packages/SettingsProvider/src/com/android/providers/settings/SettingsProvider.java

/*
 * Copyright (C) 2007 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.providers.settings;

import java.io.FileNotFoundException;
import java.security.SecureRandom;
import java.util.HashSet;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;

import android.app.ActivityManager;
import android.app.backup.BackupManager;
import android.content.BroadcastReceiver;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.pm.PackageManager;
import android.content.res.AssetFileDescriptor;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteQueryBuilder;
import android.media.RingtoneManager;
import android.net.Uri;
import android.os.Binder;
import android.os.Bundle;
import android.os.FileObserver;
import android.os.ParcelFileDescriptor;
import android.os.SystemProperties;
import android.os.UserHandle;
import android.os.UserManager;
import android.provider.DrmStore;
import android.provider.MediaStore;
import android.provider.Settings;
import android.text.TextUtils;
import android.util.Log;
import android.util.LruCache;
import android.util.Slog;
import android.util.SparseArray;

public class SettingsProvider extends ContentProvider {
    private static final String TAG = "SettingsProvider";
    private static final boolean LOCAL_LOGV = false;

    private static final String TABLE_SYSTEM = "system";
    private static final String TABLE_SECURE = "secure";
    private static final String TABLE_GLOBAL = "global";
    private static final String TABLE_FAVORITES = "favorites";
    private static final String TABLE_OLD_FAVORITES = "old_favorites";

    private static final String[] COLUMN_VALUE = new String[] { "value" };

    // Caches for each user's settings, access-ordered for acting as LRU.
    // Guarded by themselves.
    private static final int MAX_CACHE_ENTRIES = 200;
    private static final SparseArray<SettingsCache> sSystemCaches
            = new SparseArray<SettingsCache>();
    private static final SparseArray<SettingsCache> sSecureCaches
            = new SparseArray<SettingsCache>();
    private static final SettingsCache sGlobalCache = new SettingsCache(TABLE_GLOBAL);

    // The count of how many known (handled by SettingsProvider)
    // database mutations are currently being handled for this user.
    // Used by file observers to not reload the database when it's ourselves
    // modifying it.
    private static final SparseArray<AtomicInteger> sKnownMutationsInFlight
            = new SparseArray<AtomicInteger>();

    // Each defined user has their own settings
    protected final SparseArray<DatabaseHelper> mOpenHelpers = new SparseArray<DatabaseHelper>();

    // Over this size we don't reject loading or saving settings but
    // we do consider them broken/malicious and don't keep them in
    // memory at least:
    private static final int MAX_CACHE_ENTRY_SIZE = 500;

    private static final Bundle NULL_SETTING = Bundle.forPair("value", null);

    // Used as a sentinel value in an instance equality test when we
    // want to cache the existence of a key, but not store its value.
    private static final Bundle TOO_LARGE_TO_CACHE_MARKER = Bundle.forPair("_dummy", null);

    private UserManager mUserManager;
    private BackupManager mBackupManager;

