services/core/java/com/android/server/om/OverlayManagerService.java

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * 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 com.android.server.om;

import static android.app.AppGlobals.getPackageManager;
import static android.content.Intent.ACTION_PACKAGE_ADDED;
import static android.content.Intent.ACTION_PACKAGE_CHANGED;
import static android.content.Intent.ACTION_PACKAGE_REMOVED;
import static android.content.Intent.ACTION_USER_REMOVED;
import static android.content.pm.PackageManager.SIGNATURE_MATCH;

import android.annotation.NonNull;
import android.annotation.Nullable;
import android.app.ActivityManager;
import android.app.IActivityManager;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.om.IOverlayManager;
import android.content.om.OverlayInfo;
import android.content.pm.IPackageManager;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManagerInternal;
import android.content.pm.UserInfo;
import android.net.Uri;
import android.os.Binder;
import android.os.Environment;
import android.os.IBinder;
import android.os.RemoteException;
import android.os.ResultReceiver;
import android.os.ShellCallback;
import android.os.UserHandle;
import android.util.ArrayMap;
import android.util.AtomicFile;
import android.util.Slog;
import android.util.SparseArray;

import com.android.server.FgThread;
import com.android.server.IoThread;
import com.android.server.LocalServices;
import com.android.server.SystemService;
import com.android.server.pm.Installer;
import com.android.server.pm.UserManagerService;

import org.xmlpull.v1.XmlPullParserException;

import java.io.File;
import java.io.FileDescriptor;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * Service to manage asset overlays.
 *
 * <p>Asset overlays are additional resources that come from apks loaded
 * alongside the system and app apks. This service, the OverlayManagerService
 * (OMS), tracks which installed overlays to use and provides methods to change
 * this. Changes propagate to running applications as part of the Activity
 * lifecycle. This allows Activities to reread their resources at a well
 * defined point.</p>
 *
 * <p>By itself, the OMS will not change what overlays should be active.
 * Instead, it is only responsible for making sure that overlays *can* be used
 * from a technical and security point of view and to activate overlays in
 * response to external requests. The responsibility to toggle overlays on and
 * off lies within components that implement different use-cases such as themes
 * or dynamic customization.</p>
 *
 * <p>The OMS receives input from three sources:</p>
 *
 * <ul>
 *     <li>Callbacks from the SystemService class, specifically when the
 *     Android framework is booting and when the end user switches Android
 *     users.</li>
 *
 *     <li>Intents from the PackageManagerService (PMS). Overlays are regular
 *     apks, and whenever a package is installed (or removed, or has a
 *     component enabled or disabled), the PMS broadcasts this as an intent.
 *     When the OMS receives one of these intents, it updates its internal
 *     representation of the available overlays and, if there was a visible
 *     change, triggers an asset refresh in the affected apps.</li>
 *
 *     <li>External requests via the {@link IOverlayManager AIDL interface}.
 *     The interface allows clients to read information about the currently
 *     available overlays, change whether an overlay should be used or not, and
 *     change the relative order in which overlay packages are loaded.
 *     Read-access is granted if the request targets the same Android user as
 *     the caller runs as, or if the caller holds the
 *     INTERACT_ACROSS_USERS_FULL permission. Write-access is granted if the
 *     caller is granted read-access and additionaly holds the
 *     CHANGE_OVERLAY_PACKAGES permission.</li>
 * </ul>
 *
 * <p>The AIDL interface works with String package names, int user IDs, and
 * {@link OverlayInfo} objects. OverlayInfo instances are used to track a
 * specific pair of target and overlay packages and include information such as
 * the current state of the overlay. OverlayInfo objects are immutable.</p>
 *
 * <p>Internally, OverlayInfo objects are maintained by the
 * OverlayManagerSettings class. The OMS and its helper classes are notified of
 * changes to the settings by the OverlayManagerSettings.ChangeListener
 * callback interface. The file /data/system/overlays.xml is used to persist
 * the settings.</p>
 *
 * <p>Creation and deletion of idmap files are handled by the IdmapManager
 * class.</p>
 *
 * <p>The following is an overview of OMS and its related classes. Note how box
 * (2) does the heavy lifting, box (1) interacts with the Android framework,
 * and box (3) replaces box (1) during unit testing.</p>
 *
 * <pre>
 *         Android framework
 *            |         ^
 *      . . . | . . . . | . . . .
 *     .      |         |       .
 *     .    AIDL,   broadcasts  .
 *     .   intents      |       .
 *     .      |         |       . . . . . . . . . . . .
 *     .      v         |       .                     .
 *     .  OverlayManagerService . OverlayManagerTests .
 *     .                  \     .     /               .
 *     . (1)               \    .    /            (3) .
 *      . . . . . . . . . . \ . . . / . . . . . . . . .
 *     .                     \     /              .
 *     . (2)                  \   /               .
 *     .           OverlayManagerServiceImpl      .
 *     .                  |            |          .
 *     .                  |            |          .
 *     . OverlayManagerSettings     IdmapManager  .
 *     .                                          .
 *     . . . .  . . . . . . . . . . . . . . . . . .
 * </pre>
 *
 * <p>Finally, here is a list of keywords used in the OMS context.</p>
 *
 * <ul>
 *     <li><b>target [package]</b> -- A regular apk that may have its resource
 *     pool extended  by zero or more overlay packages.</li>
 *
 *     <li><b>overlay [package]</b> -- An apk that provides additional
 *     resources to another apk.</li>
 *
 *     <li><b>OMS</b> -- The OverlayManagerService, i.e. this class.</li>
 *
 *     <li><b>approved</b> -- An overlay is approved if the OMS has verified
 *     that it can be used technically speaking (its target package is
 *     installed, at least one resource name in both packages match, the
 *     idmap was created, etc) and that it is secure to do so. External
 *     clients can not change this state.</li>
 *
 *     <li><b>not approved</b> -- The opposite of approved.</li>
 *
 *     <li><b>enabled</b> -- An overlay currently in active use and thus part
 *     of resource lookups. This requires the overlay to be approved. Only
 *     external clients can change this state.</li>
 *
 *     <li><b>disabled</b> -- The opposite of enabled.</li>
 *
 *     <li><b>idmap</b> -- A mapping of resource IDs between target and overlay
 *     used during resource lookup. Also the name of the binary that creates
 *     the mapping.</li>
 * </ul>
 */
public final class OverlayManagerService extends SystemService {

