tun: use netpoll instead of rwcancel

The new sysconn function of Go 1.12 makes this possible:

package main

import "log"
import "os"
import "unsafe"
import "time"
import "syscall"
import "sync"
import "golang.org/x/sys/unix"

func main() {
	fd, err := os.OpenFile("/dev/net/tun", os.O_RDWR, 0)
	if err != nil {
		log.Fatal(err)
	}

	var ifr [unix.IFNAMSIZ + 64]byte
	copy(ifr[:], []byte("cheese"))
	*(*uint16)(unsafe.Pointer(&ifr[unix.IFNAMSIZ])) = unix.IFF_TUN

	var errno syscall.Errno
	s, _ := fd.SyscallConn()
	s.Control(func(fd uintptr) {
		_, _, errno = unix.Syscall(
			unix.SYS_IOCTL,
			fd,
			uintptr(unix.TUNSETIFF),
			uintptr(unsafe.Pointer(&ifr[0])),
		)
	})
	if errno != 0 {
		log.Fatal(errno)
	}

	b := [4]byte{}
	wait := sync.WaitGroup{}
	wait.Add(1)
	go func() {
		_, err := fd.Read(b[:])
		log.Print("Read errored: ", err)
		wait.Done()
	}()
	time.Sleep(time.Second)
	log.Print("Closing")
	err = fd.Close()
	if err != nil {
		log.Print("Close errored: " , err)
	}
	wait.Wait()
	log.Print("Exiting")
}

tun/tun_linux.go

@@ -31,7 +31,6 @@ const (
 
 type nativeTun struct {
 	tunFile                 *os.File
-	fdCancel                *rwcancel.RWCancel
 	index                   int32         // if index
 	name                    string        // name of interface
 	errors                  chan error    // async error handling
@@ -307,7 +306,7 @@ func (tun *nativeTun) Write(buff []byte, offset int) (int, error) {
 	return tun.tunFile.Write(buff)
 }
 
-func (tun *nativeTun) doRead(buff []byte, offset int) (int, error) {
+func (tun *nativeTun) Read(buff []byte, offset int) (int, error) {
 	select {
 	case err := <-tun.errors:
 		return 0, err
@@ -325,18 +324,6 @@ func (tun *nativeTun) doRead(buff []byte, offset int) (int, error) {
 	}
 }
 
-func (tun *nativeTun) Read(buff []byte, offset int) (int, error) {
-	for {
-		n, err := tun.doRead(buff, offset)
-		if err == nil || !rwcancel.RetryAfterError(err) {
-			return n, err
-		}
-		if !tun.fdCancel.ReadyRead() {
-			return 0, errors.New("tun device closed")
-		}
-	}
-}
-
 func (tun *nativeTun) Events() chan TUNEvent {
 	return tun.events
 }
@@ -352,30 +339,20 @@ func (tun *nativeTun) Close() error {
 		close(tun.events)
 	}
 	err2 := tun.tunFile.Close()
-	err3 := tun.fdCancel.Cancel()
 
 	if err1 != nil {
 		return err1
 	}
-	if err2 != nil {
-		return err2
-	}
-	return err3
+	return err2
 }
 
 func CreateTUN(name string, mtu int) (TUNDevice, error) {
-	nfd, err := unix.Open(cloneDevicePath, os.O_RDWR, 0)
-	if err != nil {
-		return nil, err
-	}
-
-	fd := os.NewFile(uintptr(nfd), cloneDevicePath)
+	tunFile, err := os.OpenFile(cloneDevicePath, os.O_RDWR, 0)
 	if err != nil {
 		return nil, err
 	}
 
 	// create new device
-
 	var ifr [ifReqSize]byte
 	var flags uint16 = unix.IFF_TUN // | unix.IFF_NO_PI (disabled for TUN status hack)
 	nameBytes := []byte(name)
@@ -385,17 +362,20 @@ func CreateTUN(name string, mtu int) (TUNDevice, error) {
 	copy(ifr[:], nameBytes)
 	*(*uint16)(unsafe.Pointer(&ifr[unix.IFNAMSIZ])) = flags
 
-	_, _, errno := unix.Syscall(
-		unix.SYS_IOCTL,
-		nfd,
-		uintptr(unix.TUNSETIFF),
-		uintptr(unsafe.Pointer(&ifr[0])),
-	)
+	var errno syscall.Errno
+	(&nativeTun{tunFile: tunFile}).operateOnFd(func(fd uintptr) {
+		_, _, errno = unix.Syscall(
+			unix.SYS_IOCTL,
+			fd,
+			uintptr(unix.TUNSETIFF),
+			uintptr(unsafe.Pointer(&ifr[0])),
+		)
+	})
 	if errno != 0 {
 		return nil, errno
 	}
 
-	return CreateTUNFromFile(fd, mtu)
+	return CreateTUNFromFile(tunFile, mtu)
 }
 
 func CreateTUNFromFile(file *os.File, mtu int) (TUNDevice, error) {
@@ -408,14 +388,6 @@ func CreateTUNFromFile(file *os.File, mtu int) (TUNDevice, error) {
 	}
 	var err error
 
-	tun.operateOnFd(func(fd uintptr) {
-		tun.fdCancel, err = rwcancel.NewRWCancel(int(fd))
-	})
-	if err != nil {
-		tun.tunFile.Close()
-		return nil, err
-	}
-
 	_, err = tun.Name()
 	if err != nil {
 		tun.tunFile.Close()