tun: add plan9 support

Reviewed-by: James Tucker <[email protected]>

Author: bradfitz

tun/tun_plan9.go

@@ -0,0 +1,147 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2017-2023 WireGuard LLC. All Rights Reserved.
+ */
+
+package tun
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+	"sync"
+)
+
+type NativeTun struct {
+	name      string // "/net/ipifc/2"
+	ctlFile   *os.File
+	dataFile  *os.File
+	events    chan Event
+	errors    chan error
+	closeOnce sync.Once
+}
+
+func CreateTUN(_ string, mtu int) (Device, error) {
+	ctl, err := os.OpenFile("/net/ipifc/clone", os.O_RDWR, 0)
+	if err != nil {
+		return nil, err
+	}
+	nbuf := make([]byte, 5)
+	n, err := ctl.Read(nbuf)
+	if err != nil {
+		ctl.Close()
+		return nil, fmt.Errorf("error reading from clone file: %w", err)
+	}
+	ifn, err := strconv.Atoi(strings.TrimSpace(string(nbuf[:n])))
+	if err != nil {
+		ctl.Close()
+		return nil, fmt.Errorf("error converting clone result %q to int: %w", nbuf[:n], err)
+	}
+
+	if _, err := fmt.Fprintf(ctl, "bind pkt\n"); err != nil {
+		ctl.Close()
+		return nil, fmt.Errorf("error binding to pkt: %w", err)
+	}
+	if mtu > 0 {
+		if _, err := fmt.Fprintf(ctl, "mtu %d\n", mtu); err != nil {
+			ctl.Close()
+			return nil, fmt.Errorf("error setting MTU: %w", err)
+		}
+	}
+
+	dataFile, err := os.OpenFile(fmt.Sprintf("/net/ipifc/%d/data", ifn), os.O_RDWR, 0)
+	if err != nil {
+		ctl.Close()
+		return nil, err
+	}
+
+	tun := &NativeTun{
+		ctlFile:  ctl,
+		dataFile: dataFile,
+		name:     fmt.Sprintf("/net/ipifc/%d", ifn),
+		events:   make(chan Event, 10),
+		errors:   make(chan error, 5),
+	}
+	tun.events <- EventUp
+
+	return tun, nil
+}
+
+func (tun *NativeTun) Name() (string, error) {
+	return tun.name, nil
+}
+
+func (tun *NativeTun) File() *os.File {
+	return tun.ctlFile
+}
+
+func (tun *NativeTun) Events() <-chan Event {
+	return tun.events
+}
+
+func (tun *NativeTun) Read(bufs [][]byte, sizes []int, offset int) (int, error) {
+	select {
+	case err := <-tun.errors:
+		return 0, err
+	default:
+		n, err := tun.dataFile.Read(bufs[0][offset:])
+		if n == 1 && bufs[0][offset] == 0 {
+			// EOF
+			err = io.EOF
+			n = 0
+		}
+		sizes[0] = n
+		return 1, err
+	}
+}
+
+func (tun *NativeTun) Write(bufs [][]byte, offset int) (int, error) {
+	for i, buf := range bufs {
+		if _, err := tun.dataFile.Write(buf[offset:]); err != nil {
+			return i, err
+		}
+	}
+	return len(bufs), nil
+}
+
+func (tun *NativeTun) Close() error {
+	var err1, err2 error
+	tun.closeOnce.Do(func() {
+		_, err1 := fmt.Fprintf(tun.ctlFile, "unbind\n")
+		if err := tun.ctlFile.Close(); err != nil && err1 == nil {
+			err1 = err
+		}
+		err2 = tun.dataFile.Close()
+	})
+	if err1 != nil {
+		return err1
+	}
+	return err2
+}
+
+func (tun *NativeTun) MTU() (int, error) {
+	var buf [100]byte
+	f, err := os.Open(tun.name + "/status")
+	if err != nil {
+		return 0, err
+	}
+	defer f.Close()
+	n, err := f.Read(buf[:])
+	_, res, ok := strings.Cut(string(buf[:n]), " maxtu ")
+	if ok {
+		if mtus, _, ok := strings.Cut(res, " "); ok {
+			mtu, err := strconv.Atoi(mtus)
+			if err != nil {
+				return 0, fmt.Errorf("error converting mtu %q to int: %w", mtus, err)
+			}
+			return mtu, nil
+		}
+	}
+	return 0, fmt.Errorf("no 'maxtu' field found in %s/status", tun.name)
+}
+
+func (tun *NativeTun) BatchSize() int {
+	return 1
+}