1、前言

在前段时间的项目中遇到客户的设备出现APN断开的情况没有自动连接，后来折腾了一段时间解决了这个问题。现在用这篇博客记录一下APN的选择和连接流程。

2、名词解析

• APN：APN指一种网络接入技术，是通过手机上网时必须配置的一个参数，它决定了手机通过哪种接入方式来访问网络。
  对于手机用户来说，可以访问的外部网络类型有很多，例如：Internet、WAP网站、集团企业内部网络、行业内部专用网络。而不同的接入点所能访问的范围以及接入的方式是不同的，网络侧如何知道手机激活以后要访问哪个网络从而分配哪个网段的IP呢，这就要靠APN来区分了，即APN决定了用户的手机通过哪种接入方式来访问什么样的网络。

• PDN:Packet data network，分组数据网，即常说的Internet，在GPRS网络中代表外部数据网络的总称

3、Android 中APN的存储形式

Android 系统中APN是以apns-conf.xml文件的形式配置的，位于设备中的system/etc目录下。
apn 的配置信息如下：

  <apn carrier="ENTEL4G" //运营商mcc="736" //Mobile Country Code，移动国家码mnc="02"  //Mobile Network Code，移动网络码apn="4g.entel" //apn名称user=""password=""proxy="" //代理port=""  //端口authtype="2"type="default,supl" //apn类型/>

4、初识TelephonyProvider

4.1 apn文件是怎么被解析的呢，设置中的apn信息怎么保存的呢?

这里就轮到TelephonyProvider 出场了。
TelephonyProvider继承自ContentProvider，在android中的代码路径为：
packages/providers/TelephonyProvider。

它的UML类图如下：

在AndroidManifest.xml中可以看到application 标签中定义了android:process=“com.android.phone” ，这样TelephonyProvider就运行在com.android.phone进程中，也就是packages\services\Telephony 目录下的Telephony服务。

4.2 TelephonyProvider 的onCreate()函数

代码如下：

    @Overridepublic boolean onCreate() {mOpenHelper = new DatabaseHelper(getContext());// Call getReadableDatabase() to make sure onUpgrade is calledif (VDBG) log("onCreate: calling getReadableDatabase to trigger onUpgrade");SQLiteDatabase db = mOpenHelper.getReadableDatabase();// Update APN db on build updateString newBuildId = SystemProperties.get("ro.build.id", null);if (!TextUtils.isEmpty(newBuildId)) {// Check if build id has changedSharedPreferences sp = getContext().getSharedPreferences(BUILD_ID_FILE,Context.MODE_PRIVATE);String oldBuildId = sp.getString(RO_BUILD_ID, "");if (!newBuildId.equals(oldBuildId)) {if (DBG) log("onCreate: build id changed from " + oldBuildId + " to " + newBuildId);// Get rid of old preferred apn shared preferencesSubscriptionManager sm = SubscriptionManager.from(getContext());if (sm != null) {List<SubscriptionInfo> subInfoList = sm.getAllSubscriptionInfoList();for (SubscriptionInfo subInfo : subInfoList) {SharedPreferences spPrefFile = getContext().getSharedPreferences(PREF_FILE_APN + subInfo.getSubscriptionId(), Context.MODE_PRIVATE);if (spPrefFile != null) {SharedPreferences.Editor editor = spPrefFile.edit();editor.clear();editor.apply();}}}// Update APN DBupdateApnDb();} else {if (VDBG) log("onCreate: build id did not change: " + oldBuildId);}sp.edit().putString(RO_BUILD_ID, newBuildId).apply();} else {if (VDBG) log("onCreate: newBuildId is empty");}if (VDBG) log("onCreate:- ret true");return true;}

从上面的代码，我们知道TelephonyProvider初始化时的主要工作包括：

1. new DatabaseHelper 创建出数据库；
2. 根据build_id的值，如果跟之前的不同则重新load apn xml文件写入到数据库中，并将之前选中的sharepreference记录选中的 apn清除，并且最后将数据中不在apn xml文件中的数据行全部删除。

4.3 TelephonyProvider 的内部类 DatabaseHelper

DatabaseHelper是 TelephonyProvider 的一个内部类，在TelephonyProvider 的onCreate函数中首先被创建。

4.3.1 DatabaseHelper的构造函数中会传入数据的名字用于创建数据库

这个DATABASE_NAME 就是"telephony.db"，创建路径位于：/data/user_de/0/com.android.providers.telephony/databases/telephony.db

  public DatabaseHelper(Context context) {super(context, DATABASE_NAME, null, getVersion(context));mContext = context;}

