2 files changed, 30 insertions, 2 deletions
diff --git a/pkg/subsystem/service.go b/pkg/subsystem/service.go
index d8c144cc4..24f86dd54 100644
--- a/pkg/subsystem/service.go
+++ b/pkg/subsystem/service.go
@@ -9,7 +9,8 @@ import (
 
 type Service struct {
 	*Extractor
-	perName map[string]*Subsystem
+	perName   map[string]*Subsystem
+	perParent map[*Subsystem][]*Subsystem
 }
 
 func MustMakeService(list []*Subsystem) *Service {
@@ -26,6 +27,7 @@ func MustMakeService(list []*Subsystem) *Service {
 func MakeService(list []*Subsystem) (*Service, error) {
 	extractor := MakeExtractor(list)
 	perName := map[string]*Subsystem{}
+	perParent := map[*Subsystem][]*Subsystem{}
 	for _, item := range list {
 		if item.Name == "" {
 			return nil, fmt.Errorf("input contains a subsystem without a name")
@@ -34,11 +36,14 @@ func MakeService(list []*Subsystem) (*Service, error) {
 			return nil, fmt.Errorf("collision on %#v name", item.Name)
 		}
 		perName[item.Name] = item
+		for _, p := range item.Parents {
+			perParent[p] = append(perParent[p], item)
+		}
 	}
-
 	return &Service{
 		Extractor: extractor,
 		perName:   perName,
+		perParent: perParent,
 	}, nil
 }
 
@@ -53,3 +58,7 @@ func (s *Service) List() []*Subsystem {
 	}
 	return ret
 }
+
+func (s *Service) Children(parent *Subsystem) []*Subsystem {
+	return append([]*Subsystem{}, s.perParent[parent]...)
+}
diff --git a/pkg/subsystem/service_test.go b/pkg/subsystem/service_test.go
new file mode 100644
index 000000000..2a95b9558
--- /dev/null
+++ b/pkg/subsystem/service_test.go
@@ -0,0 +1,19 @@
+// Copyright 2023 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package subsystem
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestServiceChildren(t *testing.T) {
+	unrelated := &Subsystem{Name: "unrelated"}
+	parent := &Subsystem{Name: "parent"}
+	childA := &Subsystem{Name: "childA", Parents: []*Subsystem{parent}}
+	childB := &Subsystem{Name: "childB", Parents: []*Subsystem{parent}}
+	service := MustMakeService([]*Subsystem{unrelated, parent, childA, childB})
+	assert.ElementsMatch(t, service.Children(parent), []*Subsystem{childA, childB})
+}