Android WiFi 架构总览(模块及接口)
2015-09-23 10:45
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Android WiFi 架构总览
本文介绍Android源码项目(AOSP)中WiFi功能的软件架构及各个模块(可执行文件、动态链接库)间的接口。SDK API
Android SDK为开发者提供了WiFi编程接口,使用起来非常方便。相关包:
android.net.wifi(写App时只需import该包,即可使用WiFi相关功能)
主要相关类:
*
WifiManagerWIFI编程入口,WIFI的多数功能都以该类的方法的形式提供
*
WifiInfo用于描述WIFI连接的状态
*
ScanResult用于描述一个AP,如SSID,信号强度,安全方式等
Overview
下图基展示了Android系统WIFI模块的架构(当然,这只是软件的控制命令部分,数据部分直接通过kernel与网络子系统、socket API交互)。(PS:一图胜千言,虽然用ppt画起来费劲)
WifiManager是管理所有Wifi连接的基本API,可以通过:
android.content.Context.getSystemService(Context.WIFI_SERVICE)
得到它的实例。
具体 IPC(Inter-Process communication)
App & system_server(WifiManager & WifiService)
如果说Binder是连接 App 和 system_server 的桥梁,那么WifiManager和WiFiService就是桥梁的两头。framework代码上和wifi相关的package位于:
frameworks/base/wifi/java(WIFI相关的一些包)
frameworks/base/services/java(各种Service,WIFI相关包为:
com.android.server.wifi)
frameworks代码中,和wifi相关的几个类的关系如下:
WifiService继承自IWifiManager.Stub;
IWifiManager.Stub又继承自Binder,同时实现了IWifiManager接口;
WifiManager.Stu.proxy也实现了IWifiManager接口;
如图:
其中,IWifiManager, IWifiManager.Stub, IWifiManager.Stub.Proxy都由IWifiManger.aidl生成;
aidl自动生成相关的java代码,简化了用Binder实现RPC的过程。
IWifiManager.Stub.Proxy,WifiManager,BinberProxy用于客户端(App进程);
而IWifiManager.Stub,WifiService,Binder用于服务端(SystemServer进程)。
App 与 system_server 通过Binder通信,但Binder本身只实现了IPC,即类似socket通信的能力。而App端的WifiManager和system_server端的WifiService及Binder等类共同实现了RPC(remote procedure call)。
WifiManager只是系统为app提供的接口。
Context.getSystemService(Context.WIFI_SERVICE)
返回的实际对象类型是
IWifiManager.Stub.Proxy。
IWifiManager.Stub.Proxy的实例是位于App端的一个代理,代理象
IWifiManager.Stub.Proxy
将WifiManager方法的参数序列化到Parcel,再经Binder发送给system_server进程。
system_server内的WifiService收App传来的WifiManager调用,完成实际工作。
这样,实际和下层通信的工作就由App转移到了system_server进程(WifiService对象)。
WifiStateMachine
另外,可以看到WifiStateMachine是wifi功能的枢纽,几种不同模式下的控制流程都经它流下。
当WIFI处在STA模式(或P2P模式)时,通过WifiNative与wpa_supplicant交互。
WifiNative定义了几个Native方法:
public native static boolean setMaxTxPower(int txpower, boolean sapRunning); public native static boolean loadDriver(); public native static boolean isDriverLoaded(); public native static boolean unloadDriver(); public native static boolean startSupplicant(boolean p2pSupported, int firstScanDelay); /* Sends a kill signal to supplicant. To be used when we have lost connection or when the supplicant is hung */ public native static boolean killSupplicant(boolean p2pSupported); private native boolean connectToSupplicantNative(); private native void closeSupplicantConnectionNative(); /** * Wait for the supplicant to send an event, returning the event string. * @return the event string sent by the supplicant. */ private native String waitForEventNative(); private native boolean doBooleanCommandNative(String command); private native int doIntCommandNative(String command); private native String doStringCommandNative(String command);