4.3.2 DatabaseHelper 的onCreate函数

       @Overridepublic void onCreate(SQLiteDatabase db) {if (DBG) log("dbh.onCreate:+ db=" + db);createSimInfoTable(db); createCarriersTable(db, CARRIERS_TABLE);initDatabase(db);if (DBG) log("dbh.onCreate:- db=" + db);}

这里可以看到它作了三件事：

• 1、创建SIM卡信息的表
• 2、创建运营商信息的表
• 3、初始化数据库，这里是重点。

4.3.2 DatabaseHelper 的 initDatabase（）初始化作了哪些事

从这个代码中可以看到函数中主要是：

• 1、使用XML 解析apn-conf.xml文件并写入到数据库中。
• 2、将数据库中不是xml中的数据清除掉。

        private void initDatabase(SQLiteDatabase db) {if (VDBG) log("dbh.initDatabase:+ db=" + db);// Read internal APNS dataResources r = mContext.getResources();XmlResourceParser parser = r.getXml(com.android.internal.R.xml.apns);int publicversion = -1;try {XmlUtils.beginDocument(parser, "apns");publicversion = Integer.parseInt(parser.getAttributeValue(null, "version"));loadApns(db, parser);} catch (Exception e) {loge("Got exception while loading APN database." + e);} finally {parser.close();}// Read external APNS data (partner-provided)XmlPullParser confparser = null;File confFile = getApnConfFile();FileReader confreader = null;if (DBG) log("confFile = " + confFile);try {confreader = new FileReader(confFile);confparser = Xml.newPullParser();confparser.setInput(confreader);XmlUtils.beginDocument(confparser, "apns");// Sanity check. Force internal version and confidential versions to agreeint confversion = Integer.parseInt(confparser.getAttributeValue(null, "version"));if (publicversion != confversion) {log("initDatabase: throwing exception due to version mismatch");throw new IllegalStateException("Internal APNS file version doesn't match "+ confFile.getAbsolutePath());}loadApns(db, confparser);} catch (FileNotFoundException e) {// It's ok if the file isn't found. It means there isn't a confidential file// Log.e(TAG, "File not found: '" + confFile.getAbsolutePath() + "'");} catch (Exception e) {loge("initDatabase: Exception while parsing '" + confFile.getAbsolutePath() + "'" +e);} finally {// Get rid of user/carrier deleted entries that are not present in apn xml file.// Those entries have edited value USER_DELETED/CARRIER_DELETED.if (VDBG) {log("initDatabase: deleting USER_DELETED and replacing "+ "DELETED_BUT_PRESENT_IN_XML with DELETED");}// Delete USER_DELETEDdb.delete(CARRIERS_TABLE, IS_USER_DELETED + " or " + IS_CARRIER_DELETED, null);// Change USER_DELETED_BUT_PRESENT_IN_XML to USER_DELETEDContentValues cv = new ContentValues();cv.put(EDITED, USER_DELETED);db.update(CARRIERS_TABLE, cv, IS_USER_DELETED_BUT_PRESENT_IN_XML, null);// Change CARRIER_DELETED_BUT_PRESENT_IN_XML to CARRIER_DELETEDcv = new ContentValues();cv.put(EDITED, CARRIER_DELETED);db.update(CARRIERS_TABLE, cv, IS_CARRIER_DELETED_BUT_PRESENT_IN_XML, null);if (confreader != null) {try {confreader.close();} catch (IOException e) {// do nothing}}// Update the stored checksumsetApnConfChecksum(getChecksum(confFile));}if (VDBG) log("dbh.initDatabase:- db=" + db);}

apn的xml 有那些呢 ？根据getApnConfFile 函数可以知道有如下这些目录。

        private File getApnConfFile() {// Environment.getRootDirectory() is a fancy way of saying ANDROID_ROOT or "/system".File confFile = new File(Environment.getRootDirectory(), PARTNER_APNS_PATH);File oemConfFile =  new File(Environment.getOemDirectory(), OEM_APNS_PATH);File updatedConfFile = new File(Environment.getDataDirectory(), OTA_UPDATED_APNS_PATH);confFile = getNewerFile(confFile, oemConfFile);confFile = getNewerFile(confFile, updatedConfFile);return confFile;}

   private static final String PARTNER_APNS_PATH = "etc/apns-conf.xml";private static final String OEM_APNS_PATH = "telephony/apns-conf.xml";private static final String OTA_UPDATED_APNS_PATH = "misc/apns-conf.xml";private static final String OLD_APNS_PATH = "etc/old-apns-conf.xml";

到这里TelephonyProvider的业务就很清晰了，他就要就是开机的时候会根据build id来判断是否试正常开机还是升级之后的不同版本，如果不同，则重新创建telephony.db数据库，并重新解析加载apn.xml文件写入到数库中。

