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, 15 insertions, 16 deletions

diff --git a/pkg/tcpip/network/ipv6/icmp.go b/pkg/tcpip/network/ipv6/icmp.go
index e3ef89d26..b18b78830 100644
--- a/pkg/tcpip/network/ipv6/icmp.go
+++ b/pkg/tcpip/network/ipv6/icmp.go
@@ -62,6 +62,7 @@ func (e *endpoint) handleControl(typ stack.ControlType, extra uint32, vv *buffer
 	e.dispatcher.DeliverTransportControlPacket(e.id.LocalAddress, h.DestinationAddress(), ProtocolNumber, p, typ, extra, vv)
 }
 
+// TODO: take buffer.VectorisedView by value.
 func (e *endpoint) handleICMP(r *stack.Route, vv *buffer.VectorisedView) {
 	v := vv.First()
 	if len(v) < header.ICMPv6MinimumSize {
@@ -105,8 +106,8 @@ func (e *endpoint) handleICMP(r *stack.Route, vv *buffer.VectorisedView) {
 		pkt[icmpV6OptOffset] = ndpOptDstLinkAddr
 		pkt[icmpV6LengthOffset] = 1
 		copy(pkt[icmpV6LengthOffset+1:], r.LocalLinkAddress[:])
-		pkt.SetChecksum(icmpChecksum(pkt, r.LocalAddress, r.RemoteAddress, nil))
-		r.WritePacket(&hdr, nil, header.ICMPv6ProtocolNumber)
+		pkt.SetChecksum(icmpChecksum(pkt, r.LocalAddress, r.RemoteAddress, buffer.VectorisedView{}))
+		r.WritePacket(&hdr, buffer.VectorisedView{}, header.ICMPv6ProtocolNumber)
 
 		e.linkAddrCache.AddLinkAddress(e.nicid, r.RemoteAddress, r.RemoteLinkAddress)
 
@@ -125,13 +126,12 @@ func (e *endpoint) handleICMP(r *stack.Route, vv *buffer.VectorisedView) {
 			return
 		}
 		vv.TrimFront(header.ICMPv6EchoMinimumSize)
-		data := vv.ToView()
 		hdr := buffer.NewPrependable(int(r.MaxHeaderLength()) + header.IPv6MinimumSize + header.ICMPv6EchoMinimumSize)
 		pkt := header.ICMPv6(hdr.Prepend(header.ICMPv6EchoMinimumSize))
 		copy(pkt, h)
 		pkt.SetType(header.ICMPv6EchoReply)
-		pkt.SetChecksum(icmpChecksum(pkt, r.LocalAddress, r.RemoteAddress, data))
-		r.WritePacket(&hdr, data, header.ICMPv6ProtocolNumber)
+		pkt.SetChecksum(icmpChecksum(pkt, r.LocalAddress, r.RemoteAddress, *vv))
+		r.WritePacket(&hdr, *vv, header.ICMPv6ProtocolNumber)
 
 	case header.ICMPv6EchoReply:
 		if len(v) < header.ICMPv6EchoMinimumSize {
@@ -185,7 +185,7 @@ func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, linkEP stack.
 	pkt[icmpV6OptOffset] = ndpOptSrcLinkAddr
 	pkt[icmpV6LengthOffset] = 1
 	copy(pkt[icmpV6LengthOffset+1:], linkEP.LinkAddress())
-	pkt.SetChecksum(icmpChecksum(pkt, r.LocalAddress, r.RemoteAddress, nil))
+	pkt.SetChecksum(icmpChecksum(pkt, r.LocalAddress, r.RemoteAddress, buffer.VectorisedView{}))
 
 	length := uint16(hdr.UsedLength())
 	ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
@@ -197,7 +197,7 @@ func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, linkEP stack.
 		DstAddr:       r.RemoteAddress,
 	})
 
-	return linkEP.WritePacket(r, &hdr, nil, ProtocolNumber)
+	return linkEP.WritePacket(r, &hdr, buffer.VectorisedView{}, ProtocolNumber)
 }
 
 // ResolveStaticAddress implements stack.LinkAddressResolver.
@@ -205,15 +205,17 @@ func (*protocol) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bo
 	return "", false
 }
 
-func icmpChecksum(h header.ICMPv6, src, dst tcpip.Address, data []byte) uint16 {
+func icmpChecksum(h header.ICMPv6, src, dst tcpip.Address, vv buffer.VectorisedView) uint16 {
 	// Calculate the IPv6 pseudo-header upper-layer checksum.
 	xsum := header.Checksum([]byte(src), 0)
 	xsum = header.Checksum([]byte(dst), xsum)
 	var upperLayerLength [4]byte
-	binary.BigEndian.PutUint32(upperLayerLength[:], uint32(len(h)+len(data)))
+	binary.BigEndian.PutUint32(upperLayerLength[:], uint32(len(h)+vv.Size()))
 	xsum = header.Checksum(upperLayerLength[:], xsum)
 	xsum = header.Checksum([]byte{0, 0, 0, uint8(header.ICMPv6ProtocolNumber)}, xsum)
-	xsum = header.Checksum(data, xsum)
+	for _, v := range vv.Views() {
+		xsum = header.Checksum(v, xsum)
+	}
 
 	// h[2:4] is the checksum itself, set it aside to avoid checksumming the checksum.
 	h2, h3 := h[2], h[3]
diff --git a/pkg/tcpip/network/ipv6/icmp_test.go b/pkg/tcpip/network/ipv6/icmp_test.go
index 582bbb40e..e9f400fe4 100644
--- a/pkg/tcpip/network/ipv6/icmp_test.go
+++ b/pkg/tcpip/network/ipv6/icmp_test.go
@@ -186,7 +186,7 @@ func TestLinkResolution(t *testing.T) {
 	hdr := buffer.NewPrependable(int(r.MaxHeaderLength()) + header.IPv6MinimumSize + header.ICMPv6EchoMinimumSize)
 	pkt := header.ICMPv6(hdr.Prepend(header.ICMPv6EchoMinimumSize))
 	pkt.SetType(header.ICMPv6EchoRequest)
-	pkt.SetChecksum(icmpChecksum(pkt, r.LocalAddress, r.RemoteAddress, nil))
+	pkt.SetChecksum(icmpChecksum(pkt, r.LocalAddress, r.RemoteAddress, buffer.VectorisedView{}))
 	payload := tcpip.SlicePayload(hdr.UsedBytes())
 
 	// We can't send our payload directly over the route because that
diff --git a/pkg/tcpip/network/ipv6/ipv6.go b/pkg/tcpip/network/ipv6/ipv6.go
index cdb8284a2..19dc1b49e 100644
--- a/pkg/tcpip/network/ipv6/ipv6.go
+++ b/pkg/tcpip/network/ipv6/ipv6.go
@@ -82,11 +82,8 @@ func (e *endpoint) MaxHeaderLength() uint16 {
 }
 
 // WritePacket writes a packet to the given destination address and protocol.
-func (e *endpoint) WritePacket(r *stack.Route, hdr *buffer.Prependable, payload buffer.View, protocol tcpip.TransportProtocolNumber) *tcpip.Error {
-	length := uint16(hdr.UsedLength())
-	if payload != nil {
-		length += uint16(len(payload))
-	}
+func (e *endpoint) WritePacket(r *stack.Route, hdr *buffer.Prependable, payload buffer.VectorisedView, protocol tcpip.TransportProtocolNumber) *tcpip.Error {
+	length := uint16(hdr.UsedLength() + payload.Size())
 	ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 	ip.Encode(&header.IPv6Fields{
 		PayloadLength: length,