Android -- Wifi的断开及关闭流程简介

Android -- Wifi的断开及关闭流程简介

当我们连接上一个AP时，Wifi的断开及关闭都会导致设备与AP之间的连接中断；关闭Wifi同时会导致Wifi断开。下面就简单介绍Wifi断开及关闭的流程。

一、Wifi的断开

我们断开Wifi，调用WifiManager::disconnect()方法，嵌套调用WifiServiceImpl的同名方法：

/**
 * see {@link android.net.wifi.WifiManager#disconnect()}
 */
public void disconnect() {
    enforceChangePermission();
    mWifiStateMachine.disconnectCommand();
}

调用Wifi状态机的内部方法，发送断开Wifi的指令CMD_DISCONNECT。由于之前网络连接成功时，State Machine停在ConnectedState，所以由它的父状态L2ConnectedState处理该消息：

case CMD_DISCONNECT:
    mWifiNative.disconnect();
    transitionTo(mDisconnectingState);
    break;

通过WifiNative::disconnect()方法下发断开指令，当驱动断开AP连接后，wpa_s反馈断开事件，WifiMonitor接收来自wpa_s的event，并向WifiStateMachine反馈NETWORK_DISCONNECTION_EVENT消息（该过程参考前面的博文）。切换到DisconnectingState状态，断开的消息尤其父状态ConnectModeState处理：

case WifiMonitor.NETWORK_DISCONNECTION_EVENT:
                    // Calling handleNetworkDisconnect here is redundant because we might already
                    // have called it when leaving L2ConnectedState to go to disconnecting state
                    // or thru other path
                    // We should normally check the mWifiInfo or mLastNetworkId so as to check
                    // if they are valid, and only in this case call handleNEtworkDisconnect,
                    // TODO: this should be fixed for a L MR release
                    // The side effect of calling handleNetworkDisconnect twice is that a bunch of
                    // idempotent commands are executed twice (stopping Dhcp, enabling the SPS mode
                    // at the chip etc...
                    if (DBG) log("ConnectModeState: Network connection lost ");
                    handleNetworkDisconnect();
                    transitionTo(mDisconnectedState);
                    break;

由代码中的注释可知，我们或许会在别的地方已经调用过handleNetworkDisconnect()，事实也确实如此；当我们离开L2ConnectedState状态时，会调用它的exit()方法：

@Override
 public void exit() {
     if (mIpReachabilityMonitor != null) {
         mIpReachabilityMonitor.stop();
         mIpReachabilityMonitor = null;
     }

     // This is handled by receiving a NETWORK_DISCONNECTION_EVENT in ConnectModeState
     // Bug: 15347363
     // For paranoia's sake, call handleNetworkDisconnect
     // only if BSSID is null or last networkId
     // is not invalid.
     if (DBG) {
         StringBuilder sb = new StringBuilder();
         sb.append("leaving L2ConnectedState state nid=" + Integer.toString(mLastNetworkId));
         if (mLastBssid !=null) {
             sb.append(" ").append(mLastBssid);
         }
     }
     if (mLastBssid != null || mLastNetworkId != WifiConfiguration.INVALID_NETWORK_ID) {
         handleNetworkDisconnect();//call the function，执行忘了断开时的处理
     }
 }

我们发现该方法中确实可能会调用handleNetworkDisconnect()，接着看该函数做了哪些处理：

/**
     * Resets the Wi-Fi Connections by clearing any state, resetting any sockets
     * using the interface, stopping DHCP & disabling interface
     */
    private void handleNetworkDisconnect() {

        clearCurrentConfigBSSID("handleNetworkDisconnect");

        stopDhcp();

        try {
            mNwService.clearInterfaceAddresses(mInterfaceName);
            mNwService.disableIpv6(mInterfaceName);
        } catch (Exception e) {
            loge("Failed to clear addresses or disable ipv6" + e);
        }

        /* Reset data structures */
        mBadLinkspeedcount = 0;
        mWifiInfo.reset();
        linkDebouncing = false;
        /* Reset roaming parameters */
        mAutoRoaming = WifiAutoJoinController.AUTO_JOIN_IDLE;

        /**
         *  fullBandConnectedTimeIntervalMilli:
         *  - start scans at mWifiConfigStore.wifiAssociatedShortScanIntervalMilli seconds interval
         *  - exponentially increase to mWifiConfigStore.associatedFullScanMaxIntervalMilli
         *  Initialize to sane value = 20 seconds
         */
        fullBandConnectedTimeIntervalMilli = 20 * 1000;

        setNetworkDetailedState(DetailedState.DISCONNECTED);
        if (mNetworkAgent != null) {
            mNetworkAgent.sendNetworkInfo(mNetworkInfo);
            mNetworkAgent = null;
        }
        mWifiConfigStore.updateStatus(mLastNetworkId, DetailedState.DISCONNECTED);