当WIFI处在AP模式。通过NetworkManagementService与netd交互,具体是通过LocalSocket(Framework封装的UNIX域socket)与netd进程通信。
比如,NetworkManagementService.startAccessPoint方法:
@Override public void startAccessPoint( WifiConfiguration wifiConfig, String wlanIface) { mContext.enforceCallingOrSelfPermission(CONNECTIVITY_INTERNAL, TAG); try { wifiFirmwareReload(wlanIface, "AP"); if (wifiConfig == null) { mConnector.execute("softap", "set", wlanIface); // 向 netd 发送控制命令 } else { mConnector.execute("softap", "set", wlanIface, wifiConfig.SSID, wifiConfig.hiddenSSID ? "hidden" : "broadcast", "1", getSecurityType(wifiConfig), new SensitiveArg(wifiConfig.preSharedKey)); } mConnector.execute("softap", "startap"); } catch (NativeDaemonConnectorException e) { throw e.rethrowAsParcelableException(); } }
WifiNative
从功能上来说,WifiNative是system_server 和 wpa_supplicant 对话的窗口,实际上主要依靠wpa_supplicant项目编译出来的动态库libwpa_client.so。WifiNative的几个native方法的具体实现在:
frameworks/base/core/jni/android_net_wifi_WifiNative.cpp
WifiNative的native方法的实现:
static JNINativeMethod gWifiMethods[] = { /* name, signature, funcPtr */ { "loadDriver", "()Z", (void *)android_net_wifi_loadDriver }, { "isDriverLoaded", "()Z", (void *)android_net_wifi_isDriverLoaded }, { "unloadDriver", "()Z", (void *)android_net_wifi_unloadDriver }, { "startSupplicant", "(ZI)Z", (void *)android_net_wifi_startSupplicant }, { "killSupplicant", "(Z)Z", (void *)android_net_wifi_killSupplicant }, { "connectToSupplicantNative", "()Z", (void *)android_net_wifi_connectToSupplicant }, { "closeSupplicantConnectionNative", "()V", (void *)android_net_wifi_closeSupplicantConnection }, { "waitForEventNative", "()Ljava/lang/String;", (void*)android_net_wifi_waitForEvent }, { "doBooleanCommandNative", "(Ljava/lang/String;)Z", (void*)android_net_wifi_doBooleanCommand }, { "doIntCommandNative", "(Ljava/lang/String;)I", (void*)android_net_wifi_doIntCommand }, { "doStringCommandNative", "(Ljava/lang/String;)Ljava/lang/String;", (void*) android_net_wifi_doStringCommand }, { "setMaxTxPower", "(IZ)Z", (void *)android_net_wifi_setMaxTxPower }, };
android_net_wifi_WifiNative.cpp并没有做多少实际工作,大多是直接调用 wifi.h wifi_maxtxpower.h 定义的函数:
wifi.h 的具体实现在 hardware/libhardware_legacy/wifi/wifi.c (会被编译为 libhardware_legacy.so)
wifi_maxtxpower.h 的具体实现在 hardware/qcom/wlan/libmaxtxpower/wifi_maxtxpower.c (会被编译为 libmaxtxpower.so)
所以native代码依赖libhardware_legacy.so模块、libmaxtxpower.so模块。
WIFI HAL
实现SystemServer与wpa_supplicant(hostapd)通信的,即Wifi HAL。Wifi HAL封装了UNIX域socket,SystemServer通过UNIX域socket与wpa_supplicant(hostapd)
通信;SystemServer发送的消息和wpa_supplicant响应的消息都是为ASCII字符串。
Wifi HAL代码主要分布在:
hardware/libhardware_legacy/wifi
hardware/qcom/wlan/libmaxtxpower
分别被编译为:
hardware/libhardware_legacy/wifi -> libhardware_legacy.so
hardware/qcom/wlan/libmaxtxpower -> libmaxtxpower.so
wifi.h定义了WIFI HAL的接口,具体函数有:
// 驱动相关: int wifi_load_driver(); int wifi_unload_driver(); int is_wifi_driver_loaded(); // supplicant相关: int wifi_start_supplicant(int p2pSupported, int first_scan_delay); int wifi_stop_supplicant(int p2pSupported); int wifi_connect_to_supplicant(); void wifi_close_supplicant_connection(); // 等待WIFI事发生,该函数会阻塞当前调用,直到有wifi事件发生时,返回一个表示wifi事件的字符 int wifi_wait_for_event(char *buf, size_t len); // 向wifi驱动发一个命,(多数功能经该函数向下层发命令) int wifi_command(const char *command, char *reply, size_t *reply_len); // 发起一dhcp请求 int do_dhcp_request(int *ipaddr, int *gateway, int *mask, int *dns1, int *dns2, int *server, int *lease); // 返回一个do_dhcp_request()的错误字符串 const char *get_dhcp_error_string(); #define WIFI_GET_FW_PATH_STA 0 #define WIFI_GET_FW_PATH_AP 1 #define WIFI_GET_FW_PATH_P2P 2 // 返一个请的firmware路径 const char *wifi_get_fw_path(int fw_type); // 为wlan驱动改变firmware路径 int wifi_change_fw_path(const char *fwpath); #define WIFI_ENTROPY_FILE "/data/misc/wifi/entropy.bin" int ensure_entropy_file_exists();
wifi_maxtxpower.h 只定义了一个函数:
int set_max_tx_power(int power, int sap_running);
android_net_wifi_WifiNative.cpp 调用了这些函数。
wifi.c调用了wpa_ctrl.h定义的一些函数,而wpa_ctrl.h中的函数
在external/wpa_supplicant_8 项目实现,并被编译为libwpa_client.so,
详见external/wpa_supplicant_8/Android.mk。
wpa_supplicant(hostapd)
代码位于:external/wpa_supplicant_8
该项目内包含两个互相相关的开源项目wpa_supplicant和hostapd,它们将会生成两个可执行文件:
wpa_supplicant和hostapd,分别为STA模式和AP模式时的守护进程。
除此之外,还会生成用于测试的wpa_cli,hostapd_cli,
以及WIFI HAL依赖的wpa_client.so,具体可以到Android.mk中找到。
wpa_supplicant源码结构和hostapd类似,下面只介绍wpa_supplicant。
wpa_ctrl.h 定义了与wpa_supplicant(或hostapd)进程通信的接口:
struct wpa_ctrl * wpa_ctrl_open(const char *ctrl_path); // Close a control interface to wpa_supplicant/hostapd void wpa_ctrl_close(struct wpa_ctrl *ctrl); // Send a command to wpa_supplicant/hostapd int wpa_ctrl_request(struct wpa_ctrl *ctrl, const char *cmd, size_t cmd_len, char *reply, size_t *reply_len, void (*msg_cb)(char *msg, size_t len)); // Register as an event monitor for the control interface int wpa_ctrl_attach(struct wpa_ctrl *ctrl); // Unregister event monitor from the control interface int wpa_ctrl_detach(struct wpa_ctrl *ctrl); // Receive a pending control interface message int wpa_ctrl_recv(struct wpa_ctrl *ctrl, char *reply, size_t *reply_len); // Check whether there are pending event messages int wpa_ctrl_pending(struct wpa_ctrl *ctrl); // Get file descriptor used by the control interface int wpa_ctrl_get_fd(struct wpa_ctrl *ctrl); char * wpa_ctrl_get_remote_ifname(struct wpa_ctrl *ctrl);
wpa_ctrl_open 创建一个UNIX域socket 与 wpa_supplicant(或hostapd)进程相连,
wpa_ctrl_close 用于关闭wpa_ctrl_open创建的连接,
wpa_ctrl_request 用于向wpa_supplicant/hostapd发送控制命令,并阻塞,
直到wpa_supplicant/hostapd返回命令响应。控制命令和相应都是ASCII字符串。
wpa_ctrl.h除了声明了这些函数外,还定义了wpa_supplicant/hostapd的一些消息,这里没有详细列出。
源码中wpa_supplicant_global_ctrl_iface_receive
负责分派上层发来的控制命令,进而调用具体处理函数:
"ATTACH" -> wpa_supplicant_ctrl_iface_attach "DETACH" -> wpa_supplicant_ctrl_iface_detach else -> wpa_supplicant_global_ctrl_iface_process: "IFNAME="(prefix) // 多数控制命令以IFNAME=开头 -> wpas_global_ctrl_iface_ifname -> wpa_supplicant_ctrl_iface_process # "IFNAME="开头的命令的处理 wpas_global_ctrl_iface_redir -> wpas_global_ctrl_iface_redir_p2p -> wpa_supplicant_ctrl_iface_process # "IFNAME="开头的命令的处理 -> wpas_global_ctrl_iface_redir_wfd -> wpa_supplicant_ctrl_iface_process # "IFNAME="开头的命令的处理 "PING" -> "PONG" "INTERFACE_ADD" -> wpa_supplicant_global_iface_add "INTERFACE_REMOVE" -> wpa_supplicant_global_iface_remove "INTERFACE_LIST" -> wpa_supplicant_global_iface_list "INTERFACES" -> wpa_supplicant_global_iface_interfaces "TERMINATE" -> wpa_supplicant_terminate_proc "SUSPEND" -> wpas_notify_suspend "RESUME" -> wpas_notify_resume "SET" -> wpas_global_ctrl_iface_set "S***E_CONFIG" -> wpas_global_ctrl_iface_save_config "STATUS" -> wpas_global_ctrl_iface_status
该函数在wpa_supplicant目录下的
ctrl_iface_unix.c和
ctrl_iface_udp.c内都有实现,可由该目录下的android.config切换
(android.config被Android.mk包含,具体参见Android.mk)
wpa_supplicant与内核通信
wpa_supplicant的运行模型是单进程单线程的 Reactor(IO multiplexing)。wpa_supplicant通过NETLINK socket与内核通信。wpa_supplicant项目支持多种驱动编程接口,在Android上使用的是nl80211;
nl80211是新的802.11netlink接口公共头,与cfg80211一同组成了Wireless-Extensions的替代方案。
cfg80211是Linux 802.11配置API, nl80211用于配置cfg80211设备,同时用于内核到用户空间的通信。
实际使用nl80211时,只需要在程序中包含头文件
wireless module(in kernel)
代码位于:kernel/net/wireless
nl80211.c 中的 nl80211_init 使用genl_register_family_with_ops 注册了响应应用程序的
struct genl_ops nl80211_ops[], 该数组定义了响应NETLINK消息的函数。
而 nl80211_init 在 cfg80211_init 内被调用,cfg80211_init是被subsys_initcall注册的
子系统初始化程序,被编译为cfg80211.ko。
nl80211_ops[] 节选:
static struct genl_ops nl80211_ops[] = { // ... { .cmd = NL80211_CMD_TRIGGER_SCAN, .doit = nl80211_trigger_scan, .policy = nl80211_policy, .flags = GENL_ADMIN_PERM, .internal_flags = NL80211_FLAG_NEED_NETDEV_UP | NL80211_FLAG_NEED_RTNL, }, { .cmd = NL80211_CMD_GET_SCAN, .policy = nl80211_policy, .dumpit = nl80211_dump_scan, }, { .cmd = NL80211_CMD_START_SCHED_SCAN, .doit = nl80211_start_sched_scan, .policy = nl80211_policy, .flags = GENL_ADMIN_PERM, .internal_flags = NL80211_FLAG_NEED_NETDEV_UP | NL80211_FLAG_NEED_RTNL, }, { .cmd = NL80211_CMD_STOP_SCHED_SCAN, .doit = nl80211_stop_sched_scan, .policy = nl80211_policy, .flags = GENL_ADMIN_PERM, .internal_flags = NL80211_FLAG_NEED_NETDEV_UP | NL80211_FLAG_NEED_RTNL, }, // ... };
wlan driver
代码位于:vendor/qcom/opensource/wlan/prima
模块初始化(module_init),模块退出(module_exit):
CORE/HDD/src/wlan_hdd_main.c
模型:
多线程 + 队列
创建内核线程:
CORE/VOSS/src/vos_sched.c的 vos_sched_open()
线程任务(vos_sched.c):
* VosMcThread() - The VOSS Main Controller thread
* VosWdThread() - The VOSS Watchdog thread
* VosTXThread() - The VOSS Main Tx thread
* VosRXThread() - The VOSS Main Rx thread
线程环境(context) (vos_sched.h):
