Address comment of local_ip_detector_linux.go

pkg/agent/controller/egress/local_ip_detector_linux.go

@@ -69,6 +69,17 @@ func (d *localIPDetector) notify(ip string, added bool) {
 }
 
 func (d *localIPDetector) listAndWatchIPAddresses(stopCh <-chan struct{}) {
+	// Subscribe IP address update before listing existing IP addresses to prevent event loss.
+	ch := make(chan netlink.AddrUpdate)
+	if err := netlink.AddrSubscribeWithOptions(ch, stopCh, netlink.AddrSubscribeOptions{
+		ErrorCallback: func(err error) {
+			klog.Errorf("Received error from IP address update subscription: %v", err)
+		},
+	}); err != nil {
+		klog.Errorf("Failed to subscribe IP address update: %v", err)
+		return
+	}
+
 	// List existing IP addresses first.
 	addresses, err := netlink.AddrList(nil, netlink.FAMILY_ALL)
 	if err != nil {
@@ -98,21 +109,6 @@ func (d *localIPDetector) listAndWatchIPAddresses(stopCh <-chan struct{}) {
 		d.notify(addr, false)
 	}
 
-	// Subscribe IP address update.
-	// TODO: It's unlikely but possible that an IP is removed or added in-between the list and the watch calls, in which
-	// situation the update will be missing. Ideally we should subscribe the update with the option ListExisting to
-	// avoid it. However, "HasSynced" would not be deterministic as the subscribe function doesn't have a mechanism to
-	// notify that the list call is done yet. This should be fixed once the subscribe function is improved.
-	ch := make(chan netlink.AddrUpdate)
-	if err := netlink.AddrSubscribeWithOptions(ch, stopCh, netlink.AddrSubscribeOptions{
-		ErrorCallback: func(err error) {
-			klog.Errorf("Received error from IP address update subscription: %v", err)
-		},
-	}); err != nil {
-		klog.Errorf("Failed to subscribe IP address update: %v", err)
-		return
-	}
-
 	for {
 		select {
 		case <-stopCh:
@@ -126,11 +122,15 @@ func (d *localIPDetector) listAndWatchIPAddresses(stopCh <-chan struct{}) {
 			ip := addrUpdate.LinkAddress.IP.String()
 			d.mutex.Lock()
 			if addrUpdate.NewAddr {
-				d.localIPs.Insert(ip)
-				d.notify(ip, true)
+				if !d.localIPs.Has(ip) {
+					d.localIPs.Insert(ip)
+					d.notify(ip, true)
+				}
 			} else {
-				d.localIPs.Delete(ip)
-				d.notify(ip, false)
+				if d.localIPs.Has(ip) {
+					d.localIPs.Delete(ip)
+					d.notify(ip, false)
+				}
 			}
 			d.mutex.Unlock()
 		}