cursed gso

cmd/gso/gso.go

@@ -0,0 +1,191 @@
+package main
+
+import (
+	"encoding/binary"
+	"errors"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"net/netip"
+	"time"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+const (
+	// UDP_SEGMENT enables GSO segmentation
+	UDP_SEGMENT = 103
+	// Maximum GSO segment size (typical MTU - headers)
+	maxGSOSize = 1400
+)
+
+func main() {
+	destAddr := flag.String("dest", "10.4.0.16:4202", "Destination address")
+	gsoSize := flag.Int("gso", 1400, "GSO segment size")
+	totalSize := flag.Int("size", 14000, "Total payload size to send")
+	count := flag.Int("count", 1, "Number of packets to send")
+	flag.Parse()
+
+	if *gsoSize > maxGSOSize {
+		log.Fatalf("GSO size %d exceeds maximum %d", *gsoSize, maxGSOSize)
+	}
+
+	// Resolve destination address
+	_, err := net.ResolveUDPAddr("udp", *destAddr)
+	if err != nil {
+		log.Fatalf("Failed to resolve address: %v", err)
+	}
+
+	// Create a raw UDP socket with GSO support
+	fd, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM, unix.IPPROTO_UDP)
+	if err != nil {
+		log.Fatalf("Failed to create socket: %v", err)
+	}
+	defer unix.Close(fd)
+
+	// Bind to a local address
+	localAddr := &unix.SockaddrInet4{
+		Port: 0, // Let the system choose a port
+	}
+	if err := unix.Bind(fd, localAddr); err != nil {
+		log.Fatalf("Failed to bind socket: %v", err)
+	}
+
+	fmt.Printf("Sending UDP packets with GSO enabled\n")
+	fmt.Printf("Destination: %s\n", *destAddr)
+	fmt.Printf("GSO segment size: %d bytes\n", *gsoSize)
+	fmt.Printf("Total payload size: %d bytes\n", *totalSize)
+	fmt.Printf("Number of packets: %d\n\n", *count)
+
+	// Create payload
+	payload := make([]byte, *totalSize)
+	for i := range payload {
+		payload[i] = byte(i % 256)
+	}
+
+	dest := netip.MustParseAddrPort(*destAddr)
+
+	//if err := unix.SetsockoptInt(fd, unix.SOL_UDP, unix.UDP_SEGMENT, 1400); err != nil {
+	//	panic(err)
+	//}
+
+	for i := 0; i < *count; i++ {
+		err := WriteBatch(fd, payload, dest, uint16(*gsoSize), true)
+		if err != nil {
+			log.Printf("Send error on packet %d: %v", i, err)
+			continue
+		}
+
+		if (i+1)%100 == 0 || i == *count-1 {
+			fmt.Printf("Sent %d packets\n", i+1)
+		}
+	}
+	fmt.Printf("now, let's send without the correct ctrl header\n")
+	time.Sleep(time.Second)
+	for i := 0; i < *count; i++ {
+		err := WriteBatch(fd, payload, dest, uint16(*gsoSize), false)
+		if err != nil {
+			log.Printf("Send error on packet %d: %v", i, err)
+			continue
+		}
+
+		if (i+1)%100 == 0 || i == *count-1 {
+			fmt.Printf("Sent %d packets\n", i+1)
+		}
+	}
+
+}
+
+func WriteBatch(fd int, payload []byte, addr netip.AddrPort, segSize uint16, withHeader bool) error {
+	msgs := make([]rawMessage, 0, 1)
+	iovs := make([]iovec, 0, 1)
+	names := make([][unix.SizeofSockaddrInet6]byte, 0, 1)
+
+	sent := 0
+
+	pkts := []BatchPacket{
+		{
+			Payload: payload,
+			Addr:    addr,
+		},
+	}
+
+	for _, pkt := range pkts {
+		if len(pkt.Payload) == 0 {
+			sent++
+			continue
+		}
+
+		msgs = append(msgs, rawMessage{})
+		iovs = append(iovs, iovec{})
+		names = append(names, [unix.SizeofSockaddrInet6]byte{})
+
+		idx := len(msgs) - 1
+		msg := &msgs[idx]
+		iov := &iovs[idx]
+		name := &names[idx]
+
+		setIovecSlice(iov, pkt.Payload)
+		msg.Hdr.Iov = iov
+		msg.Hdr.Iovlen = 1
+
+		if withHeader {
+			setRawMessageControl(msg, buildGSOControlMessage(segSize)) //
+		} else {
+			setRawMessageControl(msg, nil) //
+		}
+
+		msg.Hdr.Flags = 0
+
+		nameLen, err := encodeSockaddr(name[:], pkt.Addr)
+		if err != nil {
+			return err
+		}
+		msg.Hdr.Name = &name[0]
+		msg.Hdr.Namelen = nameLen
+	}
+
+	if len(msgs) == 0 {
+		return errors.New("nothing to write")
+	}
+
+	offset := 0
+	for offset < len(msgs) {
+		n, _, errno := unix.Syscall6(
+			unix.SYS_SENDMMSG,
+			uintptr(fd),
+			uintptr(unsafe.Pointer(&msgs[offset])),
+			uintptr(len(msgs)-offset),
+			0,
+			0,
+			0,
+		)
+
+		if errno != 0 {
+			if errno == unix.EINTR {
+				continue
+			}
+			return &net.OpError{Op: "sendmmsg", Err: errno}
+		}
+
+		if n == 0 {
+			break
+		}
+		offset += int(n)
+	}
+
+	return nil
+}
+
+func buildGSOControlMessage(segSize uint16) []byte {
+	control := make([]byte, unix.CmsgSpace(2))
+	hdr := (*unix.Cmsghdr)(unsafe.Pointer(&control[0]))
+	hdr.Level = unix.SOL_UDP
+	hdr.Type = unix.UDP_SEGMENT
+	setCmsgLen(hdr, unix.CmsgLen(2))
+	binary.NativeEndian.PutUint16(control[unix.CmsgLen(0):unix.CmsgLen(0)+2], uint16(segSize))
+
+	return control
+}

