tun: windows: get rid of retry logic

Things work fine on Windows 8.

tun/tun_windows.go

@@ -9,7 +9,6 @@ import (
 	"errors"
 	"fmt"
 	"os"
-	"sync"
 	"sync/atomic"
 	"time"
 	"unsafe"
@@ -21,14 +20,10 @@ import (
 
 const (
 	packetAlignment    uint32 = 4        // Number of bytes packets are aligned to in rings
-	packetSizeMax      uint32 = 0xffff   // Maximum packet size
+	packetSizeMax             = 0xffff   // Maximum packet size
-	packetCapacity     uint32 = 0x800000 // Ring capacity, 8MiB
+	packetCapacity            = 0x800000 // Ring capacity, 8MiB
-	packetTrailingSize uint32 = uint32(unsafe.Sizeof(packetHeader{})) + ((packetSizeMax + (packetAlignment - 1)) &^ (packetAlignment - 1)) - packetAlignment
+	packetTrailingSize        = uint32(unsafe.Sizeof(packetHeader{})) + ((packetSizeMax + (packetAlignment - 1)) &^ (packetAlignment - 1)) - packetAlignment
-
+	ioctlRegisterRings        = (51820 << 16) | (0x970 << 2) | 0 /*METHOD_BUFFERED*/ | (0x3 /*FILE_READ_DATA | FILE_WRITE_DATA*/ << 14)
-	ioctlRegisterRings uint32 = (51820 << 16) | (0x970 << 2) | 0 /*METHOD_BUFFERED*/ | (0x3 /*FILE_READ_DATA | FILE_WRITE_DATA*/ << 14)
-
-	retryRate    = 4  // Number of retries per second to reopen device pipe
-	retryTimeout = 30 // Number of seconds to tolerate adapter unavailable
 )
 
 type packetHeader struct {
@@ -57,8 +52,7 @@ type ringDescriptor struct {
 
 type NativeTun struct {
 	wt        *wintun.Wintun
-	tunDev    windows.Handle
+	handle    windows.Handle
-	tunLock   sync.Mutex
 	close     bool
 	rings     ringDescriptor
 	events    chan Event
@@ -70,15 +64,6 @@ func packetAlign(size uint32) uint32 {
 	return (size + (packetAlignment - 1)) &^ (packetAlignment - 1)
 }
 
-var shouldRetryOpen = windows.RtlGetVersion().MajorVersion < 10
-
-func maybeRetry(x int) int {
-	if shouldRetryOpen {
-		return x
-	}
-	return 0
-}
-
 //
 // CreateTUN creates a Wintun adapter with the given name. Should a Wintun
 // adapter with the same name exist, it is reused.
@@ -119,7 +104,7 @@ func CreateTUNWithRequestedGUID(ifname string, requestedGUID *windows.GUID) (Dev
 
 	tun := &NativeTun{
 		wt:        wt,
-		tunDev:    windows.InvalidHandle,
+		handle: windows.InvalidHandle,
 		events:    make(chan Event, 10),
 		errors:    make(chan error, 1),
 		forcedMTU: 1500,
@@ -129,7 +114,7 @@ func CreateTUNWithRequestedGUID(ifname string, requestedGUID *windows.GUID) (Dev
 	tun.rings.send.ring = &ring{}
 	tun.rings.send.tailMoved, err = windows.CreateEvent(nil, 0, 0, nil)
 	if err != nil {
-		wt.DeleteInterface()
+		tun.Close()
 		return nil, fmt.Errorf("Error creating event: %v", err)
 	}
 
@@ -137,100 +122,25 @@ func CreateTUNWithRequestedGUID(ifname string, requestedGUID *windows.GUID) (Dev
 	tun.rings.receive.ring = &ring{}
 	tun.rings.receive.tailMoved, err = windows.CreateEvent(nil, 0, 0, nil)
 	if err != nil {
-		windows.CloseHandle(tun.rings.send.tailMoved)
+		tun.Close()
-		wt.DeleteInterface()
 		return nil, fmt.Errorf("Error creating event: %v", err)
 	}
 
-	_, err = tun.getTUN()
+	tun.handle, err = tun.wt.AdapterHandle()
 	if err != nil {
-		windows.CloseHandle(tun.rings.send.tailMoved)
+		tun.Close()
-		windows.CloseHandle(tun.rings.receive.tailMoved)
-		tun.closeTUN()
-		wt.DeleteInterface()
 		return nil, err
 	}
 
+	var bytesReturned uint32
+	err = windows.DeviceIoControl(tun.handle, ioctlRegisterRings, (*byte)(unsafe.Pointer(&tun.rings)), uint32(unsafe.Sizeof(tun.rings)), nil, 0, &bytesReturned, nil)
+	if err != nil {
+		tun.Close()
+		return nil, fmt.Errorf("Error registering rings: %v", err)
+	}
 	return tun, nil
 }
 