    /**
     * Settings which need to be treated as global/shared in multi-user environments.
     */
    static final HashSet<String> sSecureGlobalKeys;
    static final HashSet<String> sSystemGlobalKeys;
    static {
        // Keys (name column) from the 'secure' table that are now in the owner user's 'global'
        // table, shared across all users
        // These must match Settings.Secure.MOVED_TO_GLOBAL
        sSecureGlobalKeys = new HashSet<String>();
        sSecureGlobalKeys.add(Settings.Global.ADB_ENABLED);
        sSecureGlobalKeys.add(Settings.Global.ASSISTED_GPS_ENABLED);
        sSecureGlobalKeys.add(Settings.Global.BLUETOOTH_ON);
        sSecureGlobalKeys.add(Settings.Global.CDMA_CELL_BROADCAST_SMS);
        sSecureGlobalKeys.add(Settings.Global.CDMA_ROAMING_MODE);
        sSecureGlobalKeys.add(Settings.Global.CDMA_SUBSCRIPTION_MODE);
        sSecureGlobalKeys.add(Settings.Global.DATA_ACTIVITY_TIMEOUT_MOBILE);
        sSecureGlobalKeys.add(Settings.Global.DATA_ACTIVITY_TIMEOUT_WIFI);
        sSecureGlobalKeys.add(Settings.Global.DATA_ROAMING);
        sSecureGlobalKeys.add(Settings.Global.DEVELOPMENT_SETTINGS_ENABLED);
        sSecureGlobalKeys.add(Settings.Global.DEVICE_PROVISIONED);
        sSecureGlobalKeys.add(Settings.Global.DISPLAY_DENSITY_FORCED);
        sSecureGlobalKeys.add(Settings.Global.DISPLAY_SIZE_FORCED);
        sSecureGlobalKeys.add(Settings.Global.DOWNLOAD_MAX_BYTES_OVER_MOBILE);
        sSecureGlobalKeys.add(Settings.Global.DOWNLOAD_RECOMMENDED_MAX_BYTES_OVER_MOBILE);
        sSecureGlobalKeys.add(Settings.Global.INSTALL_NON_MARKET_APPS);
        sSecureGlobalKeys.add(Settings.Global.MOBILE_DATA);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_DEV_BUCKET_DURATION);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_DEV_DELETE_AGE);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_DEV_PERSIST_BYTES);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_DEV_ROTATE_AGE);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_ENABLED);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_GLOBAL_ALERT_BYTES);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_POLL_INTERVAL);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_REPORT_XT_OVER_DEV);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_SAMPLE_ENABLED);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_TIME_CACHE_MAX_AGE);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_UID_BUCKET_DURATION);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_UID_DELETE_AGE);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_UID_PERSIST_BYTES);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_UID_ROTATE_AGE);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_UID_TAG_BUCKET_DURATION);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_UID_TAG_DELETE_AGE);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_UID_TAG_PERSIST_BYTES);
        sSecureGlobalKeys.add(Settings.Global.NETSTATS_UID_TAG_ROTATE_AGE);
        sSecureGlobalKeys.add(Settings.Global.NETWORK_PREFERENCE);
        sSecureGlobalKeys.add(Settings.Global.NITZ_UPDATE_DIFF);
        sSecureGlobalKeys.add(Settings.Global.NITZ_UPDATE_SPACING);
        sSecureGlobalKeys.add(Settings.Global.NTP_SERVER);
        sSecureGlobalKeys.add(Settings.Global.NTP_TIMEOUT);
        sSecureGlobalKeys.add(Settings.Global.PDP_WATCHDOG_ERROR_POLL_COUNT);
        sSecureGlobalKeys.add(Settings.Global.PDP_WATCHDOG_LONG_POLL_INTERVAL_MS);
        sSecureGlobalKeys.add(Settings.Global.PDP_WATCHDOG_MAX_PDP_RESET_FAIL_COUNT);
        sSecureGlobalKeys.add(Settings.Global.PDP_WATCHDOG_POLL_INTERVAL_MS);
        sSecureGlobalKeys.add(Settings.Global.PDP_WATCHDOG_TRIGGER_PACKET_COUNT);
        sSecureGlobalKeys.add(Settings.Global.SAMPLING_PROFILER_MS);
        sSecureGlobalKeys.add(Settings.Global.SETUP_PREPAID_DATA_SERVICE_URL);
        sSecureGlobalKeys.add(Settings.Global.SETUP_PREPAID_DETECTION_REDIR_HOST);
        sSecureGlobalKeys.add(Settings.Global.SETUP_PREPAID_DETECTION_TARGET_URL);
        sSecureGlobalKeys.add(Settings.Global.TETHER_DUN_APN);
        sSecureGlobalKeys.add(Settings.Global.TETHER_DUN_REQUIRED);
        sSecureGlobalKeys.add(Settings.Global.TETHER_SUPPORTED);
        sSecureGlobalKeys.add(Settings.Global.THROTTLE_HELP_URI);
        sSecureGlobalKeys.add(Settings.Global.THROTTLE_MAX_NTP_CACHE_AGE_SEC);
        sSecureGlobalKeys.add(Settings.Global.THROTTLE_NOTIFICATION_TYPE);
        sSecureGlobalKeys.add(Settings.Global.THROTTLE_POLLING_SEC);
        sSecureGlobalKeys.add(Settings.Global.THROTTLE_RESET_DAY);
        sSecureGlobalKeys.add(Settings.Global.THROTTLE_THRESHOLD_BYTES);
        sSecureGlobalKeys.add(Settings.Global.THROTTLE_VALUE_KBITSPS);
        sSecureGlobalKeys.add(Settings.Global.USB_MASS_STORAGE_ENABLED);
        sSecureGlobalKeys.add(Settings.Global.USE_GOOGLE_MAIL);
        sSecureGlobalKeys.add(Settings.Global.WEB_AUTOFILL_QUERY_URL);
        sSecureGlobalKeys.add(Settings.Global.WIFI_COUNTRY_CODE);
        sSecureGlobalKeys.add(Settings.Global.WIFI_FRAMEWORK_SCAN_INTERVAL_MS);
        sSecureGlobalKeys.add(Settings.Global.WIFI_FREQUENCY_BAND);
        sSecureGlobalKeys.add(Settings.Global.WIFI_IDLE_MS);
        sSecureGlobalKeys.add(Settings.Global.WIFI_MAX_DHCP_RETRY_COUNT);
        sSecureGlobalKeys.add(Settings.Global.WIFI_MOBILE_DATA_TRANSITION_WAKELOCK_TIMEOUT_MS);
        sSecureGlobalKeys.add(Settings.Global.WIFI_NETWORKS_AVAILABLE_NOTIFICATION_ON);
        sSecureGlobalKeys.add(Settings.Global.WIFI_NETWORKS_AVAILABLE_REPEAT_DELAY);
        sSecureGlobalKeys.add(Settings.Global.WIFI_NUM_OPEN_NETWORKS_KEPT);
        sSecureGlobalKeys.add(Settings.Global.WIFI_ON);
        sSecureGlobalKeys.add(Settings.Global.WIFI_P2P_DEVICE_NAME);
        sSecureGlobalKeys.add(Settings.Global.WIFI_SAVED_STATE);
        sSecureGlobalKeys.add(Settings.Global.WIFI_SUPPLICANT_SCAN_INTERVAL_MS);
        sSecureGlobalKeys.add(Settings.Global.WIFI_SUSPEND_OPTIMIZATIONS_ENABLED);
        sSecureGlobalKeys.add(Settings.Global.WIFI_WATCHDOG_NUM_ARP_PINGS);
        sSecureGlobalKeys.add(Settings.Global.WIFI_WATCHDOG_ON);
        sSecureGlobalKeys.add(Settings.Global.WIFI_WATCHDOG_POOR_NETWORK_TEST_ENABLED);
        sSecureGlobalKeys.add(Settings.Global.WIFI_WATCHDOG_RSSI_FETCH_INTERVAL_MS);
        sSecureGlobalKeys.add(Settings.Global.WIMAX_NETWORKS_AVAILABLE_NOTIFICATION_ON);
        sSecureGlobalKeys.add(Settings.Global.PACKAGE_VERIFIER_ENABLE);
        sSecureGlobalKeys.add(Settings.Global.PACKAGE_VERIFIER_TIMEOUT);
        sSecureGlobalKeys.add(Settings.Global.PACKAGE_VERIFIER_DEFAULT_RESPONSE);
        sSecureGlobalKeys.add(Settings.Global.DATA_STALL_ALARM_NON_AGGRESSIVE_DELAY_IN_MS);
        sSecureGlobalKeys.add(Settings.Global.DATA_STALL_ALARM_AGGRESSIVE_DELAY_IN_MS);
        sSecureGlobalKeys.add(Settings.Global.GPRS_REGISTER_CHECK_PERIOD_MS);
        sSecureGlobalKeys.add(Settings.Global.WTF_IS_FATAL);

        // Keys from the 'system' table now moved to 'global'
        // These must match Settings.System.MOVED_TO_GLOBAL
        sSystemGlobalKeys = new HashSet<String>();

        sSystemGlobalKeys.add(Settings.System.AIRPLANE_MODE_ON);
        sSystemGlobalKeys.add(Settings.System.AIRPLANE_MODE_RADIOS);
        sSystemGlobalKeys.add(Settings.System.AIRPLANE_MODE_TOGGLEABLE_RADIOS);
        sSystemGlobalKeys.add(Settings.System.AUTO_TIME);
        sSystemGlobalKeys.add(Settings.System.AUTO_TIME_ZONE);
        sSystemGlobalKeys.add(Settings.System.CAR_DOCK_SOUND);
        sSystemGlobalKeys.add(Settings.System.CAR_UNDOCK_SOUND);
        sSystemGlobalKeys.add(Settings.System.DESK_DOCK_SOUND);
        sSystemGlobalKeys.add(Settings.System.DESK_UNDOCK_SOUND);
        sSystemGlobalKeys.add(Settings.System.DOCK_SOUNDS_ENABLED);
        sSystemGlobalKeys.add(Settings.System.LOCK_SOUND);
        sSystemGlobalKeys.add(Settings.System.UNLOCK_SOUND);
        sSystemGlobalKeys.add(Settings.System.LOW_BATTERY_SOUND);
        sSystemGlobalKeys.add(Settings.System.POWER_SOUNDS_ENABLED);
        sSystemGlobalKeys.add(Settings.System.STAY_ON_WHILE_PLUGGED_IN);
        sSystemGlobalKeys.add(Settings.System.WIFI_SLEEP_POLICY);
    }

    private boolean settingMovedToGlobal(final String name) {
        return sSecureGlobalKeys.contains(name) || sSystemGlobalKeys.contains(name);
    }

