Only carry GSO options in the packet buffer

With this change, GSO options no longer needs to be passed around as
a function argument in the write path.

This change is done in preparation for a later change that defers
segmentation, and may change GSO options for a packet as it flows
down the stack.

Updates #170.

PiperOrigin-RevId: 369774872

16 files changed, 87 insertions, 91 deletions

diff --git a/pkg/tcpip/link/channel/channel.go b/pkg/tcpip/link/channel/channel.go
index cd76272de..f75ee34ab 100644
--- a/pkg/tcpip/link/channel/channel.go
+++ b/pkg/tcpip/link/channel/channel.go
@@ -30,7 +30,6 @@ import (
 type PacketInfo struct {
 	Pkt   *stack.PacketBuffer
 	Proto tcpip.NetworkProtocolNumber
-	GSO   *stack.GSO
 	Route stack.RouteInfo
 }
 
@@ -229,11 +228,10 @@ func (e *Endpoint) LinkAddress() tcpip.LinkAddress {
 }
 
 // WritePacket stores outbound packets into the channel.
-func (e *Endpoint) WritePacket(r stack.RouteInfo, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
+func (e *Endpoint) WritePacket(r stack.RouteInfo, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
 	p := PacketInfo{
 		Pkt:   pkt,
 		Proto: protocol,
-		GSO:   gso,
 		Route: r,
 	}
 
@@ -243,13 +241,12 @@ func (e *Endpoint) WritePacket(r stack.RouteInfo, gso *stack.GSO, protocol tcpip
 }
 
 // WritePackets stores outbound packets into the channel.
-func (e *Endpoint) WritePackets(r stack.RouteInfo, gso *stack.GSO, pkts stack.PacketBufferList, protocol tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
+func (e *Endpoint) WritePackets(r stack.RouteInfo, pkts stack.PacketBufferList, protocol tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
 	n := 0
 	for pkt := pkts.Front(); pkt != nil; pkt = pkt.Next() {
 		p := PacketInfo{
 			Pkt:   pkt,
 			Proto: protocol,
-			GSO:   gso,
 			Route: r,
 		}
 
diff --git a/pkg/tcpip/link/ethernet/ethernet.go b/pkg/tcpip/link/ethernet/ethernet.go
index d873766a6..b427c6170 100644
--- a/pkg/tcpip/link/ethernet/ethernet.go
+++ b/pkg/tcpip/link/ethernet/ethernet.go
@@ -61,20 +61,20 @@ func (e *Endpoint) Capabilities() stack.LinkEndpointCapabilities {
 }
 
 // WritePacket implements stack.LinkEndpoint.
-func (e *Endpoint) WritePacket(r stack.RouteInfo, gso *stack.GSO, proto tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
+func (e *Endpoint) WritePacket(r stack.RouteInfo, proto tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
 	e.AddHeader(e.Endpoint.LinkAddress(), r.RemoteLinkAddress, proto, pkt)
-	return e.Endpoint.WritePacket(r, gso, proto, pkt)
+	return e.Endpoint.WritePacket(r, proto, pkt)
 }
 
 // WritePackets implements stack.LinkEndpoint.
-func (e *Endpoint) WritePackets(r stack.RouteInfo, gso *stack.GSO, pkts stack.PacketBufferList, proto tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
+func (e *Endpoint) WritePackets(r stack.RouteInfo, pkts stack.PacketBufferList, proto tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
 	linkAddr := e.Endpoint.LinkAddress()
 
 	for pkt := pkts.Front(); pkt != nil; pkt = pkt.Next() {
 		e.AddHeader(linkAddr, r.RemoteLinkAddress, proto, pkt)
 	}
 
-	return e.Endpoint.WritePackets(r, gso, pkts, proto)
+	return e.Endpoint.WritePackets(r, pkts, proto)
 }
 
 // MaxHeaderLength implements stack.LinkEndpoint.
diff --git a/pkg/tcpip/link/fdbased/endpoint.go b/pkg/tcpip/link/fdbased/endpoint.go
index 6be945116..feb79fe0e 100644
--- a/pkg/tcpip/link/fdbased/endpoint.go
+++ b/pkg/tcpip/link/fdbased/endpoint.go
@@ -433,7 +433,7 @@ func (e *endpoint) AddHeader(local, remote tcpip.LinkAddress, protocol tcpip.Net
 
