Update {LinkEndpoint,NetworkEndpoint}#WritePacket to take a VectorisedView

Makes it possible to avoid copying or allocating in cases where DeliverNetworkPacket (rx)
needs to turn around and call WritePacket (tx) with its VectorisedView.

Also removes the restriction on having VectorisedViews with multiple views in the write path.

PiperOrigin-RevId: 211728717
Change-Id: Ie03a65ecb4e28bd15ebdb9c69f05eced18fdfcff

3 files changed, 22 insertions, 32 deletions

diff --git a/pkg/tcpip/transport/tcp/connect.go b/pkg/tcpip/transport/tcp/connect.go
index 558dbc50a..de5f963cf 100644
--- a/pkg/tcpip/transport/tcp/connect.go
+++ b/pkg/tcpip/transport/tcp/connect.go
@@ -166,7 +166,7 @@ func (h *handshake) checkAck(s *segment) bool {
 		// incoming segment acknowledges something not yet sent. The
 		// connection remains in the same state.
 		ack := s.sequenceNumber.Add(s.logicalLen())
-		h.ep.sendRaw(nil, flagRst|flagAck, s.ackNumber, ack, 0)
+		h.ep.sendRaw(buffer.VectorisedView{}, flagRst|flagAck, s.ackNumber, ack, 0)
 		return false
 	}
 
@@ -214,7 +214,7 @@ func (h *handshake) synSentState(s *segment) *tcpip.Error {
 	// and the handshake is completed.
 	if s.flagIsSet(flagAck) {
 		h.state = handshakeCompleted
-		h.ep.sendRaw(nil, flagAck, h.iss+1, h.ackNum, h.rcvWnd>>h.effectiveRcvWndScale())
+		h.ep.sendRaw(buffer.VectorisedView{}, flagAck, h.iss+1, h.ackNum, h.rcvWnd>>h.effectiveRcvWndScale())
 		return nil
 	}
 
@@ -263,7 +263,7 @@ func (h *handshake) synRcvdState(s *segment) *tcpip.Error {
 		if s.flagIsSet(flagAck) {
 			seq = s.ackNumber
 		}
-		h.ep.sendRaw(nil, flagRst|flagAck, seq, ack, 0)
+		h.ep.sendRaw(buffer.VectorisedView{}, flagRst|flagAck, seq, ack, 0)
 
 		if !h.active {
 			return tcpip.ErrInvalidEndpointState
@@ -563,14 +563,14 @@ func sendSynTCP(r *stack.Route, id stack.TransportEndpointID, flags byte, seq, a
 	}
 
 	options := makeSynOptions(opts)
-	err := sendTCPWithOptions(r, id, nil, flags, seq, ack, rcvWnd, options)
+	err := sendTCPWithOptions(r, id, buffer.VectorisedView{}, flags, seq, ack, rcvWnd, options)
 	putOptions(options)
 	return err
 }
 
 // sendTCPWithOptions sends a TCP segment with the provided options via the
 // provided network endpoint and under the provided identity.
-func sendTCPWithOptions(r *stack.Route, id stack.TransportEndpointID, data buffer.View, flags byte, seq, ack seqnum.Value, rcvWnd seqnum.Size, opts []byte) *tcpip.Error {
+func sendTCPWithOptions(r *stack.Route, id stack.TransportEndpointID, data buffer.VectorisedView, flags byte, seq, ack seqnum.Value, rcvWnd seqnum.Size, opts []byte) *tcpip.Error {
 	optLen := len(opts)
 	// Allocate a buffer for the TCP header.
 	hdr := buffer.NewPrependable(header.TCPMinimumSize + int(r.MaxHeaderLength()) + optLen)
@@ -594,11 +594,10 @@ func sendTCPWithOptions(r *stack.Route, id stack.TransportEndpointID, data buffe
 