    /**
     * Decode a content URL into the table, projection, and arguments
     * used to access the corresponding database rows.
     */
    private static class SqlArguments {
        public String table;
        public final String where;
        public final String[] args;

        /** Operate on existing rows. */
        SqlArguments(Uri url, String where, String[] args) {
            if (url.getPathSegments().size() == 1) {
                this.table = url.getPathSegments().get(0);
                if (!DatabaseHelper.isValidTable(this.table)) {
                    throw new IllegalArgumentException("Bad root path: " + this.table);
                }
                this.where = where;
                this.args = args;
            } else if (url.getPathSegments().size() != 2) {
                throw new IllegalArgumentException("Invalid URI: " + url);
            } else if (!TextUtils.isEmpty(where)) {
                throw new UnsupportedOperationException("WHERE clause not supported: " + url);
            } else {
                this.table = url.getPathSegments().get(0);
                if (!DatabaseHelper.isValidTable(this.table)) {
                    throw new IllegalArgumentException("Bad root path: " + this.table);
                }
                if (TABLE_SYSTEM.equals(this.table) || TABLE_SECURE.equals(this.table) ||
                    TABLE_GLOBAL.equals(this.table)) {
                    this.where = Settings.NameValueTable.NAME + "=?";
                    this.args = new String[] { url.getPathSegments().get(1) };
                } else {
                    this.where = "_id=" + ContentUris.parseId(url);
                    this.args = null;
                }
            }
        }

        /** Insert new rows (no where clause allowed). */
        SqlArguments(Uri url) {
            if (url.getPathSegments().size() == 1) {
                this.table = url.getPathSegments().get(0);
                if (!DatabaseHelper.isValidTable(this.table)) {
                    throw new IllegalArgumentException("Bad root path: " + this.table);
                }
                this.where = null;
                this.args = null;
            } else {
                throw new IllegalArgumentException("Invalid URI: " + url);
            }
        }
    }

    /**
     * Get the content URI of a row added to a table.
     * @param tableUri of the entire table
     * @param values found in the row
     * @param rowId of the row
     * @return the content URI for this particular row
     */
    private Uri getUriFor(Uri tableUri, ContentValues values, long rowId) {
        if (tableUri.getPathSegments().size() != 1) {
            throw new IllegalArgumentException("Invalid URI: " + tableUri);
        }
        String table = tableUri.getPathSegments().get(0);
        if (TABLE_SYSTEM.equals(table) ||
                TABLE_SECURE.equals(table) ||
                TABLE_GLOBAL.equals(table)) {
            String name = values.getAsString(Settings.NameValueTable.NAME);
            return Uri.withAppendedPath(tableUri, name);
        } else {
            return ContentUris.withAppendedId(tableUri, rowId);
        }
    }

    /**
     * Send a notification when a particular content URI changes.
     * Modify the system property used to communicate the version of
     * this table, for tables which have such a property.  (The Settings
     * contract class uses these to provide client-side caches.)
     * @param uri to send notifications for
     */
    private void sendNotify(Uri uri, int userHandle) {
        // Update the system property *first*, so if someone is listening for
        // a notification and then using the contract class to get their data,
        // the system property will be updated and they'll get the new data.

        boolean backedUpDataChanged = false;
        String property = null, table = uri.getPathSegments().get(0);
        final boolean isGlobal = table.equals(TABLE_GLOBAL);
        if (table.equals(TABLE_SYSTEM)) {
            property = Settings.System.SYS_PROP_SETTING_VERSION;
            backedUpDataChanged = true;
        } else if (table.equals(TABLE_SECURE)) {
            property = Settings.Secure.SYS_PROP_SETTING_VERSION;
            backedUpDataChanged = true;
        } else if (isGlobal) {
            property = Settings.Global.SYS_PROP_SETTING_VERSION;    // this one is global
            backedUpDataChanged = true;
        }

        if (property != null) {
            long version = SystemProperties.getLong(property, 0) + 1;
            if (LOCAL_LOGV) Log.v(TAG, "property: " + property + "=" + version);
            SystemProperties.set(property, Long.toString(version));
        }

        // Inform the backup manager about a data change
        if (backedUpDataChanged) {
            mBackupManager.dataChanged();
        }
        // Now send the notification through the content framework.

        String notify = uri.getQueryParameter("notify");
        if (notify == null || "true".equals(notify)) {
            final int notifyTarget = isGlobal ? UserHandle.USER_ALL : userHandle;
            final long oldId = Binder.clearCallingIdentity();
            try {
                getContext().getContentResolver().notifyChange(uri, null, true, notifyTarget);
            } finally {
                Binder.restoreCallingIdentity(oldId);
            }
            if (LOCAL_LOGV) Log.v(TAG, "notifying for " + notifyTarget + ": " + uri);
        } else {
            if (LOCAL_LOGV) Log.v(TAG, "notification suppressed: " + uri);
        }
    }

    /**
     * Make sure the caller has permission to write this data.
     * @param args supplied by the caller
     * @throws SecurityException if the caller is forbidden to write.
     */
    private void checkWritePermissions(SqlArguments args) {
        if ((TABLE_SECURE.equals(args.table) || TABLE_GLOBAL.equals(args.table)) &&
            getContext().checkCallingOrSelfPermission(
                    android.Manifest.permission.WRITE_SECURE_SETTINGS) !=
            PackageManager.PERMISSION_GRANTED) {
            throw new SecurityException(
                    String.format("Permission denial: writing to secure settings requires %1$s",
                                  android.Manifest.permission.WRITE_SECURE_SETTINGS));
        }
    }