 // WritePacket writes outbound packets to the file descriptor. If it is not
 // currently writable, the packet is dropped.
-func (e *endpoint) WritePacket(r stack.RouteInfo, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
+func (e *endpoint) WritePacket(r stack.RouteInfo, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
 	if e.hdrSize > 0 {
 		e.AddHeader(r.LocalLinkAddress, r.RemoteLinkAddress, protocol, pkt)
 	}
@@ -443,23 +443,23 @@ func (e *endpoint) WritePacket(r stack.RouteInfo, gso *stack.GSO, protocol tcpip
 	fd := e.fds[pkt.Hash%uint32(len(e.fds))]
 	if e.Capabilities()&stack.CapabilityHardwareGSO != 0 {
 		vnetHdr := virtioNetHdr{}
-		if gso != nil {
+		if pkt.GSOOptions.Type != stack.GSONone {
 			vnetHdr.hdrLen = uint16(pkt.HeaderSize())
-			if gso.NeedsCsum {
+			if pkt.GSOOptions.NeedsCsum {
 				vnetHdr.flags = _VIRTIO_NET_HDR_F_NEEDS_CSUM
-				vnetHdr.csumStart = header.EthernetMinimumSize + gso.L3HdrLen
-				vnetHdr.csumOffset = gso.CsumOffset
+				vnetHdr.csumStart = header.EthernetMinimumSize + pkt.GSOOptions.L3HdrLen
+				vnetHdr.csumOffset = pkt.GSOOptions.CsumOffset
 			}
-			if gso.Type != stack.GSONone && uint16(pkt.Data().Size()) > gso.MSS {
-				switch gso.Type {
+			if pkt.GSOOptions.Type != stack.GSONone && uint16(pkt.Data().Size()) > pkt.GSOOptions.MSS {
+				switch pkt.GSOOptions.Type {
 				case stack.GSOTCPv4:
 					vnetHdr.gsoType = _VIRTIO_NET_HDR_GSO_TCPV4
 				case stack.GSOTCPv6:
 					vnetHdr.gsoType = _VIRTIO_NET_HDR_GSO_TCPV6
 				default:
-					panic(fmt.Sprintf("Unknown gso type: %v", gso.Type))
+					panic(fmt.Sprintf("Unknown gso type: %v", pkt.GSOOptions.Type))
 				}
-				vnetHdr.gsoSize = gso.MSS
+				vnetHdr.gsoSize = pkt.GSOOptions.MSS
 			}
 		}
 
@@ -484,7 +484,7 @@ func (e *endpoint) sendBatch(batchFD int, batch []*stack.PacketBuffer) (int, tcp
 		var vnetHdrBuf []byte
 		if e.Capabilities()&stack.CapabilityHardwareGSO != 0 {
 			vnetHdr := virtioNetHdr{}
-			if pkt.GSOOptions != nil {
+			if pkt.GSOOptions.Type != stack.GSONone {
 				vnetHdr.hdrLen = uint16(pkt.HeaderSize())
 				if pkt.GSOOptions.NeedsCsum {
 					vnetHdr.flags = _VIRTIO_NET_HDR_F_NEEDS_CSUM
@@ -540,7 +540,7 @@ func (e *endpoint) sendBatch(batchFD int, batch []*stack.PacketBuffer) (int, tcp
 //  - pkt.EgressRoute
 //  - pkt.GSOOptions
 //  - pkt.NetworkProtocolNumber
-func (e *endpoint) WritePackets(_ stack.RouteInfo, _ *stack.GSO, pkts stack.PacketBufferList, _ tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
+func (e *endpoint) WritePackets(_ stack.RouteInfo, pkts stack.PacketBufferList, _ tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
 	// Preallocate to avoid repeated reallocation as we append to batch.
 	// batchSz is 47 because when SWGSO is in use then a single 65KB TCP
 	// segment can get split into 46 segments of 1420 bytes and a single 216
diff --git a/pkg/tcpip/link/fdbased/endpoint_test.go b/pkg/tcpip/link/fdbased/endpoint_test.go
index 1e40f3fef..8aad338b6 100644
--- a/pkg/tcpip/link/fdbased/endpoint_test.go
+++ b/pkg/tcpip/link/fdbased/endpoint_test.go
@@ -207,18 +207,17 @@ func testWritePacket(t *testing.T, plen int, eth bool, gsoMaxSize uint32, hash u
 
 	// Write.
 	want := append(append(buffer.View(nil), b...), payload...)
-	var gso *stack.GSO
+	const l3HdrLen = header.IPv6MinimumSize
 	if gsoMaxSize != 0 {
-		gso = &stack.GSO{
+		pkt.GSOOptions = stack.GSO{
 			Type:       stack.GSOTCPv6,
 			NeedsCsum:  true,
 			CsumOffset: csumOffset,
 			MSS:        gsoMSS,
-			MaxSize:    gsoMaxSize,
-			L3HdrLen:   header.IPv4MaximumHeaderSize,
+			L3HdrLen:   l3HdrLen,
 		}
 	}
-	if err := c.ep.WritePacket(r, gso, proto, pkt); err != nil {
+	if err := c.ep.WritePacket(r, proto, pkt); err != nil {
 		t.Fatalf("WritePacket failed: %v", err)
 	}
 