    static final String TAG = "OverlayManager";

    static final boolean DEBUG = false;

    static final String PERMISSION_DENIED = "Operation not permitted for user shell";

    private final Object mLock = new Object();

    private final AtomicFile mSettingsFile;

    private final PackageManagerHelper mPackageManager;

    private final UserManagerService mUserManager;

    private final OverlayManagerSettings mSettings;

    private final OverlayManagerServiceImpl mImpl;

    private final AtomicBoolean mPersistSettingsScheduled = new AtomicBoolean(false);

    public OverlayManagerService(@NonNull final Context context,
            @NonNull final Installer installer) {
        super(context);
        mSettingsFile =
            new AtomicFile(new File(Environment.getDataSystemDirectory(), "overlays.xml"));
        mPackageManager = new PackageManagerHelper();
        mUserManager = UserManagerService.getInstance();
        IdmapManager im = new IdmapManager(installer);
        mSettings = new OverlayManagerSettings();
        mImpl = new OverlayManagerServiceImpl(mPackageManager, im, mSettings);

        final IntentFilter packageFilter = new IntentFilter();
        packageFilter.addAction(ACTION_PACKAGE_ADDED);
        packageFilter.addAction(ACTION_PACKAGE_CHANGED);
        packageFilter.addAction(ACTION_PACKAGE_REMOVED);
        packageFilter.addDataScheme("package");
        getContext().registerReceiverAsUser(new PackageReceiver(), UserHandle.ALL,
                packageFilter, null, null);

        final IntentFilter userFilter = new IntentFilter();
        userFilter.addAction(ACTION_USER_REMOVED);
        getContext().registerReceiverAsUser(new UserReceiver(), UserHandle.ALL,
                userFilter, null, null);

        restoreSettings();
        onSwitchUser(UserHandle.USER_SYSTEM);
        schedulePersistSettings();

        mSettings.addChangeListener(new OverlayChangeListener());

        publishBinderService(Context.OVERLAY_SERVICE, mService);
        publishLocalService(OverlayManagerService.class, this);
    }

