systemd: add SetUnified for direct cgroupfs writes bypassing dbus

systemd/systemd_test.go

@@ -3,6 +3,7 @@ package systemd
 import (
 	"os"
 	"reflect"
+	"strings"
 	"testing"
 
 	systemdDbus "github.com/coreos/go-systemd/v22/dbus"
@@ -97,6 +98,82 @@ func TestUnitExistsIgnored(t *testing.T) {
 	}
 }
 
+func TestSetUnified(t *testing.T) {
+	if !IsRunningSystemd() {
+		t.Skip("Test requires systemd.")
+	}
+	if !cgroups.IsCgroup2UnifiedMode() {
+		t.Skip("Test requires cgroup v2.")
+	}
+	if os.Geteuid() != 0 {
+		t.Skip("Test requires root.")
+	}
+
+	testCases := []struct {
+		name     string
+		file     string
+		setVal   string
+		clearVal string
+	}{
+		{
+			name:     "memory.min",
+			file:     "memory.min",
+			setVal:   "4096",
+			clearVal: "0",
+		},
+		{
+			name:     "memory.low",
+			file:     "memory.low",
+			setVal:   "4096",
+			clearVal: "0",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			config := &cgroups.Cgroup{
+				Parent: "system.slice",
+				Name:   "system-runc_test_set_unified_" + tc.name + ".slice",
+				Resources: &cgroups.Resources{
+					Unified: map[string]string{tc.file: tc.setVal},
+				},
+			}
+			m, err := NewUnifiedManager(config, "")
+			if err != nil {
+				t.Fatal(err)
+			}
+			t.Cleanup(func() { _ = m.Destroy() })
+
+			if err := m.Apply(-1); err != nil {
+				t.Fatal(err)
+			}
+			if err := m.Set(config.Resources); err != nil {
+				t.Fatal(err)
+			}
+
+			val, err := cgroups.ReadFile(m.Path(""), tc.file)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if v := strings.TrimSpace(val); v != tc.setVal {
+				t.Fatalf("after Set: expected %s=%s, got %q", tc.file, tc.setVal, v)
+			}
+
+			if err := m.SetUnified(map[string]string{tc.file: tc.clearVal}); err != nil {
+				t.Fatal(err)
+			}
+
+			val, err = cgroups.ReadFile(m.Path(""), tc.file)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if v := strings.TrimSpace(val); v != tc.clearVal {
+				t.Fatalf("after SetUnified: expected %s=%s, got %q", tc.file, tc.clearVal, v)
+			}
+		})
+	}
+}
+
 func TestUnifiedResToSystemdProps(t *testing.T) {
 	if !IsRunningSystemd() {
 		t.Skip("Test requires systemd.")

systemd/v2.go

@@ -516,6 +516,19 @@ func (m *UnifiedManager) Set(r *cgroups.Resources) error {
 	return m.fsMgr.Set(r)
 }
 
+// SetUnified writes unified cgroup v2 resource values directly to cgroupfs,
+// bypassing systemd's SetUnitProperties. This avoids the side effect where
+// systemd may reset unrelated cgroup properties when processing a property
+// update via dbus.
+func (m *UnifiedManager) SetUnified(unified map[string]string) error {
+	for k, v := range unified {
+		if err := cgroups.WriteFileByLine(m.path, k, v); err != nil {
+			return fmt.Errorf("unable to set unified resource %q: %w", k, err)
+		}
+	}
+	return nil
+}
+
 func (m *UnifiedManager) GetPaths() map[string]string {
 	paths := make(map[string]string, 1)
 	paths[""] = m.path