@@ -235,7 +234,7 @@ func testWritePacket(t *testing.T, plen int, eth bool, gsoMaxSize uint32, hash u
 		if vnetHdr.flags&_VIRTIO_NET_HDR_F_NEEDS_CSUM == 0 {
 			t.Fatalf("virtioNetHdr.flags %v  doesn't contain %v", vnetHdr.flags, _VIRTIO_NET_HDR_F_NEEDS_CSUM)
 		}
-		csumStart := header.EthernetMinimumSize + gso.L3HdrLen
+		const csumStart = header.EthernetMinimumSize + l3HdrLen
 		if vnetHdr.csumStart != csumStart {
 			t.Fatalf("vnetHdr.csumStart = %v, want %v", vnetHdr.csumStart, csumStart)
 		}
@@ -243,7 +242,7 @@ func testWritePacket(t *testing.T, plen int, eth bool, gsoMaxSize uint32, hash u
 			t.Fatalf("vnetHdr.csumOffset = %v, want %v", vnetHdr.csumOffset, csumOffset)
 		}
 		gsoType := uint8(0)
-		if int(gso.MSS) < plen {
+		if plen > gsoMSS {
 			gsoType = _VIRTIO_NET_HDR_GSO_TCPV6
 		}
 		if vnetHdr.gsoType != gsoType {
@@ -333,7 +332,7 @@ func TestPreserveSrcAddress(t *testing.T) {
 		ReserveHeaderBytes: header.EthernetMinimumSize,
 		Data:               buffer.VectorisedView{},
 	})
-	if err := c.ep.WritePacket(r, nil /* gso */, proto, pkt); err != nil {
+	if err := c.ep.WritePacket(r, proto, pkt); err != nil {
 		t.Fatalf("WritePacket failed: %v", err)
 	}
 
diff --git a/pkg/tcpip/link/loopback/loopback.go b/pkg/tcpip/link/loopback/loopback.go
index 691467870..7012d8829 100644
--- a/pkg/tcpip/link/loopback/loopback.go
+++ b/pkg/tcpip/link/loopback/loopback.go
@@ -76,7 +76,7 @@ func (*endpoint) Wait() {}
 
 // WritePacket implements stack.LinkEndpoint.WritePacket. It delivers outbound
 // packets to the network-layer dispatcher.
-func (e *endpoint) WritePacket(_ stack.RouteInfo, _ *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
+func (e *endpoint) WritePacket(_ stack.RouteInfo, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
 	// Construct data as the unparsed portion for the loopback packet.
 	data := buffer.NewVectorisedView(pkt.Size(), pkt.Views())
 
@@ -92,7 +92,7 @@ func (e *endpoint) WritePacket(_ stack.RouteInfo, _ *stack.GSO, protocol tcpip.N
 }
 
 // WritePackets implements stack.LinkEndpoint.WritePackets.
-func (e *endpoint) WritePackets(stack.RouteInfo, *stack.GSO, stack.PacketBufferList, tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
+func (e *endpoint) WritePackets(stack.RouteInfo, stack.PacketBufferList, tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
 	panic("not implemented")
 }
 
diff --git a/pkg/tcpip/link/muxed/injectable.go b/pkg/tcpip/link/muxed/injectable.go
index 668f72eee..3e2a1aa94 100644
--- a/pkg/tcpip/link/muxed/injectable.go
+++ b/pkg/tcpip/link/muxed/injectable.go
@@ -87,20 +87,20 @@ func (m *InjectableEndpoint) InjectInbound(protocol tcpip.NetworkProtocolNumber,
 // WritePackets writes outbound packets to the appropriate
 // LinkInjectableEndpoint based on the RemoteAddress. HandleLocal only works if
 // r.RemoteAddress has a route registered in this endpoint.
-func (m *InjectableEndpoint) WritePackets(r stack.RouteInfo, gso *stack.GSO, pkts stack.PacketBufferList, protocol tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
+func (m *InjectableEndpoint) WritePackets(r stack.RouteInfo, pkts stack.PacketBufferList, protocol tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
 	endpoint, ok := m.routes[r.RemoteAddress]
 	if !ok {
 		return 0, &tcpip.ErrNoRoute{}
 	}
-	return endpoint.WritePackets(r, gso, pkts, protocol)
+	return endpoint.WritePackets(r, pkts, protocol)
 }
 
 // WritePacket writes outbound packets to the appropriate LinkInjectableEndpoint
 // based on the RemoteAddress. HandleLocal only works if r.RemoteAddress has a
 // route registered in this endpoint.
-func (m *InjectableEndpoint) WritePacket(r stack.RouteInfo, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
+func (m *InjectableEndpoint) WritePacket(r stack.RouteInfo, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
 	if endpoint, ok := m.routes[r.RemoteAddress]; ok {
-		return endpoint.WritePacket(r, gso, protocol, pkt)
+		return endpoint.WritePacket(r, protocol, pkt)
 	}
 	return &tcpip.ErrNoRoute{}
 }
diff --git a/pkg/tcpip/link/muxed/injectable_test.go b/pkg/tcpip/link/muxed/injectable_test.go
index 5806f7fdf..040e3a35b 100644
--- a/pkg/tcpip/link/muxed/injectable_test.go
+++ b/pkg/tcpip/link/muxed/injectable_test.go
@@ -54,7 +54,7 @@ func TestInjectableEndpointDispatch(t *testing.T) {
 	var packetRoute stack.RouteInfo
 	packetRoute.RemoteAddress = dstIP
 
