Android 4.0 WIFI初始化与启动流程

这几天闲着没事，我就随便拿起Android源码看看。以下要讲的是在ICS中wifi初始化的一些流程。

涉及的文件有：

SystemServer.java

WifiSettings.java

WifiEnabler.java

WifiManager.java

WifiService.java

WifiStateMachine.java

android_net_wifi_wifi.cpp

wifi.c

首先从SystemServer.java开始，它做了3个动作：

1.添加注册ConnectivityService连接服务，它跟所有手机的无线通信都有联系，包括wifi，蓝牙，2g网络，3g网络等

connectivity = new ConnectivityService(
                        context, networkManagement, networkStats, networkPolicy);
ServiceManager.addService(Context.CONNECTIVITY_SERVICE, connectivity);

2.管理开机wifi开启与否的问题

wifi.checkAndStartWifi();

    public void checkAndStartWifi() {
        mAirplaneModeOn.set(isAirplaneModeOn());
        mPersistWifiState.set(getPersistedWifiState());
        boolean wifiEnabled = shouldWifiBeEnabled() || testAndClearWifiSavedState();
        setWifiEnabled(wifiEnabled);
        mWifiWatchdogStateMachine = WifiWatchdogStateMachine.
               makeWifiWatchdogStateMachine(mContext);

    }

3.添加注册wifi的核心服务wifiservice

 wifi = new WifiService(context);
 ServiceManager.addService(Context.WIFI_SERVICE, wifi);

好了，机器启动的时候动作就这些。要开启wifi，还需要人在设置界面进行开启。·

下面将一步步介绍wifi是怎样开启起来的

进入wifi设置界面，相关文件WifiSettings.java

开启Wifi的组件是一个CompoundButton，跟它关联起来的是一个WifiEnabler.java类，它是在WifiSettings里面初始化的

    public void onActivityCreated(Bundle savedInstanceState) {
                mWifiEnabler = new WifiEnabler(activity, actionBarSwitch);

    }

当用户点击wifi的开启按钮时候，会触发WifiEnabler里面的onCheckedChanged函数

    public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {

        if (mWifiManager.setWifiEnabled(isChecked)) {
            mSwitch.setEnabled(false);
         } else {
                Toast.makeText(mContext, R.string.wifi_error, Toast.LENGTH_SHORT).show();
    }

在onCheckedChanged函数里面，调用了WifiManager的setWifiEnabled方法

    public boolean setWifiEnabled(boolean enabled) {
        try {
            return mService.setWifiEnabled(enabled);
        } catch (RemoteException e) {
            return false;
        }
    }

它返回的是mService.setWifiEnabled(enabled)，这里的mService是WifiService的代理，所以它实际调用的是wifiService里面的setWifiEnabled函数

public class WifiService extends IWifiManager.Stub ，我们可以看到WifiService继承一个接口IWifiManager.Stub，凡是继承了像这种形式写法的接口服务，都可以进行远程调用，这就是Android内部的aidl通信。接下来进入wifiservice

    public synchronized boolean setWifiEnabled(boolean enable) {

        mWifiStateMachine.setWifiEnabled(enable);

    }

可以看到，又进入WifiStateMachine的setWifiEnabled方法，mWifiStateMachine是在Wifiservice的构造函数完成初始化 的

    WifiService(Context context) {

        mWifiStateMachine = new WifiStateMachine(mContext, mInterfaceName);

    }

先介绍一下WifiStateMachine这个类，光看名字就知道wifi状态机，它里面记录了wifi的各种状态，driverUnloadedstate、mDriverUnloadingState、mDriverLoadingState、mDriverLoadedState、mSupplicantStartingState，每种状态都有enter（）、exit（）、processMessage（）3个函数，分别处理进入该状态，退出该状态的动作，以及消息处理。在WifiStateMachine构造函数里面，它把所有状态都添加进状态机去，形成一个状态树，并在结尾出启动这个状态机工作。

