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

2 files changed, 18 insertions, 19 deletions

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)
 	}