-	endpoint.WritePacket(packetRoute, nil /* gso */, ipv4.ProtocolNumber, pkt)
+	endpoint.WritePacket(packetRoute, ipv4.ProtocolNumber, pkt)
 
 	buf := make([]byte, 6500)
 	bytesRead, err := sock.Read(buf)
@@ -76,7 +76,7 @@ func TestInjectableEndpointDispatchHdrOnly(t *testing.T) {
 	pkt.TransportHeader().Push(1)[0] = 0xFA
 	var packetRoute stack.RouteInfo
 	packetRoute.RemoteAddress = dstIP
-	endpoint.WritePacket(packetRoute, nil /* gso */, ipv4.ProtocolNumber, pkt)
+	endpoint.WritePacket(packetRoute, ipv4.ProtocolNumber, pkt)
 	buf := make([]byte, 6500)
 	bytesRead, err := sock.Read(buf)
 	if err != nil {
diff --git a/pkg/tcpip/link/nested/nested.go b/pkg/tcpip/link/nested/nested.go
index 97ad9fdd5..89df35822 100644
--- a/pkg/tcpip/link/nested/nested.go
+++ b/pkg/tcpip/link/nested/nested.go
@@ -113,13 +113,13 @@ func (e *Endpoint) LinkAddress() tcpip.LinkAddress {
 }
 
 // WritePacket implements stack.LinkEndpoint.
-func (e *Endpoint) WritePacket(r stack.RouteInfo, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
-	return e.child.WritePacket(r, gso, protocol, pkt)
+func (e *Endpoint) WritePacket(r stack.RouteInfo, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
+	return e.child.WritePacket(r, protocol, pkt)
 }
 
 // WritePackets implements stack.LinkEndpoint.
-func (e *Endpoint) WritePackets(r stack.RouteInfo, gso *stack.GSO, pkts stack.PacketBufferList, protocol tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
-	return e.child.WritePackets(r, gso, pkts, protocol)
+func (e *Endpoint) WritePackets(r stack.RouteInfo, pkts stack.PacketBufferList, protocol tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
+	return e.child.WritePackets(r, pkts, protocol)
 }
 
 // Wait implements stack.LinkEndpoint.
diff --git a/pkg/tcpip/link/packetsocket/endpoint.go b/pkg/tcpip/link/packetsocket/endpoint.go
index 6cbe18a56..e01837e2d 100644
--- a/pkg/tcpip/link/packetsocket/endpoint.go
+++ b/pkg/tcpip/link/packetsocket/endpoint.go
@@ -35,16 +35,16 @@ func New(lower stack.LinkEndpoint) stack.LinkEndpoint {
 }
 
 // WritePacket implements stack.LinkEndpoint.WritePacket.
-func (e *endpoint) WritePacket(r stack.RouteInfo, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
+func (e *endpoint) WritePacket(r stack.RouteInfo, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
 	e.Endpoint.DeliverOutboundPacket(r.RemoteLinkAddress, r.LocalLinkAddress, protocol, pkt)
-	return e.Endpoint.WritePacket(r, gso, protocol, pkt)
+	return e.Endpoint.WritePacket(r, protocol, pkt)
 }
 
 // WritePackets implements stack.LinkEndpoint.WritePackets.
-func (e *endpoint) WritePackets(r stack.RouteInfo, gso *stack.GSO, pkts stack.PacketBufferList, proto tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
+func (e *endpoint) WritePackets(r stack.RouteInfo, pkts stack.PacketBufferList, proto tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
 	for pkt := pkts.Front(); pkt != nil; pkt = pkt.Next() {
 		e.Endpoint.DeliverOutboundPacket(r.RemoteLinkAddress, r.LocalLinkAddress, pkt.NetworkProtocolNumber, pkt)
 	}
 
-	return e.Endpoint.WritePackets(r, gso, pkts, proto)
+	return e.Endpoint.WritePackets(r, pkts, proto)
 }
diff --git a/pkg/tcpip/link/pipe/pipe.go b/pkg/tcpip/link/pipe/pipe.go
index 21fb87757..5030b6ba1 100644
--- a/pkg/tcpip/link/pipe/pipe.go
+++ b/pkg/tcpip/link/pipe/pipe.go
@@ -66,7 +66,7 @@ func (e *Endpoint) deliverPackets(r stack.RouteInfo, proto tcpip.NetworkProtocol
 }
 
 // WritePacket implements stack.LinkEndpoint.
-func (e *Endpoint) WritePacket(r stack.RouteInfo, _ *stack.GSO, proto tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
+func (e *Endpoint) WritePacket(r stack.RouteInfo, proto tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
 	var pkts stack.PacketBufferList
 	pkts.PushBack(pkt)
 	e.deliverPackets(r, proto, pkts)
@@ -74,7 +74,7 @@ func (e *Endpoint) WritePacket(r stack.RouteInfo, _ *stack.GSO, proto tcpip.Netw
 }
 
