增加本地环回网卡设备实现

tcpip/link/loopback/loopback.go

@@ -0,0 +1,62 @@
+package loopback
+
+import (
+	"netstack/tcpip"
+	"netstack/tcpip/buffer"
+	"netstack/tcpip/stack"
+)
+
+type endpoint struct {
+	dispatcher stack.NetworkDispatcher
+}
+
+func New() tcpip.LinkEndpointID {
+	return stack.RegisterLinkEndpoint(&endpoint{})
+}
+
+func (e *endpoint) MTU() uint32 {
+	return 65536
+}
+
+// Capabilities返回链路层端点支持的功能集。
+func (e *endpoint) Capabilities() stack.LinkEndpointCapabilities {
+	return stack.CapabilityChecksumOffload | stack.CapabilitySaveRestore | stack.CapabilityLoopback
+}
+
+// MaxHeaderLength 返回数据链接（和较低级别的图层组合）标头可以具有的最大大小。
+// 较高级别使用此信息来保留它们正在构建的数据包前面预留空间。
+func (e *endpoint) MaxHeaderLength() uint16 {
+	return 0
+}
+
+// 本地链路层地址
+func (e *endpoint) LinkAddress() tcpip.LinkAddress {
+	return ""
+}
+
+// 要参与透明桥接，LinkEndpoint实现应调用eth.Encode，
+// 并将header.EthernetFields.SrcAddr设置为r.LocalLinkAddress（如果已提供）。
+func (e *endpoint) WritePacket(r *stack.Route, hdr buffer.Prependable, payload buffer.VectorisedView,
+	protocol tcpip.NetworkProtocolNumber) *tcpip.Error {
+	views := make([]buffer.View, 1, 1+len(payload.Views()))
+	views[0] = hdr.View()
+	views = append(views, payload.Views()...)
+	vv := buffer.NewVectorisedView(len(views[0])+payload.Size(), views)
+
+	// Because we're immediately turning around and writing the packet back to the
+	// rx path, we intentionally don't preserve the remote and local link
+	// addresses from the stack.Route we're passed.
+	e.dispatcher.DeliverNetworkPacket(e, "" /* remoteLinkAddr */, "" /* localLinkAddr */, protocol, vv)
+
+	return nil
+}
+
+// Attach 将数据链路层端点附加到协议栈的网络层调度程序。
+func (e *endpoint) Attach(dispatcher stack.NetworkDispatcher) {
+	e.dispatcher = dispatcher
+}
+
+// 是否已经添加了网络层调度器
+func (e *endpoint) IsAttached() bool {
+	return e.dispatcher != nil
+}