        /* Clear network properties */
        clearLinkProperties();

        /* Cend event to CM & network change broadcast */
        sendNetworkStateChangeBroadcast(mLastBssid);

        /* Cancel auto roam requests */
        autoRoamSetBSSID(mLastNetworkId, "any");

        mLastBssid = null;
        registerDisconnected();
        mLastNetworkId = WifiConfiguration.INVALID_NETWORK_ID;
    }

当一个AP连接断开时，主要会做如下几处理：

1. stopDhcp()：停止DHCP过程，即停止dhcpcd进程
   
2. mNwService.clearInterfaceAddresses(mInterfaceName)：通过NetworkManagementService通知Netd清除wlan0的地址信息
   
3. mWifiInfo.reset()：重置WifiInfo对象的状态
   
4. setNetworkDetailedState(DetailedState.DISCONNECTED)：将mNetworkInfo的连接状态设为DISCONNECTED
   
5. mWifiConfigStore.updateStatus(mLastNetworkId, DetailedState.DISCONNECTED)：将mLastNetworkId对应的 WifiConfiguration对象状态设为DISCONNECTED
   
6. clearLinkProperties()：清除mLinkProperties对象的配置信息
7. sendNetworkStateChangeBroadcast()：发广播通知上层网络状态变化
   
8. registerDisconnected()：做一些清理、记录工作
   

最后状态切换到DisconnectedState，等待下一次连接的发起，断开流程结束。

二、Wifi的关闭

从前面的博文可知，Wifi的开启、关闭都是调用WifiManager::setWifiEnabled()，嵌套调用WifiServiceImpl中的同名方法，向WifiController发送CMD_WIFI_TOGGLED消息：

/**
 * see {@link android.net.wifi.WifiManager#setWifiEnabled(boolean)}
 * @param enable {@code true} to enable, {@code false} to disable.
 * @return {@code true} if the enable/disable operation was
 *         started or is already in the queue.
 */
public synchronized boolean setWifiEnabled(boolean enable) {
    enforceChangePermission();
    Slog.d(TAG, "setWifiEnabled: " + enable + " pid=" + Binder.getCallingPid()
                + ", uid=" + Binder.getCallingUid());
    if (DBG) {
        Slog.e(TAG, "Invoking mWifiStateMachine.setWifiEnabled\n");
    }

    /*
    * Caller might not have WRITE_SECURE_SETTINGS,
    * only CHANGE_WIFI_STATE is enforced
    */

    long ident = Binder.clearCallingIdentity();
    try {
        if (! mSettingsStore.handleWifiToggled(enable)) {
            // Nothing to do if wifi cannot be toggled
            return true;
        }
    } finally {
        Binder.restoreCallingIdentity(ident);
    }

    mWifiController.sendMessage(CMD_WIFI_TOGGLED);
    return true;
}

前面的博文介绍过Wifi的启动流程，当WifiController向Wifi状态机发送启动wpa_s消息的时候，状态停留在DeviceActiveState。DeviceActiveState不处理CMD_WIFI_TOGGLED消息，交由其父状态StaEnabledState处理：

case CMD_WIFI_TOGGLED:
                   if (! mSettingsStore.isWifiToggleEnabled()) {
                       if (mSettingsStore.isScanAlwaysAvailable()) {
                           transitionTo(mStaDisabledWithScanState);
                       } else {
                           transitionTo(mApStaDisabledState);
                       }
                   }
                   break;

结合前面的所讲的内容，可知状态切换到ApStaDisabledState，进行关闭流程，调用它的enter()方法：

@Override
public void enter() {
    mWifiStateMachine.setSupplicantRunning(false);
    // Supplicant can't restart right away, so not the time we switched off
    mDisabledTimestamp = SystemClock.elapsedRealtime();
    mDeferredEnableSerialNumber++;
    mHaveDeferredEnable = false;
    mWifiStateMachine.clearANQPCache();
}

调用WifiStateMachine::setSupplicantRunning(false)向WifiStateMachine发送停止wpa_s的消息：CMD_STOP_SUPPLICANT。

SupplicantStartedState接收、处理该消息：

case CMD_STOP_SUPPLICANT:   /* Supplicant stopped by user */
    if (mP2pSupported) {
        transitionTo(mWaitForP2pDisableState);
    } else {
        transitionTo(mSupplicantStoppingState);
    }
    break;

切换到SupplicantStoppingState，进入enter()方法：

public void enter() {
            /* Send any reset commands to supplicant before shutting it down */
            handleNetworkDisconnect();
            if (mDhcpStateMachine != null) {
                mDhcpStateMachine.doQuit();
            }