 // WritePackets implements stack.LinkEndpoint.
-func (e *Endpoint) WritePackets(r stack.RouteInfo, _ *stack.GSO, pkts stack.PacketBufferList, proto tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
+func (e *Endpoint) WritePackets(r stack.RouteInfo, pkts stack.PacketBufferList, proto tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
 	n := pkts.Len()
 	e.deliverPackets(r, proto, pkts)
 	return n, nil
diff --git a/pkg/tcpip/link/qdisc/fifo/endpoint.go b/pkg/tcpip/link/qdisc/fifo/endpoint.go
index 128ef6e87..bba6a6973 100644
--- a/pkg/tcpip/link/qdisc/fifo/endpoint.go
+++ b/pkg/tcpip/link/qdisc/fifo/endpoint.go
@@ -91,7 +91,7 @@ func (q *queueDispatcher) dispatchLoop() {
 			}
 			// We pass a protocol of zero here because each packet carries its
 			// NetworkProtocol.
-			q.lower.WritePackets(stack.RouteInfo{}, nil /* gso */, batch, 0 /* protocol */)
+			q.lower.WritePackets(stack.RouteInfo{}, batch, 0 /* protocol */)
 			for pkt := batch.Front(); pkt != nil; pkt = pkt.Next() {
 				batch.Remove(pkt)
 			}
@@ -150,12 +150,12 @@ func (e *endpoint) GSOMaxSize() uint32 {
 }
 
 // WritePacket implements stack.LinkEndpoint.WritePacket.
-func (e *endpoint) WritePacket(r stack.RouteInfo, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
-	// WritePacket caller's do not set the following fields in PacketBuffer
-	// so we populate them here.
-	pkt.EgressRoute = r
-	pkt.GSOOptions = gso
-	pkt.NetworkProtocolNumber = protocol
+//
+// The packet must have the following fields populated:
+//  - pkt.EgressRoute
+//  - pkt.GSOOptions
+//  - pkt.NetworkProtocolNumber
+func (e *endpoint) WritePacket(r stack.RouteInfo, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
 	d := e.dispatchers[int(pkt.Hash)%len(e.dispatchers)]
 	if !d.q.enqueue(pkt) {
 		return &tcpip.ErrNoBufferSpace{}
@@ -166,12 +166,12 @@ func (e *endpoint) WritePacket(r stack.RouteInfo, gso *stack.GSO, protocol tcpip
 
 // WritePackets implements stack.LinkEndpoint.WritePackets.
 //
-// Being a batch API, each packet in pkts should have the following
-// fields populated:
+// Each packet in the packet buffer list must have the following fields
+// populated:
 //  - pkt.EgressRoute
 //  - pkt.GSOOptions
 //  - pkt.NetworkProtocolNumber
-func (e *endpoint) WritePackets(r stack.RouteInfo, gso *stack.GSO, pkts stack.PacketBufferList, protocol tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
+func (e *endpoint) WritePackets(r stack.RouteInfo, pkts stack.PacketBufferList, protocol tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
 	enqueued := 0
 	for pkt := pkts.Front(); pkt != nil; {
 		d := e.dispatchers[int(pkt.Hash)%len(e.dispatchers)]
diff --git a/pkg/tcpip/link/sharedmem/sharedmem.go b/pkg/tcpip/link/sharedmem/sharedmem.go
index d8d0b16b2..df9a0b90a 100644
--- a/pkg/tcpip/link/sharedmem/sharedmem.go
+++ b/pkg/tcpip/link/sharedmem/sharedmem.go
@@ -203,7 +203,7 @@ func (e *endpoint) AddHeader(local, remote tcpip.LinkAddress, protocol tcpip.Net
 
 // WritePacket writes outbound packets to the file descriptor. If it is not
 // currently writable, the packet is dropped.
-func (e *endpoint) WritePacket(r stack.RouteInfo, _ *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
+func (e *endpoint) WritePacket(r stack.RouteInfo, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
 	e.AddHeader(r.LocalLinkAddress, r.RemoteLinkAddress, protocol, pkt)
 
 	views := pkt.Views()
@@ -220,7 +220,7 @@ func (e *endpoint) WritePacket(r stack.RouteInfo, _ *stack.GSO, protocol tcpip.N
 }
 
 // WritePackets implements stack.LinkEndpoint.WritePackets.
-func (*endpoint) WritePackets(stack.RouteInfo, *stack.GSO, stack.PacketBufferList, tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
+func (*endpoint) WritePackets(stack.RouteInfo, stack.PacketBufferList, tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
 	panic("not implemented")
 }
 
diff --git a/pkg/tcpip/link/sharedmem/sharedmem_test.go b/pkg/tcpip/link/sharedmem/sharedmem_test.go
index d4b3ddd5c..0f72d4e95 100644
--- a/pkg/tcpip/link/sharedmem/sharedmem_test.go
+++ b/pkg/tcpip/link/sharedmem/sharedmem_test.go
@@ -281,7 +281,7 @@ func TestSimpleSend(t *testing.T) {
 			copy(pkt.NetworkHeader().Push(hdrLen), hdrBuf)
 
 			proto := tcpip.NetworkProtocolNumber(rand.Intn(0x10000))
-			if err := c.ep.WritePacket(r, nil /* gso */, proto, pkt); err != nil {
+			if err := c.ep.WritePacket(r, proto, pkt); err != nil {
 				t.Fatalf("WritePacket failed: %v", err)
 			}
 
@@ -351,7 +351,7 @@ func TestPreserveSrcAddressInSend(t *testing.T) {
 	})
 
 	proto := tcpip.NetworkProtocolNumber(rand.Intn(0x10000))
-	if err := c.ep.WritePacket(r, nil /* gso */, proto, pkt); err != nil {
+	if err := c.ep.WritePacket(r, proto, pkt); err != nil {
 		t.Fatalf("WritePacket failed: %v", err)
 	}
 