-func (tun *NativeTun) openTUN() error {
-	filename, err := tun.wt.NdisFileName()
-	if err != nil {
-		return err
-	}
-
-	retries := maybeRetry(retryTimeout * retryRate)
-	if tun.close {
-		return os.ErrClosed
-	}
-
-	name, err := windows.UTF16PtrFromString(filename)
-	if err != nil {
-		return err
-	}
-	for tun.tunDev == windows.InvalidHandle {
-		tun.tunDev, err = windows.CreateFile(name, windows.GENERIC_READ|windows.GENERIC_WRITE, 0, nil, windows.OPEN_EXISTING, 0, 0)
-		if err != nil {
-			if retries > 0 && !tun.close {
-				time.Sleep(time.Second / retryRate)
-				retries--
-				continue
-			}
-			return err
-		}
-
-		atomic.StoreUint32(&tun.rings.send.ring.head, 0)
-		atomic.StoreUint32(&tun.rings.send.ring.tail, 0)
-		atomic.StoreInt32(&tun.rings.send.ring.alertable, 0)
-		atomic.StoreUint32(&tun.rings.receive.ring.head, 0)
-		atomic.StoreUint32(&tun.rings.receive.ring.tail, 0)
-		atomic.StoreInt32(&tun.rings.receive.ring.alertable, 0)
-
-		var bytesReturned uint32
-		err = windows.DeviceIoControl(tun.tunDev, ioctlRegisterRings, (*byte)(unsafe.Pointer(&tun.rings)), uint32(unsafe.Sizeof(tun.rings)), nil, 0, &bytesReturned, nil)
-		if err != nil {
-			return fmt.Errorf("Error registering rings: %v", err)
-		}
-	}
-	return nil
-}
-
-func (tun *NativeTun) closeTUN() (err error) {
-	for tun.tunDev != windows.InvalidHandle {
-		tun.tunLock.Lock()
-		if tun.tunDev == windows.InvalidHandle {
-			tun.tunLock.Unlock()
-			break
-		}
-		t := tun.tunDev
-		tun.tunDev = windows.InvalidHandle
-		err = windows.CloseHandle(t)
-		tun.tunLock.Unlock()
-		break
-	}
-	return
-}
-
-func (tun *NativeTun) getTUN() (handle windows.Handle, err error) {
-	handle = tun.tunDev
-	if handle == windows.InvalidHandle {
-		tun.tunLock.Lock()
-		if tun.tunDev != windows.InvalidHandle {
-			handle = tun.tunDev
-			tun.tunLock.Unlock()
-			return
-		}
-		err = tun.openTUN()
-		if err == nil {
-			handle = tun.tunDev
-		}
-		tun.tunLock.Unlock()
-		return
-	}
-	return
-}
-
 func (tun *NativeTun) Name() (string, error) {
 	return tun.wt.InterfaceName()
 }
@@ -245,29 +155,22 @@ func (tun *NativeTun) Events() chan Event {
 
 func (tun *NativeTun) Close() error {
 	tun.close = true
-	windows.SetEvent(tun.rings.send.tailMoved) // wake the reader if it's sleeping
+	if tun.rings.send.tailMoved != 0 {
-	var err, err2 error
+		windows.SetEvent(tun.rings.send.tailMoved) // wake the reader if it's sleeping
-	err = tun.closeTUN()
-
-	if tun.events != nil {
-		close(tun.events)
 	}
-
+	if tun.handle != windows.InvalidHandle {
-	err2 = windows.CloseHandle(tun.rings.receive.tailMoved)
+		windows.CloseHandle(tun.handle)
-	if err == nil {
-		err = err2
 	}
-
+	if tun.rings.send.tailMoved != 0 {
-	err2 = windows.CloseHandle(tun.rings.send.tailMoved)
+		windows.CloseHandle(tun.rings.send.tailMoved)
-	if err == nil {
-		err = err2
 	}
-
+	if tun.rings.send.tailMoved != 0 {
-	_, err2 = tun.wt.DeleteInterface()
+		windows.CloseHandle(tun.rings.receive.tailMoved)
-	if err == nil {
+	}
-		err = err2
+	var err error
+	if tun.wt != nil {
+		_, err = tun.wt.DeleteInterface()
 	}
-
 	return err
 }
 
@@ -286,74 +189,60 @@ func procyield(cycles uint32)
 // Note: Read() and Write() assume the caller comes only from a single thread; there's no locking.
 