cmd/gso/helper.go

@@ -0,0 +1,85 @@
+package main
+
+import (
+	"encoding/binary"
+	"fmt"
+	"net/netip"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+type iovec struct {
+	Base *byte
+	Len  uint64
+}
+
+type msghdr struct {
+	Name       *byte
+	Namelen    uint32
+	Pad0       [4]byte
+	Iov        *iovec
+	Iovlen     uint64
+	Control    *byte
+	Controllen uint64
+	Flags      int32
+	Pad1       [4]byte
+}
+
+type rawMessage struct {
+	Hdr  msghdr
+	Len  uint32
+	Pad0 [4]byte
+}
+
+type BatchPacket struct {
+	Payload []byte
+	Addr    netip.AddrPort
+}
+
+func encodeSockaddr(dst []byte, addr netip.AddrPort) (uint32, error) {
+	if addr.Addr().Is4() {
+		if !addr.Addr().Is4() {
+			return 0, fmt.Errorf("Listener is IPv4, but writing to IPv6 remote")
+		}
+		var sa unix.RawSockaddrInet4
+		sa.Family = unix.AF_INET
+		sa.Addr = addr.Addr().As4()
+		binary.BigEndian.PutUint16((*[2]byte)(unsafe.Pointer(&sa.Port))[:], addr.Port())
+		size := unix.SizeofSockaddrInet4
+		copy(dst[:size], (*(*[unix.SizeofSockaddrInet4]byte)(unsafe.Pointer(&sa)))[:])
+		return uint32(size), nil
+	}
+
+	var sa unix.RawSockaddrInet6
+	sa.Family = unix.AF_INET6
+	sa.Addr = addr.Addr().As16()
+	binary.BigEndian.PutUint16((*[2]byte)(unsafe.Pointer(&sa.Port))[:], addr.Port())
+	size := unix.SizeofSockaddrInet6
+	copy(dst[:size], (*(*[unix.SizeofSockaddrInet6]byte)(unsafe.Pointer(&sa)))[:])
+	return uint32(size), nil
+}
+
+func setRawMessageControl(msg *rawMessage, buf []byte) {
+	if len(buf) == 0 {
+		msg.Hdr.Control = nil
+		msg.Hdr.Controllen = 0
+		return
+	}
+	msg.Hdr.Control = &buf[0]
+	msg.Hdr.Controllen = uint64(len(buf))
+}
+
+func setCmsgLen(h *unix.Cmsghdr, l int) {
+	h.Len = uint64(l)
+}
+
+func setIovecSlice(iov *iovec, b []byte) {
+	if len(b) == 0 {
+		iov.Base = nil
+		iov.Len = 0
+		return
+	}
+	iov.Base = &b[0]
+	iov.Len = uint64(len(b))
+}

connection_manager.go

@@ -518,12 +518,12 @@ func (cm *connectionManager) sendPunch(hostinfo *HostInfo) {
 	if cm.punchy.GetTargetEverything() {
 		hostinfo.remotes.ForEach(cm.hostMap.GetPreferredRanges(), func(addr netip.AddrPort, preferred bool) {
 			cm.metricsTxPunchy.Inc(1)
-			cm.intf.outside.WriteTo([]byte{1}, addr)
+			cm.intf.outside.WriteDirect([]byte{1}, addr)
 		})
 
