Android SoftAp支持 （一）

SoftAP 打开时调用的相关函数解析

Softap字面意思是用软件实现AP的功能，让你的移动设备可以作为一个路由，让别的站点链接。比如让别人的手机连上你的已经打开AP功能的手机，玩联机游戏或者上网等等

但事实上此功能是需要硬件以及驱动的支持才能真正的实现的。

Softap打开流程。

        在Android系统的Setting界面的wireless配置项中会看到一个“Portable Wi-Fi hotspot” 跟一个"Configure Wi-Fi hotspot setting"选项，可以进入系统配置AP的名称，加密方式，密码等。 如下图

        当你做完这些设置，系统接受的AP设置界面变化打开的响应，从此开启了整个Android SoftAP的序幕。

首先./packages/apps/Settings/src/com/android/settings/TetherSettings.java 的onPreferenceChange 函数接收到Softap状态改变信息

    public boolean onPreferenceChange(Preference preference, Object value) {
        boolean enable = (Boolean) value;

        if (enable) {
            startProvisioningIfNecessary(WIFI_TETHERING);
        } else {
            mWifiApEnabler.setSoftapEnabled(false);
        }
        return false;
    }

 Softap开启时，enable 为真，因而执行startProvisioningIfNecessary(WIFI_TETHERING);

    private void startProvisioningIfNecessary(int choice) {
        mTetherChoice = choice;
        if (isProvisioningNeeded()) {
            Intent intent = new Intent(Intent.ACTION_MAIN);
            intent.setClassName(mProvisionApp[0], mProvisionApp[1]);
            startActivityForResult(intent, PROVISION_REQUEST);
        } else {
            startTethering();
        }
    }

isProvisioningNeeded 用来检测是否需要进行一些准备工作

如果无需准备工作则执行startTethering  大戏即将上演了 期待ing

    private void startTethering() {
        switch (mTetherChoice) {
            case WIFI_TETHERING:
                mWifiApEnabler.setSoftapEnabled(true);
                break;
            case BLUETOOTH_TETHERING:
                // turn on Bluetooth first
                break;
            case USB_TETHERING:
                setUsbTethering(true);
                break;
            default:
                //should not happen
                break;
        }
    }

这里 mTetherChoice == WIFI_TETHERING 所以继而执行WiFiApEnable.java中的setSoftapEnabled(true)函数

也从此处也跳出了Setting的代码 跳入了Android WIFI 子系统的framework层

./packages/apps/Settings/src/com/android/settings/wifi/WifiApEnabler.java

    public void setSoftapEnabled(boolean enable) {
        final ContentResolver cr = mContext.getContentResolver();
        /**
         * Disable Wifi if enabling tethering
         */
        int wifiState = mWifiManager.getWifiState(); //获取当前wifi的状态 如果开启则关闭且保存状态信息到变量中
        if (enable && ((wifiState == WifiManager.WIFI_STATE_ENABLING) ||
                    (wifiState == WifiManager.WIFI_STATE_ENABLED))) {
            mWifiManager.setWifiEnabled(false);
            Settings.Global.putInt(cr, Settings.Global.WIFI_SAVED_STATE, 1);
        }

        if (mWifiManager.setWifiApEnabled(null, enable)) {
            /* Disable here, enabled on receiving success broadcast */
            mCheckBox.setEnabled(false);
        } else {
            mCheckBox.setSummary(R.string.wifi_error);
        }

        /**
         *  If needed, restore Wifi on tether disable
         */
        if (!enable) {
            int wifiSavedState = 0;
            try {
                wifiSavedState = Settings.Global.getInt(cr, Settings.Global.WIFI_SAVED_STATE);
            } catch (Settings.SettingNotFoundException e) {
                ;
            }
            if (wifiSavedState == 1) {
                mWifiManager.setWifiEnabled(true);
                Settings.Global.putInt(cr, Settings.Global.WIFI_SAVED_STATE, 0);
            }
        }
    }

上面的代码中我们看到了Google人的考虑事情的周全。首先检测Wifi当前状态如果正在打开或者已经打开则关闭WIFI并将此状态记录下来，以便关闭softap时它能自动恢复到之前打开wifi的状态。 Android代码不愧牛X，这些都能想到...  崇拜那些大牛。