    // FileObserver for external modifications to the database file.
    // Note that this is for platform developers only with
    // userdebug/eng builds who should be able to tinker with the
    // sqlite database out from under the SettingsProvider, which is
    // normally the exclusive owner of the database.  But we keep this
    // enabled all the time to minimize development-vs-user
    // differences in testing.
    private static SparseArray<SettingsFileObserver> sObserverInstances
            = new SparseArray<SettingsFileObserver>();
    private class SettingsFileObserver extends FileObserver {
        private final AtomicBoolean mIsDirty = new AtomicBoolean(false);
        private final int mUserHandle;
        private final String mPath;

        public SettingsFileObserver(int userHandle, String path) {
            super(path, FileObserver.CLOSE_WRITE |
                  FileObserver.CREATE | FileObserver.DELETE |
                  FileObserver.MOVED_TO | FileObserver.MODIFY);
            mUserHandle = userHandle;
            mPath = path;
        }

        public void onEvent(int event, String path) {
            int modsInFlight = sKnownMutationsInFlight.get(mUserHandle).get();
            if (modsInFlight > 0) {
                // our own modification.
                return;
            }
            Log.d(TAG, "User " + mUserHandle + " external modification to " + mPath
                    + "; event=" + event);
            if (!mIsDirty.compareAndSet(false, true)) {
                // already handled. (we get a few update events
                // during an sqlite write)
                return;
            }
            Log.d(TAG, "User " + mUserHandle + " updating our caches for " + mPath);
            fullyPopulateCaches(mUserHandle);
            mIsDirty.set(false);
        }
    }

    @Override
    public boolean onCreate() {
        mBackupManager = new BackupManager(getContext());
        mUserManager = (UserManager) getContext().getSystemService(Context.USER_SERVICE);

        establishDbTracking(UserHandle.USER_OWNER);

        IntentFilter userFilter = new IntentFilter();
        userFilter.addAction(Intent.ACTION_USER_REMOVED);
        getContext().registerReceiver(new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                if (intent.getAction().equals(Intent.ACTION_USER_REMOVED)) {
                    final int userHandle = intent.getIntExtra(Intent.EXTRA_USER_HANDLE,
                            UserHandle.USER_OWNER);
                    if (userHandle != UserHandle.USER_OWNER) {
                        onUserRemoved(userHandle);
                    }
                }
            }
        }, userFilter);
        return true;
    }

    void onUserRemoved(int userHandle) {
        synchronized (this) {
            // the db file itself will be deleted automatically, but we need to tear down
            // our caches and other internal bookkeeping.
            FileObserver observer = sObserverInstances.get(userHandle);
            if (observer != null) {
                observer.stopWatching();
                sObserverInstances.delete(userHandle);
            }

            mOpenHelpers.delete(userHandle);
            sSystemCaches.delete(userHandle);
            sSecureCaches.delete(userHandle);
            sKnownMutationsInFlight.delete(userHandle);
        }
    }

    private void establishDbTracking(int userHandle) {
        if (LOCAL_LOGV) {
            Slog.i(TAG, "Installing settings db helper and caches for user " + userHandle);
        }

        DatabaseHelper dbhelper;

        synchronized (this) {
            dbhelper = mOpenHelpers.get(userHandle);
            if (dbhelper == null) {
                dbhelper = new DatabaseHelper(getContext(), userHandle);
                mOpenHelpers.append(userHandle, dbhelper);

                sSystemCaches.append(userHandle, new SettingsCache(TABLE_SYSTEM));
                sSecureCaches.append(userHandle, new SettingsCache(TABLE_SECURE));
                sKnownMutationsInFlight.append(userHandle, new AtomicInteger(0));
            }
        }

        // Initialization of the db *outside* the locks.  It's possible that racing
        // threads might wind up here, the second having read the cache entries
        // written by the first, but that's benign: the SQLite helper implementation
        // manages concurrency itself, and it's important that we not run the db
        // initialization with any of our own locks held, so we're fine.
        SQLiteDatabase db = dbhelper.getWritableDatabase();

        // Watch for external modifications to the database files,
        // keeping our caches in sync.  We synchronize the observer set
        // separately, and of course it has to run after the db file
        // itself was set up by the DatabaseHelper.
        synchronized (sObserverInstances) {
            if (sObserverInstances.get(userHandle) == null) {
                SettingsFileObserver observer = new SettingsFileObserver(userHandle, db.getPath());
                sObserverInstances.append(userHandle, observer);
                observer.startWatching();
            }
        }

        ensureAndroidIdIsSet(userHandle);

        startAsyncCachePopulation(userHandle);
    }

    class CachePrefetchThread extends Thread {
        private int mUserHandle;

        CachePrefetchThread(int userHandle) {
            super("populate-settings-caches");
            mUserHandle = userHandle;
        }

        @Override
        public void run() {
            fullyPopulateCaches(mUserHandle);
        }
    }

    private void startAsyncCachePopulation(int userHandle) {
        new CachePrefetchThread(userHandle).start();
    }

    private void fullyPopulateCaches(final int userHandle) {
        DatabaseHelper dbHelper = mOpenHelpers.get(userHandle);
        // Only populate the globals cache once, for the owning user
        if (userHandle == UserHandle.USER_OWNER) {
            fullyPopulateCache(dbHelper, TABLE_GLOBAL, sGlobalCache);
        }
        fullyPopulateCache(dbHelper, TABLE_SECURE, sSecureCaches.get(userHandle));
        fullyPopulateCache(dbHelper, TABLE_SYSTEM, sSystemCaches.get(userHandle));
    }

    // Slurp all values (if sane in number & size) into cache.
    private void fullyPopulateCache(DatabaseHelper dbHelper, String table, SettingsCache cache) {
        SQLiteDatabase db = dbHelper.getReadableDatabase();
        Cursor c = db.query(
            table,
            new String[] { Settings.NameValueTable.NAME, Settings.NameValueTable.VALUE },
            null, null, null, null, null,
            "" + (MAX_CACHE_ENTRIES + 1) /* limit */);
        try {
            synchronized (cache) {
                cache.evictAll();
                cache.setFullyMatchesDisk(true);  // optimistic
                int rows = 0;
                while (c.moveToNext()) {
                    rows++;
                    String name = c.getString(0);
                    String value = c.getString(1);
                    cache.populate(name, value);
                }
                if (rows > MAX_CACHE_ENTRIES) {
                    // Somewhat redundant, as removeEldestEntry() will
                    // have already done this, but to be explicit:
                    cache.setFullyMatchesDisk(false);
                    Log.d(TAG, "row count exceeds max cache entries for table " + table);
                }
                Log.d(TAG, "cache for settings table '" + table + "' rows=" + rows + "; fullycached=" +
                      cache.fullyMatchesDisk());
            }
        } finally {
            c.close();
        }
    }