 	} else if hostinfo.remote.IsValid() {
 		cm.metricsTxPunchy.Inc(1)
-		cm.intf.outside.WriteTo([]byte{1}, hostinfo.remote)
+		cm.intf.outside.WriteDirect([]byte{1}, hostinfo.remote)
 	}
 }
 

connection_state.go

@@ -15,7 +15,8 @@ import (
 
 // TODO: In a 5Gbps test, 1024 is not sufficient. With a 1400 MTU this is about 1.4Gbps of window, assuming full packets.
 // 4092 should be sufficient for 5Gbps
-const ReplayWindow = 8192
+// TODO this is a horrible amount of RAM to waste per-tunnel
+const ReplayWindow = 0xffff / 2
 
 type ConnectionState struct {
 	eKey           *NebulaCipherState

handshake_ix.go

@@ -348,7 +348,7 @@ func ixHandshakeStage1(f *Interface, addr netip.AddrPort, via *ViaSender, packet
 			msg = existing.HandshakePacket[2]
 			f.messageMetrics.Tx(header.Handshake, header.MessageSubType(msg[1]), 1)
 			if addr.IsValid() {
-				err := f.outside.WriteTo(msg, addr)
+				err := f.outside.WriteDirect(msg, addr)
 				if err != nil {
 					f.l.WithField("vpnAddrs", existing.vpnAddrs).WithField("udpAddr", addr).
 						WithField("handshake", m{"stage": 2, "style": "ix_psk0"}).WithField("cached", true).
@@ -417,7 +417,7 @@ func ixHandshakeStage1(f *Interface, addr netip.AddrPort, via *ViaSender, packet
 	// Do the send
 	f.messageMetrics.Tx(header.Handshake, header.MessageSubType(msg[1]), 1)
 	if addr.IsValid() {
-		err = f.outside.WriteTo(msg, addr)
+		err = f.outside.WriteDirect(msg, addr)
 		if err != nil {
 			f.l.WithField("vpnAddrs", vpnAddrs).WithField("udpAddr", addr).
 				WithField("certName", certName).

handshake_manager.go

@@ -238,7 +238,7 @@ func (hm *HandshakeManager) handleOutbound(vpnIp netip.Addr, lighthouseTriggered
 	var sentTo []netip.AddrPort
 	hostinfo.remotes.ForEach(hm.mainHostMap.GetPreferredRanges(), func(addr netip.AddrPort, _ bool) {
 		hm.messageMetrics.Tx(header.Handshake, header.MessageSubType(hostinfo.HandshakePacket[0][1]), 1)
-		err := hm.outside.WriteTo(hostinfo.HandshakePacket[0], addr)
+		err := hm.outside.WriteDirect(hostinfo.HandshakePacket[0], addr)
 		if err != nil {
 			hostinfo.logger(hm.l).WithField("udpAddr", addr).
 				WithField("initiatorIndex", hostinfo.localIndexId).

inside.go

@@ -8,6 +8,7 @@ import (
 	"github.com/slackhq/nebula/header"
 	"github.com/slackhq/nebula/iputil"
 	"github.com/slackhq/nebula/noiseutil"
+	"github.com/slackhq/nebula/packet"
 	"github.com/slackhq/nebula/routing"
 )
 
@@ -324,7 +325,7 @@ func (f *Interface) SendVia(via *HostInfo,
 		via.logger(f.l).WithError(err).Info("Failed to EncryptDanger in sendVia")
 		return
 	}
-	err = f.writers[0].WriteTo(out, via.remote)
+	err = f.writers[0].WriteDirect(out, via.remote)
 	if err != nil {
 		via.logger(f.l).WithError(err).Info("Failed to WriteTo in sendVia")
 	}
@@ -384,19 +385,29 @@ func (f *Interface) sendNoMetrics(t header.MessageType, st header.MessageSubType
 	}
 