这里调用mWifiManager.setWifiApEnabled(null, enable)    "frameworks/base/wifi/java/android/net/wifi/WifiManager.java"

    public boolean setWifiApEnabled(WifiConfiguration wifiConfig, boolean enabled) {
        try {
            mService.setWifiApEnabled(wifiConfig, enabled);
            return true;
        } catch (RemoteException e) {
            return false;
        }
    }

转向服务层的 setWifiApEnabled  "frameworks/base/services/java/com/android/server/WifiService.java"

    public void setWifiApEnabled(WifiConfiguration wifiConfig, boolean enabled) {
        enforceChangePermission();
        mWifiStateMachine.setWifiApEnabled(wifiConfig, enabled);
    }

从而调用到最基础的也是最重要的Wifi状态机中的   setWifiApEnabled 实例 其实我真搞不懂为什么Android代码要嵌套这么多层去调用，为了安全、方便... 哪个牛人解释一下。

"frameworks/base/wifi/java/android/net/wifi/WifiStateMachine.java"

    public void setWifiApEnabled(WifiConfiguration wifiConfig, boolean enable) {
        mLastApEnableUid.set(Binder.getCallingUid());
        if (enable) {
            /* Argument is the state that is entered prior to load */
            sendMessage(obtainMessage(CMD_LOAD_DRIVER, WIFI_AP_STATE_ENABLING, 0));
            sendMessage(obtainMessage(CMD_START_AP, wifiConfig));
        } else {
            sendMessage(CMD_STOP_AP);
            /* Argument is the state that is entered upon success */
            sendMessage(obtainMessage(CMD_UNLOAD_DRIVER, WIFI_AP_STATE_DISABLED, 0));
        }
    }

        发送CMD_LOAD_DRIVER状态迁移到mDriverLoadingState 加载AP对应的驱动 这里把WIFI的驱动跟 AP的驱动做了区分，可见SoftAP不仅仅是软件实现的，需要硬件驱动的相应支持。

    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(mWifiNative.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();
        }

        @Override
        public boolean processMessage(Message message) {
            if (DBG) log(getName() + message.toString() + "\n");
            switch (message.what) {
                case CMD_LOAD_DRIVER_SUCCESS:
                    transitionTo(mDriverLoadedState);
                    break;
                case CMD_LOAD_DRIVER_FAILURE:
                    transitionTo(mDriverFailedState);
                    break;
                default:
                    return NOT_HANDLED;
            }
            return HANDLED;
        }
    }

加载驱动成功后 系统迁移到mDriverLoadedState 状态

接收到 CMD_START_AP消息  状态又被迁移至mSoftApStartingState

    class DriverLoadedState extends State {
        @Override
        public void enter() {
            if (DBG) log(getName() + "\n");
            EventLog.writeEvent(EVENTLOG_WIFI_STATE_CHANGED, getName());
        }
        @Override
        public boolean processMessage(Message message) {
            if (DBG) log(getName() + message.toString() + "\n");
            switch(message.what) {
                    /* 
                    ******
                    */
                case CMD_START_AP:
                    transitionTo(mSoftApStartingState);
                    break;
                default:
                    return NOT_HANDLED;
            }
            return HANDLED;
        }
    }

 SoftApStartingState 会检测上层传下的参数的有效性并调用startSoftApWithConfig 配置、打开SoftAP

    class SoftApStartingState extends State {
        @Override
        public void enter() {
            if (DBG) log(getName() + "\n");
            EventLog.writeEvent(EVENTLOG_WIFI_STATE_CHANGED, getName());

            final Message message = getCurrentMessage();
            if (message.what == CMD_START_AP) {
                final WifiConfiguration config = (WifiConfiguration) message.obj;

                if (config == null) {
                    mWifiApConfigChannel.sendMessage(CMD_REQUEST_AP_CONFIG);
                } else {
                    mWifiApConfigChannel.sendMessage(CMD_SET_AP_CONFIG, config);
                    startSoftApWithConfig(config);
                }
            } else {
                throw new RuntimeException("Illegal transition to SoftApStartingState: " + message);
            }
        }
        @Override
        public boolean processMessage(Message message) {
            if (DBG) log(getName() + message.toString() + "\n");
            switch(message.what) {
                case CMD_LOAD_DRIVER:
                case CMD_UNLOAD_DRIVER:
                //....
                case CMD_STOP_SUPPLICANT:
                case CMD_START_AP:
                //....
            }
        }
    }

获取SoftAp的网络配置AP名称 加密方式密码....