5、开机之后APN界面是怎么自动选择APN连接的呢 ？

刚开始我以为设置界面开机之后会默认选择一个已连接的APN的逻辑是在设置里面做的，看了一下设置ApnSettings.java相关的代码发现并没有如何选择apn去拨号的操作。

代码路径：packages\apps\Settings\src\com\android\settings\ApnSettings.java

    @Overridepublic void onCreate(Bundle icicle) {super.onCreate(icicle);final Activity activity = getActivity();final int subId = activity.getIntent().getIntExtra(SUB_ID,SubscriptionManager.INVALID_SUBSCRIPTION_ID);mMobileStateFilter = new IntentFilter(TelephonyIntents.ACTION_ANY_DATA_CONNECTION_STATE_CHANGED);setIfOnlyAvailableForAdmins(true);mSubscriptionInfo = SubscriptionManager.from(activity).getActiveSubscriptionInfo(subId);mUiccController = UiccController.getInstance();CarrierConfigManager configManager = (CarrierConfigManager)getSystemService(Context.CARRIER_CONFIG_SERVICE);PersistableBundle b = configManager.getConfig();mHideImsApn = b.getBoolean(CarrierConfigManager.KEY_HIDE_IMS_APN_BOOL);mAllowAddingApns = b.getBoolean(CarrierConfigManager.KEY_ALLOW_ADDING_APNS_BOOL);mUserManager = UserManager.get(activity);}

如果不是上层应用自动拨号的，那就是底层自动选择的了 ？带着疑问我看了一下开机后的log打印流程发现了端倪：在DCTracker的log中发现DcTracker对象被创建后会注册监听RILD上报事件，当上报EVENT_DATA_CONNECTION_ATTACHED 就会创建apn列表并且获取preference apn 进行拨号，当然第一次没有设置是没有preference apn 的，这里就从 apn 列表中选择apn 进行拨号，按着这条线索继续看一下DCTracker 的代码逻辑吧。

6、DCTracker 登场

这里先放一张DCTracker 的相关类图，它是Telephony架构中监听SIM状态的状态变化和拨号的结果，类似于WifiTrakcker或者NetworkMonitor这样的角色。它是跟随着com.android.phone进程启动的时候创建的，不同类型phone 对应着一种DcTracker。

6.1 DcTracker的构造函数

代码路径：frameworks/opt/telephony/src/java/com/android/internal/telephony/dataconnection/DcTracker.java

构造函数很长，但是总结一下就主要干了这几件事：

• 1、初始化mUiccController 并注册监听SIM状态。
• 2、registerForAllEvents() 注册监听事件。
• 3、监听数据库变化以及其他的一些初始化工作。

这里看看registerForAllEvents 监听事件。

    //***** Constructorpublic DcTracker(Phone phone) {super();mPhone = phone;if (DBG) log("DCT.constructor");mResolver = mPhone.getContext().getContentResolver();mUiccController = UiccController.getInstance();mUiccController.registerForIccChanged(this, DctConstants.EVENT_ICC_CHANGED, null);mAlarmManager =(AlarmManager) mPhone.getContext().getSystemService(Context.ALARM_SERVICE);mCm = (ConnectivityManager) mPhone.getContext().getSystemService(Context.CONNECTIVITY_SERVICE);IntentFilter filter = new IntentFilter();filter.addAction(Intent.ACTION_SCREEN_ON);filter.addAction(Intent.ACTION_SCREEN_OFF);filter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION);filter.addAction(WifiManager.WIFI_STATE_CHANGED_ACTION);filter.addAction(INTENT_DATA_STALL_ALARM);filter.addAction(INTENT_PROVISIONING_APN_ALARM);// TODO - redundent with update call below?mDataEnabledSettings.setUserDataEnabled(getDataEnabled());mPhone.getContext().registerReceiver(mIntentReceiver, filter, null, mPhone);SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(mPhone.getContext());mAutoAttachOnCreation.set(sp.getBoolean(Phone.DATA_DISABLED_ON_BOOT_KEY, false));mSubscriptionManager = SubscriptionManager.from(mPhone.getContext());mSubscriptionManager.addOnSubscriptionsChangedListener(mOnSubscriptionsChangedListener);HandlerThread dcHandlerThread = new HandlerThread("DcHandlerThread");dcHandlerThread.start();Handler dcHandler = new Handler(dcHandlerThread.getLooper());mDcc = DcController.makeDcc(mPhone, this, dcHandler);mDcTesterFailBringUpAll = new DcTesterFailBringUpAll(mPhone, dcHandler);mDataConnectionTracker = this;registerForAllEvents();update();mApnObserver = new ApnChangeObserver();phone.getContext().getContentResolver().registerContentObserver(Telephony.Carriers.CONTENT_URI, true, mApnObserver);initApnContexts();for (ApnContext apnContext : mApnContexts.values()) {// Register the reconnect and restart actions.filter = new IntentFilter();filter.addAction(INTENT_RECONNECT_ALARM + '.' + apnContext.getApnType());mPhone.getContext().registerReceiver(mIntentReceiver, filter, null, mPhone);}// Add Emergency APN to APN setting list by default to support EPDN in sim absent casesinitEmergencyApnSetting();addEmergencyApnSetting();mProvisionActionName = "com.android.internal.telephony.PROVISION" + phone.getPhoneId();mSettingsObserver = new SettingsObserver(mPhone.getContext(), this);registerSettingsObserver();//[FEATURE]-Add-BEGIN by (songzhihao@paxsz.com) 2021/03/30 for network occour problem.SystemProperties.set(paxRestRadio, "120000");//[FEATURE]-Add-END by (songzhihao@paxsz.com) 2021/03/30 for network occour problem.}