 	if remote.IsValid() {
-		err = f.writers[q].WriteTo(out, remote)
+		pkt := packet.GetPool().Get()
+		copy(pkt.Payload[:], out)
+		pkt.Payload = pkt.Payload[:len(out)]
+		pkt.Addr = remote
+		err = f.writers[q].WriteTo(pkt)
 		if err != nil {
 			hostinfo.logger(f.l).WithError(err).
 				WithField("udpAddr", remote).Error("Failed to write outgoing packet")
 		}
 	} else if hostinfo.remote.IsValid() {
-		err = f.writers[q].WriteTo(out, hostinfo.remote)
+		pkt := packet.GetPool().Get()
+		copy(pkt.Payload, out)
+		pkt.Payload = pkt.Payload[:len(out)]
+		pkt.Addr = hostinfo.remote
+		err = f.writers[q].WriteTo(pkt)
 		if err != nil {
 			hostinfo.logger(f.l).WithError(err).
 				WithField("udpAddr", remote).Error("Failed to write outgoing packet")
 		}
 	} else {
 		// Try to send via a relay
+
+		//todo relay is slow sorryyy
 		for _, relayIP := range hostinfo.relayState.CopyRelayIps() {
 			relayHostInfo, relay, err := f.hostMap.QueryVpnAddrsRelayFor(hostinfo.vpnAddrs, relayIP)
 			if err != nil {

interface.go

@@ -207,7 +207,7 @@ func NewInterface(ctx context.Context, c *InterfaceConfig) (*Interface, error) {
 		l: c.l,
 	}
 
-	ifce.pktPool = packet.NewPool()
+	ifce.pktPool = packet.GetPool()
 
 	ifce.tryPromoteEvery.Store(c.tryPromoteEvery)
 	ifce.reQueryEvery.Store(c.reQueryEvery)
@@ -327,6 +327,26 @@ func (f *Interface) listenIn(reader io.ReadWriteCloser, i int) {
 	f.wg.Done()
 }
 
+//// todo why? understand!
+//func normalizeGROSegSize(segSize, total int) int {
+//	if segCount > 1 && total > 0 {
+//		avg := total / segCount
+//		if avg > 0 {
+//			if segSize > avg {
+//				if segSize-8 == avg {
+//					segSize = avg
+//				} else if segSize > total {
+//					segSize = avg
+//				}
+//			}
+//		}
+//	}
+//	if segSize > total {
+//		segSize = total
+//	}
+//	return segSize
+//}
+
 func (f *Interface) workerIn(i int, ctx context.Context) {
 	lhh := f.lightHouse.NewRequestHandler()
 	conntrackCache := firewall.NewConntrackCacheTicker(f.conntrackCacheTimeout)
@@ -338,7 +358,18 @@ func (f *Interface) workerIn(i int, ctx context.Context) {
 	for {
 		select {
 		case p := <-f.inbound:
-			f.readOutsidePackets(p.Addr, nil, result2[:0], p.Payload, h, fwPacket2, lhh, nb2, i, conntrackCache.Get(f.l))
+			if p.SegSize > 0 && p.SegSize < len(p.Payload) {
+				for offset := 0; offset < len(p.Payload); offset += p.SegSize {
+					end := offset + p.SegSize
+					if end > len(p.Payload) {
+						end = len(p.Payload)
+					}
+					f.readOutsidePackets(p.Addr, nil, result2[:0], p.Payload[offset:end], h, fwPacket2, lhh, nb2, i, conntrackCache.Get(f.l))
+				}
+			} else {
+				f.readOutsidePackets(p.Addr, nil, result2[:0], p.Payload, h, fwPacket2, lhh, nb2, i, conntrackCache.Get(f.l))
+			}
+
 			f.pktPool.Put(p)
 		case <-ctx.Done():
 			f.wg.Done()
@@ -357,7 +388,7 @@ func (f *Interface) workerOut(i int, ctx context.Context) {
 		select {
 		case data := <-f.outbound:
 			f.consumeInsidePacket(data.Payload, fwPacket1, nb1, result1, i, conntrackCache.Get(f.l))
-			f.pktPool.Put(data)
+			//f.pktPool.Put(data) //todo if err pls put packet back
 		case <-ctx.Done():
 			f.wg.Done()
 			return

lighthouse.go

@@ -1329,7 +1329,7 @@ func (lhh *LightHouseHandler) handleHostPunchNotification(n *NebulaMeta, fromVpn
 		go func() {
 			time.Sleep(lhh.lh.punchy.GetDelay())
 			lhh.lh.metricHolepunchTx.Inc(1)
-			lhh.lh.punchConn.WriteTo(empty, vpnPeer)
+			lhh.lh.punchConn.WriteDirect(empty, vpnPeer)
 		}()
 
 		if lhh.l.Level >= logrus.DebugLevel {

outside.go

@@ -519,7 +519,7 @@ func (f *Interface) sendRecvError(endpoint netip.AddrPort, index uint32) {
 	f.messageMetrics.Tx(header.RecvError, 0, 1)
 
 	b := header.Encode(make([]byte, header.Len), header.Version, header.RecvError, 0, index, 0)
-	_ = f.outside.WriteTo(b, endpoint)
+	_ = f.outside.WriteDirect(b, endpoint)
 	if f.l.Level >= logrus.DebugLevel {
 		f.l.WithField("index", index).
 			WithField("udpAddr", endpoint).

