Add read/write lock in the fault handler (#4309)

* Add read/write lock in the fault injection handler

* Remove ENI ID which is used for RWMutex

* Add a comment

agent/handlers/task_server_setup.go

@@ -196,10 +196,7 @@ func registerFaultHandlers(
 	agentState *v4.TMDSAgentState,
 	metricsFactory metrics.EntryFactory,
 ) {
-	handler := fault.FaultHandler{
-		AgentState:     agentState,
-		MetricsFactory: metricsFactory,
-	}
+	handler := fault.New(agentState, metricsFactory)
 
 	if muxRouter == nil {
 		return

agent/handlers/v4/tmdsstate.go

@@ -161,7 +161,12 @@ func (s *TMDSAgentState) getTaskMetadata(v3EndpointID string, includeTags bool)
 					Path: task.GetNetworkNamespace(),
 					NetworkInterfaces: []*tmdsv4.NetworkInterface{
 						{
-							DeviceName: "",
+							// TODO: fetch the correct device name.
+							// We are exposing this information via AgentState to facilitate the fault injection
+							// handler to start/stop/check network faults.
+							// Use 'eth0'(a fake value) for existing fault injection related unit tests for now and
+							// it will be updated in the future.
+							DeviceName: "eth0",
 						},
 					},
 				},