进行系统驱动（硬件）的配置。

    private void startSoftApWithConfig(final WifiConfiguration config) {
        // start hostapd on a seperate thread
        new Thread(new Runnable() {
            public void run() {
                try {
                    mNwService.startAccessPoint(config, mInterfaceName);
                } catch (Exception e) {
                    loge("Exception in softap start " + e);
                    try {
                        mNwService.stopAccessPoint(mInterfaceName);
                        mNwService.startAccessPoint(config, mInterfaceName);
                    } catch (Exception e1) {
                        loge("Exception in softap re-start " + e1);
                        sendMessage(CMD_START_AP_FAILURE);
                        return;
                    }
                }
                if (DBG) log("Soft AP start successful");
                sendMessage(CMD_START_AP_SUCCESS);
            }
        }).start();
    }
     //...
  }

这里调用到了"frameworks/base/services/java/com/android/server/NetworkManagementService.java" 中的startAccessPoint函数

函数如下：

    public void startAccessPoint(
            WifiConfiguration wifiConfig, String wlanIface) {
        mContext.enforceCallingOrSelfPermission(CONNECTIVITY_INTERNAL, TAG);
        try {
            wifiFirmwareReload(wlanIface, "AP");
            if (wifiConfig == null) {
                mConnector.execute("softap", "set", wlanIface);
            } else {
                mConnector.execute("softap", "set", wlanIface, wifiConfig.SSID,
                        getSecurityType(wifiConfig), wifiConfig.preSharedKey);
            }
            mConnector.execute("softap", "startap");
        } catch (NativeDaemonConnectorException e) {
            throw e.rethrowAsParcelableException();
        }
    }

1、下载AP对应的 firmware

wifiFirmwareReload(wlanIface, "AP");

2、设置ap的ssid 加密方式 以及密码

mConnector.execute("softap", "set", wlanIface, wifiConfig.SSID, getSecurityType(wifiConfig), wifiConfig.preSharedKey);

3、运行softap

mConnector.execute("softap", "startap");

 这里通过一个NativeDaemonConnector的实例mConnector 调用c++程序 具体的实现我是没看懂 但是知道最后实际调用的函数， 想深入了解可以找一些其他的资料看

实际调用到了 "./system/netd/CommandListener.cpp" 中的CommandListener::SoftapCmd::runCommand

int CommandListener::SoftapCmd::runCommand(SocketClient *cli,
                                        int argc, char **argv) {
    int rc = 0, flag = 0;
    char *retbuf = NULL;

    if (argc < 2) {
        cli->sendMsg(ResponseCode::CommandSyntaxError, "Softap Missing argument", false);
        return 0;
    }

    if (!strcmp(argv[1], "startap")) {
        rc = sSoftapCtrl->startSoftap();
    } else if (!strcmp(argv[1], "stopap")) {
        rc = sSoftapCtrl->stopSoftap();
    } else if (!strcmp(argv[1], "fwreload")) {
        rc = sSoftapCtrl->fwReloadSoftap(argc, argv);
    } else if (!strcmp(argv[1], "clients")) {
        rc = sSoftapCtrl->clientsSoftap(&retbuf);
        if (!rc) {
            cli->sendMsg(ResponseCode::CommandOkay, retbuf, false);
            free(retbuf);
            return 0;
        }
    } else if (!strcmp(argv[1], "status")) {
        asprintf(&retbuf, "Softap service %s",
                 (sSoftapCtrl->isSoftapStarted() ? "started" : "stopped"));
        cli->sendMsg(ResponseCode::SoftapStatusResult, retbuf, false);
        free(retbuf);
        return 0;
    } else if (!strcmp(argv[1], "set")) {
        rc = sSoftapCtrl->setSoftap(argc, argv);
    } else {
        cli->sendMsg(ResponseCode::CommandSyntaxError, "Softap Unknown cmd", false);
        return 0;
    }

    if (!rc) {
        cli->sendMsg(ResponseCode::CommandOkay, "Softap operation succeeded", false);
    } else {
        cli->sendMsg(ResponseCode::OperationFailed, "Softap operation failed", true);
    }

    return 0;
}

首先是"set“ 命令， 调用到c = sSoftapCtrl->setSoftap(argc, argv); 来配置网络

配置即将所有上层的网络设置写到HOSTAPD_CONF_FILE[]    = "/data/misc/wifi/hostapd.conf" 中

("system/netd/SoftapController.cpp")