    private boolean ensureAndroidIdIsSet(int userHandle) {
        final Cursor c = queryForUser(Settings.Secure.CONTENT_URI,
                new String[] { Settings.NameValueTable.VALUE },
                Settings.NameValueTable.NAME + "=?",
                new String[] { Settings.Secure.ANDROID_ID }, null,
                userHandle);
        try {
            final String value = c.moveToNext() ? c.getString(0) : null;
            if (value == null) {
                final SecureRandom random = new SecureRandom();
                final String newAndroidIdValue = Long.toHexString(random.nextLong());
                final ContentValues values = new ContentValues();
                values.put(Settings.NameValueTable.NAME, Settings.Secure.ANDROID_ID);
                values.put(Settings.NameValueTable.VALUE, newAndroidIdValue);
                final Uri uri = insertForUser(Settings.Secure.CONTENT_URI, values, userHandle);
                if (uri == null) {
                    Slog.e(TAG, "Unable to generate new ANDROID_ID for user " + userHandle);
                    return false;
                }
                Slog.d(TAG, "Generated and saved new ANDROID_ID [" + newAndroidIdValue
                        + "] for user " + userHandle);
            }
            return true;
        } finally {
            c.close();
        }
    }

    // Lazy-initialize the settings caches for non-primary users
    private SettingsCache getOrConstructCache(int callingUser, SparseArray<SettingsCache> which) {
        getOrEstablishDatabase(callingUser); // ignore return value; we don't need it
        return which.get(callingUser);
    }

    // Lazy initialize the database helper and caches for this user, if necessary
    private DatabaseHelper getOrEstablishDatabase(int callingUser) {
        long oldId = Binder.clearCallingIdentity();
        try {
            DatabaseHelper dbHelper = mOpenHelpers.get(callingUser);
            if (null == dbHelper) {
                establishDbTracking(callingUser);
                dbHelper = mOpenHelpers.get(callingUser);
            }
            return dbHelper;
        } finally {
            Binder.restoreCallingIdentity(oldId);
        }
    }

    public SettingsCache cacheForTable(final int callingUser, String tableName) {
        if (TABLE_SYSTEM.equals(tableName)) {
            return getOrConstructCache(callingUser, sSystemCaches);
        }
        if (TABLE_SECURE.equals(tableName)) {
            return getOrConstructCache(callingUser, sSecureCaches);
        }
        if (TABLE_GLOBAL.equals(tableName)) {
            return sGlobalCache;
        }
        return null;
    }

    /**
     * Used for wiping a whole cache on deletes when we're not
     * sure what exactly was deleted or changed.
     */
    public void invalidateCache(final int callingUser, String tableName) {
        SettingsCache cache = cacheForTable(callingUser, tableName);
        if (cache == null) {
            return;
        }
        synchronized (cache) {
            cache.evictAll();
            cache.mCacheFullyMatchesDisk = false;
        }
    }

    /**
     * Fast path that avoids the use of chatty remoted Cursors.
     */
    @Override
    public Bundle call(String method, String request, Bundle args) {
        int callingUser = UserHandle.getCallingUserId();
        if (args != null) {
            int reqUser = args.getInt(Settings.CALL_METHOD_USER_KEY, callingUser);
            if (reqUser != callingUser) {
                callingUser = ActivityManager.handleIncomingUser(Binder.getCallingPid(),
                        Binder.getCallingUid(), reqUser, false, true,
                        "get/set setting for user", null);
                if (LOCAL_LOGV) Slog.v(TAG, "   access setting for user " + callingUser);
            }
        }

        // Okay, permission checks have cleared.  Reset to our own identity so we can
        // manipulate all users' data with impunity.
        long oldId = Binder.clearCallingIdentity();
        try {
            // Note: we assume that get/put operations for moved-to-global names have already
            // been directed to the new location on the caller side (otherwise we'd fix them
            // up here).
            DatabaseHelper dbHelper;
            SettingsCache cache;

            // Get methods
            if (Settings.CALL_METHOD_GET_SYSTEM.equals(method)) {
                if (LOCAL_LOGV) Slog.v(TAG, "call(system:" + request + ") for " + callingUser);
                dbHelper = getOrEstablishDatabase(callingUser);
                cache = sSystemCaches.get(callingUser);
                return lookupValue(dbHelper, TABLE_SYSTEM, cache, request);
            }
            if (Settings.CALL_METHOD_GET_SECURE.equals(method)) {
                if (LOCAL_LOGV) Slog.v(TAG, "call(secure:" + request + ") for " + callingUser);
                dbHelper = getOrEstablishDatabase(callingUser);
                cache = sSecureCaches.get(callingUser);
                return lookupValue(dbHelper, TABLE_SECURE, cache, request);
            }
            if (Settings.CALL_METHOD_GET_GLOBAL.equals(method)) {
                if (LOCAL_LOGV) Slog.v(TAG, "call(global:" + request + ") for " + callingUser);
                // fast path: owner db & cache are immutable after onCreate() so we need not
                // guard on the attempt to look them up
                return lookupValue(getOrEstablishDatabase(UserHandle.USER_OWNER), TABLE_GLOBAL,
                        sGlobalCache, request);
            }

            // Put methods - new value is in the args bundle under the key named by
            // the Settings.NameValueTable.VALUE static.
            final String newValue = (args == null)
                    ? null : args.getString(Settings.NameValueTable.VALUE);

            final ContentValues values = new ContentValues();
            values.put(Settings.NameValueTable.NAME, request);
            values.put(Settings.NameValueTable.VALUE, newValue);
            if (Settings.CALL_METHOD_PUT_SYSTEM.equals(method)) {
                if (LOCAL_LOGV) Slog.v(TAG, "call_put(system:" + request + "=" + newValue + ") for " + callingUser);
                insertForUser(Settings.System.CONTENT_URI, values, callingUser);
            } else if (Settings.CALL_METHOD_PUT_SECURE.equals(method)) {
                if (LOCAL_LOGV) Slog.v(TAG, "call_put(secure:" + request + "=" + newValue + ") for " + callingUser);
                insertForUser(Settings.Secure.CONTENT_URI, values, callingUser);
            } else if (Settings.CALL_METHOD_PUT_GLOBAL.equals(method)) {
                if (LOCAL_LOGV) Slog.v(TAG, "call_put(global:" + request + "=" + newValue + ") for " + callingUser);
                insertForUser(Settings.Global.CONTENT_URI, values, callingUser);
            } else {
                Slog.w(TAG, "call() with invalid method: " + method);
            }
        } finally {
            Binder.restoreCallingIdentity(oldId);
        }

