cluster version(%v) supported", clusterv.String(), maxV.String())
			return false
		}
		ok = true
	}
	return ok
}

func mustSaveClusterVersionToBackend(be backend.Backend, ver *semver.Version) {
	ckey := backendClusterVersionKey()

	tx := be.BatchTx()
	tx.Lock()
	defer tx.Unlock()
	tx.UnsafePut(clusterBucketName, ckey, []byte(ver.String()))
}

func (c *cluster) SetVersion(ver *semver.Version) {
	c.Lock()
	defer c.Unlock()
	if c.version != nil {
		plog.Noticef("updated the cluster version from %v to %v", c.version.String(), ver.String())
	} else {
		plog.Noticef("set the initial cluster version to %v", ver.String())
	}
	c.version = ver
}

// describe returns a word describing the process we're about to do ("update", "downgrading", etc)
func describe(a, b semver.Version, verb bool) string {
	if verb && a.LessThan(b) {
		return "Downgrading"
	} else if verb {
		return "Upgrading"
	} else if a.LessThan(b) {
		return "Downgrade"
	}
	return "Upgrade"
}

func (c *RaftCluster) SetVersion(ver *semver.Version) {
	c.Lock()
	defer c.Unlock()
	if c.version != nil {
		plog.Noticef("updated the cluster version from %v to %v", version.Cluster(c.version.String()), version.Cluster(ver.String()))
	} else {
		plog.Noticef("set the initial cluster version to %v", version.Cluster(ver.String()))
	}
	c.version = ver
	mustDetectDowngrade(c.version)
}

// UpdateCapability updates the enabledMap when the cluster version increases.
func UpdateCapability(v *semver.Version) {
	if v == nil {
		// if recovered but version was never set by cluster
		return
	}
	enableMapMu.Lock()
	if curVersion != nil && !curVersion.LessThan(*v) {
		enableMapMu.Unlock()
		return
	}
	curVersion = v
	enabledMap = capabilityMaps[curVersion.String()]
	enableMapMu.Unlock()
	plog.Infof("enabled capabilities for version %s", version.Cluster(v.String()))
}

func (c *RaftCluster) SetVersion(ver *semver.Version, onSet func(*semver.Version)) {
	c.Lock()
	defer c.Unlock()
	if c.version != nil {
		plog.Noticef("updated the cluster version from %v to %v", version.Cluster(c.version.String()), version.Cluster(ver.String()))
	} else {
		plog.Noticef("set the initial cluster version to %v", version.Cluster(ver.String()))
	}
	c.version = ver
	mustDetectDowngrade(c.version)
	if c.store != nil {
		mustSaveClusterVersionToStore(c.store, ver)
	}
	if c.be != nil {
		mustSaveClusterVersionToBackend(c.be, ver)
	}
	onSet(ver)
}

// LatestDaemonVersion attempts to retrieve the latest version of fleetd
// that has been registered in the Registry. It returns the version if
// it can be determined (or nil otherwise), and any error encountered.
func (r *EtcdRegistry) LatestDaemonVersion() (*semver.Version, error) {
	machs, err := r.Machines()
	if err != nil {
		if isEtcdError(err, etcd.ErrorCodeKeyNotFound) {
			err = nil
		}
		return nil, err
	}
	var lv *semver.Version
	for _, m := range machs {
		v, err := semver.NewVersion(m.Version)
		if err != nil {
			continue
		} else if lv == nil || lv.LessThan(*v) {
			lv = v
		}
	}
	return lv, nil
}

// capabilityLoop checks the cluster version every 500ms and updates
// the enabledMap when the cluster version increased.
// capabilityLoop MUST be ran in a goroutine before checking capability
// or using capabilityHandler.
func capabilityLoop(s *etcdserver.EtcdServer) {
	stopped := s.StopNotify()

	var pv *semver.Version
	for {
		if v := s.ClusterVersion(); v != pv {
			if pv == nil || (v != nil && pv.LessThan(*v)) {
				pv = v
				enableMapMu.Lock()
				enabledMap = capabilityMaps[pv.String()]
				enableMapMu.Unlock()
				plog.Infof("enabled capabilities for version %s", pv)
			}
		}

		select {
		case <-stopped:
			return
		case <-time.After(500 * time.Millisecond):
		}
	}
}

