Function tryEngine

cmd/tailscaled/tailscaled.go:749–842

(logf logger.Logf, sys *tsd.System, name string)

var tstunNew = tstun.New

func tryEngine(logf logger.Logf, sys *tsd.System, name string) (onlyNetstack bool, err error) {
	conf := wgengine.Config{
		ListenPort:    args.port,
		NetMon:        sys.NetMon.Get(),
		HealthTracker: sys.HealthTracker.Get(),
		ExtraRootCAs:  sys.ExtraRootCAs,
		Metrics:       sys.UserMetricsRegistry(),
		Dialer:        sys.Dialer.Get(),
		SetSubsystem:  sys.Set,
		ControlKnobs:  sys.ControlKnobs(),
		EventBus:      sys.Bus.Get(),
	}
	if f, ok := hookSetWgEnginConfigDrive.GetOk(); ok {
		f(&conf, logf)
	}

	sys.HealthTracker.Get().SetMetricsRegistry(sys.UserMetricsRegistry())

	onlyNetstack = name == "userspace-networking"
	netstackSubnetRouter := onlyNetstack // but mutated later on some platforms
	netns.SetEnabled(!onlyNetstack)

	if args.birdSocketPath != "" && createBIRDClient != nil {
		log.Printf("Connecting to BIRD at %s ...", args.birdSocketPath)
		conf.BIRDClient, err = createBIRDClient(args.birdSocketPath)
		if err != nil {
			return false, fmt.Errorf("createBIRDClient: %w", err)
		}
	}
	if onlyNetstack {
		if runtime.GOOS == "linux" && distro.Get() == distro.Synology {
			// On Synology in netstack mode, still init a DNS
			// manager (directManager) to avoid the health check
			// warnings in 'tailscale status' about DNS base
			// configuration being unavailable (from the noop
			// manager). More in Issue 4017.
			// TODO(bradfitz): add a Synology-specific DNS manager.
			conf.DNS, err = dns.NewOSConfigurator(logf, sys.HealthTracker.Get(), sys.Bus.Get(), sys.PolicyClientOrDefault(), sys.ControlKnobs(), "") // empty interface name
			if err != nil {
				return false, fmt.Errorf("dns.NewOSConfigurator: %w", err)
			}
		}
	} else {
		dev, devName, err := tstunNew(logf, name)
		if err != nil {
			tstun.Diagnose(logf, name, err)
			return false, fmt.Errorf("tstun.New(%q): %w", name, err)
		}
		conf.Tun = dev
		if strings.HasPrefix(name, "tap:") {
			conf.IsTAP = true
			e, err := wgengine.NewUserspaceEngine(logf, conf)
			if err != nil {
				return false, err
			}
			sys.Set(e)
			return false, err
		}