Android系统关于ntp的修改（网络时间同步）

一，现象：

1. NTP介绍

NTP：网络时间协议，英文名称：Network Time Protocol（NTP）是用来使计算机时间同步化的一种协议，它可以使计算机对其服务器或时钟源（如石英钟，GPS等等)做同步化，它可以提供高精准度的时间校正（LAN上与标准间差小于1毫秒，WAN上几十毫秒），且可介由加密确认的方式来防止恶毒的协议攻击。NTP的目的是在无序的Internet环境中提供精确和健壮的时间服务。

Android系统使用NTP自动更新系统时间的触发机制：

监听数据库字段AUTO_TIME，当这个字段发生变化的时候，会立即触发一次时间同步
网络连接发生变化，当网络接通，会触发一次时间检查和同步
定时更新机制，当预定的时间到了，会触发一次时间检查和同步

Android自动同步时间是通过NtpServer来同步时间的，但是默认的服务器使用的是Google的所以无法连接，会导致自动同步日期和时间无效。

2. NTP时间设置流程示意图：

在这里插入图片描述

二，解决方案：

以下修改都在源码frameworks/base/下

1. 修改默认的Ntp服务器

diff --git a/packages/SettingsProvider/res/values/defaults.xml b/packages/SettingsProvider/res/values/defaults.xml
index 129cee58078..8ffc237c7e1 100755
--- a/packages/SettingsProvider/res/values/defaults.xml
+++ b/packages/SettingsProvider/res/values/defaults.xml
@@ -229,4 +229,6 @@<integer name="def_screenshot_button_show">1</integer><!-- the store location of screen capture by default--><string name="def_screenshot_location">internal_storage</string>
+
+    <string name="def_ntp_server" translatable="false">time.windows.com</string>
</resources>

diff --git a/packages/SettingsProvider/src/com/android/providers/settings/DatabaseHelper.java b/packages/SettingsProvider/src/com/android/providers/settings/DatabaseHelper.java
index 0ba3a5289ed..29361ad19bc 100644
--- a/packages/SettingsProvider/src/com/android/providers/settings/DatabaseHelper.java
+++ b/packages/SettingsProvider/src/com/android/providers/settings/DatabaseHelper.java
@@ -2733,6 +2733,9 @@ class DatabaseHelper extends SQLiteOpenHelper {loadSetting(stmt, Settings.Global.ENHANCED_4G_MODE_ENABLED,ImsConfig.FeatureValueConstants.ON);+            loadStringSetting(stmt, Settings.Global.NTP_SERVER,
+                    R.string.def_ntp_server);
+/** IMPORTANT: Do not add any more upgrade steps here as the global,* secure, and system settings are no longer stored in a database

2. 修改NTP基础配置

<!-- Remote server that can provide NTP responses. -->
<string translatable="false" name="config_ntpServer">2.android.pool.ntp.org</string>
<!-- Normal polling frequency in milliseconds -->
<integer name="config_ntpPollingInterval">86400000</integer>  
<!-- Try-again polling interval in milliseconds, in case the network request failed -->
<integer name="config_ntpPollingIntervalShorter">30000</integer>  
<!-- Number of times to try again with the shorter interval, before backingoff until the normal polling interval. A value < 0 indicates infinite. -->
<integer name="config_ntpRetry">5</integer>   
<!-- Timeout to wait for NTP server response in milliseconds. -->
<integer name="config_ntpTimeout">10</integer>

2.android.pool.ntp.org：这个是NTP服务器地址
86400000：周期默认8640000ms，即1天，一般不改
30000：是由于网络原因，时间同步失败后，retry的时间间隔，默认是60000ms，即60s这里改成30s
5：retry的次数，默认是3次
10：时间误差，默认是5000ms，当时间误差超过5s，会更新系统时间，改成10ms.