            String suppState = System.getProperty("init.svc.wpa_supplicant");
            if (suppState == null) suppState = "unknown";
            String p2pSuppState = System.getProperty("init.svc.p2p_supplicant");
            if (p2pSuppState == null) p2pSuppState = "unknown";

            logd("SupplicantStoppingState: stopSupplicant "
                    + " init.svc.wpa_supplicant=" + suppState
                    + " init.svc.p2p_supplicant=" + p2pSuppState);
            mWifiMonitor.stopSupplicant();

            /* Send ourselves a delayed message to indicate failure after a wait time */
            sendMessageDelayed(obtainMessage(CMD_STOP_SUPPLICANT_FAILED,
                    ++mSupplicantStopFailureToken, 0), SUPPLICANT_RESTART_INTERVAL_MSECS);
            setWifiState(WIFI_STATE_DISABLING);
            mSupplicantStateTracker.sendMessage(CMD_RESET_SUPPLICANT_STATE);
        }

1. 调用handleNetworkDisconnect()处理AP连接的断开部分，第一部分已经讲过。
2. 设置DhcpStateMachine的状态，停止DhcpStateMachine
3. 调用WifiMonitor::stopSupplicant()停掉wpa_s
4. 将wifi状态设置为disabling；setWifiState()函数会设置当前Wifi的状态，比如disabled、disabling、enabled等；我们通过监听函数发送的WifiManager.WIFI_STATE_CHANGED_ACTION广播，可以得知当前Wifi的具体状态。

WifiMonitor中下发终止指令后，会收到wpa_s断开的event：

else if (event == TERMINATING) {
            /**
             * Close the supplicant connection if we see
             * too many recv errors
             */
            if (eventData.startsWith(WPA_RECV_ERROR_STR)) {
                if (++sRecvErrors > MAX_RECV_ERRORS) {
                    if (DBG) {
                        Log.d(TAG, "too many recv errors, closing connection");
                    }
                } else {
                    eventLogCounter++;
                    return false;
                }
            }

            // Notify and exit
            mStateMachine.sendMessage(SUP_DISCONNECTION_EVENT, eventLogCounter);
            return true;

WifiMonitor会向wifi状态机发送SUP_DISCONNECTION_EVENT消息并最终退出，等待下一次重新与wpa_s建立通信。SupplicantStoppingState处理该消息：

case WifiMonitor.SUP_DISCONNECTION_EVENT:
     if (DBG) log("Supplicant connection lost");
     handleSupplicantConnectionLoss(false);
     transitionTo(mInitialState);
     break;

private void handleSupplicantConnectionLoss(boolean killSupplicant) {
    /* Socket connection can be lost when we do a graceful shutdown
    * or when the driver is hung. Ensure supplicant is stopped here.
    */
    if (killSupplicant) {
        mWifiMonitor.killSupplicant(mP2pSupported);
    }
    mWifiNative.closeSupplicantConnection();
    sendSupplicantConnectionChangedBroadcast(false);
    setWifiState(WIFI_STATE_DISABLED);
}

handleSupplicantConnectionLoss()函数中，因为之前已经执行过stopSupplicant()的操作，killSupplicant传入false，所以不会重复执行关闭wpa_s的killSupplicant()函数；随后关闭wpa_s与wifi之间传递指令、事件的socket连接，最后设置当前Wifi状态为disabled，代表Wifi已经关闭完成。

handleSupplicantConnectionLoss()执行完毕后，wpa_s的状态已经被彻底清除掉，随之将Wifi状态机切换到InitialState：

@Override
public void enter() {
    WifiNative.stopHal();
    mWifiNative.unloadDriver();
    if (mWifiP2pChannel == null) {
        mWifiP2pChannel = new AsyncChannel();
        mWifiP2pChannel.connect(mContext, getHandler(),
            mWifiP2pServiceImpl.getP2pStateMachineMessenger());
    }

    if (mWifiApConfigChannel == null) {
        mWifiApConfigChannel = new AsyncChannel();
        mWifiApConfigStore = WifiApConfigStore.makeWifiApConfigStore(
                mContext, getHandler());
        mWifiApConfigStore.loadApConfiguration();
        mWifiApConfigChannel.connectSync(mContext, getHandler(),
                mWifiApConfigStore.getMessenger());
    }

    if (mWifiConfigStore.enableHalBasedPno.get()) {
        // make sure developer Settings are in sync with the config option
        mHalBasedPnoEnableInDevSettings = true;
    }
}

在enter()函数中，比较重要的操作就是mWifiNative.unloadDriver()，当Wifi完全关闭后，将驱动也卸载掉。当下一次Wifi启动流程启动时，再重新加载驱动、启动wpa_s。

到此，Wifi关闭的流程就结束了。