From 366cbd11a40a6a3fde5d0dc803ca6895859ed188 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Wed, 27 Feb 2019 01:48:58 +0100
Subject: 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")
}
---
 main.go | 5 +++++
 1 file changed, 5 insertions(+)

(limited to 'main.go')

diff --git a/main.go b/main.go
index 23a1d2d..08f8cc6 100644
--- a/main.go
+++ b/main.go
@@ -145,6 +145,11 @@ func main() {
 			return nil, err
 		}
 
+		err = syscall.SetNonblock(int(fd), true)
+		if err != nil {
+			return nil, err
+		}
+
 		file := os.NewFile(uintptr(fd), "")
 		return tun.CreateTUNFromFile(file, DefaultMTU)
 	}()
-- 
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