    public WifiStateMachine(Context context, String wlanInterface) {

        addState(mDefaultState);
            addState(mInitialState, mDefaultState);
            addState(mDriverUnloadingState, mDefaultState);
            addState(mDriverUnloadedState, mDefaultState);
                addState(mDriverFailedState, mDriverUnloadedState);
            addState(mDriverLoadingState, mDefaultState);
            addState(mDriverLoadedState, mDefaultState);
            addState(mSupplicantStartingState, mDefaultState);
            addState(mSupplicantStartedState, mDefaultState);
                addState(mDriverStartingState, mSupplicantStartedState);
                addState(mDriverStartedState, mSupplicantStartedState);
                    addState(mScanModeState, mDriverStartedState);
                    addState(mConnectModeState, mDriverStartedState);
                        addState(mConnectingState, mConnectModeState);
                        addState(mConnectedState, mConnectModeState);
                        addState(mDisconnectingState, mConnectModeState);
                        addState(mDisconnectedState, mConnectModeState);
                        addState(mWaitForWpsCompletionState, mConnectModeState);
                addState(mDriverStoppingState, mSupplicantStartedState);
                addState(mDriverStoppedState, mSupplicantStartedState);
            addState(mSupplicantStoppingState, mDefaultState);
            addState(mSoftApStartingState, mDefaultState);
            addState(mSoftApStartedState, mDefaultState);
                addState(mTetheringState, mSoftApStartedState);
                addState(mTetheredState, mSoftApStartedState);
            addState(mSoftApStoppingState, mDefaultState);
            addState(mWaitForP2pDisableState, mDefaultState);

    。。。。。。。。。。

         start();

    }

具体状态机是如何工作的，这篇文章有很详细的介绍，我就不累赘了。

http://archive.cnblogs.com/a/2424626/

我们再回到mWifiStateMachine.setWifiEnabled(enable)函数;

    public void setWifiEnabled(boolean enable) {
        mLastEnableUid.set(Binder.getCallingUid());
        if (enable) {
            /* Argument is the state that is entered prior to load */
            sendMessage(obtainMessage(CMD_LOAD_DRIVER, WIFI_STATE_ENABLING, 0));
            sendMessage(CMD_START_SUPPLICANT);
        } else {
            sendMessage(CMD_STOP_SUPPLICANT);
            /* Argument is the state that is entered upon success */
            sendMessage(obtainMessage(CMD_UNLOAD_DRIVER, WIFI_STATE_DISABLED, 0));
        }
    }

它做了两个动作，向状态机发送了2个消息

sendMessage(obtainMessage(CMD_LOAD_DRIVER, WIFI_STATE_ENABLING, 0));加载驱动

sendMessage(CMD_START_SUPPLICANT);开启supplicant

它在哪里处理的呢？

状态机构造函数初始化时候，设置有个一个初始状态

        setInitialState(mInitialState);

我们进入mInitialState状态看看

        public void enter() {
            if (WifiNative.isDriverLoaded()) {
                transitionTo(mDriverLoadedState);
            }
            else {
                transitionTo(mDriverUnloadedState);
            }
因为最开始驱动都是没有加载的，所以进入transitionTo(mDriverUnloadedState);

transitionTo函数是状态切换的函数。

继续mDriverUnloadedState

    class DriverUnloadedState extends State {
         @Override
        public boolean processMessage(Message message) {
               switch (message.what) {
                case CMD_LOAD_DRIVER:
                    mWifiP2pChannel.sendMessage(WIFI_ENABLE_PENDING);
                    transitionTo(mWaitForP2pDisableState);
                    break;
                case WifiP2pService.P2P_ENABLE_PENDING:
                    mReplyChannel.replyToMessage(message, P2P_ENABLE_PROCEED);
                    break;
                default:
                    return NOT_HANDLED;
            }
            EventLog.writeEvent(EVENTLOG_WIFI_EVENT_HANDLED, message.what);
            return HANDLED;
        }
    }

这里会处理刚才的CMD_LOAD_DRIVER这个消息，继续切换到mWaitForP2pDisableState

    class WaitForP2pDisableState extends State {
        @Override
        public boolean processMessage(Message message) {
            if (DBG) log(getName() + message.toString() + "\n");
            switch(message.what) {
                case WifiP2pService.WIFI_ENABLE_PROCEED:
                    //restore argument from original message (CMD_LOAD_DRIVER)
                    message.arg1 = mSavedArg;
                    transitionTo(mDriverLoadingState);

                    break;

    }

状态继续切换到mDriverLoadingState

    class DriverLoadingState extends State {
        @Override
        public void enter() {
 
            new Thread(new Runnable() {
                public void run() {
                    mWakeLock.acquire();
                    //enabling state
                    switch(message.arg1) {
                        case WIFI_STATE_ENABLING:
                            setWifiState(WIFI_STATE_ENABLING);
                            break;
                        case WIFI_AP_STATE_ENABLING:
                            setWifiApState(WIFI_AP_STATE_ENABLING);
                            break;
                    }

                    if(WifiNative.loadDriver()) {
                        if (DBG) log("Driver load successful");
                        sendMessage(CMD_LOAD_DRIVER_SUCCESS);
                    } else {
                        loge("Failed to load driver!");
                        switch(message.arg1) {
                            case WIFI_STATE_ENABLING:
                                setWifiState(WIFI_STATE_UNKNOWN);
                                break;
                            case WIFI_AP_STATE_ENABLING:
                                setWifiApState(WIFI_AP_STATE_FAILED);
                                break;
                        }
                        sendMessage(CMD_LOAD_DRIVER_FAILURE);
                    }
                    mWakeLock.release();
                }
            }).start();
        }