packet/packet.go

@@ -3,27 +3,36 @@ package packet
 import (
 	"net/netip"
 	"sync"
+
+	"golang.org/x/sys/unix"
 )
 
-const Size = 9001
+const Size = 0xffff
 
 type Packet struct {
 	Payload []byte
+	Control []byte
+	SegSize int
 	Addr    netip.AddrPort
 }
 
 func New() *Packet {
-	return &Packet{Payload: make([]byte, Size)}
+	return &Packet{
+		Payload: make([]byte, Size),
+		Control: make([]byte, unix.CmsgSpace(2)),
+	}
 }
 
 type Pool struct {
 	pool sync.Pool
 }
 
-func NewPool() *Pool {
-	return &Pool{
-		pool: sync.Pool{New: func() any { return New() }},
-	}
+var bigPool = &Pool{
+	pool: sync.Pool{New: func() any { return New() }},
+}
+
+func GetPool() *Pool {
+	return bigPool
 }
 
 func (p *Pool) Get() *Packet {

udp/conn.go

@@ -17,7 +17,8 @@ type Conn interface {
 	Rebind() error
 	LocalAddr() (netip.AddrPort, error)
 	ListenOut(pg PacketBufferGetter, pc chan *packet.Packet) error
-	WriteTo(b []byte, addr netip.AddrPort) error
+	WriteTo(p *packet.Packet) error
+	WriteDirect(b []byte, port netip.AddrPort) error
 	ReloadConfig(c *config.C)
 	Close() error
 }

udp/udp_linux.go

@@ -5,9 +5,11 @@ package udp
 
 import (
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"net"
 	"net/netip"
+	"sync"
 	"syscall"
 	"time"
 	"unsafe"
@@ -19,13 +21,136 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+const (
+	defaultGSOMaxSegments  = 16
+	defaultGSOFlushTimeout = 150 * time.Microsecond
+	maxGSOBatchBytes       = 0xFFFF
+)
+
+var (
+	errGSOFallback = errors.New("udp gso fallback")
+	errGSODisabled = errors.New("udp gso disabled")
+)
+
 var readTimeout = unix.NsecToTimeval(int64(time.Millisecond * 500))
 