6.2 registerForAllEvents监听事件

这里最重要的还是EVENT_DATA_CONNECTION_ATTACHED 表示modem 注网完成接下来进行拨号的状态。

    private void registerForAllEvents() {mPhone.mCi.registerForAvailable(this, DctConstants.EVENT_RADIO_AVAILABLE, null);mPhone.mCi.registerForOffOrNotAvailable(this,DctConstants.EVENT_RADIO_OFF_OR_NOT_AVAILABLE, null);mPhone.mCi.registerForDataNetworkStateChanged(this,DctConstants.EVENT_DATA_STATE_CHANGED, null);// Note, this is fragile - the Phone is now presenting a merged picture// of PS (volte) & CS and by diving into its internals you're just seeing// the CS data.  This works well for the purposes this is currently used for// but that may not always be the case.  Should probably be redesigned to// accurately reflect what we're really interested in (registerForCSVoiceCallEnded).mPhone.getCallTracker().registerForVoiceCallEnded(this,DctConstants.EVENT_VOICE_CALL_ENDED, null);mPhone.getCallTracker().registerForVoiceCallStarted(this,DctConstants.EVENT_VOICE_CALL_STARTED, null);registerServiceStateTrackerEvents();//   SubscriptionManager.registerForDdsSwitch(this,//          DctConstants.EVENT_CLEAN_UP_ALL_CONNECTIONS, null);mPhone.mCi.registerForPcoData(this, DctConstants.EVENT_PCO_DATA_RECEIVED, null);}public void registerServiceStateTrackerEvents() {mPhone.getServiceStateTracker().registerForDataConnectionAttached(this,DctConstants.EVENT_DATA_CONNECTION_ATTACHED, null);mPhone.getServiceStateTracker().registerForDataConnectionDetached(this,DctConstants.EVENT_DATA_CONNECTION_DETACHED, null);mPhone.getServiceStateTracker().registerForDataRoamingOn(this,DctConstants.EVENT_ROAMING_ON, null);mPhone.getServiceStateTracker().registerForDataRoamingOff(this,DctConstants.EVENT_ROAMING_OFF, null);mPhone.getServiceStateTracker().registerForPsRestrictedEnabled(this,DctConstants.EVENT_PS_RESTRICT_ENABLED, null);mPhone.getServiceStateTracker().registerForPsRestrictedDisabled(this,DctConstants.EVENT_PS_RESTRICT_DISABLED, null);mPhone.getServiceStateTracker().registerForDataRegStateOrRatChanged(this,DctConstants.EVENT_DATA_RAT_CHANGED, null);}

6.3 拨号前的准备工作setupDataOnConnectableApns

RILD注网成功之后会上报Attached 事件，也就是DcTracker监听到EVENT_DATA_CONNECTION_ATTACHED 事件之后会 执行onDataConnectionAttached.

case DctConstants.EVENT_DATA_CONNECTION_ATTACHED:onDataConnectionAttached();break;

onDataConnectionAttached()函数做一些notify phone 的操作后会执行setupDataOnConnectableApns，这里就开始准备拨号工作了。