 	// Only calculate the checksum if offloading isn't supported.
 	if r.Capabilities()&stack.CapabilityChecksumOffload == 0 {
-		length := uint16(hdr.UsedLength())
+		length := uint16(hdr.UsedLength() + data.Size())
 		xsum := r.PseudoHeaderChecksum(ProtocolNumber)
-		if data != nil {
-			length += uint16(len(data))
-			xsum = header.Checksum(data, xsum)
+		for _, v := range data.Views() {
+			xsum = header.Checksum(v, xsum)
 		}
 
 		tcp.SetChecksum(^tcp.CalculateChecksum(xsum, length))
@@ -614,7 +613,7 @@ func sendTCPWithOptions(r *stack.Route, id stack.TransportEndpointID, data buffe
 
 // sendTCP sends a TCP segment via the provided network endpoint and under the
 // provided identity.
-func sendTCP(r *stack.Route, id stack.TransportEndpointID, data buffer.View, flags byte, seq, ack seqnum.Value, rcvWnd seqnum.Size) *tcpip.Error {
+func sendTCP(r *stack.Route, id stack.TransportEndpointID, payload buffer.VectorisedView, flags byte, seq, ack seqnum.Value, rcvWnd seqnum.Size) *tcpip.Error {
 	// Allocate a buffer for the TCP header.
 	hdr := buffer.NewPrependable(header.TCPMinimumSize + int(r.MaxHeaderLength()))
 
@@ -636,11 +635,10 @@ func sendTCP(r *stack.Route, id stack.TransportEndpointID, data buffer.View, fla
 
 	// Only calculate the checksum if offloading isn't supported.
 	if r.Capabilities()&stack.CapabilityChecksumOffload == 0 {
-		length := uint16(hdr.UsedLength())
+		length := uint16(hdr.UsedLength() + payload.Size())
 		xsum := r.PseudoHeaderChecksum(ProtocolNumber)
-		if data != nil {
-			length += uint16(len(data))
-			xsum = header.Checksum(data, xsum)
+		for _, v := range payload.Views() {
+			xsum = header.Checksum(v, xsum)
 		}
 
 		tcp.SetChecksum(^tcp.CalculateChecksum(xsum, length))
@@ -651,7 +649,7 @@ func sendTCP(r *stack.Route, id stack.TransportEndpointID, data buffer.View, fla
 		r.Stats().TCP.ResetsSent.Increment()
 	}
 
-	return r.WritePacket(&hdr, data, ProtocolNumber)
+	return r.WritePacket(&hdr, payload, ProtocolNumber)
 }
 
 // makeOptions makes an options slice.
@@ -694,7 +692,7 @@ func (e *endpoint) makeOptions(sackBlocks []header.SACKBlock) []byte {
 }
 
 // sendRaw sends a TCP segment to the endpoint's peer.
-func (e *endpoint) sendRaw(data buffer.View, flags byte, seq, ack seqnum.Value, rcvWnd seqnum.Size) *tcpip.Error {
+func (e *endpoint) sendRaw(data buffer.VectorisedView, flags byte, seq, ack seqnum.Value, rcvWnd seqnum.Size) *tcpip.Error {
 	var sackBlocks []header.SACKBlock
 	if e.state == stateConnected && e.rcv.pendingBufSize > 0 && (flags&flagAck != 0) {
 		sackBlocks = e.sack.Blocks[:e.sack.NumBlocks]
@@ -751,7 +749,7 @@ func (e *endpoint) handleClose() *tcpip.Error {
 // state with the given error code. This method must only be called from the
 // protocol goroutine.
 func (e *endpoint) resetConnectionLocked(err *tcpip.Error) {
-	e.sendRaw(nil, flagAck|flagRst, e.snd.sndUna, e.rcv.rcvNxt, 0)
+	e.sendRaw(buffer.VectorisedView{}, flagAck|flagRst, e.snd.sndUna, e.rcv.rcvNxt, 0)
 