+type gsoState struct {
+	m            sync.Mutex
+	Buf          []byte
+	Addr         netip.AddrPort
+	SegSize      int
+	MaxSegments  int
+	MaxBytes     int
+	FlushTimeout time.Duration
+	Timer        *time.Timer
+
+	packets []*packet.Packet
+	msg     rawMessage
+	name    [unix.SizeofSockaddrInet6]byte
+	iov     []iovec
+	ctrl    []byte
+}
+
+func (g *gsoState) Init() {
+	g.iov = make([]iovec, g.MaxSegments)
+	for i := 0; i < g.MaxSegments; i++ {
+		g.iov[i] = iovec{}
+	}
+	g.msg.Hdr.Iov = &g.iov[0]
+	g.msg.Hdr.Iovlen = 1
+
+	g.packets = make([]*packet.Packet, 0, g.MaxSegments)
+	g.ctrl = make([]byte, unix.CmsgSpace(2))
+	hdr := (*unix.Cmsghdr)(unsafe.Pointer(&g.ctrl[0]))
+	hdr.Level = unix.SOL_UDP
+	hdr.Type = unix.UDP_SEGMENT
+	setCmsgLen(hdr, unix.CmsgLen(2))
+	g.msg.Hdr.Control = &g.ctrl[0]
+	g.msg.Hdr.Controllen = uint64(len(g.ctrl))
+
+	g.name = [unix.SizeofSockaddrInet6]byte{}
+	g.msg.Hdr.Name = &g.name[0]
+
+}
+
+func (g *gsoState) setSegSizeLocked(segSize int) {
+	g.SegSize = segSize
+	x := unix.CmsgLen(0)
+	binary.LittleEndian.PutUint16(g.ctrl[x:x+2], uint16(segSize))
+}
+
+func (g *gsoState) setNameLocked(x netip.AddrPort, isV4 bool) {
+	g.Addr = x
+	nameLen := encodeSockaddr(g.name[:], g.Addr, isV4)
+	g.msg.Hdr.Name = &g.name[0]
+	g.msg.Hdr.Namelen = nameLen
+}
+
+func encodeSockaddr(dst []byte, addr netip.AddrPort, isV4 bool) uint32 {
+	if isV4 {
+		//todo?
+		//if !addr.Addr().Is4() {
+		//	return 0, fmt.Errorf("Listener is IPv4, but writing to IPv6 remote")
+		//}
+		var sa unix.RawSockaddrInet4
+		sa.Family = unix.AF_INET
+		sa.Addr = addr.Addr().As4()
+		binary.BigEndian.PutUint16((*[2]byte)(unsafe.Pointer(&sa.Port))[:], addr.Port())
+		size := unix.SizeofSockaddrInet4
+		copy(dst[:size], (*(*[unix.SizeofSockaddrInet4]byte)(unsafe.Pointer(&sa)))[:])
+		return uint32(size)
+	}
+
+	var sa unix.RawSockaddrInet6
+	sa.Family = unix.AF_INET6
+	sa.Addr = addr.Addr().As16()
+	binary.BigEndian.PutUint16((*[2]byte)(unsafe.Pointer(&sa.Port))[:], addr.Port())
+	size := unix.SizeofSockaddrInet6
+	copy(dst[:size], (*(*[unix.SizeofSockaddrInet6]byte)(unsafe.Pointer(&sa)))[:])
+	return uint32(size)
+}
+
+func (g *gsoState) sendmsgLocked(fd int) error {
+	//name already set
+	//ctrl already set
+	//g.iov = g.iov[:0]
+	g.msg.Hdr.Iovlen = uint64(len(g.packets))
+	for i := range g.packets {
+		g.iov[i].Base = &g.packets[i].Payload[0]
+		g.iov[i].Len = uint64(len(g.packets[i].Payload))
+	}
+
+	const flags = 0
+	for {
+		_, _, err := unix.Syscall(
+			unix.SYS_SENDMSG,
+			uintptr(fd),
+			uintptr(unsafe.Pointer(&g.msg)),
+			uintptr(flags),
+		)
+		//todo no matter what, reset things
+		for i := range g.packets {
+			pool := packet.GetPool()
+			pool.Put(g.packets[i])
+		}
+		g.packets = g.packets[:0]
+
+		if err != 0 {
+			return &net.OpError{Op: "sendmsg", Err: err}
+		}
+
+		return nil
+	}
+}
+
 type StdConn struct {
-	sysFd int
-	isV4  bool
-	l     *logrus.Logger
-	batch int
+	sysFd     int
+	isV4      bool
+	l         *logrus.Logger
+	batch     int
+	enableGRO bool
+	enableGSO bool
+	gso       gsoState
 }
 
 func NewListener(l *logrus.Logger, ip netip.Addr, port int, multi bool, batch int) (Conn, error) {
@@ -145,15 +270,47 @@ func (u *StdConn) ListenOut(pg PacketBufferGetter, pc chan *packet.Packet) error
 				ip, _ = netip.AddrFromSlice(names[i][8:24])
 			}
 			out.Addr = netip.AddrPortFrom(ip.Unmap(), binary.BigEndian.Uint16(names[i][2:4]))
+			ctrlLen := getRawMessageControlLen(&msgs[i])
+			if ctrlLen > 0 {
+				packets[i].SegSize = parseGROControl(packets[i].Control[:ctrlLen])
+			} else {
+				packets[i].SegSize = 0
+			}
+
 			pc <- out
 
 			//rotate this packet out so we don't overwrite it
 			packets[i] = pg()
 			msgs[i].Hdr.Iov.Base = &packets[i].Payload[0]
+			if u.enableGRO {
+				msgs[i].Hdr.Control = &packets[i].Control[0]
+				msgs[i].Hdr.Controllen = uint64(cap(packets[i].Control))
+			}
+
 		}
 	}
 }
 
+func parseGROControl(control []byte) int {
+	if len(control) == 0 {
+		return 0
+	}
+
+	cmsgs, err := unix.ParseSocketControlMessage(control)
+	if err != nil {
+		return 0
+	}
+
+	for _, c := range cmsgs {
+		if c.Header.Level == unix.SOL_UDP && c.Header.Type == unix.UDP_GRO && len(c.Data) >= 2 {
+			segSize := int(binary.LittleEndian.Uint16(c.Data[:2]))
+			return segSize
+		}
+	}
+
+	return 0
+}
+
 func (u *StdConn) ReadSingle(msgs []rawMessage) (int, error) {
 	for {
 		n, _, err := unix.Syscall6(
@@ -201,11 +358,123 @@ func (u *StdConn) ReadMulti(msgs []rawMessage) (int, error) {
 	}
 }
 