这里APN的类型可能有多种，进行遍历之后清除APN的连接状态。最后根据APN的状态判断如果当前APN的类型是isConnectable就开始调用trySetupData(apnContext, waitingApns)正式进入拨号流程了，因为调用setupDataOnConnectableApns时传入的参数是RetryFailures.ALWAYS，所以这里waitingApns 是null。

    private void setupDataOnConnectableApns(String reason, RetryFailures retryFailures) {if (VDBG) log("setupDataOnConnectableApns: " + reason);if (DBG && !VDBG) {StringBuilder sb = new StringBuilder(120);for (ApnContext apnContext : mPrioritySortedApnContexts) {sb.append(apnContext.getApnType());sb.append(":[state=");sb.append(apnContext.getState());sb.append(",enabled=");sb.append(apnContext.isEnabled());sb.append("] ");}log("setupDataOnConnectableApns: " + reason + " " + sb);}for (ApnContext apnContext : mPrioritySortedApnContexts) {ArrayList<ApnSetting> waitingApns = null;if (VDBG) log("setupDataOnConnectableApns: apnContext " + apnContext);if (apnContext.getState() == DctConstants.State.FAILED|| apnContext.getState() == DctConstants.State.SCANNING) {if (retryFailures == RetryFailures.ALWAYS) {apnContext.releaseDataConnection(reason);} else if (apnContext.isConcurrentVoiceAndDataAllowed() == false &&mPhone.getServiceStateTracker().isConcurrentVoiceAndDataAllowed()) {// RetryFailures.ONLY_ON_CHANGE - check if voice concurrency has changedapnContext.releaseDataConnection(reason);} else {// RetryFailures.ONLY_ON_CHANGE - check if the apns have changedint radioTech = mPhone.getServiceState().getRilDataRadioTechnology();ArrayList<ApnSetting> originalApns = apnContext.getWaitingApns();if (originalApns != null && originalApns.isEmpty() == false) {waitingApns = buildWaitingApns(apnContext.getApnType(), radioTech);if (originalApns.size() != waitingApns.size() ||originalApns.containsAll(waitingApns) == false) {apnContext.releaseDataConnection(reason);} else {continue;}} else {continue;}}}if (apnContext.isConnectable()) {log("isConnectable() call trySetupData");apnContext.setReason(reason);trySetupData(apnContext, waitingApns);}}}

6.4 、开始拨号工作trySetupData

trySetupData（）函数主要做两件事

• 1、判断APN状态是DctConstants.State.IDLE 的时候调用buildWaitingApns 构建拨号APN列表 并通过apnContext.setWaitingApns(waitingApns)将waitingApns列表设置到apnContext 中。
• 2、调用setupData(apnContext, radioTech)使用apn进行拨号连接。

 if (apnContext.getState() == DctConstants.State.IDLE) {if (waitingApns == null) {waitingApns = buildWaitingApns(apnContext.getApnType(), radioTech);}if (waitingApns.isEmpty()) {notifyNoData(DcFailCause.MISSING_UNKNOWN_APN, apnContext);notifyOffApnsOfAvailability(apnContext.getReason());String str = "trySetupData: X No APN found retValue=false";if (DBG) log(str);apnContext.requestLog(str);return false;} else {apnContext.setWaitingApns(waitingApns);isReconnectedFinsh = false;if (DBG) {log ("trySetupData: Create from mAllApnSettings : "+ apnListToString(mAllApnSettings)+" isReconnectedFinsh "+isReconnectedFinsh);}}}

6.5、buildWaitingApns分析

buildWaitingApns函数新建的一个WaitingApns集合的APN来源有两个：

• 1、getPreferredApn()从文件存储中去获取之前选中过的APN，如果该APN 的Type类型为上网的类型并且numeric 国家码和SIM卡的国家码一致，就将此apn添加到apn拨号列表中，如果不同就清除保存的preferenceAPN为-1，这样可以防止换了SIM卡的情况。当然恢复出厂设置或者刷机第一次起来的时候这个preferenceAPN也是NULL的，因为没有设置过。

• 2、从mAllApnSettings 中遍历选中APN的type 为拨号相同type的APN 添加到拨号列表中，mAllApnSettings 自动从代码里面搜一下可以看到它是从数据库中搜索而来的，根据MMC国家码来判断如果和SIM卡相同就添加到mAllApnSettings 列表中，这样mAllApnSettings 列表中实际上是有很多不同type 比如上网，短信等等类型的apn。