 	e.state = stateError
 	e.hardError = err
@@ -851,7 +849,7 @@ func (e *endpoint) keepaliveTimerExpired() *tcpip.Error {
 	// seg.seq = snd.nxt-1.
 	e.keepalive.unacked++
 	e.keepalive.Unlock()
-	e.snd.sendSegment(nil, flagAck, e.snd.sndNxt-1)
+	e.snd.sendSegment(buffer.VectorisedView{}, flagAck, e.snd.sndNxt-1)
 	e.resetKeepaliveTimer(false)
 	return nil
 }
diff --git a/pkg/tcpip/transport/tcp/protocol.go b/pkg/tcpip/transport/tcp/protocol.go
index 194d3f41d..006b2f074 100644
--- a/pkg/tcpip/transport/tcp/protocol.go
+++ b/pkg/tcpip/transport/tcp/protocol.go
@@ -147,7 +147,7 @@ func replyWithReset(s *segment) {
 
 	ack := s.sequenceNumber.Add(s.logicalLen())
 
-	sendTCP(&s.route, s.id, nil, flagRst|flagAck, seq, ack, 0)
+	sendTCP(&s.route, s.id, buffer.VectorisedView{}, flagRst|flagAck, seq, ack, 0)
 }
 
 // SetOption implements TransportProtocol.SetOption.
diff --git a/pkg/tcpip/transport/tcp/snd.go b/pkg/tcpip/transport/tcp/snd.go
index e4fa89912..284e720c6 100644
--- a/pkg/tcpip/transport/tcp/snd.go
+++ b/pkg/tcpip/transport/tcp/snd.go
@@ -270,7 +270,7 @@ func (s *sender) updateMaxPayloadSize(mtu, count int) {
 
 // sendAck sends an ACK segment.
 func (s *sender) sendAck() {
-	s.sendSegment(nil, flagAck, s.sndNxt)
+	s.sendSegment(buffer.VectorisedView{}, flagAck, s.sndNxt)
 }
 
 // updateRTO updates the retransmit timeout when a new roud-trip time is
@@ -305,7 +305,7 @@ func (s *sender) resendSegment() {
 
 	// Resend the segment.
 	if seg := s.writeList.Front(); seg != nil {
-		s.sendSegment(&seg.data, seg.flags, seg.sequenceNumber)
+		s.sendSegment(seg.data, seg.flags, seg.sequenceNumber)
 	}
 }
 
@@ -419,7 +419,7 @@ func (s *sender) sendData() {
 			segEnd = seg.sequenceNumber.Add(seqnum.Size(seg.data.Size()))
 		}
 
-		s.sendSegment(&seg.data, seg.flags, seg.sequenceNumber)
+		s.sendSegment(seg.data, seg.flags, seg.sequenceNumber)
 
 		// Update sndNxt if we actually sent new data (as opposed to
 		// retransmitting some previously sent data).
@@ -642,7 +642,7 @@ func (s *sender) handleRcvdSegment(seg *segment) {
 
 // sendSegment sends a new segment containing the given payload, flags and
 // sequence number.
-func (s *sender) sendSegment(data *buffer.VectorisedView, flags byte, seq seqnum.Value) *tcpip.Error {
+func (s *sender) sendSegment(data buffer.VectorisedView, flags byte, seq seqnum.Value) *tcpip.Error {
 	s.lastSendTime = time.Now()
 	if seq == s.rttMeasureSeqNum {
 		s.rttMeasureTime = s.lastSendTime
@@ -653,13 +653,5 @@ func (s *sender) sendSegment(data *buffer.VectorisedView, flags byte, seq seqnum
 	// Remember the max sent ack.
 	s.maxSentAck = rcvNxt
 
-	if data == nil {
-		return s.ep.sendRaw(nil, flags, seq, rcvNxt, rcvWnd)
-	}
-
-	if len(data.Views()) > 1 {
-		panic("send path does not support views with multiple buffers")
-	}
-
-	return s.ep.sendRaw(data.First(), flags, seq, rcvNxt, rcvWnd)
+	return s.ep.sendRaw(data, flags, seq, rcvNxt, rcvWnd)
 }