    @Override
    public void onStart() {
        // Intentionally left empty.
    }

    @Override
    public void onSwitchUser(final int newUserId) {
        // ensure overlays in the settings are up-to-date, and propagate
        // any asset changes to the rest of the system
        final List<String> targets;
        synchronized (mLock) {
            targets = mImpl.onSwitchUser(newUserId);
        }
        updateAssets(newUserId, targets);
    }

    private final class PackageReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(@NonNull final Context context, @NonNull final Intent intent) {
            final Uri data = intent.getData();
            if (data == null) {
                Slog.e(TAG, "Cannot handle package broadcast with null data");
                return;
            }
            final String packageName = data.getSchemeSpecificPart();

            final boolean replacing = intent.getBooleanExtra(Intent.EXTRA_REPLACING, false);

            final int[] userIds;
            final int extraUid = intent.getIntExtra(Intent.EXTRA_UID, UserHandle.USER_NULL);
            if (extraUid == UserHandle.USER_NULL) {
                userIds = mUserManager.getUserIds();
            } else {
                userIds = new int[] { UserHandle.getUserId(extraUid) };
            }

            switch (intent.getAction()) {
                case ACTION_PACKAGE_ADDED:
                    if (replacing) {
                        onPackageUpgraded(packageName, userIds);
                    } else {
                        onPackageAdded(packageName, userIds);
                    }
                    break;
                case ACTION_PACKAGE_CHANGED:
                    onPackageChanged(packageName, userIds);
                    break;
                case ACTION_PACKAGE_REMOVED:
                    if (replacing) {
                        onPackageUpgrading(packageName, userIds);
                    } else {
                        onPackageRemoved(packageName, userIds);
                    }
                    break;
                default:
                    // do nothing
                    break;
            }
        }

        private void onPackageAdded(@NonNull final String packageName,
                @NonNull final int[] userIds) {
            for (final int userId : userIds) {
                synchronized (mLock) {
                    final PackageInfo pi = mPackageManager.getPackageInfo(packageName, userId, false);
                    if (pi != null) {
                        mPackageManager.cachePackageInfo(packageName, userId, pi);
                        if (!isOverlayPackage(pi)) {
                            mImpl.onTargetPackageAdded(packageName, userId);
                        } else {
                            mImpl.onOverlayPackageAdded(packageName, userId);
                        }
                    }
                }
            }
        }

        private void onPackageChanged(@NonNull final String packageName,
                @NonNull final int[] userIds) {
            for (int userId : userIds) {
                synchronized (mLock) {
                    final PackageInfo pi = mPackageManager.getPackageInfo(packageName, userId, false);
                    if (pi != null) {
                        mPackageManager.cachePackageInfo(packageName, userId, pi);
                        if (!isOverlayPackage(pi)) {
                            mImpl.onTargetPackageChanged(packageName, userId);
                        } else {
                            mImpl.onOverlayPackageChanged(packageName, userId);
                        }
                    }
                }
            }
        }

        private void onPackageUpgrading(@NonNull final String packageName,
                @NonNull final int[] userIds) {
            for (int userId : userIds) {
                synchronized (mLock) {
                    mPackageManager.forgetPackageInfo(packageName, userId);
                    final OverlayInfo oi = mImpl.getOverlayInfo(packageName, userId);
                    if (oi == null) {
                        mImpl.onTargetPackageUpgrading(packageName, userId);
                    } else {
                        mImpl.onOverlayPackageUpgrading(packageName, userId);
                    }
                }
            }
        }

        private void onPackageUpgraded(@NonNull final String packageName,
                @NonNull final int[] userIds) {
            for (int userId : userIds) {
                synchronized (mLock) {
                    final PackageInfo pi = mPackageManager.getPackageInfo(packageName, userId, false);
                    if (pi != null) {
                        mPackageManager.cachePackageInfo(packageName, userId, pi);
                        if (!isOverlayPackage(pi)) {
                            mImpl.onTargetPackageUpgraded(packageName, userId);
                        } else {
                            mImpl.onOverlayPackageUpgraded(packageName, userId);
                        }
                    }
                }
            }
        }