 func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
+retry:
 	select {
 	case err := <-tun.errors:
 		return 0, err
 	default:
 	}
-
+	if tun.close {
-	retries := maybeRetry(1000)
+		return 0, os.ErrClosed
-top:
-	for !tun.close {
-		_, err := tun.getTUN()
-		if err != nil {
-			return 0, err
-		}
-
-		buffHead := atomic.LoadUint32(&tun.rings.send.ring.head)
-		if buffHead >= packetCapacity {
-			return 0, errors.New("send ring head out of bounds")
-		}
-
-		start := time.Now()
-		var buffTail uint32
-		for {
-			buffTail = atomic.LoadUint32(&tun.rings.send.ring.tail)
-			if buffHead != buffTail {
-				break
-			}
-			if tun.close {
-				return 0, os.ErrClosed
-			}
-			if time.Since(start) >= time.Millisecond*50 {
-				windows.WaitForSingleObject(tun.rings.send.tailMoved, windows.INFINITE)
-				continue top
-			}
-			procyield(1)
-		}
-		if buffTail >= packetCapacity {
-			if retries > 0 {
-				tun.closeTUN()
-				time.Sleep(time.Millisecond * 2)
-				retries--
-				continue
-			}
-			return 0, errors.New("send ring tail out of bounds")
-		}
-		retries = maybeRetry(1000)
-
-		buffContent := tun.rings.send.ring.wrap(buffTail - buffHead)
-		if buffContent < uint32(unsafe.Sizeof(packetHeader{})) {
-			return 0, errors.New("incomplete packet header in send ring")
-		}
-
-		packet := (*packet)(unsafe.Pointer(&tun.rings.send.ring.data[buffHead]))
-		if packet.size > packetSizeMax {
-			return 0, errors.New("packet too big in send ring")
-		}
-
-		alignedPacketSize := packetAlign(uint32(unsafe.Sizeof(packetHeader{})) + packet.size)
-		if alignedPacketSize > buffContent {
-			return 0, errors.New("incomplete packet in send ring")
-		}
-
-		copy(buff[offset:], packet.data[:packet.size])
-		buffHead = tun.rings.send.ring.wrap(buffHead + alignedPacketSize)
-		atomic.StoreUint32(&tun.rings.send.ring.head, buffHead)
-		return int(packet.size), nil
 	}
 
-	return 0, os.ErrClosed
+	buffHead := atomic.LoadUint32(&tun.rings.send.ring.head)
+	if buffHead >= packetCapacity {
+		return 0, os.ErrClosed
+	}
+
+	start := time.Now()
+	var buffTail uint32
+	for {
+		buffTail = atomic.LoadUint32(&tun.rings.send.ring.tail)
+		if buffHead != buffTail {
+			break
+		}
+		if tun.close {
+			return 0, os.ErrClosed
+		}
+		if time.Since(start) >= time.Millisecond*50 {
+			windows.WaitForSingleObject(tun.rings.send.tailMoved, windows.INFINITE)
+			goto retry
+		}
+		procyield(1)
+	}
+	if buffTail >= packetCapacity {
+		return 0, os.ErrClosed
+	}
+
+	buffContent := tun.rings.send.ring.wrap(buffTail - buffHead)
+	if buffContent < uint32(unsafe.Sizeof(packetHeader{})) {
+		return 0, errors.New("incomplete packet header in send ring")
+	}
+
+	packet := (*packet)(unsafe.Pointer(&tun.rings.send.ring.data[buffHead]))
+	if packet.size > packetSizeMax {
+		return 0, errors.New("packet too big in send ring")
+	}
+
+	alignedPacketSize := packetAlign(uint32(unsafe.Sizeof(packetHeader{})) + packet.size)
+	if alignedPacketSize > buffContent {
+		return 0, errors.New("incomplete packet in send ring")
+	}
+
+	copy(buff[offset:], packet.data[:packet.size])
+	buffHead = tun.rings.send.ring.wrap(buffHead + alignedPacketSize)
+	atomic.StoreUint32(&tun.rings.send.ring.head, buffHead)
+	return int(packet.size), nil
 }
 
 func (tun *NativeTun) Flush() error {
@@ -361,47 +250,36 @@ func (tun *NativeTun) Flush() error {
 }
 
