全面解析Android系统指纹启动流程

时间：2022-01-13 09:41:51|栏目：Android代码|点击：次

本章主要整理Android 指纹启动流程，侧重于hal和framework部分。

一.从Android系统启动流程看指纹启动流程

下图图片出处 →

第一阶段

Boot ROM，Android设备上电后，首先会从处理器片上ROM的启动引导代码开始执行，片上ROM会寻找Bootloader代码，并加载到内存。主要就是上电让系统启动。

第二阶段

Bootloader开始执行，首先负责完成硬件的初始化，然后找到Linux内核代码，并加载到内存。

启动过程中，bootloader(默认是bootable/bootloader/lk)会根据机器硬件信息选择合适的devicetree（dts）装入内存，如果采用pin id兼容，那么在此时就可以通过读取ID pin的值（这个是硬件拉的，跟硬件工程师确认是怎么对应IC的即可）判断指纹的IC了。

第三阶段

Kernel，Linux内核开始启动，初始化各种软硬件环境，加载驱动程序，挂载根文件系统，在系统文件中寻找init.rc文件，并启动init进程。Kernel中，加载指纹驱动，根据传入的dts信息创建设备节点，注册设备。

第四阶段

Init，初始化和启动属性服务，并且启动Zygote进程。

找到android.hardware.biometrics.fingerprint@2.1-service.rc，启动android.hardware.biometrics.fingerprint@2.1-service，会去open fingerprint.deault.so，等待与上层通信。

第五阶段

Zygote进程启动，创建java虚拟机并为java虚拟机注册JNI方法，创建服务器端Socket，启动SystemServer进程。

第六阶段

SystemServer进程启动，启动Binder线程池和SystemServiceManager，并且启动各种系统服务。会启动Fingerprintservice

以上是从Android启动流程看每个阶段指纹的启动流程，下面依次详细展开介绍。

二.驱动层

主要就是设备节点驱动的注册，在此不再详细说了，重点关注probe函数。

三.hal层

首先，hardware/interfaces/biometrics/fingerprint/2.1/default/android.hardware.biometrics.fingerprint@2.1-service.rc（以下简称2.1 rc）

service vendor.fps_hal /vendor/bin/hw/android.hardware.biometrics.fingerprint@2.1-service
    # "class hal" causes a race condition on some devices due to files created
    # in /data. As a workaround, postpone startup until later in boot once
    # /data is mounted.
    class late_start
    user system
    group system input
    writepid /dev/cpuset/system-background/tasks

会使位于系统vendor/bin/hw下的android.hardware.biometrics.fingerprint@2.1-service（以下简称2.1 bin）开机自启动，启动后会注册2.1 service

该bin服务对应的代码在：hardware/interfaces/biometrics/fingerprint/2.1/default/service.cpp，整个注册过程只有两步，首先实例化传入的 IBiometricsFingerprint 接口对象，然后通过 registerAsService 将服务注册到 hwservicemanager。

int main() {
    android::sp<IBiometricsFingerprint> bio = BiometricsFingerprint::getInstance();
 
    configureRpcThreadpool(1, true /*callerWillJoin*/);
 
    if (bio != nullptr) {
        if (::android::OK != bio->registerAsService()) { //*****注册服务*****
            return 1;
        }
    } else {
        ALOGE("Can't create instance of BiometricsFingerprint, nullptr");
    }
 
    joinRpcThreadpool();
 
    return 0; // should never get here
}

hardware/interfaces/biometrics/fingerprint/2.1/default/BiometricsFingerprint.cpp，重点关注openHal函数，会去打开fingerprint.default.so

fingerprint_device_t* BiometricsFingerprint::openHal() {
    int err;
    const hw_module_t *hw_mdl = nullptr;
    ALOGD("Opening fingerprint hal library...");
    //*******打开fingerprint.default.so********
    if (0 != (err = hw_get_module(FINGERPRINT_HARDWARE_MODULE_ID, &hw_mdl))) {
        ALOGE("Can't open fingerprint HW Module, error: %d", err);
        return nullptr;
    }
 
    if (hw_mdl == nullptr) {
        ALOGE("No valid fingerprint module");
        return nullptr;
    }
 
    fingerprint_module_t const *module =
        reinterpret_cast<const fingerprint_module_t*>(hw_mdl);
    if (module->common.methods->open == nullptr) {
        ALOGE("No valid open method");
        return nullptr;
    }
 
