Provide MTU for pipe LinkEndpoint

...so that callers can set different MTUs for different configurations.

PiperOrigin-RevId: 416629560

pkg/tcpip/link/pipe/pipe.go

@@ -26,12 +26,14 @@ import (
 var _ stack.LinkEndpoint = (*Endpoint)(nil)
 
 // New returns both ends of a new pipe.
-func New(linkAddr1, linkAddr2 tcpip.LinkAddress) (*Endpoint, *Endpoint) {
+func New(linkAddr1, linkAddr2 tcpip.LinkAddress, mtu uint32) (*Endpoint, *Endpoint) {
 	ep1 := &Endpoint{
 		linkAddr: linkAddr1,
+		mtu:      mtu,
 	}
 	ep2 := &Endpoint{
 		linkAddr: linkAddr2,
+		mtu:      mtu,
 	}
 	ep1.linked = ep2
 	ep2.linked = ep1
@@ -43,6 +45,7 @@ type Endpoint struct {
 	dispatcher stack.NetworkDispatcher
 	linked     *Endpoint
 	linkAddr   tcpip.LinkAddress
+	mtu        uint32
 }
 
 func (e *Endpoint) deliverPackets(r stack.RouteInfo, proto tcpip.NetworkProtocolNumber, pkts stack.PacketBufferList) {
@@ -96,8 +99,8 @@ func (e *Endpoint) IsAttached() bool {
 func (*Endpoint) Wait() {}
 
 // MTU implements stack.LinkEndpoint.
-func (*Endpoint) MTU() uint32 {
-	return header.IPv6MinimumMTU
+func (e *Endpoint) MTU() uint32 {
+	return e.mtu
 }
 
 // Capabilities implements stack.LinkEndpoint.

pkg/tcpip/tests/integration/istio_test.go

@@ -113,7 +113,7 @@ var (
 
 func newTestContext(t *testing.T) *testContext {
 	t.Helper()
-	localNIC, remoteNIC := pipe.New("" /* linkAddr1 */, "" /* linkAddr2 */)
+	localNIC, remoteNIC := pipe.New("" /* linkAddr1 */, "" /* linkAddr2 */, header.IPv4MinimumMTU)
 
 	localStack := stack.New(stack.Options{
 		NetworkProtocols:   []stack.NetworkProtocolFactory{ipv4.NewProtocol},

pkg/tcpip/tests/integration/link_resolution_test.go

@@ -44,10 +44,12 @@ import (
 )
 
 func setupStack(t *testing.T, stackOpts stack.Options, host1NICID, host2NICID tcpip.NICID) (*stack.Stack, *stack.Stack) {
+	const maxFrameSize = header.IPv6MinimumMTU + header.EthernetMinimumSize
+
 	host1Stack := stack.New(stackOpts)
 	host2Stack := stack.New(stackOpts)
 
-	host1NIC, host2NIC := pipe.New(utils.LinkAddr1, utils.LinkAddr2)
+	host1NIC, host2NIC := pipe.New(utils.LinkAddr1, utils.LinkAddr2, maxFrameSize)
 
 	if err := host1Stack.CreateNIC(host1NICID, utils.NewEthernetEndpoint(host1NIC)); err != nil {
 		t.Fatalf("host1Stack.CreateNIC(%d, _): %s", host1NICID, err)

pkg/tcpip/tests/utils/utils.go

@@ -279,8 +279,9 @@ func SetupRouterStack(t *testing.T, s *stack.Stack, ep1, ep2 stack.LinkEndpoint)
 // SetupRoutedStacks creates the NICs, sets forwarding, adds addresses and sets
 // the route tables for the passed stacks.
 func SetupRoutedStacks(t *testing.T, host1Stack, routerStack, host2Stack *stack.Stack) {
-	host1NIC, routerNIC1 := pipe.New(LinkAddr1, LinkAddr2)
-	routerNIC2, host2NIC := pipe.New(LinkAddr3, LinkAddr4)
+	const maxFrameSize = header.IPv6MinimumMTU + header.EthernetMinimumSize
+	host1NIC, routerNIC1 := pipe.New(LinkAddr1, LinkAddr2, maxFrameSize)
+	routerNIC2, host2NIC := pipe.New(LinkAddr3, LinkAddr4, maxFrameSize)
 
 	SetupRouterStack(t, routerStack, NewEthernetEndpoint(routerNIC1), NewEthernetEndpoint(routerNIC2))