add support for linux and udp

netstack/tun_linux.go

@@ -0,0 +1,105 @@
+//go:build linux
+
+package netstack
+
+import (
+	"fmt"
+
+	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/pkg/rawfile"
+	"gvisor.dev/gvisor/pkg/tcpip/link/fdbased"
+	"gvisor.dev/gvisor/pkg/tcpip/link/tun"
+	"gvisor.dev/gvisor/pkg/tcpip/stack"
+)
+
+type TUN struct {
+	stack.LinkEndpoint
+
+	fd   int
+	mtu  uint32
+	name string
+}
+
+func Open(name string, mtu uint32) (Device, error) {
+	t := &TUN{name: name, mtu: mtu}
+
+	if len(t.name) >= unix.IFNAMSIZ {
+		return nil, fmt.Errorf("interface name too long: %s", t.name)
+	}
+
+	fd, err := tun.Open(t.name)
+	if err != nil {
+		return nil, fmt.Errorf("create tun: %w", err)
+	}
+	t.fd = fd
+
+	if t.mtu > 0 {
+		if err := setMTU(t.name, t.mtu); err != nil {
+			return nil, fmt.Errorf("set mtu: %w", err)
+		}
+	}
+
+	_mtu, err := rawfile.GetMTU(t.name)
+	if err != nil {
+		return nil, fmt.Errorf("get mtu: %w", err)
+	}
+	t.mtu = _mtu
+
+	ep, err := fdbased.New(&fdbased.Options{
+		FDs: []int{fd},
+		MTU: t.mtu,
+		// TUN only, ignore ethernet header.
+		EthernetHeader: false,
+		// SYS_READV support only for TUN fd.
+		PacketDispatchMode: fdbased.Readv,
+		// TAP/TUN fd's are not sockets and using the WritePackets calls results
+		// in errors as it always defaults to using SendMMsg which is not supported
+		// for tap/tun device fds.
+		//
+		// This CL changes WritePackets to gracefully degrade to using writev instead
+		// of sendmmsg if the underlying fd is not a socket.
+		//
+		// Fixed: https://github.com/google/gvisor/commit/f33d034fecd7723a1e560ccc62aeeba328454fd0
+		MaxSyscallHeaderBytes: 0x00,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("create endpoint: %w", err)
+	}
+	t.LinkEndpoint = ep
+
+	return t, nil
+}
+
+func (t *TUN) Name() string {
+	return t.name
+}
+
+func (t *TUN) Close() {
+	defer t.LinkEndpoint.Close()
+	_ = unix.Close(t.fd)
+}
+
+func (t *TUN) Type() string {
+	return "tun" // 返回固定的设备类型标识符
+}
+
+func setMTU(name string, n uint32) error {
+	// open datagram socket
+	fd, err := unix.Socket(
+		unix.AF_INET,
+		unix.SOCK_DGRAM,
+		0,
+	)
+	if err != nil {
+		return err
+	}
+
+	defer unix.Close(fd)
+
+	ifr, err := unix.NewIfreq(name)
+	if err != nil {
+		return err
+	}
+	ifr.SetUint32(n)
+	return unix.IoctlIfreq(fd, unix.SIOCSIFMTU, ifr)
+}