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 firstbreak;case USB_TETHERING:setUsbTethering(true);break;default://should not happenbreak;}}

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 {@Overridepublic void enter() {new Thread(new Runnable() {public void run() {mWakeLock.acquire();//enabling stateswitch(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();}@Overridepublic 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 {@Overridepublic void enter() {if (DBG) log(getName() + "\n");EventLog.writeEvent(EVENTLOG_WIFI_STATE_CHANGED, getName());}@Overridepublic 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 {@Overridepublic 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);}}@Overridepublic 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 threadnew 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

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