-func (u *StdConn) WriteTo(b []byte, ip netip.AddrPort) error {
-	if u.isV4 {
-		return u.writeTo4(b, ip)
+func (u *StdConn) WriteTo(p *packet.Packet) error {
+	if u.enableGSO && p.Addr.IsValid() {
+		if err := u.queueGSOPacket(p); err == nil {
+			return nil
+		} else if !errors.Is(err, errGSOFallback) {
+			return err
+		}
 	}
-	return u.writeTo6(b, ip)
+
+	var err error
+	if u.isV4 {
+		err = u.writeTo4(p.Payload, p.Addr)
+	} else {
+		err = u.writeTo4(p.Payload, p.Addr)
+	}
+	packet.GetPool().Put(p)
+	return err
+}
+
+func (u *StdConn) WriteDirect(b []byte, addr netip.AddrPort) error {
+	if u.isV4 {
+		return u.writeTo4(b, addr)
+	}
+	return u.writeTo6(b, addr)
+}
+
+func (u *StdConn) scheduleGSOFlushLocked() {
+	if u.gso.Timer == nil {
+		u.gso.Timer = time.AfterFunc(u.gso.FlushTimeout, u.gsoFlushTimer)
+		return
+	}
+	u.gso.Timer.Reset(u.gso.FlushTimeout)
+}
+
+func (u *StdConn) stopGSOTimerLocked() {
+	if u.gso.Timer != nil {
+		u.gso.Timer.Stop()
+		u.gso.Timer = nil //todo I also don't like this
+	}
+}
+
+func (u *StdConn) queueGSOPacket(p *packet.Packet) error {
+	if len(p.Payload) == 0 {
+		return nil
+	}
+
+	u.gso.m.Lock()
+	defer u.gso.m.Unlock()
+
+	if !u.enableGSO || !p.Addr.IsValid() || len(p.Payload) > u.gso.MaxBytes {
+		if err := u.flushGSOlocked(); err != nil {
+			return err
+		}
+		return errGSOFallback
+	}
+
+	if len(u.gso.packets) == 0 {
+		u.gso.setNameLocked(p.Addr, u.isV4)
+		u.gso.SegSize = len(p.Payload)
+		u.gso.packets = append(u.gso.packets, p)
+	} else if p.Addr != u.gso.Addr || len(p.Payload) != u.gso.SegSize {
+		if err := u.flushGSOlocked(); err != nil {
+			return err
+		} //todo deal with "one small packet" case
+		u.gso.setNameLocked(p.Addr, u.isV4)
+		u.gso.SegSize = len(p.Payload)
+		u.gso.packets = append(u.gso.packets, p)
+	} else {
+		u.gso.packets = append(u.gso.packets, p)
+	}
+
+	//big todo
+	//if len(u.gso.Buf)+len(p.Payload) > u.gso.MaxBytes {
+	//	if err := u.flushGSOlocked(); err != nil {
+	//		return err
+	//	}
+	//	u.gso.setNameLocked(p.Addr, u.isV4)
+	//	u.gso.SegSize = len(p.Payload)
+	//	u.gso.packets = append(u.gso.packets, p)
+	//}
+
+	if len(u.gso.packets) >= u.gso.MaxSegments || u.gso.FlushTimeout <= 0 {
+		return u.flushGSOlocked()
+	}
+
+	u.scheduleGSOFlushLocked()
+	return nil
+}
+
+func (u *StdConn) flushGSOlocked() error {
+	if len(u.gso.packets) == 0 {
+		u.stopGSOTimerLocked()
+		return nil
+	}
+
+	u.stopGSOTimerLocked()
+
+	if u.gso.SegSize <= 0 {
+		return errGSOFallback
+	}
+
+	err := u.gso.sendmsgLocked(u.sysFd)
+	if errors.Is(err, errGSODisabled) {
+		u.l.WithField("addr", u.gso.Addr).Warn("UDP GSO disabled by kernel, falling back to sendto")
+		u.enableGSO = false
+		//todo!
+		//return u.sendSegmentsIndividually(payload, addr, segSize)
+	}
+	u.gso.SegSize = 0
+
+	return err
+}
+
+func (u *StdConn) gsoFlushTimer() {
+	u.gso.m.Lock()
+	_ = u.flushGSOlocked()
+	u.gso.m.Unlock()
 }
 
