source/local: implement new "local" custom rule

Makes it possible to write custom rules that match against labels from
feature files and hooks.

source/custom/custom.go

@@ -25,6 +25,7 @@ import (
 	"sigs.k8s.io/node-feature-discovery/source"
 	"sigs.k8s.io/node-feature-discovery/source/cpu"
 	"sigs.k8s.io/node-feature-discovery/source/kernel"
+	"sigs.k8s.io/node-feature-discovery/source/local"
 	"sigs.k8s.io/node-feature-discovery/source/pci"
 	"sigs.k8s.io/node-feature-discovery/source/system"
 	"sigs.k8s.io/node-feature-discovery/source/usb"
@@ -40,6 +41,7 @@ type MatchRule struct {
 	Nodename   *system.NodenameRule   `json:"nodename,omitempty"`
 	CPU        *cpu.CustomRule        `json:"cpu,omitempty"`
 	Kernel     *kernel.CustomRule     `json:"kernel,omitempty"`
+	Local      *local.CustomRule      `json:"local,omitempty"`
 	System     *system.CustomRule     `json:"system,omitempty"`
 }
 
@@ -128,6 +130,7 @@ func (s *customSource) discoverFeature(feature FeatureSpec) (bool, error) {
 			matchRules.Nodename,
 			matchRules.CPU,
 			matchRules.Kernel,
+			matchRules.Local,
 			matchRules.System,
 		}
 

source/local/custom_rule.go

@@ -0,0 +1,36 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package local
+
+import (
+	"k8s.io/klog/v2"
+
+	"sigs.k8s.io/node-feature-discovery/source"
+)
+
+// CustomRule implements the source.CustomRule interface
+type CustomRule struct {
+	Labels source.MatchExpressionSet
+}
+
+func (r *CustomRule) Match() (bool, error) {
+	if m, err := r.Labels.MatchValues(src.features.Labels); err != nil || m == false {
+		klog.V(2).Infof("local CustomRule: failed to match labels")
+		return m, err
+	}
+	return true, nil
+}