@@ -407,7 +407,7 @@ func TestFillTxQueue(t *testing.T) {
 			Data:               buf.ToVectorisedView(),
 		})
 
-		if err := c.ep.WritePacket(r, nil /* gso */, header.IPv4ProtocolNumber, pkt); err != nil {
+		if err := c.ep.WritePacket(r, header.IPv4ProtocolNumber, pkt); err != nil {
 			t.Fatalf("WritePacket failed unexpectedly: %v", err)
 		}
 
@@ -425,7 +425,7 @@ func TestFillTxQueue(t *testing.T) {
 		ReserveHeaderBytes: int(c.ep.MaxHeaderLength()),
 		Data:               buf.ToVectorisedView(),
 	})
-	err := c.ep.WritePacket(r, nil /* gso */, header.IPv4ProtocolNumber, pkt)
+	err := c.ep.WritePacket(r, header.IPv4ProtocolNumber, pkt)
 	if _, ok := err.(*tcpip.ErrWouldBlock); !ok {
 		t.Fatalf("got WritePacket(...) = %v, want %s", err, &tcpip.ErrWouldBlock{})
 	}
@@ -453,7 +453,7 @@ func TestFillTxQueueAfterBadCompletion(t *testing.T) {
 			ReserveHeaderBytes: int(c.ep.MaxHeaderLength()),
 			Data:               buf.ToVectorisedView(),
 		})
-		if err := c.ep.WritePacket(r, nil /* gso */, header.IPv4ProtocolNumber, pkt); err != nil {
+		if err := c.ep.WritePacket(r, header.IPv4ProtocolNumber, pkt); err != nil {
 			t.Fatalf("WritePacket failed unexpectedly: %v", err)
 		}
 	}
@@ -476,7 +476,7 @@ func TestFillTxQueueAfterBadCompletion(t *testing.T) {
 			ReserveHeaderBytes: int(c.ep.MaxHeaderLength()),
 			Data:               buf.ToVectorisedView(),
 		})
-		if err := c.ep.WritePacket(r, nil /* gso */, header.IPv4ProtocolNumber, pkt); err != nil {
+		if err := c.ep.WritePacket(r, header.IPv4ProtocolNumber, pkt); err != nil {
 			t.Fatalf("WritePacket failed unexpectedly: %v", err)
 		}
 
@@ -494,7 +494,7 @@ func TestFillTxQueueAfterBadCompletion(t *testing.T) {
 		ReserveHeaderBytes: int(c.ep.MaxHeaderLength()),
 		Data:               buf.ToVectorisedView(),
 	})
-	err := c.ep.WritePacket(r, nil /* gso */, header.IPv4ProtocolNumber, pkt)
+	err := c.ep.WritePacket(r, header.IPv4ProtocolNumber, pkt)
 	if _, ok := err.(*tcpip.ErrWouldBlock); !ok {
 		t.Fatalf("got WritePacket(...) = %v, want %s", err, &tcpip.ErrWouldBlock{})
 	}
@@ -520,7 +520,7 @@ func TestFillTxMemory(t *testing.T) {
 			ReserveHeaderBytes: int(c.ep.MaxHeaderLength()),
 			Data:               buf.ToVectorisedView(),
 		})
-		if err := c.ep.WritePacket(r, nil /* gso */, header.IPv4ProtocolNumber, pkt); err != nil {
+		if err := c.ep.WritePacket(r, header.IPv4ProtocolNumber, pkt); err != nil {
 			t.Fatalf("WritePacket failed unexpectedly: %v", err)
 		}
 
@@ -539,7 +539,7 @@ func TestFillTxMemory(t *testing.T) {
 		ReserveHeaderBytes: int(c.ep.MaxHeaderLength()),
 		Data:               buf.ToVectorisedView(),
 	})
-	err := c.ep.WritePacket(r, nil /* gso */, header.IPv4ProtocolNumber, pkt)
+	err := c.ep.WritePacket(r, header.IPv4ProtocolNumber, pkt)
 	if _, ok := err.(*tcpip.ErrWouldBlock); !ok {
 		t.Fatalf("got WritePacket(...) = %v, want %s", err, &tcpip.ErrWouldBlock{})
 	}
@@ -566,7 +566,7 @@ func TestFillTxMemoryWithMultiBuffer(t *testing.T) {
 			ReserveHeaderBytes: int(c.ep.MaxHeaderLength()),
 			Data:               buf.ToVectorisedView(),
 		})
-		if err := c.ep.WritePacket(r, nil /* gso */, header.IPv4ProtocolNumber, pkt); err != nil {
+		if err := c.ep.WritePacket(r, header.IPv4ProtocolNumber, pkt); err != nil {
 			t.Fatalf("WritePacket failed unexpectedly: %v", err)
 		}
 