 func (u *StdConn) writeTo6(b []byte, ip netip.AddrPort) error {
@@ -308,6 +577,72 @@ func (u *StdConn) ReloadConfig(c *config.C) {
 			u.l.WithError(err).Error("Failed to set listen.so_mark")
 		}
 	}
+	u.configureGRO(true)
+	u.configureGSO(c)
+}
+
+func (u *StdConn) configureGRO(enable bool) {
+	if enable == u.enableGRO {
+		return
+	}
+
+	if enable {
+		if err := unix.SetsockoptInt(u.sysFd, unix.SOL_UDP, unix.UDP_GRO, 1); err != nil {
+			u.l.WithError(err).Warn("Failed to enable UDP GRO")
+			return
+		}
+		u.enableGRO = true
+		u.l.Info("UDP GRO enabled")
+		return
+	}
+
+	if err := unix.SetsockoptInt(u.sysFd, unix.SOL_UDP, unix.UDP_GRO, 0); err != nil && err != unix.ENOPROTOOPT {
+		u.l.WithError(err).Warn("Failed to disable UDP GRO")
+	}
+	u.enableGRO = false
+}
+
+func (u *StdConn) configureGSO(c *config.C) {
+	enable := c.GetBool("listen.enable_gso", true)
+	if !enable {
+		u.disableGSO()
+	} else {
+		u.enableGSO = true
+	}
+
+	segments := c.GetInt("listen.gso_max_segments", defaultGSOMaxSegments)
+	if segments < 1 {
+		segments = 1
+	}
+	u.gso.MaxSegments = segments
+
+	maxBytes := c.GetInt("listen.gso_max_bytes", 0)
+	if maxBytes <= 0 {
+		maxBytes = MTU * segments
+	}
+	if maxBytes > maxGSOBatchBytes {
+		u.l.WithField("requested", maxBytes).Warn("listen.gso_max_bytes larger than UDP limit; clamping")
+		maxBytes = maxGSOBatchBytes
+	}
+	u.gso.MaxBytes = maxBytes
+
+	timeout := c.GetDuration("listen.gso_flush_timeout", defaultGSOFlushTimeout)
+	if timeout < 0 {
+		timeout = 0
+	}
+	u.gso.FlushTimeout = timeout
+	u.gso.Init()
+}
+
+func (u *StdConn) disableGSO() {
+	u.gso.m.Lock()
+	defer u.gso.m.Unlock()
+	u.enableGSO = false
+	_ = u.flushGSOlocked()
+	u.gso.Buf = nil
+	u.gso.packets = u.gso.packets[:0]
+	u.gso.SegSize = 0
+	u.stopGSOTimerLocked()
 }
 
 func (u *StdConn) getMemInfo(meminfo *[unix.SK_MEMINFO_VARS]uint32) error {

udp/udp_linux_64.go

@@ -34,6 +34,24 @@ type rawMessage struct {
 	Pad0 [4]byte
 }
 
+func setRawMessageControl(msg *rawMessage, buf []byte) {
+	if len(buf) == 0 {
+		msg.Hdr.Control = nil
+		msg.Hdr.Controllen = 0
+		return
+	}
+	msg.Hdr.Control = &buf[0]
+	msg.Hdr.Controllen = uint64(len(buf))
+}
+
+func getRawMessageControlLen(msg *rawMessage) int {
+	return int(msg.Hdr.Controllen)
+}
+
+func setCmsgLen(h *unix.Cmsghdr, l int) {
+	h.Len = uint64(l)
+}
+
 func (u *StdConn) PrepareRawMessages(n int, pg PacketBufferGetter) ([]rawMessage, []*packet.Packet, [][]byte) {
 	msgs := make([]rawMessage, n)
 	names := make([][]byte, n)
@@ -42,6 +60,7 @@ func (u *StdConn) PrepareRawMessages(n int, pg PacketBufferGetter) ([]rawMessage
 	for i := range packets {
 		packets[i] = pg()
 	}
+	//todo?
 
 	for i := range msgs {
 		names[i] = make([]byte, unix.SizeofSockaddrInet6)
@@ -55,6 +74,13 @@ func (u *StdConn) PrepareRawMessages(n int, pg PacketBufferGetter) ([]rawMessage
 
 		msgs[i].Hdr.Name = &names[i][0]
 		msgs[i].Hdr.Namelen = uint32(len(names[i]))
+		if u.enableGRO {
+			msgs[i].Hdr.Control = &packets[i].Control[0]
+			msgs[i].Hdr.Controllen = uint64(len(packets[i].Control))
+		} else {
+			msgs[i].Hdr.Control = nil
+			msgs[i].Hdr.Controllen = 0
+		}
 	}
 
 	return msgs, packets, names