        private void onPackageRemoved(@NonNull final String packageName,
                @NonNull final int[] userIds) {
            for (int userId : userIds) {
                synchronized (mLock) {
                    mPackageManager.forgetPackageInfo(packageName, userId);
                    final OverlayInfo oi = mImpl.getOverlayInfo(packageName, userId);
                    if (oi == null) {
                        mImpl.onTargetPackageRemoved(packageName, userId);
                    } else {
                        mImpl.onOverlayPackageRemoved(packageName, userId);
                    }
                }
            }
        }
    }

    private final class UserReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(@NonNull final Context context, @NonNull final Intent intent) {
            switch (intent.getAction()) {
                case ACTION_USER_REMOVED:
                    final int userId =
                            intent.getIntExtra(Intent.EXTRA_USER_HANDLE, UserHandle.USER_NULL);
                    if (userId != UserHandle.USER_NULL) {
                        synchronized (mLock) {
                            mImpl.onUserRemoved(userId);
                            mPackageManager.forgetAllPackageInfos(userId);
                        }
                    }
                    break;
                default:
                    // do nothing
                    break;
            }
        }
    }

    private final IBinder mService = new IOverlayManager.Stub() {
        @Override
        public Map<String, List<OverlayInfo>> getAllOverlays(int userId)
                throws RemoteException {
            userId = handleIncomingUser(userId, "getAllOverlays");

            synchronized (mLock) {
                return mImpl.getOverlaysForUser(userId);
            }
        }

        @Override
        public List<OverlayInfo> getOverlayInfosForTarget(@Nullable final String targetPackageName,
                int userId) throws RemoteException {
            userId = handleIncomingUser(userId, "getOverlayInfosForTarget");
            if (targetPackageName == null) {
                return Collections.emptyList();
            }

            synchronized (mLock) {
                return mImpl.getOverlayInfosForTarget(targetPackageName, userId);
            }
        }

        @Override
        public OverlayInfo getOverlayInfo(@Nullable final String packageName,
                int userId) throws RemoteException {
            userId = handleIncomingUser(userId, "getOverlayInfo");
            if (packageName == null) {
                return null;
            }

            synchronized (mLock) {
                return mImpl.getOverlayInfo(packageName, userId);
            }
        }

        @Override
        public boolean setEnabled(@Nullable final String packageName, final boolean enable,
                int userId) throws RemoteException {
            enforceChangeOverlayPackagesPermission("setEnabled");
            userId = handleIncomingUser(userId, "setEnabled");
            if (packageName == null) {
                return false;
            }

            final long ident = Binder.clearCallingIdentity();
            try {
                synchronized (mLock) {
                    return mImpl.setEnabled(packageName, enable, userId);
                }
            } finally {
                Binder.restoreCallingIdentity(ident);
            }
        }

        @Override
        public boolean setPriority(@Nullable final String packageName,
                @Nullable final String parentPackageName, int userId) throws RemoteException {
            enforceChangeOverlayPackagesPermission("setPriority");
            userId = handleIncomingUser(userId, "setPriority");
            if (packageName == null || parentPackageName == null) {
                return false;
            }

            final long ident = Binder.clearCallingIdentity();
            try {
                synchronized (mLock) {
                    return mImpl.setPriority(packageName, parentPackageName, userId);
                }
            } finally {
                Binder.restoreCallingIdentity(ident);
            }
        }

        @Override
        public boolean setHighestPriority(@Nullable final String packageName, int userId)
                throws RemoteException {
            enforceChangeOverlayPackagesPermission("setHighestPriority");
            userId = handleIncomingUser(userId, "setHighestPriority");
            if (packageName == null) {
                return false;
            }

            final long ident = Binder.clearCallingIdentity();
            try {
                synchronized (mLock) {
                    return mImpl.setHighestPriority(packageName, userId);
                }
            } finally {
                Binder.restoreCallingIdentity(ident);
            }
        }

        @Override
        public boolean setLowestPriority(@Nullable final String packageName, int userId)
                throws RemoteException {
            enforceChangeOverlayPackagesPermission("setLowestPriority");
            userId = handleIncomingUser(userId, "setLowestPriority");
            if (packageName == null) {
                return false;
            }

            final long ident = Binder.clearCallingIdentity();
            try {
                synchronized (mLock) {
                    return mImpl.setLowestPriority(packageName, userId);
                }
            } finally {
                Binder.restoreCallingIdentity(ident);
            }
        }

