simplify change point

at the cost of some very, very naughty unsafe

net/tstun/wrap.go

@@ -12,13 +12,10 @@
 	"os"
 	"sync"
 	"sync/atomic"
-	"syscall"
 	"time"
 
-	"golang.org/x/net/ipv6"
 	"golang.zx2c4.com/wireguard/device"
 	"golang.zx2c4.com/wireguard/tun"
-	wgtun "golang.zx2c4.com/wireguard/tun" // import twice to work around shadowing (TODO: fix properly)
 	"inet.af/netaddr"
 	"tailscale.com/net/packet"
 	"tailscale.com/net/uring"
@@ -66,9 +63,6 @@ type Wrapper struct {
 	// tdev is the underlying Wrapper device.
 	tdev tun.Device
 
-	// uring performs writes to the underlying Wrapper device.
-	ring *uring.File
-
 	closeOnce sync.Once
 
 	lastActivityAtomic int64 // unix seconds of last send or receive
@@ -167,12 +161,15 @@ func Wrap(logf logger.Logf, tdev tun.Device) *Wrapper {
 		filterFlags: filter.LogAccepts | filter.LogDrops,
 	}
 
-	f := tdev.(*wgtun.NativeTun).File()
-	ring, err := uring.NewFile(f)
-	if err != nil {
-		panic(err) // TODO: just log? wat?
-	} else {
-		tun.ring = ring
+	if uring.Available() {
+		uringTun, err := uring.NewTUN(tdev)
+		name, _ := tdev.Name()
+		if err != nil {
+			logf("not using io_uring for TUN %v: %v", name, err)
+		} else {
+			logf("using uring for TUN %v", name)
+			tdev = uringTun
+		}
 	}
 
 	go tun.poll()
@@ -315,7 +312,7 @@ func (t *Wrapper) poll() {
 			if t.isClosed() {
 				return
 			}
-			n, err = t.read(t.buffer[:], PacketStartOffset)
+			n, err = t.tdev.Read(t.buffer[:], PacketStartOffset)
 		}
 		t.sendOutbound(tunReadResult{data: t.buffer[PacketStartOffset : PacketStartOffset+n], err: err})
 	}
@@ -534,55 +531,7 @@ func (t *Wrapper) Write(buf []byte, offset int) (int, error) {
 	}
 
 	t.noteActivity()
-	return t.write(buf, offset)
-}
-
-func (t *Wrapper) write(buf []byte, offset int) (int, error) {
-	if t.ring == nil {
-		return t.tdev.Write(buf, offset)
-	}
-
-	// below copied from wireguard-go NativeTUN.Write
-
-	// reserve space for header
-	buf = buf[offset-4:]
-
-	// add packet information header
-	buf[0] = 0x00
-	buf[1] = 0x00
-	if buf[4]>>4 == ipv6.Version {
-		buf[2] = 0x86
-		buf[3] = 0xdd
-	} else {
-		buf[2] = 0x08
-		buf[3] = 0x00
-	}
-
-	n, err := t.ring.Write(buf)
-	if errors.Is(err, syscall.EBADFD) {
-		err = os.ErrClosed
-	}
-	return n, err
-}
-
-func (t *Wrapper) read(buf []byte, offset int) (n int, err error) {
-	// TODO: upstream has graceful shutdown error handling here.
-	buff := buf[offset-4:]
-	const useIOUring = true
-	if useIOUring {
-		n, err = t.ring.Read(buff[:])
-	} else {
-		n, err = t.tdev.(*wgtun.NativeTun).File().Read(buff[:])
-	}
-	if errors.Is(err, syscall.EBADFD) {
-		err = os.ErrClosed
-	}
-	if n < 4 {
-		n = 0
-	} else {
-		n -= 4
-	}
-	return
+	return t.tdev.Write(buf, offset)
 }
 
 func (t *Wrapper) GetFilter() *filter.Filter {

net/uring/file_test.go

@@ -21,7 +21,7 @@ func TestFileRead(t *testing.T) {
 	c.Assert(err, qt.IsNil)
 	t.Cleanup(func() { f.Close() })
 
-	uf, err := NewFile(f)
+	uf, err := newFile(f)
 	if err != nil {
 		t.Skipf("io_uring not available: %v", err)
 	}

net/uring/io_uring_linux.go

@@ -16,7 +16,9 @@
 	"time"
 	"unsafe"
 
+	"golang.org/x/net/ipv6"
 	"golang.zx2c4.com/wireguard/device"
+	"golang.zx2c4.com/wireguard/tun"
 	"inet.af/netaddr"
 )
 
@@ -48,7 +50,11 @@ type UDPConn struct {
 	is4      bool
 }
 
-func NewUDPConn(conn *net.UDPConn) (*UDPConn, error) {
+func NewUDPConn(pconn net.PacketConn) (*UDPConn, error) {
+	conn, ok := pconn.(*net.UDPConn)
+	if !ok {
+		return nil, fmt.Errorf("cannot use io_uring with conn of type %T", pconn)
+	}
 	// this is dumb
 	local := conn.LocalAddr().String()
 	ip, err := netaddr.ParseIPPort(local)
@@ -290,7 +296,7 @@ func (c *UDPConn) SetWriteDeadline(t time.Time) error {
 // A File is a write-only file fd manager.
 // TODO: Support reads
 // TODO: all the todos from UDPConn
-type File struct {
+type file struct {
 	writeRing *C.go_uring
 	readRing  *C.go_uring
 	close     sync.Once
@@ -301,10 +307,10 @@ type File struct {
 	writeReqC chan int // indices into reqs
 }
 
