Avoid writing configuration files when they already exist on wicked a…

…nd (#410)

NetworkManager, nits in netplan

google_guest_agent/network/manager/netplan_linux.go

@@ -154,7 +154,7 @@ func (n netplan) IsManaging(ctx context.Context, iface string) (bool, error) {
 		if errors.Is(err, exec.ErrNotFound) {
 			return false, nil
 		}
-		return false, fmt.Errorf("error looking up dhclient path: %v", err)
+		return false, fmt.Errorf("error looking up netplan path: %v", err)
 	}
 	return true, nil
 }
@@ -186,7 +186,7 @@ func (n netplan) SetupEthernetInterface(ctx context.Context, config *cfg.Section
 		return fmt.Errorf("error reloading systemd-networkd network configs: %v", err)
 	}
 
-	// Avoid restarting systemd-networkd.
+	// Avoid restarting netplan.
 	if err := run.Quiet(ctx, "netplan", "apply"); err != nil {
 		return fmt.Errorf("error applying netplan changes: %w", err)
 	}

google_guest_agent/network/manager/network_manager_linux.go

@@ -204,14 +204,17 @@ func (n networkManager) writeNetworkManagerConfigs(ifaces []string) ([]string, e
 			return []string{}, fmt.Errorf("error updating permissions for %s connection config: %v", iface, err)
 		}
 
+		// Clean up the files written by the old agent. Make sure they're managed
+		// by the agent before deleting them.
 		ifcfgFilePath := n.ifcfgFilePath(iface)
-		_, err := os.Stat(ifcfgFilePath)
-		if err != nil {
-			if !os.IsNotExist(err) {
-				return nil, fmt.Errorf("failed to stat ifcfg file(%s): %v", ifcfgFilePath, err)
-			}
-		} else {
-			if err := os.Remove(ifcfgFilePath); err != nil {
+		contents, err := os.ReadFile(ifcfgFilePath)
+		if err != nil && !os.IsNotExist(err) {
+			return nil, fmt.Errorf("failed to read ifcfg file(%s): %v", ifcfgFilePath, err)
+		}
+
+		// Check for the google comment.
+		if strings.Contains(string(contents), "# Added by Google Compute Engine OS Login.") {
+			if err = os.Remove(ifcfgFilePath); err != nil {
 				return nil, fmt.Errorf("failed to remove previously managed ifcfg file(%s): %v", ifcfgFilePath, err)
 			}
 		}

google_guest_agent/network/manager/wicked_linux.go

@@ -226,23 +226,28 @@ func (n wicked) writeEthernetConfigs(ifaces []string) error {
 	// Write the config for all the non-primary network interfaces.
 	for _, iface := range ifaces {
 		logger.Debugf("write enabling ifcfg-%s config", iface)
-
-		var ifcfg *os.File
-
-		ifcfg, err := os.Create(n.ifcfgFilePath(iface))
-		if err != nil {
-			return err
+		ifcfg := n.ifcfgFilePath(iface)
+
+		// Avoid writing the configuration file if the configuration already exists.
+		if _, err := os.Stat(ifcfg); err != nil {
+			if os.IsNotExist(err) {
+				logger.Debugf("%s already exists, skipping", ifcfg)
+				continue
+			}
+			return fmt.Errorf("error getting config file %s: %v", ifcfg, err)
 		}
-		defer ifcfg.Close()
+
 		contents := []string{
 			googleComment,
 			"STARTMODE=hotplug",
 			// NOTE: 'dhcp' is the dhcp4+dhcp6 option.
 			"BOOTPROTO=dhcp",
 			fmt.Sprintf("DHCLIENT_ROUTE_PRIORITY=%d", priority),
 		}
-		_, err = ifcfg.WriteString(strings.Join(contents, "\n"))
-		if err != nil {
+		contentBytes := []byte(strings.Join(contents, "\n"))
+
+		// Write the file.
+		if err := os.WriteFile(ifcfg, contentBytes, 0644); err != nil {
 			return fmt.Errorf("error writing config file for %s: %v", iface, err)
 		}
 		priority += 100