@@ -581,7 +581,7 @@ func TestFillTxMemoryWithMultiBuffer(t *testing.T) {
 			ReserveHeaderBytes: int(c.ep.MaxHeaderLength()),
 			Data:               buffer.NewView(bufferSize).ToVectorisedView(),
 		})
-		err := c.ep.WritePacket(r, nil /* gso */, header.IPv4ProtocolNumber, pkt)
+		err := c.ep.WritePacket(r, header.IPv4ProtocolNumber, pkt)
 		if _, ok := err.(*tcpip.ErrWouldBlock); !ok {
 			t.Fatalf("got WritePacket(...) = %v, want %s", err, &tcpip.ErrWouldBlock{})
 		}
@@ -593,7 +593,7 @@ func TestFillTxMemoryWithMultiBuffer(t *testing.T) {
 			ReserveHeaderBytes: int(c.ep.MaxHeaderLength()),
 			Data:               buf.ToVectorisedView(),
 		})
-		if err := c.ep.WritePacket(r, nil /* gso */, header.IPv4ProtocolNumber, pkt); err != nil {
+		if err := c.ep.WritePacket(r, header.IPv4ProtocolNumber, pkt); err != nil {
 			t.Fatalf("WritePacket failed unexpectedly: %v", err)
 		}
 	}
diff --git a/pkg/tcpip/link/sniffer/sniffer.go b/pkg/tcpip/link/sniffer/sniffer.go
index 7aaee3d13..2d6a3a833 100644
--- a/pkg/tcpip/link/sniffer/sniffer.go
+++ b/pkg/tcpip/link/sniffer/sniffer.go
@@ -139,7 +139,7 @@ func NewWithWriter(lower stack.LinkEndpoint, writer io.Writer, snapLen uint32) (
 // called by the link-layer endpoint being wrapped when a packet arrives, and
 // logs the packet before forwarding to the actual dispatcher.
 func (e *endpoint) DeliverNetworkPacket(remote, local tcpip.LinkAddress, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) {
-	e.dumpPacket(directionRecv, nil, protocol, pkt)
+	e.dumpPacket(directionRecv, protocol, pkt)
 	e.Endpoint.DeliverNetworkPacket(remote, local, protocol, pkt)
 }
 
@@ -148,10 +148,10 @@ func (e *endpoint) DeliverOutboundPacket(remote, local tcpip.LinkAddress, protoc
 	e.Endpoint.DeliverOutboundPacket(remote, local, protocol, pkt)
 }
 
-func (e *endpoint) dumpPacket(dir direction, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) {
+func (e *endpoint) dumpPacket(dir direction, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) {
 	writer := e.writer
 	if writer == nil && atomic.LoadUint32(&LogPackets) == 1 {
-		logPacket(e.logPrefix, dir, protocol, pkt, gso)
+		logPacket(e.logPrefix, dir, protocol, pkt)
 	}
 	if writer != nil && atomic.LoadUint32(&LogPacketsToPCAP) == 1 {
 		totalLength := pkt.Size()
@@ -187,22 +187,22 @@ func (e *endpoint) dumpPacket(dir direction, gso *stack.GSO, protocol tcpip.Netw
 // WritePacket implements the stack.LinkEndpoint interface. It is called by
 // higher-level protocols to write packets; it just logs the packet and
 // forwards the request to the lower endpoint.
-func (e *endpoint) WritePacket(r stack.RouteInfo, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
-	e.dumpPacket(directionSend, gso, protocol, pkt)
-	return e.Endpoint.WritePacket(r, gso, protocol, pkt)
+func (e *endpoint) WritePacket(r stack.RouteInfo, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
+	e.dumpPacket(directionSend, protocol, pkt)
+	return e.Endpoint.WritePacket(r, protocol, pkt)
 }
 
 // WritePackets implements the stack.LinkEndpoint interface. It is called by
 // higher-level protocols to write packets; it just logs the packet and
 // forwards the request to the lower endpoint.
-func (e *endpoint) WritePackets(r stack.RouteInfo, gso *stack.GSO, pkts stack.PacketBufferList, protocol tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
+func (e *endpoint) WritePackets(r stack.RouteInfo, pkts stack.PacketBufferList, protocol tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
 	for pkt := pkts.Front(); pkt != nil; pkt = pkt.Next() {
-		e.dumpPacket(directionSend, gso, protocol, pkt)
+		e.dumpPacket(directionSend, protocol, pkt)
 	}
-	return e.Endpoint.WritePackets(r, gso, pkts, protocol)
+	return e.Endpoint.WritePackets(r, pkts, protocol)
 }
 
-func logPacket(prefix string, dir direction, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer, gso *stack.GSO) {
+func logPacket(prefix string, dir direction, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) {
 	// Figure out the network layer info.
 	var transProto uint8
 	src := tcpip.Address("unknown")
@@ -411,8 +411,8 @@ func logPacket(prefix string, dir direction, protocol tcpip.NetworkProtocolNumbe
 		return
 	}
 