typedef struct _VosSchedContext { /* Place holder to the VOSS Context */ v_PVOID_t pVContext; /* WDA Message queue on the Main thread*/ VosMqType wdaMcMq; /* PE Message queue on the Main thread*/ VosMqType peMcMq; /* SME Message queue on the Main thread*/ VosMqType smeMcMq; /* TL Message queue on the Main thread */ VosMqType tlMcMq; /* SYS Message queue on the Main thread */ VosMqType sysMcMq; /* WDI Message queue on the Main thread*/ VosMqType wdiMcMq; /* WDI Message queue on the Tx Thread*/ VosMqType wdiTxMq; /* WDI Message queue on the Rx Thread*/ VosMqType wdiRxMq; /* TL Message queue on the Tx thread */ VosMqType tlTxMq; /* TL Message queue on the Rx thread */ VosMqType tlRxMq; /* SYS Message queue on the Tx thread */ VosMqType sysTxMq; VosMqType sysRxMq; // ... struct task_struct* McThread; /* TX Thread handle */ struct task_struct* TxThread; /* RX Thread handle */ struct task_struct* RxThread; // ... } VosSchedContext, *pVosSchedContext;
高通资料:
80-Y0513-1_G_QCA_WCN36x0_Software_Architecture.pdf
chapter: Android WLAN Host Software Architecture
SCAN过程跟踪
App
WifiManager wifiManager = (WifiManager)Context.getService(Contex.WIFI_SERVICE); wifiManager.startScan(); //wifiManager --> IWifiManager.Stub.Proxy IWifiManager.Stub.Proxy implements android.net.wifi.IWifiManager wifiManager.startScan() -> IWifiManager.Stub.Proxy.startScan(WorkSource=null); -> BinderProxy.transact(Stub.TRANSACTION_startScan, _data, _reply, 0);
systerm_server
wifi –> WifiServiceWifiService extends IWifiManager.Stub IWifiManager.Stub extends android.os.Binder implements android.net.wifi.IWifiManager -> IWifiManager.Stub.onTransact(int code, Parcel data, Parcel reply, int flags); case TRANSACTION_startScan: -> WifiService.startScan(WorkSource workSource); -> WifiStateMachine.startScan(int callingUid, WorkSource workSource); -> StateMachine.sendMessage(CMD_START_SCAN, callingUid, 0, workSource); case CMD_START_SCAN: -> handleScanRequest(WifiNative.SCAN_WITHOUT_CONNECTION_SETUP, message); -> startScanNative(type, freqs) -> WifiNative.scan(type, freqs) -> doBooleanCommand("SCAN ..."); // AF_UNIX socket, send to wpa_supplicant
wpa_supplicant
external/wpa_supplicant_8/wpa_supplicant$ grep -nr "\"SCAN " . ./ChangeLog:197: - "SCAN freq=<freq list>" can be used to specify which channels are ./ChangeLog:199: - "SCAN passive=1" can be used to request a passive scan (no Probe ./ChangeLog:201: - "SCAN use_id" can be used to request a scan id to be returned and ./ChangeLog:203: - "SCAN only_new=1" can be used to request the driver/cfg80211 to ./ctrl_iface.c:6986: } else if (os_strncmp(buf, "SCAN ", 5) == 0) { ./src/drivers/driver_test.c:1289: ret = os_snprintf(pos, end - pos, "SCAN " MACSTR, ./src/drivers/driver_test.c:1994: } else if (os_strncmp(buf, "SCAN ", 5) == 0) { ./ctrl_iface.c:6986: } else if (os_strncmp(buf, "SCAN ", 5) == 0) {
refer to ./ctrl_iface.c:6986
} else if (os_strcmp(buf, "SCAN") == 0) { wpas_ctrl_scan(wpa_s, NULL, reply, reply_size, &reply_len); } else if (os_strncmp(buf, "SCAN ", 5) == 0) { wpas_ctrl_scan(wpa_s, buf + 5, reply, reply_size, &reply_len);