wifi自动确定时间的问题时，NTP服务器可以自行更换为自己增加列表中的地址，例如：

<string translatable="false" name="config_ntpServer">ntp1.aliyun.com</string>

3. 增加NTP列表

添加多个Ntp服务器用于轮询，避免默认Ntp服务器失效；安卓10以后ntp的判定规则有所不同，所以代码有所差异。

1. Android10之前（Android7.1）修改

diff --git a/core/java/android/util/NtpTrustedTime.java b/core/java/android/util/NtpTrustedTime.java
index ed2d3c60fcd..60ad5d9f132 100644
--- a/core/java/android/util/NtpTrustedTime.java
+++ b/core/java/android/util/NtpTrustedTime.java
@@ -39,7 +39,7 @@ public class NtpTrustedTime implements TrustedTime {private static NtpTrustedTime sSingleton;private static Context sContext;-    private final String mServer;
+    private String mServer;private final long mTimeout;private ConnectivityManager mCM;
@@ -49,6 +49,15 @@ public class NtpTrustedTime implements TrustedTime {private long mCachedNtpElapsedRealtime;private long mCachedNtpCertainty;+    String[] backupNtpServers = new String[]{
+            "tw.pool.ntp.org",
+            "time.nist.gov",
+            "time-a.nist.gov",
+            "ntp1.aliyun.com"
+    };
+    int index = -1;
+
+private NtpTrustedTime(String server, long timeout) {if (LOGD) Log.d(TAG, "creating NtpTrustedTime using " + server);mServer = server;
@@ -101,15 +110,29 @@ public class NtpTrustedTime implements TrustedTime {if (LOGD) Log.d(TAG, "forceRefresh() from cache miss");final SntpClient client = new SntpClient();
-        if (client.requestTime(mServer, (int) mTimeout)) {
-            mHasCache = true;
-            mCachedNtpTime = client.getNtpTime();
-            mCachedNtpElapsedRealtime = client.getNtpTimeReference();
-            mCachedNtpCertainty = client.getRoundTripTime() / 2;
-            return true;
-        } else {
-            return false;
+
+        boolean result = false;
+               while(!(result = client.requestTime(mServer, (int)mTimeout)) && index < (backupNtpServers.length-1)){
+               index++;
+               mServer = backupNtpServers[index];}
+        index = -1;
+               Resources res = sContext.getResources();
+               String defaultServer = res.getString(
+                    com.android.internal.R.string.config_ntpServer);
+               String secureServer = Settings.Global.getString(
+                     sContext.getContentResolver(), Settings.Global.NTP_SERVER);
+
+               mServer  = secureServer != null ? secureServer : defaultServer;
+
+               if(result){
+                       mHasCache = true;
+                       mCachedNtpTime = client.getNtpTime();
+                       mCachedNtpElapsedRealtime = client.getNtpTimeReference();
+                       mCachedNtpCertainty = client.getRoundTripTime() / 2;
+               }
+
+               return result;}@Override

2. Android10之后（Android11.0）修改

diff --git a/frameworks/base/core/java/android/util/NtpTrustedTime.java b/frameworks/base/core/java/android/util/NtpTrustedTime.java
old mode 100644
new mode 100755
index 0892c94d5b..bb8f894cb3
--- a/frameworks/base/core/java/android/util/NtpTrustedTime.java
+++ b/frameworks/base/core/java/android/util/NtpTrustedTime.java
@@ -98,6 +98,27 @@ public class NtpTrustedTime implements TrustedTime {private static NtpTrustedTime sSingleton;
+       String[] backupNtpServers = new String[]{
+               "time.nist.gov",
+               "time-a.nist.gov",
+               "ntp1.aliyun.com",
+               "ntp2.aliyun.com",
+               "ntp3.aliyun.com",
+               "ntp-sz.chl.la",
+               "3.cn.pool.ntp.org",
+               "asia.pool.ntp.org",
+               "cn.pool.ntp.org",
+               "sg.pool.ntp.org",
+               "jp.pool.ntp.org",
+               "hk.pool.ntp.org",
+               "s2g.time.edu.cn",
+               "oceania.pool.ntp.org",
+               "south-america.pool.ntp.org",
+               "north-america.pool.ntp.org",
+               "tw.pool.ntp.org",
+       };
+       int index = -1;
+@NonNullprivate final Context mContext;
@@ -162,12 +183,18 @@ public class NtpTrustedTime implements TrustedTime {if (LOGD) Log.d(TAG, "forceRefresh() from cache miss");final SntpClient client = new SntpClient();
-            final String serverName = connectionInfo.getServer();
+            boolean result = false;
+            String serverName = connectionInfo.getServer();
+            if (LOGD) Log.d(TAG, "----------rockemd-add-20221027-serverName--1------"+serverName);final int timeoutMillis = connectionInfo.getTimeoutMillis();
-            if (client.requestTime(serverName, timeoutMillis, network)) {
+            while (!(result = client.requestTime(serverName, timeoutMillis, network)) && index < (backupNtpServers.length-1) ) {
+                index++;
+                serverName = backupNtpServers[index];
+                if (LOGD) Log.d(TAG, "----------rockemd-add-20221027-serverName--------"+serverName);
+            }
+            if(result){long ntpCertainty = client.getRoundTripTime() / 2;
-                mTimeResult = new TimeResult(
-                        client.getNtpTime(), client.getNtpTimeReference(), ntpCertainty);
+                mTimeResult = new TimeResult(client.getNtpTime(), client.getNtpTimeReference(), ntpCertainty);return true;} else {return false;

三，调试：

1. 通过adb更改当前服务器地址

adb shell settings put global ntp_server ntp.ntsc.ac.cn  //更改服务器地址
adb shell setprop persist.sys.timezone Asia/Shangha  //更改时区
adb shell settings get global ntp_server  //查看当前使用地址
adb shel1 settings put global auto_time 1  //打开网络同步时间开关
adb shel1 settings put global auto_time 0  //关闭网络同步时间开关