        @Override
        public void onShellCommand(@NonNull final FileDescriptor in,
                @NonNull final FileDescriptor out, @NonNull final FileDescriptor err,
                @NonNull final String[] args, @NonNull final ShellCallback callback,
                @NonNull final ResultReceiver resultReceiver) {
            (new OverlayManagerShellCommand(this)).exec(
                    this, in, out, err, args, callback, resultReceiver);
        }

        @Override
        protected void dump(@NonNull final FileDescriptor fd, @NonNull final PrintWriter pw,
                @NonNull final String[] argv) {
            enforceDumpPermission("dump");

            final boolean verbose = argv.length > 0 && "--verbose".equals(argv[0]);

            synchronized (mLock) {
                mImpl.onDump(pw);
                mPackageManager.dump(pw, verbose);
            }
        }

        /**
         * Ensure that the caller has permission to interact with the given userId.
         * If the calling user is not the same as the provided user, the caller needs
         * to hold the INTERACT_ACROSS_USERS_FULL permission (or be system uid or
         * root).
         *
         * @param userId the user to interact with
         * @param message message for any SecurityException
         */
        private int handleIncomingUser(final int userId, @NonNull final String message) {
            return ActivityManager.handleIncomingUser(Binder.getCallingPid(),
                    Binder.getCallingUid(), userId, false, true, message, null);
        }

        /**
         * Enforce that the caller holds the CHANGE_OVERLAY_PACKAGES permission (or is
         * system or root).
         *
         * @param message used as message if SecurityException is thrown
         * @throws SecurityException if the permission check fails
         */
        private void enforceChangeOverlayPackagesPermission(@NonNull final String message) {
            getContext().enforceCallingOrSelfPermission(
                    android.Manifest.permission.CHANGE_OVERLAY_PACKAGES, message);
        }

        /**
         * Enforce that the caller holds the DUMP permission (or is system or root).
         *
         * @param message used as message if SecurityException is thrown
         * @throws SecurityException if the permission check fails
         */
        private void enforceDumpPermission(@NonNull final String message) {
            getContext().enforceCallingOrSelfPermission(android.Manifest.permission.DUMP,
                    message);
        }
    };

    private boolean isOverlayPackage(@NonNull final PackageInfo pi) {
        return pi != null && pi.overlayTarget != null;
    }

    private final class OverlayChangeListener implements OverlayManagerSettings.ChangeListener {
        @Override
        public void onSettingsChanged() {
            schedulePersistSettings();
        }

        @Override
        public void onOverlayAdded(@NonNull final OverlayInfo oi) {
            scheduleBroadcast(Intent.ACTION_OVERLAY_ADDED, oi, oi.isEnabled());
        }

        @Override
        public void onOverlayRemoved(@NonNull final OverlayInfo oi) {
            scheduleBroadcast(Intent.ACTION_OVERLAY_REMOVED, oi, oi.isEnabled());
        }

        @Override
        public void onOverlayChanged(@NonNull final OverlayInfo oi,
                @NonNull final OverlayInfo oldOi) {
            scheduleBroadcast(Intent.ACTION_OVERLAY_CHANGED, oi, oi.isEnabled() != oldOi.isEnabled());
        }

        @Override
        public void onOverlayPriorityChanged(@NonNull final OverlayInfo oi) {
            scheduleBroadcast(Intent.ACTION_OVERLAY_PRIORITY_CHANGED, oi, oi.isEnabled());
        }

        private void scheduleBroadcast(@NonNull final String action, @NonNull final OverlayInfo oi,
                final boolean doUpdate) {
            FgThread.getHandler().post(new BroadcastRunnable(action, oi, doUpdate));
        }

        private final class BroadcastRunnable implements Runnable {
            private final String mAction;
            private final OverlayInfo mOverlayInfo;
            private final boolean mDoUpdate;

            BroadcastRunnable(@NonNull final String action, @NonNull final OverlayInfo oi,
                    final boolean doUpdate) {
                mAction = action;
                mOverlayInfo = oi;
                mDoUpdate = doUpdate;
            }