-func NewFile(file *os.File) (*File, error) {
-	fd := C.int(file.Fd())
-	u := &File{
-		file: file,
+func newFile(f *os.File) (*file, error) {
+	fd := C.int(f.Fd())
+	u := &file{
+		file: f,
 		fd:   fd,
 	}
 	for _, ringPtr := range []**C.go_uring{&u.writeRing, &u.readRing} {
@@ -340,7 +346,7 @@ func NewFile(file *os.File) (*File, error) {
 	return u, nil
 }
 
-func (u *File) submitReadvRequest(idx int) error {
+func (u *file) submitReadvRequest(idx int) error {
 	// TODO: make a C struct instead of a Go struct, and pass that in, to simplify call sites.
 	errno := C.submit_readv_request(u.readRing, u.readReqs[idx], C.size_t(idx))
 	if errno < 0 {
@@ -363,7 +369,7 @@ type fileReq struct {
 
 // Read data into buf[offset:].
 // We are allowed to write junk into buf[offset-4:offset].
-func (u *File) Read(buf []byte) (n int, err error) { // read a packet from the device (without any additional headers)
+func (u *file) Read(buf []byte) (n int, err error) { // read a packet from the device (without any additional headers)
 	if u.fd == 0 {
 		return 0, errors.New("invalid uring.File")
 	}
@@ -383,7 +389,7 @@ func (u *File) Read(buf []byte) (n int, err error) { // read a packet from the d
 	return n, nil
 }
 
-func (u *File) Write(buf []byte) (int, error) {
+func (u *file) Write(buf []byte) (int, error) {
 	if u.fd == 0 {
 		return 0, errors.New("invalid uring.FileConn")
 	}
@@ -421,7 +427,7 @@ func (u *File) Write(buf []byte) (int, error) {
 }
 
 // TODO: the TODOs from UDPConn.Close
-func (u *File) Close() error {
+func (u *file) Close() error {
 	u.close.Do(func() {
 		u.file.Close()
 		// TODO: require kernel 5.5, send an abort SQE, handle aborts gracefully
@@ -442,3 +448,94 @@ func (u *File) Close() error {
 	})
 	return nil
 }
+
+// Wrap files into TUN devices.
+
+func NewTUN(d tun.Device) (tun.Device, error) {
+	nt, ok := d.(*tun.NativeTun)
+	if !ok {
+		return nil, fmt.Errorf("NewTUN only wraps *tun.NativeTun, got %T", d)
+	}
+	f, err := newFile(nt.File())
+	if err != nil {
+		return nil, err
+	}
+	v := reflect.ValueOf(nt)
+	field, ok := v.Elem().Type().FieldByName("errors")
+	if !ok {
+		return nil, errors.New("could not find internal tun.NativeTun errors field")
+	}
+	ptr := unsafe.Pointer(nt)
+	ptr = unsafe.Pointer(uintptr(ptr) + field.Offset) // TODO: switch to unsafe.Add with Go 1.17...as if that's the worst thing in this line
+	c := *(*chan error)(ptr)
+	return &TUN{d: nt, f: f, errors: c}, nil
+}
+
+// No nopi
+type TUN struct {
+	d      *tun.NativeTun
+	f      *file
+	errors chan error
+}
+
+func (t *TUN) File() *os.File {
+	return t.f.file
+}
+
+func (t *TUN) Read(buf []byte, offset int) (int, error) {
+	select {
+	case err := <-t.errors:
+		return 0, err
+	default:
+	}
+	// TODO: upstream has graceful shutdown error handling here.
+	buff := buf[offset-4:]
+	n, err := t.f.Read(buff[:])
+	if errors.Is(err, syscall.EBADFD) {
+		err = os.ErrClosed
+	}
+	if n < 4 {
+		n = 0
+	} else {
+		n -= 4
+	}
+	return n, err
+}
+
+func (t *TUN) Write(buf []byte, offset int) (int, error) {
+	// below copied from wireguard-go NativeTun.Write
+
+	// reserve space for header
+	buf = buf[offset-4:]
+
+	// add packet information header
+	buf[0] = 0x00
+	buf[1] = 0x00
+	if buf[4]>>4 == ipv6.Version {
+		buf[2] = 0x86
+		buf[3] = 0xdd
+	} else {
+		buf[2] = 0x08
+		buf[3] = 0x00
+	}
+
+	n, err := t.f.Write(buf)
+	if errors.Is(err, syscall.EBADFD) {
+		err = os.ErrClosed
+	}
+	return n, err
+}
+
+func (t *TUN) Flush() error           { return t.d.Flush() }
+func (t *TUN) MTU() (int, error)      { return t.d.MTU() }
+func (t *TUN) Name() (string, error)  { return t.d.Name() }
+func (t *TUN) Events() chan tun.Event { return t.d.Events() }
+
+func (t *TUN) Close() error {
+	err1 := t.f.Close()
+	err2 := t.d.Close()
+	if err1 != nil {
+		return err1
+	}
+	return err2
+}

wgengine/magicsock/magicsock.go

@@ -2698,11 +2698,11 @@ func (c *Conn) bindSocket(rucPtr **RebindingUDPConn, network string, curPortFate
 		// Success.
 		ruc.pconn = pconn
 		if uring.Available() {
-			uringConn, err := uring.NewUDPConn(pconn.(*net.UDPConn))
+			uringConn, err := uring.NewUDPConn(pconn)
 			if err != nil {
-				c.logf("not using io_uring for %v: %v", pconn.LocalAddr(), err)
+				c.logf("not using io_uring for UDP %v: %v", pconn.LocalAddr(), err)
 			} else {
-				c.logf("using uring for %v", pconn.LocalAddr())
+				c.logf("using uring for UDP %v", pconn.LocalAddr())
 				ruc.pconn = uringConn
 			}
 		}