这里回调用WifiNative.loadDriver()加载驱动，成功后发送消息CMD_LOAD_DRIVER_SUCCESS，否则CMD_LOAD_DRIVER_FAILURE，进入JNI

static jboolean android_net_wifi_loadDriver(JNIEnv* env, jobject)
{
    return (jboolean)(::wifi_load_driver() == 0);
}

会继续到wifi.c处理

int wifi_load_driver()
{
#ifdef WIFI_DRIVER_MODULE_PATH
    char driver_status[PROPERTY_VALUE_MAX];
    int count = 100; /* wait at most 20 seconds for completion */
    int status = -1;

    if (is_wifi_driver_loaded()) {
        return 0;
    }
    /* ensure that wlan driver config file exists (if specified) */
    if (ensure_wlan_driver_config_file_exists()) {
        return -1;
    }
    property_set(DRIVER_PROP_NAME, "loading");

    if(system(SDIO_POLLING_ON))
        LOGW("Couldn't turn on SDIO polling: %s", SDIO_POLLING_ON);

    if ('\0' != *DRIVER_SDIO_IF_MODULE_PATH) {
       if (insmod(DRIVER_SDIO_IF_MODULE_PATH, DRIVER_SDIO_IF_MODULE_ARG) < 0) {
           goto end;
       }
    }

    if (insmod(DRIVER_MODULE_PATH, DRIVER_MODULE_ARG) < 0) {
        if ('\0' != *DRIVER_SDIO_IF_MODULE_NAME) {
           rmmod(DRIVER_SDIO_IF_MODULE_NAME);
        }
        goto end;
    }

    if (strcmp(FIRMWARE_LOADER,"") == 0) {
        /* usleep(WIFI_DRIVER_LOADER_DELAY); */
        property_set(DRIVER_PROP_NAME, "ok");
    }
    else {
        property_set("ctl.start", FIRMWARE_LOADER);
    }

    sched_yield();
    while (count-- > 0) {
        if (property_get(DRIVER_PROP_NAME, driver_status, NULL)) {
            if (strcmp(driver_status, "ok") == 0) {
                status = 0;
                goto end;
            }
            else if (strcmp(driver_status, "failed") == 0) {
                _wifi_unload_driver();
                goto end;
            }
        }
        usleep(200000);
    }
    property_set(DRIVER_PROP_NAME, "timeout");
    wifi_unload_driver();
end:
    system(SDIO_POLLING_OFF);
    return status;
#else
    property_set(DRIVER_PROP_NAME, "ok");
    return 0;
#endif
}

这里有几个比较重要的宏

#define WIFI_DRIVER_MODULE_PATH         "/system/lib/modules/wlan.ko"驱动模块地址

static const char SUPP_CONFIG_FILE[]    = "/data/misc/wifi/wpa_supplicant.conf";  supplicant配置文件

在这里wifi.c会跟wpa_supplicant通信，加载驱动

来看另一个消息sendMessage(CMD_START_SUPPLICANT);在DriverLoadedState处理

    class DriverLoadedState extends State {
        @Override
        public boolean processMessage(Message message) {
        
                case CMD_START_SUPPLICANT:
                    try {
                        mNwService.wifiFirmwareReload(mInterfaceName, "STA");
                    } catch (Exception e) {
                        loge("Failed to reload STA firmware " + e);
                        // continue
                    }
                   try {
                         mNwService.setInterfaceIpv6PrivacyExtensions(mInterfaceName, true);
                    } catch (RemoteException re) {
                        loge("Unable to change interface settings: " + re);
                    } catch (IllegalStateException ie) {
                        loge("Unable to change interface settings: " + ie);
                    }

                    if(WifiNative.startSupplicant()) {
                        if (DBG) log("Supplicant start successful");
                        mWifiMonitor.startMonitoring();
                        transitionTo(mSupplicantStartingState);
                    } else {
                        loge("Failed to start supplicant!");
                        sendMessage(obtainMessage(CMD_UNLOAD_DRIVER, WIFI_STATE_UNKNOWN, 0));
                    }
                    break;