            @Override
            public void run() {
                if (mDoUpdate) {
                    updateAssets(mOverlayInfo.userId, mOverlayInfo.targetPackageName);
                }
                sendBroadcast(mAction, mOverlayInfo.targetPackageName, mOverlayInfo.packageName,
                        mOverlayInfo.userId);
            }

            private void sendBroadcast(@NonNull final String action,
                    @NonNull final String targetPackageName, @NonNull final String packageName,
                    final int userId) {
                final Intent intent = new Intent(action, Uri.fromParts("package",
                            String.format("%s/%s", targetPackageName, packageName), null));
                intent.setFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
                if (DEBUG) {
                    Slog.d(TAG, String.format("send broadcast %s", intent));
                }
                try {
                    ActivityManager.getService().broadcastIntent(null, intent, null, null, 0,
                            null, null, null, android.app.AppOpsManager.OP_NONE, null, false, false,
                            userId);
                } catch (RemoteException e) {
                    // Intentionally left empty.
                }
            }

        }
    }

    private void updateAssets(final int userId, final String targetPackageName) {
        final List<String> list = new ArrayList<>();
        list.add(targetPackageName);
        updateAssets(userId, list);
    }

    private void updateAssets(final int userId, List<String> targetPackageNames) {
        final PackageManagerInternal pm = LocalServices.getService(PackageManagerInternal.class);
        final boolean updateFrameworkRes = targetPackageNames.contains("android");
        if (updateFrameworkRes) {
            targetPackageNames = pm.getTargetPackageNames(userId);
        }

        final Map<String, List<String>> pendingChanges = new ArrayMap<>(targetPackageNames.size());
        synchronized (mLock) {
            final int N = targetPackageNames.size();
            for (int i = 0; i < N; i++) {
                final String targetPackageName = targetPackageNames.get(i);
                pendingChanges.put(targetPackageName,
                        mImpl.getEnabledOverlayPackageNames(targetPackageName, userId));
            }
        }

        final int N = targetPackageNames.size();
        for (int i = 0; i < N; i++) {
            final String targetPackageName = targetPackageNames.get(i);
            if (!pm.setEnabledOverlayPackages(
                        userId, targetPackageName, pendingChanges.get(targetPackageName))) {
                Slog.e(TAG, String.format("Failed to change enabled overlays for %s user %d",
                            targetPackageName, userId));
            }
        }

        final IActivityManager am = ActivityManager.getService();
        try {
            am.scheduleApplicationInfoChanged(targetPackageNames, userId);
        } catch (RemoteException e) {
            // Intentionally left empty.
        }
    }

    private void schedulePersistSettings() {
        if (mPersistSettingsScheduled.getAndSet(true)) {
            return;
        }
        IoThread.getHandler().post(new Runnable() {
            @Override
            public void run() {
                mPersistSettingsScheduled.set(false);
                synchronized (mLock) {
                    FileOutputStream stream = null;
                    try {
                        stream = mSettingsFile.startWrite();
                        mSettings.persist(stream);
                        mSettingsFile.finishWrite(stream);
                    } catch (IOException | XmlPullParserException e) {
                        mSettingsFile.failWrite(stream);
                        Slog.e(TAG, "failed to persist overlay state", e);
                    }
                }
            }
        });
    }

    private void restoreSettings() {
        synchronized (mLock) {
            if (!mSettingsFile.getBaseFile().exists()) {
                return;
            }
            try (final FileInputStream stream = mSettingsFile.openRead()) {
                mSettings.restore(stream);

                // We might have data for dying users if the device was
                // restarted before we received USER_REMOVED. Remove data for
                // users that will not exist after the system is ready.

                final List<UserInfo> deadUsers = getDeadUsers();
                final int N = deadUsers.size();
                for (int i = 0; i < N; i++) {
                    final UserInfo deadUser = deadUsers.get(i);
                    final int userId = deadUser.getUserHandle().getIdentifier();
                    mSettings.removeUser(userId);
                }
            } catch (IOException | XmlPullParserException e) {
                Slog.e(TAG, "failed to restore overlay state", e);
            }
        }
    }

    private List<UserInfo> getDeadUsers() {
        final List<UserInfo> users = mUserManager.getUsers(false);
        final List<UserInfo> onlyLiveUsers = mUserManager.getUsers(true);
        users.removeAll(onlyLiveUsers);
        return users;
    }

    private static final class PackageManagerHelper implements
            OverlayManagerServiceImpl.PackageManagerHelper {

        private final IPackageManager mPackageManager;
        private final PackageManagerInternal mPackageManagerInternal;