-	if gso != nil {
-		details += fmt.Sprintf(" gso: %+v", gso)
+	if pkt.GSOOptions.Type != stack.GSONone {
+		details += fmt.Sprintf(" gso: %#v", pkt.GSOOptions)
 	}
 
 	log.Infof("%s%s %s %s:%d -> %s:%d len:%d id:%04x %s", prefix, directionPrefix, transName, src, srcPort, dst, dstPort, size, id, details)
diff --git a/pkg/tcpip/link/waitable/waitable.go b/pkg/tcpip/link/waitable/waitable.go
index ce5113746..a95602aa5 100644
--- a/pkg/tcpip/link/waitable/waitable.go
+++ b/pkg/tcpip/link/waitable/waitable.go
@@ -108,12 +108,12 @@ func (e *Endpoint) LinkAddress() tcpip.LinkAddress {
 // WritePacket implements stack.LinkEndpoint.WritePacket. It is called by
 // higher-level protocols to write packets. It only forwards packets to the
 // lower endpoint if Wait or WaitWrite haven't been called.
-func (e *Endpoint) WritePacket(r stack.RouteInfo, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
+func (e *Endpoint) WritePacket(r stack.RouteInfo, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
 	if !e.writeGate.Enter() {
 		return nil
 	}
 
-	err := e.lower.WritePacket(r, gso, protocol, pkt)
+	err := e.lower.WritePacket(r, protocol, pkt)
 	e.writeGate.Leave()
 	return err
 }
@@ -121,12 +121,12 @@ func (e *Endpoint) WritePacket(r stack.RouteInfo, gso *stack.GSO, protocol tcpip
 // WritePackets implements stack.LinkEndpoint.WritePackets. It is called by
 // higher-level protocols to write packets. It only forwards packets to the
 // lower endpoint if Wait or WaitWrite haven't been called.
-func (e *Endpoint) WritePackets(r stack.RouteInfo, gso *stack.GSO, pkts stack.PacketBufferList, protocol tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
+func (e *Endpoint) WritePackets(r stack.RouteInfo, pkts stack.PacketBufferList, protocol tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
 	if !e.writeGate.Enter() {
 		return pkts.Len(), nil
 	}
 
-	n, err := e.lower.WritePackets(r, gso, pkts, protocol)
+	n, err := e.lower.WritePackets(r, pkts, protocol)
 	e.writeGate.Leave()
 	return n, err
 }
diff --git a/pkg/tcpip/link/waitable/waitable_test.go b/pkg/tcpip/link/waitable/waitable_test.go
index e368a9eaa..a71400ee9 100644
--- a/pkg/tcpip/link/waitable/waitable_test.go
+++ b/pkg/tcpip/link/waitable/waitable_test.go
@@ -69,13 +69,13 @@ func (e *countedEndpoint) LinkAddress() tcpip.LinkAddress {
 	return e.linkAddr
 }
 
-func (e *countedEndpoint) WritePacket(stack.RouteInfo, *stack.GSO, tcpip.NetworkProtocolNumber, *stack.PacketBuffer) tcpip.Error {
+func (e *countedEndpoint) WritePacket(stack.RouteInfo, tcpip.NetworkProtocolNumber, *stack.PacketBuffer) tcpip.Error {
 	e.writeCount++
 	return nil
 }
 
 // WritePackets implements stack.LinkEndpoint.WritePackets.
-func (e *countedEndpoint) WritePackets(_ stack.RouteInfo, _ *stack.GSO, pkts stack.PacketBufferList, _ tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
+func (e *countedEndpoint) WritePackets(_ stack.RouteInfo, pkts stack.PacketBufferList, _ tcpip.NetworkProtocolNumber) (int, tcpip.Error) {
 	e.writeCount += pkts.Len()
 	return pkts.Len(), nil
 }
@@ -98,21 +98,21 @@ func TestWaitWrite(t *testing.T) {
 	wep := New(ep)
 
 	// Write and check that it goes through.
-	wep.WritePacket(stack.RouteInfo{}, nil /* gso */, 0, stack.NewPacketBuffer(stack.PacketBufferOptions{}))
+	wep.WritePacket(stack.RouteInfo{}, 0, stack.NewPacketBuffer(stack.PacketBufferOptions{}))
 	if want := 1; ep.writeCount != want {
 		t.Fatalf("Unexpected writeCount: got=%v, want=%v", ep.writeCount, want)
 	}
 
 	// Wait on dispatches, then try to write. It must go through.
 	wep.WaitDispatch()
-	wep.WritePacket(stack.RouteInfo{}, nil /* gso */, 0, stack.NewPacketBuffer(stack.PacketBufferOptions{}))
+	wep.WritePacket(stack.RouteInfo{}, 0, stack.NewPacketBuffer(stack.PacketBufferOptions{}))
 	if want := 2; ep.writeCount != want {
 		t.Fatalf("Unexpected writeCount: got=%v, want=%v", ep.writeCount, want)
 	}
 
 	// Wait on writes, then try to write. It must not go through.
 	wep.WaitWrite()
-	wep.WritePacket(stack.RouteInfo{}, nil /* gso */, 0, stack.NewPacketBuffer(stack.PacketBufferOptions{}))
+	wep.WritePacket(stack.RouteInfo{}, 0, stack.NewPacketBuffer(stack.PacketBufferOptions{}))
 	if want := 2; ep.writeCount != want {
 		t.Fatalf("Unexpected writeCount: got=%v, want=%v", ep.writeCount, want)
 	}