 func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
-	retries := maybeRetry(1000)
+	if tun.close {
-	for {
+		return 0, os.ErrClosed
-		_, err := tun.getTUN()
-		if err != nil {
-			return 0, err
-		}
-
-		packetSize := uint32(len(buff) - offset)
-		alignedPacketSize := packetAlign(uint32(unsafe.Sizeof(packetHeader{})) + packetSize)
-
-		buffHead := atomic.LoadUint32(&tun.rings.receive.ring.head)
-		if buffHead >= packetCapacity {
-			if retries > 0 {
-				tun.closeTUN()
-				time.Sleep(time.Millisecond * 2)
-				retries--
-				continue
-			}
-			return 0, errors.New("receive ring head out of bounds")
-		}
-		retries = maybeRetry(1000)
-
-		buffTail := atomic.LoadUint32(&tun.rings.receive.ring.tail)
-		if buffTail >= packetCapacity {
-			return 0, errors.New("receive ring tail out of bounds")
-		}
-
-		buffSpace := tun.rings.receive.ring.wrap(buffHead - buffTail - packetAlignment)
-		if alignedPacketSize > buffSpace {
-			return 0, nil // Dropping when ring is full.
-		}
-
-		packet := (*packet)(unsafe.Pointer(&tun.rings.receive.ring.data[buffTail]))
-		packet.size = packetSize
-		copy(packet.data[:packetSize], buff[offset:])
-		atomic.StoreUint32(&tun.rings.receive.ring.tail, tun.rings.receive.ring.wrap(buffTail+alignedPacketSize))
-		if atomic.LoadInt32(&tun.rings.receive.ring.alertable) != 0 {
-			windows.SetEvent(tun.rings.receive.tailMoved)
-		}
-		return int(packetSize), nil
 	}
+
+	packetSize := uint32(len(buff) - offset)
+	alignedPacketSize := packetAlign(uint32(unsafe.Sizeof(packetHeader{})) + packetSize)
+
+	buffHead := atomic.LoadUint32(&tun.rings.receive.ring.head)
+	if buffHead >= packetCapacity {
+		return 0, os.ErrClosed
+	}
+
+	buffTail := atomic.LoadUint32(&tun.rings.receive.ring.tail)
+	if buffTail >= packetCapacity {
+		return 0, os.ErrClosed
+	}
+
+	buffSpace := tun.rings.receive.ring.wrap(buffHead - buffTail - packetAlignment)
+	if alignedPacketSize > buffSpace {
+		return 0, nil // Dropping when ring is full.
+	}
+
+	packet := (*packet)(unsafe.Pointer(&tun.rings.receive.ring.data[buffTail]))
+	packet.size = packetSize
+	copy(packet.data[:packetSize], buff[offset:])
+	atomic.StoreUint32(&tun.rings.receive.ring.tail, tun.rings.receive.ring.wrap(buffTail+alignedPacketSize))
+	if atomic.LoadInt32(&tun.rings.receive.ring.alertable) != 0 {
+		windows.SetEvent(tun.rings.receive.tailMoved)
+	}
+	return int(packetSize), nil
 }
 
 // LUID returns Windows adapter instance ID.

tun/wintun/wintun_windows.go

@@ -612,21 +612,25 @@ func (wintun *Wintun) deviceData() (setupapi.DevInfo, *setupapi.DevInfoData, err
 	return 0, nil, windows.ERROR_OBJECT_NOT_FOUND
 }
 
-// NdisFileName returns the Wintun NDIS device object name.
+// AdapterHandle returns a handle to the adapter device object.
-func (wintun *Wintun) NdisFileName() (string, error) {
+func (wintun *Wintun) AdapterHandle() (windows.Handle, error) {
 	key, err := registry.OpenKey(registry.LOCAL_MACHINE, wintun.netRegKeyName(), registry.QUERY_VALUE)
 	if err != nil {
-		return "", fmt.Errorf("Network-specific registry key open failed: %v", err)
+		return windows.InvalidHandle, fmt.Errorf("Network-specific registry key open failed: %v", err)
 	}
 	defer key.Close()
 
 	// Get the interface name.
 	pnpInstanceID, err := registryEx.GetStringValue(key, "PnPInstanceId")
 	if err != nil {
-		return "", fmt.Errorf("PnpInstanceId registry key read failed: %v", err)
+		return windows.InvalidHandle, fmt.Errorf("PnPInstanceId registry key read failed: %v", err)
 	}
 	mangledPnpNode := strings.ReplaceAll(fmt.Sprintf("%s\\{cac88484-7515-4c03-82e6-71a87abac361}", pnpInstanceID), "\\", "#")
-	return fmt.Sprintf("\\\\.\\Global\\%s", mangledPnpNode), nil
+	handle, err := windows.CreateFile(windows.StringToUTF16Ptr(fmt.Sprintf("\\\\.\\Global\\%s", mangledPnpNode)), windows.GENERIC_READ|windows.GENERIC_WRITE, 0, nil, windows.OPEN_EXISTING, 0, 0)
+	if err != nil {
+		return windows.InvalidHandle, fmt.Errorf("CreateFile on mangled PnPInstanceId path failed: %v", err)
+	}
+	return handle, nil
 }
 
 // GUID returns the GUID of the interface.