    /*** Build a list of APNs to be used to create PDP's.** @param requestedApnType* @return waitingApns list to be used to create PDP*          error when waitingApns.isEmpty()*/private ArrayList<ApnSetting> buildWaitingApns(String requestedApnType, int radioTech) {if (DBG) log("buildWaitingApns: E requestedApnType=" + requestedApnType);ArrayList<ApnSetting> apnList = new ArrayList<ApnSetting>();if (requestedApnType.equals(PhoneConstants.APN_TYPE_DUN)) {ApnSetting dun = fetchDunApn();if (dun != null) {apnList.add(dun);if (DBG) log("buildWaitingApns: X added APN_TYPE_DUN apnList=" + apnList);return apnList;}}IccRecords r = mIccRecords.get();String operator = (r != null) ? r.getOperatorNumeric() : "";// This is a workaround for a bug (7305641) where we don't failover to other// suitable APNs if our preferred APN fails.  On prepaid ATT sims we need to// failover to a provisioning APN, but once we've used their default data// connection we are locked to it for life.  This change allows ATT devices// to say they don't want to use preferred at all.boolean usePreferred = true;try {usePreferred = ! mPhone.getContext().getResources().getBoolean(com.android.internal.R.bool.config_dontPreferApn);} catch (Resources.NotFoundException e) {if (DBG) log("buildWaitingApns: usePreferred NotFoundException set to true");usePreferred = true;}if (usePreferred) {//查询数据库看是否有志气设置的已经选中过的APNmPreferredApn = getPreferredApn();}if (DBG) {log("buildWaitingApns: usePreferred=" + usePreferred+ " canSetPreferApn=" + mCanSetPreferApn+ " mPreferredApn=" + mPreferredApn+ " operator=" + operator + " radioTech=" + radioTech+ " IccRecords r=" + r);}if (usePreferred && mCanSetPreferApn && mPreferredApn != null &&mPreferredApn.canHandleType(requestedApnType)) {if (DBG) {log("buildWaitingApns: Preferred APN:" + operator + ":"+ mPreferredApn.numeric + ":" + mPreferredApn);}if (mPreferredApn.numeric.equals(operator)) {if (ServiceState.bitmaskHasTech(mPreferredApn.bearerBitmask, radioTech)) {apnList.add(mPreferredApn);if (DBG) log("buildWaitingApns: X added preferred apnList=" + apnList);return apnList;} else {if (DBG) log("buildWaitingApns: no preferred APN");setPreferredApn(-1);mPreferredApn = null;}} else {if (DBG) log("buildWaitingApns: no preferred APN");setPreferredApn(-1);mPreferredApn = null;}}if (mAllApnSettings != null) {if (DBG) log("buildWaitingApns: mAllApnSettings=" + mAllApnSettings);for (ApnSetting apn : mAllApnSettings) {if (apn.canHandleType(requestedApnType)) {if (ServiceState.bitmaskHasTech(apn.bearerBitmask, radioTech)) {if (DBG) log("buildWaitingApns: adding apn=" + apn);apnList.add(apn);} else {if (DBG) {log("buildWaitingApns: bearerBitmask:" + apn.bearerBitmask + " does " +"not include radioTech:" + radioTech);}}} else if (DBG) {log("buildWaitingApns: couldn't handle requested ApnType="+ requestedApnType);}}} else {loge("mAllApnSettings is null!");}if (DBG) log("buildWaitingApns: " + apnList.size() + " APNs in the list: " + apnList);return apnList;}

6.6 、apnContext.setWaitingApns(waitingApns)

setWaitingApns是RetryManager.java的一个方法，代码路径是：frameworks/opt/telephony/src/java/com/android/internal/telephony/RetryManager.java

设置apnContext的waitingApns 时会配置RetryManager的config 信息，debug 版本可以通过SystemProperties.get("test.data_retry_config")配置测试，我们这里用默认的SIM配置。包含apn重试最大次数，apn重试延迟时间等等，和获取当前重试apn列表的mCurrentApnIndex 索引，在每次设置setWaitingApns都会将这些config信息全部reset。这就意味着如果设置一次setWaitingApns，所有的重试策略都会重置，apn列表选择重新开始。这里其实是有点问题的，后面再说。

    private void reset() {mMaxRetryCount = 0;mRetryCount = 0;mCurrentApnIndex = -1;mSameApnRetryCount = 0;mModemSuggestedDelay = NO_SUGGESTED_RETRY_DELAY;mRetryArray.clear();}

6.7、setupData（）拨号函数。

• 1、setupData拨号的时候首先通过apnSetting = apnContext.getNextApnSetting() 从apnContext中获取拨号列表中的apn。
• 2、这里有几种情况下会替换apnContext 中的apnSetting:

1>还有dataConnection没有断开，直接dcacApnSetting = dcac.getApnSettingSync()获取dcac的apnSetting 替换用来拨号。

2> dcac断开的情况下，如果isOnlySingleDcAllowed或者isHigherPriorityApnContextActive ，就是如果是只允许单dcac模式或者有更高优先级的apnContext也是不用getNextApnSetting得到的apnSetting直接return返回停止拨号。

3>上述情况都不满足的情况下会cleanUpAllConnections断开 当前所以apnContext连接，如果是不是IDLE或者FAILED状态则表示cleanUpAllConnections没有完成清除，这种情况下也是直接return停止拨号操作。