wpas_ctrl_scan -> wpa_supplicant_req_scan
int res = eloop_deplete_timeout(sec, usec, wpa_supplicant_scan, wpa_s, NULL); if (res == 1) { wpa_dbg(wpa_s, MSG_DEBUG, "Rescheduling scan request: %d.%06d sec", sec, usec); }
wpa_supplicant_scan -> wpa_supplicant_trigger_scan
-> radio_add_work(wpa_s, 0, "scan", 0, wpas_trigger_scan_cb, ctx)
wpas_trigger_scan_cb -> wpa_drv_scan
static inline int wpa_drv_scan(struct wpa_supplicant *wpa_s, struct wpa_driver_scan_params *params) { if (wpa_s->driver->scan2) // callback return wpa_s->driver->scan2(wpa_s->drv_priv, params); return -1; }
grep scan2 callback
external/wpa_supplicant_8/wpa_supplicant$ grep -nr "scan2\s*=" . ./src/drivers/driver_wext.c:2401: .scan2 = wpa_driver_wext_scan, ./src/drivers/driver_privsep.c:726: .scan2 = wpa_driver_privsep_scan, ./src/drivers/driver_test.c:2677: .scan2 = wpa_driver_test_scan, ./src/drivers/driver_bsd.c:1618: .scan2 = wpa_driver_bsd_scan, ./src/drivers/driver_nl80211.c:12612: .scan2 = driver_nl80211_scan2, ./src/drivers/driver_ndis.c:3217: wpa_driver_ndis_ops.scan2 = wpa_driver_ndis_scan;
refer to ./src/drivers/driver_nl80211.c:12612
driver_nl80211_scan2 -> wpa_driver_nl80211_scan
msg = nl80211_scan_common(drv, NL80211_CMD_TRIGGER_SCAN, params, bss->wdev_id_set ? &bss->wdev_id : NULL); if (!msg) return -1;
use
NL80211_CMD_TRIGGER_SCANtalk with kernel(cfg80211.ko)
kernel
grepNL80211_CMD_TRIGGER_SCANin kernel source:
kernel$ cgrep NL80211_CMD_TRIGGER_SCAN ./net/wireless/nl80211.c:9053: .cmd = NL80211_CMD_TRIGGER_SCAN, ./net/wireless/nl80211.c:9605: NL80211_CMD_TRIGGER_SCAN) < 0) { ./include/uapi/linux/nl80211.h:255: * option to specify additional IEs in NL80211_CMD_TRIGGER_SCAN, ./include/uapi/linux/nl80211.h:260: * @NL80211_CMD_TRIGGER_SCAN: trigger a new scan with the given parameters ./include/uapi/linux/nl80211.h:759: NL80211_CMD_TRIGGER_SCAN, ./include/uapi/linux/nl80211.h:1362: * This attribute is used with %NL80211_CMD_TRIGGER_SCAN and ./include/uapi/linux/nl80211.h:3863: * of NL80211_CMD_TRIGGER_SCAN and NL80211_CMD_START_SCHED_SCAN
refer to net/wireless/nl80211.c:9053
static struct genl_ops nl80211_ops[] = { // ... ... { .cmd = NL80211_CMD_TRIGGER_SCAN, .doit = nl80211_trigger_scan, .policy = nl80211_policy, .flags = GENL_ADMIN_PERM, .internal_flags = NL80211_FLAG_NEED_WDEV_UP | NL80211_FLAG_NEED_RTNL, }, // ... ... };
nl80211_trigger_scan -> rdev_scan(rdev, request);
static inline int rdev_scan(struct cfg80211_registered_device *rdev, struct cfg80211_scan_request *request) { int ret; trace_rdev_scan(&rdev->wiphy, request); ret = rdev->ops->scan(&rdev->wiphy, request); // callback trace_rdev_return_int(&rdev->wiphy, ret); return ret; }
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driver
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