netlink: add L2 bridge/bond/vlan intermediate drivers

This adds three new L2 (intermediate) drivers for bridge/bond/vlan.
Theses drivers are incomplete but illustrate how to stack L2 drivers.
Here are some examples of how these driver would stack with the cy243439
driver:

  Bridge: bridge two cyw43 devices together, connecting the two LANs:

	cyw43_0 := cyw43439.NewDevice(...)
	cyw43_1 := cyw43439.NewDevice(...)

	bridge := NewBridge([]netlink.Netlinker{cyw43_0, cyw43_1})

	stack := tcpip.NewStack(bridge)
	netdev.UseNetdev(stack)

  Bond: bond two cyw43 devices together, creating one logical device.
  The first physical device is primary, the second is backup (fail-over)
  device:

	cyw43_0 := cyw43439.NewDevice(...)  // primary
	cyw43_1 := cyw43439.NewDevice(...)  // secondary (backup)

	bond := NewBond([]netlink.Netlinker{cyw43_0, cyw43_1})

	stack := tcpip.NewStack(bond)
	netdev.UseNetdev(stack)

   Vlan: add tagged VLAN ID=100 to cyw43:

	cyw43 := cyw43439.NewDevice(...)

	vlan100 := NewVlan(100, cyw43)

	stack := tcpip.NewStack(vlan100)
	netdev.UseNetdev(stack)

netlink/bond.go

@@ -0,0 +1,15 @@
+package netlink
+
+// Bond aggregates links as one
+type Bond struct {
+	*Bridge
+}
+
+func NewBond(links []Netlinker) *Bond {
+	return &Bond{Bridge: NewBridge(links)}
+}
+
+func (b *Bond) SendEth(pkt []byte) error {
+	// Send Ethernet pkt to active link(s)
+	return nil
+}

netlink/bridge.go

@@ -0,0 +1,39 @@
+package netlink
+
+import (
+	"net"
+)
+
+// Bridge connects links into an Ethernet (L2) broadcast domain
+type Bridge struct {
+	ip      net.IP
+	links   []Netlinker
+	recvEth func([]byte) error
+}
+
+func NewBridge(links []Netlinker) *Bridge {
+	return &Bridge{links: links}
+}
+
+func (b *Bridge) NetConnect(params *ConnectParams) error {
+	return nil
+}
+
+func (b *Bridge) NetDisconnect() {
+}
+
+func (b *Bridge) NetNotify(cb func(Event)) {
+}
+
+func (b *Bridge) GetHardwareAddr() (net.HardwareAddr, error) {
+	return net.HardwareAddr{}, nil
+}
+
+func (b *Bridge) SendEth(pkt []byte) error {
+	// L2 Forward ethernet pkt to zero of more []links
+	return nil
+}
+
+func (b *Bridge) RecvEthFunc(cb func(pkt []byte) error) {
+	b.recvEth = cb
+}

netlink/netlink.go

@@ -99,5 +99,5 @@ type Netlinker interface {
 
 	// RecvEth callback function for receiving Ethernet pkt
 	// TODO describe content of pkt
-	RecvEthFunc(func(pkt []byte) error)
+	RecvEthFunc(cb func(pkt []byte) error)
 }

netlink/vlan.go

@@ -0,0 +1,41 @@
+package netlink
+
+import (
+	"net"
+)
+
+// Vlan is a virtual LAN
+type Vlan struct {
+	ip net.IP
+	// Vlan ID
+	id      uint16
+	link    Netlinker
+	recvEth func([]byte) error
+}
+
+func NewVlan(id uint16, link Netlinker) *Vlan {
+	return &Vlan{id: id, link: link}
+}
+
+func (v *Vlan) NetConnect(params *ConnectParams) error {
+	return nil
+}
+
+func (v *Vlan) NetDisconnect() {
+}
+
+func (v *Vlan) NetNotify(cb func(Event)) {
+}
+
+func (v *Vlan) GetHardwareAddr() (net.HardwareAddr, error) {
+	return net.HardwareAddr{}, nil
+}
+
+func (v *Vlan) SendEth(pkt []byte) error {
+	// Prepend VLAN hdr to pkt and send on link
+	return nil
+}
+
+func (v *Vlan) RecvEthFunc(cb func(pkt []byte) error) {
+	v.recvEth = cb
+}