继续调用JNI，WifiNative.startSupplicant()，过程差不多最后在wifi.c处理

int wifi_start_supplicant()
{
    return wifi_start_supplicant_common(SUPP_CONFIG_FILE);
}

int wifi_start_supplicant_common(const char *config_file)

。。。。。。。

最后也是在这里跟Wpa_supplicant驱动通信

在wifi状态发生改变的时候，wifistatemachine会通过setwifistate发送WIFI_STATE_CHANGED_ACTION消息通知外面

    private void setWifiState(int wifiState) {

        final Intent intent = new Intent(WifiManager.WIFI_STATE_CHANGED_ACTION);
        intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
        intent.putExtra(WifiManager.EXTRA_WIFI_STATE, wifiState);
        intent.putExtra(WifiManager.EXTRA_PREVIOUS_WIFI_STATE, previousWifiState);
        mContext.sendStickyBroadcast(intent);

}

例如在驱动加载状态

    class DriverLoadingState extends State {

            new Thread(new Runnable() {
                public void run() {
                    mWakeLock.acquire();
                    //enabling state
                    switch(message.arg1) {
                        case WIFI_STATE_ENABLING:
                            setWifiState(WIFI_STATE_ENABLING);
                            break;
                        case WIFI_AP_STATE_ENABLING:
                            setWifiApState(WIFI_AP_STATE_ENABLING);
                            break;
                    }

    }

    class SupplicantStartingState extends State {

        public boolean processMessage(Message message) {
            if (DBG) log(getName() + message.toString() + "\n");
            switch(message.what) {
                case WifiMonitor.SUP_CONNECTION_EVENT:
                    if (DBG) log("Supplicant connection established");
                    setWifiState(WIFI_STATE_ENABLED);

   }

在wifisettings里面也有广播监听器

    public WifiSettings() {
        mFilter = new IntentFilter();
        mFilter.addAction(WifiManager.WIFI_STATE_CHANGED_ACTION);
        mFilter.addAction(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION);
        mFilter.addAction(WifiManager.NETWORK_IDS_CHANGED_ACTION);
        mFilter.addAction(WifiManager.SUPPLICANT_STATE_CHANGED_ACTION);
        mFilter.addAction(WifiManager.CONFIGURED_NETWORKS_CHANGED_ACTION);
        mFilter.addAction(WifiManager.LINK_CONFIGURATION_CHANGED_ACTION);
        mFilter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION);
        mFilter.addAction(WifiManager.RSSI_CHANGED_ACTION);
        mFilter.addAction(WifiManager.ERROR_ACTION);

        mReceiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                handleEvent(context, intent);
            }
        };

        mScanner = new Scanner();
    }

当接受到广播会相应处理handleEvent

    private void handleEvent(Context context, Intent intent) {
        String action = intent.getAction();
        if (WifiManager.WIFI_STATE_CHANGED_ACTION.equals(action)) {
            updateWifiState(intent.getIntExtra(WifiManager.EXTRA_WIFI_STATE,
                    WifiManager.WIFI_STATE_UNKNOWN));
        }
    }

更新wifi状态

    private void updateWifiState(int state) {
        getActivity().invalidateOptionsMenu();

        switch (state) {
            case WifiManager.WIFI_STATE_ENABLED:
                mScanner.resume();
                return; // not break, to avoid the call to pause() below

            case WifiManager.WIFI_STATE_ENABLING:
                addMessagePreference(R.string.wifi_starting);
                break;

            case WifiManager.WIFI_STATE_DISABLED:
                addMessagePreference(R.string.wifi_empty_list_wifi_off);
                break;
        }

        mLastInfo = null;
        mLastState = null;
        mScanner.pause();
    }

        比如 case WifiManager.WIFI_STATE_ENABLED:当WIFI可用通知接受到的时候
                mScanner.resume();

Scanner resume函数

        void resume() {
            if (!hasMessages(0)) {
                sendEmptyMessage(0);
            }
        }

再看处理

        @Override
        public void handleMessage(Message message) {
            if (mWifiManager.startScanActive()) {
                mRetry = 0;
            } else if (++mRetry >= 3) {
                mRetry = 0;
                Toast.makeText(getActivity(), R.string.wifi_fail_to_scan,
                        Toast.LENGTH_LONG).show();
                return;
            }
            sendEmptyMessageDelayed(0, WIFI_RESCAN_INTERVAL_MS);
        }
    }

会调用mWifiManager.startScanActive()进行ap的扫描

所以当你点击wifi按钮，到驱动加载完成，发出WIFI_STATE_ENABLED消息的时候，

设置里面会进行扫描ap的动作