        return null;
    }

    // Looks up value 'key' in 'table' and returns either a single-pair Bundle,
    // possibly with a null value, or null on failure.
    private Bundle lookupValue(DatabaseHelper dbHelper, String table,
            final SettingsCache cache, String key) {
        if (cache == null) {
           Slog.e(TAG, "cache is null for user " + UserHandle.getCallingUserId() + " : key=" + key);
           return null;
        }
        synchronized (cache) {
            Bundle value = cache.get(key);
            if (value != null) {
                if (value != TOO_LARGE_TO_CACHE_MARKER) {
                    return value;
                }
                // else we fall through and read the value from disk
            } else if (cache.fullyMatchesDisk()) {
                // Fast path (very common).  Don't even try touch disk
                // if we know we've slurped it all in.  Trying to
                // touch the disk would mean waiting for yaffs2 to
                // give us access, which could takes hundreds of
                // milliseconds.  And we're very likely being called
                // from somebody's UI thread...
                return NULL_SETTING;
            }
        }

        SQLiteDatabase db = dbHelper.getReadableDatabase();
        Cursor cursor = null;
        try {
            cursor = db.query(table, COLUMN_VALUE, "name=?", new String[]{key},
                              null, null, null, null);
            if (cursor != null && cursor.getCount() == 1) {
                cursor.moveToFirst();
                return cache.putIfAbsent(key, cursor.getString(0));
            }
        } catch (SQLiteException e) {
            Log.w(TAG, "settings lookup error", e);
            return null;
        } finally {
            if (cursor != null) cursor.close();
        }
        cache.putIfAbsent(key, null);
        return NULL_SETTING;
    }

    @Override
    public Cursor query(Uri url, String[] select, String where, String[] whereArgs, String sort) {
        return queryForUser(url, select, where, whereArgs, sort, UserHandle.getCallingUserId());
    }

    private Cursor queryForUser(Uri url, String[] select, String where, String[] whereArgs,
            String sort, int forUser) {
        if (LOCAL_LOGV) Slog.v(TAG, "query(" + url + ") for user " + forUser);
        SqlArguments args = new SqlArguments(url, where, whereArgs);
        DatabaseHelper dbH;
        dbH = getOrEstablishDatabase(
                TABLE_GLOBAL.equals(args.table) ? UserHandle.USER_OWNER : forUser);
        SQLiteDatabase db = dbH.getReadableDatabase();

        // The favorites table was moved from this provider to a provider inside Home
        // Home still need to query this table to upgrade from pre-cupcake builds
        // However, a cupcake+ build with no data does not contain this table which will
        // cause an exception in the SQL stack. The following line is a special case to
        // let the caller of the query have a chance to recover and avoid the exception
        if (TABLE_FAVORITES.equals(args.table)) {
            return null;
        } else if (TABLE_OLD_FAVORITES.equals(args.table)) {
            args.table = TABLE_FAVORITES;
            Cursor cursor = db.rawQuery("PRAGMA table_info(favorites);", null);
            if (cursor != null) {
                boolean exists = cursor.getCount() > 0;
                cursor.close();
                if (!exists) return null;
            } else {
                return null;
            }
        }

        SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
        qb.setTables(args.table);

        Cursor ret = qb.query(db, select, args.where, args.args, null, null, sort);
        ret.setNotificationUri(getContext().getContentResolver(), url);
        return ret;
    }

    @Override
    public String getType(Uri url) {
        // If SqlArguments supplies a where clause, then it must be an item
        // (because we aren't supplying our own where clause).
        SqlArguments args = new SqlArguments(url, null, null);
        if (TextUtils.isEmpty(args.where)) {
            return "vnd.android.cursor.dir/" + args.table;
        } else {
            return "vnd.android.cursor.item/" + args.table;
        }
    }

    @Override
    public int bulkInsert(Uri uri, ContentValues[] values) {
        final int callingUser = UserHandle.getCallingUserId();
        if (LOCAL_LOGV) Slog.v(TAG, "bulkInsert() for user " + callingUser);
        SqlArguments args = new SqlArguments(uri);
        if (TABLE_FAVORITES.equals(args.table)) {
            return 0;
        }
        checkWritePermissions(args);
        SettingsCache cache = cacheForTable(callingUser, args.table);

        final AtomicInteger mutationCount = sKnownMutationsInFlight.get(callingUser);
        mutationCount.incrementAndGet();
        DatabaseHelper dbH = getOrEstablishDatabase(
                TABLE_GLOBAL.equals(args.table) ? UserHandle.USER_OWNER : callingUser);
        SQLiteDatabase db = dbH.getWritableDatabase();
        db.beginTransaction();
        try {
            int numValues = values.length;
            for (int i = 0; i < numValues; i++) {
                if (db.insert(args.table, null, values[i]) < 0) return 0;
                SettingsCache.populate(cache, values[i]);
                if (LOCAL_LOGV) Log.v(TAG, args.table + " <- " + values[i]);
            }
            db.setTransactionSuccessful();
        } finally {
            db.endTransaction();
            mutationCount.decrementAndGet();
        }

        sendNotify(uri, callingUser);
        return values.length;
    }

    /*
     * Used to parse changes to the value of Settings.Secure.LOCATION_PROVIDERS_ALLOWED.
     * This setting contains a list of the currently enabled location providers.
     * But helper functions in android.providers.Settings can enable or disable
     * a single provider by using a "+" or "-" prefix before the provider name.
     *
     * @returns whether the database needs to be updated or not, also modifying
     *     'initialValues' if needed.
     */
    private boolean parseProviderList(Uri url, ContentValues initialValues) {
        String value = initialValues.getAsString(Settings.Secure.VALUE);
        String newProviders = null;
        if (value != null && value.length() > 1) {
            char prefix = value.charAt(0);
            if (prefix == '+' || prefix == '-') {
                // skip prefix
                value = value.substring(1);