• 3、以上判断走完后就会将当前的apnContext设置为参数通过EVENT_DATA_SETUP_COMPLETE 发送给RILD最终完成拨号。

      Message msg = obtainMessage();msg.what = DctConstants.EVENT_DATA_SETUP_COMPLETE;msg.obj = new Pair<ApnContext, Integer>(apnContext, generation);dcac.bringUp(apnContext, profileId, radioTech, msg, generation);private boolean setupData(ApnContext apnContext, int radioTech) {if (DBG) log("setupData: apnContext=" + apnContext);apnContext.requestLog("setupData");ApnSetting apnSetting;DcAsyncChannel dcac = null;apnSetting = apnContext.getNextApnSetting();log("try this apnSetting:"+apnSetting);if (apnSetting == null) {if (DBG) log("setupData: return for no apn found!");return false;}int profileId = apnSetting.profileId;if (profileId == 0) {profileId = getApnProfileID(apnContext.getApnType());}// On CDMA, if we're explicitly asking for DUN, we need have// a dun-profiled connection so we can't share an existing one// On GSM/LTE we can share existing apn connections provided they support// this type.if (apnContext.getApnType() != PhoneConstants.APN_TYPE_DUN ||teardownForDun() == false) {dcac = checkForCompatibleConnectedApnContext(apnContext);if (dcac != null) {// Get the dcacApnSetting for the connection we want to share.ApnSetting dcacApnSetting = dcac.getApnSettingSync();if (dcacApnSetting != null) {// Setting is good, so use it.log("dcac still connect, dcac.getApnSettingSync():"+dcacApnSetting);apnSetting = dcacApnSetting;}}}if (dcac == null) {if (isOnlySingleDcAllowed(radioTech)) {if (isHigherPriorityApnContextActive(apnContext)) {if (DBG) {log("setupData: Higher priority ApnContext active.  Ignoring call");}return false;}// Only lower priority calls left.  Disconnect them all in this single PDP case// so that we can bring up the requested higher priority call (once we receive// response for deactivate request for the calls we are about to disconnectif (cleanUpAllConnections(true, Phone.REASON_SINGLE_PDN_ARBITRATION)) {// If any call actually requested to be disconnected, means we can't// bring up this connection yet as we need to wait for those data calls// to be disconnected.if (DBG) log("setupData: Some calls are disconnecting first.  Wait and retry");return false;}// No other calls are active, so proceedif (DBG) log("setupData: Single pdp. Continue setting up data call.");}dcac = findFreeDataConnection();if (dcac == null) {dcac = createDataConnection();}if (dcac == null) {if (DBG) log("setupData: No free DataConnection and couldn't create one, WEIRD");return false;}}final int generation = apnContext.incAndGetConnectionGeneration();if (DBG) {log("setupData: dcac=" + dcac + " apnSetting=" + apnSetting + " gen#=" + generation);}apnContext.setDataConnectionAc(dcac);apnContext.setApnSetting(apnSetting);apnContext.setState(DctConstants.State.CONNECTING);mPhone.notifyDataConnection(apnContext.getReason(), apnContext.getApnType());Message msg = obtainMessage();msg.what = DctConstants.EVENT_DATA_SETUP_COMPLETE;msg.obj = new Pair<ApnContext, Integer>(apnContext, generation);dcac.bringUp(apnContext, profileId, radioTech, msg, generation);if (DBG) log("setupData: initing!");return true;}private void setInitialAttachApn() {ApnSetting iaApnSetting = null;ApnSetting defaultApnSetting = null;ApnSetting firstApnSetting = null;log("setInitialApn: E mPreferredApn=" + mPreferredApn);if (mAllApnSettings != null && !mAllApnSettings.isEmpty()) {firstApnSetting = mAllApnSettings.get(0);log("setInitialApn: firstApnSetting=" + firstApnSetting);// Search for Initial APN setting and the first apn that can handle defaultfor (ApnSetting apn : mAllApnSettings) {// Can't use apn.canHandleType(), as that returns true for APNs that have no type.if (ArrayUtils.contains(apn.types, PhoneConstants.APN_TYPE_IA) &&apn.carrierEnabled) {// The Initial Attach APN is highest priority so use it if there is onelog("setInitialApn: iaApnSetting=" + apn);iaApnSetting = apn;break;} else if ((defaultApnSetting == null)&& (apn.canHandleType(PhoneConstants.APN_TYPE_DEFAULT))) {// Use the first default apn if no better choicelog("setInitialApn: defaultApnSetting=" + apn);defaultApnSetting = apn;}}}// The priority of apn candidates from highest to lowest is://   1) APN_TYPE_IA (Initial Attach)//   2) mPreferredApn, i.e. the current preferred apn//   3) The first apn that than handle APN_TYPE_DEFAULT//   4) The first APN we can find.ApnSetting initialAttachApnSetting = null;if (iaApnSetting != null) {if (DBG) log("setInitialAttachApn: using iaApnSetting");initialAttachApnSetting = iaApnSetting;} else if (mPreferredApn != null) {if (DBG) log("setInitialAttachApn: using mPreferredApn");initialAttachApnSetting = mPreferredApn;} else if (defaultApnSetting != null) {if (DBG) log("setInitialAttachApn: using defaultApnSetting");initialAttachApnSetting = defaultApnSetting;} else if (firstApnSetting != null) {if (DBG) log("setInitialAttachApn: using firstApnSetting");initialAttachApnSetting = firstApnSetting;}if (initialAttachApnSetting == null) {if (DBG) log("setInitialAttachApn: X There in no available apn");} else {if (DBG) log("setInitialAttachApn: X selected Apn=" + initialAttachApnSetting);mPhone.mCi.setInitialAttachApn(initialAttachApnSetting.apn,initialAttachApnSetting.protocol, initialAttachApnSetting.authType,initialAttachApnSetting.user, initialAttachApnSetting.password, null);}}

