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      1 /*
      2  * Copyright (C) 2018 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License
     15  */
     16 
     17 package com.android.server.am;
     18 
     19 import android.content.ContentResolver;
     20 import android.database.ContentObserver;
     21 import android.net.Uri;
     22 import android.os.Build;
     23 import android.os.SystemProperties;
     24 import android.provider.Settings;
     25 import android.text.TextUtils;
     26 import android.util.Slog;
     27 import android.view.ThreadedRenderer;
     28 
     29 import com.android.internal.annotations.VisibleForTesting;
     30 import com.android.internal.util.Preconditions;
     31 
     32 /**
     33  * Maps global system settings to system properties.
     34  * <p>The properties are dynamically updated when settings change.
     35  */
     36 class GlobalSettingsToPropertiesMapper {
     37 
     38     private static final String TAG = "GlobalSettingsToPropertiesMapper";
     39 
     40     // List mapping entries in the following format:
     41     // {Settings.Global.SETTING_NAME, "system_property_name"}
     42     // Important: Property being added should be whitelisted by SELinux policy or have one of the
     43     // already whitelisted prefixes in system_server.te, e.g. sys.
     44     private static final String[][] sGlobalSettingsMapping = new String[][] {
     45         {Settings.Global.SYS_VDSO, "sys.vdso"},
     46         {Settings.Global.FPS_DEVISOR, ThreadedRenderer.DEBUG_FPS_DIVISOR},
     47         {Settings.Global.DISPLAY_PANEL_LPM, "sys.display_panel_lpm"},
     48         {Settings.Global.SYS_UIDCPUPOWER, "sys.uidcpupower"},
     49         {Settings.Global.SYS_TRACED, "sys.traced.enable_override"},
     50     };
     51 
     52 
     53     private final ContentResolver mContentResolver;
     54     private final String[][] mGlobalSettingsMapping;
     55 
     56     @VisibleForTesting
     57     GlobalSettingsToPropertiesMapper(ContentResolver contentResolver,
     58             String[][] globalSettingsMapping) {
     59         mContentResolver = contentResolver;
     60         mGlobalSettingsMapping = globalSettingsMapping;
     61     }
     62 
     63     void updatePropertiesFromGlobalSettings() {
     64         for (String[] entry : mGlobalSettingsMapping) {
     65             final String settingName = entry[0];
     66             final String propName = entry[1];
     67             Uri settingUri = Settings.Global.getUriFor(settingName);
     68             Preconditions.checkNotNull(settingUri, "Setting " + settingName + " not found");
     69             ContentObserver co = new ContentObserver(null) {
     70                 @Override
     71                 public void onChange(boolean selfChange) {
     72                     updatePropertyFromSetting(settingName, propName);
     73                 }
     74             };
     75             updatePropertyFromSetting(settingName, propName);
     76             mContentResolver.registerContentObserver(settingUri, false, co);
     77         }
     78     }
     79 
     80     public static void start(ContentResolver contentResolver) {
     81         new GlobalSettingsToPropertiesMapper(contentResolver, sGlobalSettingsMapping)
     82                 .updatePropertiesFromGlobalSettings();
     83     }
     84 
     85     private String getGlobalSetting(String name) {
     86         return Settings.Global.getString(mContentResolver, name);
     87     }
     88 
     89     private void setProperty(String key, String value) {
     90         // Check if need to clear the property
     91         if (value == null) {
     92             // It's impossible to remove system property, therefore we check previous value to
     93             // avoid setting an empty string if the property wasn't set.
     94             if (TextUtils.isEmpty(systemPropertiesGet(key))) {
     95                 return;
     96             }
     97             value = "";
     98         }
     99         try {
    100             systemPropertiesSet(key, value);
    101         } catch (Exception e) {
    102             // Failure to set a property can be caused by SELinux denial. This usually indicates
    103             // that the property wasn't whitelisted in sepolicy.
    104             // No need to report it on all user devices, only on debug builds.
    105             if (Build.IS_DEBUGGABLE) {
    106                 Slog.wtf(TAG, "Unable to set property " + key + " value '" + value + "'", e);
    107             } else {
    108                 Slog.e(TAG, "Unable to set property " + key + " value '" + value + "'", e);
    109             }
    110         }
    111     }
    112 
    113     @VisibleForTesting
    114     protected String systemPropertiesGet(String key) {
    115         return SystemProperties.get(key);
    116     }
    117 
    118     @VisibleForTesting
    119     protected void systemPropertiesSet(String key, String value) {
    120         SystemProperties.set(key, value);
    121     }
    122 
    123     @VisibleForTesting
    124     void updatePropertyFromSetting(String settingName, String propName) {
    125         String settingValue = getGlobalSetting(settingName);
    126         setProperty(propName, settingValue);
    127     }
    128 }
    129