                // read list of enabled providers into "providers"
                String providers = "";
                String[] columns = {Settings.Secure.VALUE};
                String where = Settings.Secure.NAME + "=\'" + Settings.Secure.LOCATION_PROVIDERS_ALLOWED + "\'";
                Cursor cursor = query(url, columns, where, null, null);
                if (cursor != null && cursor.getCount() == 1) {
                    try {
                        cursor.moveToFirst();
                        providers = cursor.getString(0);
                    } finally {
                        cursor.close();
                    }
                }

                int index = providers.indexOf(value);
                int end = index + value.length();
                // check for commas to avoid matching on partial string
                if (index > 0 && providers.charAt(index - 1) != ',') index = -1;
                if (end < providers.length() && providers.charAt(end) != ',') index = -1;

                if (prefix == '+' && index < 0) {
                    // append the provider to the list if not present
                    if (providers.length() == 0) {
                        newProviders = value;
                    } else {
                        newProviders = providers + ',' + value;
                    }
                } else if (prefix == '-' && index >= 0) {
                    // remove the provider from the list if present
                    // remove leading or trailing comma
                    if (index > 0) {
                        index--;
                    } else if (end < providers.length()) {
                        end++;
                    }

                    newProviders = providers.substring(0, index);
                    if (end < providers.length()) {
                        newProviders += providers.substring(end);
                    }
                } else {
                    // nothing changed, so no need to update the database
                    return false;
                }

                if (newProviders != null) {
                    initialValues.put(Settings.Secure.VALUE, newProviders);
                }
            }
        }

        return true;
    }

    @Override
    public Uri insert(Uri url, ContentValues initialValues) {
        return insertForUser(url, initialValues, UserHandle.getCallingUserId());
    }

    // Settings.put*ForUser() always winds up here, so this is where we apply
    // policy around permission to write settings for other users.
    private Uri insertForUser(Uri url, ContentValues initialValues, int desiredUserHandle) {
        final int callingUser = UserHandle.getCallingUserId();
        if (callingUser != desiredUserHandle) {
            getContext().enforceCallingOrSelfPermission(
                    android.Manifest.permission.INTERACT_ACROSS_USERS_FULL,
                    "Not permitted to access settings for other users");
        }

        if (LOCAL_LOGV) Slog.v(TAG, "insert(" + url + ") for user " + desiredUserHandle
                + " by " + callingUser);

        SqlArguments args = new SqlArguments(url);
        if (TABLE_FAVORITES.equals(args.table)) {
            return null;
        }
        checkWritePermissions(args);

        // Special case LOCATION_PROVIDERS_ALLOWED.
        // Support enabling/disabling a single provider (using "+" or "-" prefix)
        String name = initialValues.getAsString(Settings.Secure.NAME);
        if (Settings.Secure.LOCATION_PROVIDERS_ALLOWED.equals(name)) {
            if (!parseProviderList(url, initialValues)) return null;
        }

        // The global table is stored under the owner, always
        if (TABLE_GLOBAL.equals(args.table)) {
            desiredUserHandle = UserHandle.USER_OWNER;
        }

        SettingsCache cache = cacheForTable(desiredUserHandle, args.table);
        String value = initialValues.getAsString(Settings.NameValueTable.VALUE);
        if (SettingsCache.isRedundantSetValue(cache, name, value)) {
            return Uri.withAppendedPath(url, name);
        }

        final AtomicInteger mutationCount = sKnownMutationsInFlight.get(desiredUserHandle);
        mutationCount.incrementAndGet();
        DatabaseHelper dbH = getOrEstablishDatabase(desiredUserHandle);
        SQLiteDatabase db = dbH.getWritableDatabase();
        final long rowId = db.insert(args.table, null, initialValues);
        mutationCount.decrementAndGet();
        if (rowId <= 0) return null;

        SettingsCache.populate(cache, initialValues);  // before we notify

        if (LOCAL_LOGV) Log.v(TAG, args.table + " <- " + initialValues
                + " for user " + desiredUserHandle);
        // Note that we use the original url here, not the potentially-rewritten table name
        url = getUriFor(url, initialValues, rowId);
        sendNotify(url, desiredUserHandle);
        return url;
    }

    @Override
    public int delete(Uri url, String where, String[] whereArgs) {
        int callingUser = UserHandle.getCallingUserId();
        if (LOCAL_LOGV) Slog.v(TAG, "delete() for user " + callingUser);
        SqlArguments args = new SqlArguments(url, where, whereArgs);
        if (TABLE_FAVORITES.equals(args.table)) {
            return 0;
        } else if (TABLE_OLD_FAVORITES.equals(args.table)) {
            args.table = TABLE_FAVORITES;
        } else if (TABLE_GLOBAL.equals(args.table)) {
            callingUser = UserHandle.USER_OWNER;
        }
        checkWritePermissions(args);

        final AtomicInteger mutationCount = sKnownMutationsInFlight.get(callingUser);
        mutationCount.incrementAndGet();
        DatabaseHelper dbH = getOrEstablishDatabase(callingUser);
        SQLiteDatabase db = dbH.getWritableDatabase();
        int count = db.delete(args.table, args.where, args.args);
        mutationCount.decrementAndGet();
        if (count > 0) {
            invalidateCache(callingUser, args.table);  // before we notify
            sendNotify(url, callingUser);
        }
        startAsyncCachePopulation(callingUser);
        if (LOCAL_LOGV) Log.v(TAG, args.table + ": " + count + " row(s) deleted");
        return count;
    }

    @Override
    public int update(Uri url, ContentValues initialValues, String where, String[] whereArgs) {
        // NOTE: update() is never called by the front-end Settings API, and updates that
        // wind up affecting rows in Secure that are globally shared will not have the
        // intended effect (the update will be invisible to the rest of the system).
        // This should have no practical effect, since writes to the Secure db can only
        // be done by system code, and that code should be using the correct API up front.
        int callingUser = UserHandle.getCallingUserId();
        if (LOCAL_LOGV) Slog.v(TAG, "update() for user " + callingUser);
        SqlArguments args = new SqlArguments(url, where, whereArgs);
        if (TABLE_FAVORITES.equals(args.table)) {
            return 0;
        } else if (TABLE_GLOBAL.equals(args.table)) {
            callingUser = UserHandle.USER_OWNER;
        }
        checkWritePermissions(args);

        final AtomicInteger mutationCount = sKnownMutationsInFlight.get(callingUser);
        mutationCount.incrementAndGet();
        DatabaseHelper dbH = getOrEstablishDatabase(callingUser);
        SQLiteDatabase db = dbH.getWritableDatabase();
        int count = db.update(args.table, initialValues, args.where, args.args);
        mutationCount.decrementAndGet();
        if (count > 0) {
            invalidateCache(callingUser, args.table);  // before we notify
            sendNotify(url, callingUser);
        }
        startAsyncCachePopulation(callingUser);
        if (LOCAL_LOGV) Log.v(TAG, args.table + ": " + count + " row(s) <- " + initialValues);
        return count;
    }