7、拨号完成，4G网络可以正常使用

framework拨号设置完成以后，RILD开始拨号分配ip 这些链路信息成功后会返回给DataConnection EVENT_SETUP_DATA_CONNECTION_DONE事件，同时DataConnection更新自己的networkAgent通知ConnectivityService改变网络状态为Connected,到这里整个拨号流程就全部结束了.

代码路径：frameworks/opt/telephony/src/java/com/android/internal/telephony/dataconnection/DataConnection.java

  private class DcActivatingState extends State {@Overridepublic boolean processMessage(Message msg) {boolean retVal;AsyncResult ar;ConnectionParams cp;if (DBG) log("DcActivatingState: msg=" + msgToString(msg));switch (msg.what) {case EVENT_DATA_CONNECTION_DRS_OR_RAT_CHANGED:case EVENT_CONNECT:// Activating can't process until we're done.deferMessage(msg);retVal = HANDLED;break;case EVENT_SETUP_DATA_CONNECTION_DONE:ar = (AsyncResult) msg.obj;cp = (ConnectionParams) ar.userObj;DataCallResponse.SetupResult result = onSetupConnectionCompleted(ar);if (result != DataCallResponse.SetupResult.ERR_Stale) {if (mConnectionParams != cp) {loge("DcActivatingState: WEIRD mConnectionsParams:"+ mConnectionParams+ " != cp:" + cp);}}if (DBG) {log("DcActivatingState onSetupConnectionCompleted result=" + result+ " dc=" + DataConnection.this);}if (cp.mApnContext != null) {cp.mApnContext.requestLog("onSetupConnectionCompleted result=" + result);}

8、结尾

6.6和6.7中提到的拨号的问题：

我们看一下6.6中 trySetupData 函数里面判断只要是当前apnContext状态为DctConstants.State.IDLE就会去 buildWaitingApns并且设置到apnContext 中，前面我们也提到
apnContext中每次设置setWaitingApns的时候都会重置currentApnSettingIndex脚本，这样每次重试的时候都是重头开始去apn拨号，而且6.7中有很多种情况会替换到从apnContext中取到的apnSetting,比如当前dcac没有断开连接，当前连接正在断开等等状态都会导致拨号跳过，好家伙，这么坑的漏洞就导致客户那边出现的每次拨号都是使用第一个APN拨号，列表的其他apn没有用到，因为都跳过了，导致拨号一直失败，自然设置界面的apn列表当然没有apn被连接上。

这个问题的解决办法就是尽量不要多次调用apnContext.setWaitingApns防止RetryManager的config参数被重置，另外setUpData拨号函数里面如果retrun跳过当前apn的话记录currentIndex这样下次还是使用这个apn拨号，这样就可以保证apn列表循环尝试了。

 if (apnContext.getState() == DctConstants.State.IDLE) {if (waitingApns == null) {waitingApns = buildWaitingApns(apnContext.getApnType(), radioTech);}if (waitingApns.isEmpty()) {notifyNoData(DcFailCause.MISSING_UNKNOWN_APN, apnContext);notifyOffApnsOfAvailability(apnContext.getReason());String str = "trySetupData: X No APN found retValue=false";if (DBG) log(str);apnContext.requestLog(str);return false;} else {apnContext.setWaitingApns(waitingApns);}

文章到这里就全部结束了，如果有不对的地方欢迎评论指正。

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