// isMinImageVersion will return true if the supplied version is greater then
// or equal to the current CoreOS release indicated by the given release
// channel.
func isMinImageVersion(minVersion semver.Version, release string) (bool, error) {
	metaData, err := coreosutil.GetAMIData(release)
	if err != nil {
		return false, fmt.Errorf("Unable to retrieve current release channel version: %v", err)
	}

	version, ok := metaData["release_info"]["version"]
	if !ok {
		return false, fmt.Errorf("Error parsing image metadata for version")
	}

	current, err := semver.NewVersion(version)
	if err != nil {
		return false, fmt.Errorf("Error parsing semver from image version %v", err)
	}

	if minVersion.LessThan(*current) {
		return false, nil
	}

	return true, nil
}

func mustSaveClusterVersionToStore(s store.Store, ver *semver.Version) {
	if _, err := s.Set(StoreClusterVersionKey(), false, ver.String(), store.TTLOptionSet{ExpireTime: store.Permanent}); err != nil {
		plog.Panicf("save cluster version should never fail: %v", err)
	}
}

func MustDetectDowngrade(cv *semver.Version) {
	lv := semver.Must(semver.NewVersion(version.Version))
	// only keep major.minor version for comparison against cluster version
	lv = &semver.Version{Major: lv.Major, Minor: lv.Minor}
	if cv != nil && lv.LessThan(*cv) {
		plog.Fatalf("cluster cannot be downgraded (current version: %s is lower than determined cluster version: %s).", version.Version, version.Cluster(cv.String()))
	}
}

func changeRefs(data []byte, major *semver.Version) (changed []byte, versions semver.Versions, err error) {
	var hlinei, hlinej int // HEAD reference line start/end
	var mlinei, mlinej int // master reference line start/end
	var vrefhash string
	var vrefname string
	var vrefv *semver.Version

	// Record all available versions, the locations of the master and HEAD lines,
	// and details of the best reference satisfying the requested major version.
	versions = semver.Versions{}
	sdata := string(data)
	for i, j := 0, 0; i < len(data); i = j {
		size, err := strconv.ParseInt(sdata[i:i+4], 16, 32)
		if err != nil {
			return nil, nil, fmt.Errorf("cannot parse refs line size: %s", string(data[i:i+4]))
		}
		if size == 0 {
			size = 4
		}
		j = i + int(size)
		if j > len(sdata) {
			return nil, nil, fmt.Errorf("incomplete refs data received from GitHub")
		}
		if sdata[0] == '#' {
			continue
		}

		hashi := i + 4
		hashj := strings.IndexByte(sdata[hashi:j], ' ')
		if hashj < 0 || hashj != 40 {
			continue
		}
		hashj += hashi

		namei := hashj + 1
		namej := strings.IndexAny(sdata[namei:j], "\n\x00")
		if namej < 0 {
			namej = j
		} else {
			namej += namei
		}

		name := sdata[namei:namej]

		if name == "HEAD" {
			hlinei = i
			hlinej = j
		}
		if name == "refs/heads/master" {
			mlinei = i
			mlinej = j
		}

		if strings.HasPrefix(name, "refs/tags/v") {
			if !strings.HasSuffix(name, "^{}") {
				continue // Only accept annotated tags.
			}
			// Annotated tag is peeled off and overrides the same version just parsed.
			name = name[:len(name)-3]

			v, err := semver.NewVersion(name[strings.IndexByte(name, 'v')+1:])
			if err == nil {
				versions = append(versions, v)
				if major.Major == v.Major && (vrefv == nil || v == vrefv || vrefv.LessThan(*v)) {
					vrefv = v
					vrefhash = sdata[hashi:hashj]
					vrefname = name
				}
			}
		}
	}

	// If the file has no HEAD line or the version was not found, report as unavailable.
	if hlinei == 0 || vrefhash == "" {
		return nil, nil, ErrNoVersion
	}

	var buf bytes.Buffer
	buf.Grow(len(data) + 256)

	// Copy the header as-is.
	buf.Write(data[:hlinei])

	// Extract the original capabilities.
	caps := ""
	if i := strings.Index(sdata[hlinei:hlinej], "\x00"); i > 0 {
		caps = strings.Replace(sdata[hlinei+i+1:hlinej-1], "symref=", "oldref=", -1)
	}

	// Insert the HEAD reference line with the right hash and a proper symref capability.
	var line string
	if strings.HasPrefix(vrefname, "refs/heads/") {
		if caps == "" {
			line = fmt.Sprintf("%s HEAD\x00symref=HEAD:%s\n", vrefhash, vrefname)
		} else {
			line = fmt.Sprintf("%s HEAD\x00symref=HEAD:%s %s\n", vrefhash, vrefname, caps)
		}
	} else {
		if caps == "" {
			line = fmt.Sprintf("%s HEAD\n", vrefhash)
//.........这里部分代码省略.........