        // Use a cache for performance and for consistency within OMS: because
        // additional PACKAGE_* intents may be delivered while we process an
        // intent, querying the PackageManagerService for the actual current
        // state may lead to contradictions within OMS. Better then to lag
        // behind until all pending intents have been processed.
        private final SparseArray<HashMap<String, PackageInfo>> mCache = new SparseArray<>();

        PackageManagerHelper() {
            mPackageManager = getPackageManager();
            mPackageManagerInternal = LocalServices.getService(PackageManagerInternal.class);
        }

        public PackageInfo getPackageInfo(@NonNull final String packageName, final int userId,
                final boolean useCache) {
            if (useCache) {
                final PackageInfo cachedPi = getCachedPackageInfo(packageName, userId);
                if (cachedPi != null) {
                    return cachedPi;
                }
            }
            try {
                final PackageInfo pi = mPackageManager.getPackageInfo(packageName, 0, userId);
                if (useCache && pi != null) {
                    cachePackageInfo(packageName, userId, pi);
                }
                return pi;
            } catch (RemoteException e) {
                // Intentionally left empty.
            }
            return null;
        }

        @Override
        public PackageInfo getPackageInfo(@NonNull final String packageName, final int userId) {
            return getPackageInfo(packageName, userId, true);
        }

        @Override
        public boolean signaturesMatching(@NonNull final String packageName1,
                @NonNull final String packageName2, final int userId) {
            // The package manager does not support different versions of packages
            // to be installed for different users: ignore userId for now.
            try {
                return mPackageManager.checkSignatures(packageName1, packageName2) == SIGNATURE_MATCH;
            } catch (RemoteException e) {
                // Intentionally left blank
            }
            return false;
        }

        @Override
        public List<PackageInfo> getOverlayPackages(final int userId) {
            return mPackageManagerInternal.getOverlayPackages(userId);
        }

        public PackageInfo getCachedPackageInfo(@NonNull final String packageName,
                final int userId) {
            final HashMap<String, PackageInfo> map = mCache.get(userId);
            return map == null ? null : map.get(packageName);
        }

        public void cachePackageInfo(@NonNull final String packageName, final int userId,
                @NonNull final PackageInfo pi) {
            HashMap<String, PackageInfo> map = mCache.get(userId);
            if (map == null) {
                map = new HashMap<>();
                mCache.put(userId, map);
            }
            map.put(packageName, pi);
        }

        public void forgetPackageInfo(@NonNull final String packageName, final int userId) {
            final HashMap<String, PackageInfo> map = mCache.get(userId);
            if (map == null) {
                return;
            }
            map.remove(packageName);
            if (map.isEmpty()) {
                mCache.delete(userId);
            }
        }

        public void forgetAllPackageInfos(final int userId) {
            mCache.delete(userId);
        }

        private static final String TAB1 = "    ";
        private static final String TAB2 = TAB1 + TAB1;

        public void dump(@NonNull final PrintWriter pw, final boolean verbose) {
            pw.println("PackageInfo cache");

            if (!verbose) {
                int count = 0;
                final int N = mCache.size();
                for (int i = 0; i < N; i++) {
                    final int userId = mCache.keyAt(i);
                    count += mCache.get(userId).size();
                }
                pw.println(TAB1 + count + " package(s)");
                return;
            }

            if (mCache.size() == 0) {
                pw.println(TAB1 + "<empty>");
                return;
            }

            final int N = mCache.size();
            for (int i = 0; i < N; i++) {
                final int userId = mCache.keyAt(i);
                pw.println(TAB1 + "User " + userId);
                final HashMap<String, PackageInfo> map = mCache.get(userId);
                for (Map.Entry<String, PackageInfo> entry : map.entrySet()) {
                    pw.println(TAB2 + entry.getKey() + ": " + entry.getValue());
                }
            }
        }
    }
}