Add EXP_ExternalConfiguration for Tailscale

tun.go

@@ -109,7 +109,8 @@ type Options struct {
 	_TXChecksumOffload bool
 
 	// For library usages.
-	EXP_DisableDNSHijack bool
+	EXP_DisableDNSHijack      bool
+	EXP_ExternalConfiguration bool
 
 	// For gvisor stack, it should be enabled when MTU is less than 32768; otherwise it should be less than or equal to 8192.
 	// The above condition is just an estimate and not exact, calculated on M4 pro.

tun_darwin.go

@@ -146,11 +146,17 @@ func New(options Options) (Tun, error) {
 }
 
 func (t *NativeTun) Start() error {
+	if t.options.EXP_ExternalConfiguration {
+		return nil
+	}
 	t.options.InterfaceMonitor.RegisterMyInterface(t.options.Name)
 	return t.setRoutes()
 }
 
 func (t *NativeTun) Close() error {
+	if t.options.EXP_ExternalConfiguration {
+		return t.tunFile.Close()
+	}
 	defer flushDNSCache()
 	return E.Errors(t.unsetRoutes(), t.tunFile.Close())
 }
@@ -232,6 +238,9 @@ func create(tunFd int, ifIndex int, name string, options Options) error {
 	if err != nil {
 		return os.NewSyscallError("IoctlSetIfreqMTU", err)
 	}
+	if options.EXP_ExternalConfiguration {
+		return nil
+	}
 	if len(options.Inet4Address) > 0 {
 		for _, address := range options.Inet4Address {
 			ifReq := ifAliasReq{
@@ -396,11 +405,14 @@ func (t *NativeTun) TXChecksumOffload() bool {
 }
 
 func (t *NativeTun) UpdateRouteOptions(tunOptions Options) error {
+	t.options = tunOptions
+	if t.options.EXP_ExternalConfiguration {
+		return nil
+	}
 	err := t.unsetRoutes()
 	if err != nil {
 		return err
 	}
-	t.options = tunOptions
 	return t.setRoutes()
 }
 

tun_linux.go

@@ -125,22 +125,23 @@ func (t *NativeTun) configure(tunLink netlink.Link) error {
 	} else if err != nil {
 		return err
 	}
-
+	if !t.options.EXP_ExternalConfiguration {
-	if len(t.options.Inet4Address) > 0 {
+		if len(t.options.Inet4Address) > 0 {
-		for _, address := range t.options.Inet4Address {
+			for _, address := range t.options.Inet4Address {
-			addr4, _ := netlink.ParseAddr(address.String())
+				addr4, _ := netlink.ParseAddr(address.String())
-			err = netlink.AddrAdd(tunLink, addr4)
+				err = netlink.AddrAdd(tunLink, addr4)
-			if err != nil {
+				if err != nil {
-				return err
+					return err
+				}
 			}
 		}
-	}
+		if len(t.options.Inet6Address) > 0 {
-	if len(t.options.Inet6Address) > 0 {
+			for _, address := range t.options.Inet6Address {
-		for _, address := range t.options.Inet6Address {
+				addr6, _ := netlink.ParseAddr(address.String())
-			addr6, _ := netlink.ParseAddr(address.String())
+				err = netlink.AddrAdd(tunLink, addr6)
-			err = netlink.AddrAdd(tunLink, addr6)
+				if err != nil {
-			if err != nil {
+					return err
-				return err
+				}
 			}
 		}
 	}
@@ -257,7 +258,9 @@ func (t *NativeTun) Start() error {
 	if t.options.FileDescriptor != 0 {
 		return nil
 	}
-	t.options.InterfaceMonitor.RegisterMyInterface(t.options.Name)
+	if !t.options.EXP_ExternalConfiguration {
+		t.options.InterfaceMonitor.RegisterMyInterface(t.options.Name)
+	}
 	tunLink, err := netlink.LinkByName(t.options.Name)
 	if err != nil {
 		return err
@@ -277,6 +280,10 @@ func (t *NativeTun) Start() error {
 		}
 	}
 
+	if t.options.EXP_ExternalConfiguration {
+		return nil
+	}
+
 	if t.options.IPRoute2TableIndex == 0 {
 		for {
 			t.options.IPRoute2TableIndex = int(rand.Uint32())
@@ -315,6 +322,9 @@ func (t *NativeTun) Close() error {
 	if t.interfaceCallback != nil {
 		t.options.InterfaceMonitor.UnregisterCallback(t.interfaceCallback)
 	}
+	if t.options.EXP_ExternalConfiguration {
+		return common.Close(common.PtrOrNil(t.tunFile))
+	}
 	return E.Errors(t.unsetRoute(), t.unsetRules(), common.Close(common.PtrOrNil(t.tunFile)))
 }
 
@@ -476,6 +486,9 @@ func prefixToIPNet(prefix netip.Prefix) *net.IPNet {
 func (t *NativeTun) UpdateRouteOptions(tunOptions Options) error {
 	if t.options.FileDescriptor > 0 {
 		return nil
+	} else if t.options.EXP_ExternalConfiguration {
+		t.options = tunOptions
+		return nil
 	} else if !t.options.AutoRoute {
 		t.options = tunOptions
 		return nil

tun_windows.go

@@ -65,6 +65,9 @@ func New(options Options) (WinTun, error) {
 }
 
 func (t *NativeTun) configure() error {
+	if t.options.EXP_ExternalConfiguration {
+		return nil
+	}
 	luid := winipcfg.LUID(t.adapter.LUID())
 	if len(t.options.Inet4Address) > 0 {
 		err := luid.SetIPAddressesForFamily(winipcfg.AddressFamily(windows.AF_INET), t.options.Inet4Address)
@@ -162,10 +165,10 @@ func (t *NativeTun) Name() (string, error) {
 }
 
 func (t *NativeTun) Start() error {
-	t.options.InterfaceMonitor.RegisterMyInterface(t.options.Name)
+	if t.options.EXP_ExternalConfiguration || !t.options.AutoRoute {
-	if !t.options.AutoRoute {
 		return nil
 	}
+	t.options.InterfaceMonitor.RegisterMyInterface(t.options.Name)
 	luid := winipcfg.LUID(t.adapter.LUID())
 	gateway4, gateway6 := t.options.Inet4GatewayAddr(), t.options.Inet6GatewayAddr()
 	routeRanges, err := t.options.BuildAutoRouteRanges(false)
@@ -393,6 +396,21 @@ retry:
 	}
 }
 
+func (t *NativeTun) MTU() (int, error) {
+	return int(t.options.MTU), nil
+}
+
+func (t *NativeTun) ForceMTU(mtu int) {
+	if mtu <= 0 {
+		return
+	}
+	t.options.MTU = uint32(mtu)
+}
+
+func (t *NativeTun) LUID() uint64 {
+	return t.adapter.LUID()
+}
+
 func (t *NativeTun) ReadPacket() ([]byte, func(), error) {
 	t.running.Add(1)
 retry:
@@ -543,6 +561,9 @@ func (t *NativeTun) Close() error {
 
 func (t *NativeTun) UpdateRouteOptions(tunOptions Options) error {
 	t.options = tunOptions
+	if t.options.EXP_ExternalConfiguration {
+		return nil
+	}
 	if !t.options.AutoRoute {
 		return nil
 	}