    @Override
    public ParcelFileDescriptor openFile(Uri uri, String mode) throws FileNotFoundException {

        /*
         * When a client attempts to openFile the default ringtone or
         * notification setting Uri, we will proxy the call to the current
         * default ringtone's Uri (if it is in the DRM or media provider).
         */
        int ringtoneType = RingtoneManager.getDefaultType(uri);
        // Above call returns -1 if the Uri doesn't match a default type
        if (ringtoneType != -1) {
            Context context = getContext();

            // Get the current value for the default sound
            Uri soundUri = RingtoneManager.getActualDefaultRingtoneUri(context, ringtoneType);

            if (soundUri != null) {
                // Only proxy the openFile call to drm or media providers
                String authority = soundUri.getAuthority();
                boolean isDrmAuthority = authority.equals(DrmStore.AUTHORITY);
                if (isDrmAuthority || authority.equals(MediaStore.AUTHORITY)) {

                    if (isDrmAuthority) {
                        try {
                            // Check DRM access permission here, since once we
                            // do the below call the DRM will be checking our
                            // permission, not our caller's permission
                            DrmStore.enforceAccessDrmPermission(context);
                        } catch (SecurityException e) {
                            throw new FileNotFoundException(e.getMessage());
                        }
                    }

                    return context.getContentResolver().openFileDescriptor(soundUri, mode);
                }
            }
        }

        return super.openFile(uri, mode);
    }

    @Override
    public AssetFileDescriptor openAssetFile(Uri uri, String mode) throws FileNotFoundException {

        /*
         * When a client attempts to openFile the default ringtone or
         * notification setting Uri, we will proxy the call to the current
         * default ringtone's Uri (if it is in the DRM or media provider).
         */
        int ringtoneType = RingtoneManager.getDefaultType(uri);
        // Above call returns -1 if the Uri doesn't match a default type
        if (ringtoneType != -1) {
            Context context = getContext();

            // Get the current value for the default sound
            Uri soundUri = RingtoneManager.getActualDefaultRingtoneUri(context, ringtoneType);

            if (soundUri != null) {
                // Only proxy the openFile call to drm or media providers
                String authority = soundUri.getAuthority();
                boolean isDrmAuthority = authority.equals(DrmStore.AUTHORITY);
                if (isDrmAuthority || authority.equals(MediaStore.AUTHORITY)) {

                    if (isDrmAuthority) {
                        try {
                            // Check DRM access permission here, since once we
                            // do the below call the DRM will be checking our
                            // permission, not our caller's permission
                            DrmStore.enforceAccessDrmPermission(context);
                        } catch (SecurityException e) {
                            throw new FileNotFoundException(e.getMessage());
                        }
                    }

                    ParcelFileDescriptor pfd = null;
                    try {
                        pfd = context.getContentResolver().openFileDescriptor(soundUri, mode);
                        return new AssetFileDescriptor(pfd, 0, -1);
                    } catch (FileNotFoundException ex) {
                        // fall through and open the fallback ringtone below
                    }
                }

                try {
                    return super.openAssetFile(soundUri, mode);
                } catch (FileNotFoundException ex) {
                    // Since a non-null Uri was specified, but couldn't be opened,
                    // fall back to the built-in ringtone.
                    return context.getResources().openRawResourceFd(
                            com.android.internal.R.raw.fallbackring);
                }
            }
            // no need to fall through and have openFile() try again, since we
            // already know that will fail.
            throw new FileNotFoundException(); // or return null ?
        }

        // Note that this will end up calling openFile() above.
        return super.openAssetFile(uri, mode);
    }

    /**
     * In-memory LRU Cache of system and secure settings, along with
     * associated helper functions to keep cache coherent with the
     * database.
     */
    private static final class SettingsCache extends LruCache<String, Bundle> {

        private final String mCacheName;
        private boolean mCacheFullyMatchesDisk = false;  // has the whole database slurped.

        public SettingsCache(String name) {
            super(MAX_CACHE_ENTRIES);
            mCacheName = name;
        }

        /**
         * Is the whole database table slurped into this cache?
         */
        public boolean fullyMatchesDisk() {
            synchronized (this) {
                return mCacheFullyMatchesDisk;
            }
        }

        public void setFullyMatchesDisk(boolean value) {
            synchronized (this) {
                mCacheFullyMatchesDisk = value;
            }
        }

        @Override
        protected void entryRemoved(boolean evicted, String key, Bundle oldValue, Bundle newValue) {
            if (evicted) {
                mCacheFullyMatchesDisk = false;
            }
        }

        /**
         * Atomic cache population, conditional on size of value and if
         * we lost a race.
         *
         * @returns a Bundle to send back to the client from call(), even
         *     if we lost the race.
         */
        public Bundle putIfAbsent(String key, String value) {
            Bundle bundle = (value == null) ? NULL_SETTING : Bundle.forPair("value", value);
            if (value == null || value.length() <= MAX_CACHE_ENTRY_SIZE) {
                synchronized (this) {
                    if (get(key) == null) {
                        put(key, bundle);
                    }
                }
            }
            return bundle;
        }

        /**
         * Populates a key in a given (possibly-null) cache.
         */
        public static void populate(SettingsCache cache, ContentValues contentValues) {
            if (cache == null) {
                return;
            }
            String name = contentValues.getAsString(Settings.NameValueTable.NAME);
            if (name == null) {
                Log.w(TAG, "null name populating settings cache.");
                return;
            }
            String value = contentValues.getAsString(Settings.NameValueTable.VALUE);
            cache.populate(name, value);
        }

        public void populate(String name, String value) {
            synchronized (this) {
                if (value == null || value.length() <= MAX_CACHE_ENTRY_SIZE) {
                    put(name, Bundle.forPair(Settings.NameValueTable.VALUE, value));
                } else {
                    put(name, TOO_LARGE_TO_CACHE_MARKER);
                }
            }
        }

        /**
         * For suppressing duplicate/redundant settings inserts early,
         * checking our cache first (but without faulting it in),
         * before going to sqlite with the mutation.
         */
        public static boolean isRedundantSetValue(SettingsCache cache, String name, String value) {
            if (cache == null) return false;
            synchronized (cache) {
                Bundle bundle = cache.get(name);
                if (bundle == null) return false;
                String oldValue = bundle.getPairValue();
                if (oldValue == null && value == null) return true;
                if ((oldValue == null) != (value == null)) return false;
                return oldValue.equals(value);
            }
        }
    }
}