/*
 * Arguments:
 *  argv[2] - wlan interface
 *  argv[3] - SSID
 *  argv[4] - Security
 *  argv[5] - Key
 *  argv[6] - Channel
 *  argv[7] - Preamble
 *  argv[8] - Max SCB
 */
int SoftapController::setSoftap(int argc, char *argv[]) {
    char psk_str[2*SHA256_DIGEST_LENGTH+1];
    int ret = 0, i = 0, fd;
    char *ssid, *iface;

    /* ..... */
    iface = argv[2];

    char *wbuf = NULL;
    char *fbuf = NULL;

    if (argc > 3) {
        ssid = argv[3];
    } else {
        ssid = (char *)"AndroidAP";
    }

    if (argc > 4) {
        if (!strcmp(argv[4], "wpa-psk")) {
            generatePsk(ssid, argv[5], psk_str);
            asprintf(&fbuf, "%swpa=1\nwpa_pairwise=TKIP CCMP\nwpa_psk=%s\n", wbuf, psk_str);
        } else if (!strcmp(argv[4], "wpa2-psk")) {
            generatePsk(ssid, argv[5], psk_str);
            asprintf(&fbuf, "%swpa=2\nrsn_pairwise=CCMP\nwpa_psk=%s\n", wbuf, psk_str);
        } else if (!strcmp(argv[4], "open")) {
            asprintf(&fbuf, "%s", wbuf);
        }
    } else {
        asprintf(&fbuf, "%s", wbuf);
    }

    fd = open(HOSTAPD_CONF_FILE, O_CREAT | O_TRUNC | O_WRONLY | O_NOFOLLOW, 0660);
    /*............*/
    if (write(fd, fbuf, strlen(fbuf)) < 0) {
        ALOGE("Cannot write to \"%s\": %s", HOSTAPD_CONF_FILE, strerror(errno));
        ret = -1;
    }
    free(wbuf);
    free(fbuf);

    /* Note: apparently open can fail to set permissions correctly at times */
    // .......
}

然后是"startap"命令调用rc = sSoftapCtrl->startSoftap(); 真正开启Softap 

int SoftapController::startSoftap() {
    pid_t pid = 1;
    int ret = 0;

    if (mPid) {
        ALOGE("Softap already started");
        return 0;
    }
    if (mSock < 0) {
        ALOGE("Softap startap - failed to open socket");
        return -1;
    }

    if ((pid = fork()) < 0) {
        ALOGE("fork failed (%s)", strerror(errno));
        return -1;
    }

    if (!pid) {
        ensure_entropy_file_exists();
        if (execl("/system/bin/hostapd", "/system/bin/hostapd",
                  "-e", WIFI_ENTROPY_FILE,
                  HOSTAPD_CONF_FILE, (char *) NULL)) {
            ALOGE("execl failed (%s)", strerror(errno));
        }
        ALOGE("Should never get here!");
        return -1;
    } else {
        mPid = pid;
        ALOGD("Softap startap - Ok");
        usleep(AP_BSS_START_DELAY);
    }
    return ret;

}

在startSoftap函数中调用了

execl("/system/bin/hostapd", "/system/bin/hostapd", "-e", WIFI_ENTROPY_FILE, HOSTAPD_CONF_FILE, (char *) NULL)

这里hostapd就是softap的deamon 程序 类似于wifi的的wpa_supplicant

 

至此所有wifi子系统从界面打开softap 到如何运行调用到deamon程序打开Softap的流程就是这样的

之后会介绍到Setting 界面"Portable Wi-Fi"的开启 以及  Hostapd 的一些东东