src/policy_manager/devicepolicy/dbus_notify.go

// Copyright 2021 Google LLC
//
// 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 devicepolicy

import (
	"fmt"
	"time"

	"github.com/godbus/dbus"
	"github.com/golang/glog"
)

const (
	sessionManagerObjectName = "org.chromium.SessionManager"
	sessionManagerObjectPath = "/org/chromium/SessionManager"
	propertyChangeSignal     = "org.chromium.SessionManagerInterface.PropertyChangeComplete"
)

// signalPropertyChange sends PropertyChangeComplete signal over
// system D-Bus on the SessionManager object.
//
// Normally in ChromiumOS this object is owned by login manager which
// is responsible for device policy updates. But because there is no
// login manager in GCI we can simulate that object and emit the same
// signal.
func signalPropertyChange() error {
	glog.V(1).Info("Sending PropertyChangeComplete signal...")

	conn, err := dbus.SystemBusPrivate()
	if err != nil {
		return err
	}
	defer conn.Close()
	if err = conn.Auth(nil); err != nil {
		return err
	}
	if err = conn.Hello(); err != nil {
		return err
	}
	reply, err := conn.RequestName(sessionManagerObjectName, dbus.NameFlagDoNotQueue)
	if err != nil {
		return err
	}
	if reply != dbus.RequestNameReplyPrimaryOwner {
		return fmt.Errorf("%s: name already taken", sessionManagerObjectName)
	}

	err = conn.Emit(sessionManagerObjectPath, propertyChangeSignal, "success")

	// After updating device policy we send a signal notifying update engine.
	// Due to a bug in dbus library that signal may be lost if the process
	// exits. The fix for that bug (https://github.com/godbus/dbus/pull/31)
	// has stalled, so we temporarily work around the bug by having this
	// sleep :(.
	time.Sleep(1 * time.Second)

	return err
}