Merge pull request #24421 from deads2k/fix-admission

Automatic merge from submit-queue

let admission plugins indicate they want nothing

An admission plugin can return `nil, nil` for construction.  This is useful for dealing with cases where the `config` passed to you effectively means, "no work".  The calling code already handles this.

@derekwaynecarr

pkg/admission/plugins.go

@@ -63,18 +63,19 @@ func RegisterPlugin(name string, plugin Factory) {
 	plugins[name] = plugin
 }
 
-// GetPlugin creates an instance of the named plugin, or nil if the name is not
-// known. The error is returned only when the named provider was known but failed
-// to initialize. The config parameter specifies the io.Reader handler of the
-// configuration file for the cloud provider, or nil for no configuration.
-func GetPlugin(name string, client clientset.Interface, config io.Reader) (Interface, error) {
+// getPlugin creates an instance of the named plugin.  It returns `false` if the
+// the name is not known. The error is returned only when the named provider was
+// known but failed to initialize.  The config parameter specifies the io.Reader
+// handler of the configuration file for the cloud provider, or nil for no configuration.
+func getPlugin(name string, client clientset.Interface, config io.Reader) (Interface, bool, error) {
 	pluginsMutex.Lock()
 	defer pluginsMutex.Unlock()
 	f, found := plugins[name]
 	if !found {
-		return nil, nil
+		return nil, false, nil
 	}
-	return f(client, config)
+	ret, err := f(client, config)
+	return ret, true, err
 }
 
 // InitPlugin creates an instance of the named interface.
@@ -99,11 +100,11 @@ func InitPlugin(name string, client clientset.Interface, configFilePath string)
 		defer config.Close()
 	}
 
-	plugin, err := GetPlugin(name, client, config)
+	plugin, found, err := getPlugin(name, client, config)
 	if err != nil {
 		glog.Fatalf("Couldn't init admission plugin %q: %v", name, err)
 	}
-	if plugin == nil {
+	if !found {
 		glog.Fatalf("Unknown admission plugin: %s", name)
 	}