    hw_device_t *device = nullptr;
 
    if (0 != (err = module->common.methods->open(hw_mdl, nullptr, &device))) {
        ALOGE("Can't open fingerprint methods, error: %d", err);
        return nullptr;
    }
 
    if (kVersion != device->version) {
        // enforce version on new devices because of HIDL@2.1 translation layer
        ALOGE("Wrong fp version. Expected %d, got %d", kVersion, device->version);
        return nullptr;
    }
 
    fingerprint_device_t* fp_device =
        reinterpret_cast<fingerprint_device_t*>(device);
 
    if (0 != (err =
            fp_device->set_notify(fp_device, BiometricsFingerprint::notify))) {
        ALOGE("Can't register fingerprint module callback, error: %d", err);
        return nullptr;
    }
 
    return fp_device;
}

关于fingerprint.default.so这个都是供应商提供的，一般都不开源，不过Android原生也是有这部分代码的（当然只是看看，并不能使用）

hardware/libhardware/include/hardware/fingerprint.h

hardware/libhardware/modules/fingerprint/fingerprint.c

这部分代码不再展开贴在这里了，大家可以自行去看看，主要就是fingerprint_open打开设备（设备节点），然后定义了一系列函数。

dev->common.tag = HARDWARE_DEVICE_TAG;
dev->common.version = FINGERPRINT_MODULE_API_VERSION_2_0;
dev->common.module = (struct hw_module_t*) module;
dev->common.close = fingerprint_close;

dev->pre_enroll = fingerprint_pre_enroll;
dev->enroll = fingerprint_enroll;
dev->get_authenticator_id = fingerprint_get_auth_id;
dev->cancel = fingerprint_cancel;
dev->remove = fingerprint_remove;
dev->set_active_group = fingerprint_set_active_group;
dev->authenticate = fingerprint_authenticate;
dev->set_notify = set_notify_callback;

四.framework层

首先是SystemServer启动后，会去判断设备是否支持指纹，如果有start FingerprintService

frameworks/base/services/java/com/android/server/SystemServer.java

if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_FINGERPRINT)) {
    traceBeginAndSlog("StartFingerprintSensor");
    mSystemServiceManager.startService(FingerprintService.class);
    traceEnd();
}

此处mPackageManager.hasSystemFeature(PackageManager.FEATURE_FINGERPRINT)的判断，大家可以去frameworks/base/core/java/android/content/pm/PackageManager.java中追代码看看，逻辑很简单。

就是判断系统内vendor/etc/permissions目录下是否有：android.hardware.fingerprint.xml 文件

调试的那篇说过这个配置是setting里有没有指纹选项的关键：

PRODUCT_COPY_FILES := frameworks/native/data/etc/android.hardware.fingerprint.xml:vendor/etc/permissions/android.hardware.fingerprint.xml

下面转到，frameworks/base/services/core/java/com/android/server/fingerprint/FingerprintService.java，以下代码前半部分是与hal 2.1 service通信的部分，通过mDaemon = IBiometricsFingerprint.getService()，获取2.1 service

后半部分可以看出其继承IFingerprintService.aidl，这个aidl类就是实现Manager和Service通信的桥梁。

 public synchronized IBiometricsFingerprint getFingerprintDaemon() {
        if (mDaemon == null) {
            Slog.v(TAG, "mDaemon was null, reconnect to fingerprint");
            try {
                mDaemon = IBiometricsFingerprint.getService();
            } catch (java.util.NoSuchElementException e) {
                // Service doesn't exist or cannot be opened. Logged below.
            } catch (RemoteException e) {
                Slog.e(TAG, "Failed to get biometric interface", e);
            }
            if (mDaemon == null) {
                Slog.w(TAG, "fingerprint HIDL not available");
                return null;
            }
 
            mDaemon.asBinder().linkToDeath(this, 0);
 
            try {
                mHalDeviceId = mDaemon.setNotify(mDaemonCallback);
            } catch (RemoteException e) {
                Slog.e(TAG, "Failed to open fingerprint HAL", e);
                mDaemon = null; // try again later!
            }
 
            if (DEBUG) Slog.v(TAG, "Fingerprint HAL id: " + mHalDeviceId);
            if (mHalDeviceId != 0) {
                loadAuthenticatorIds();
                updateActiveGroup(ActivityManager.getCurrentUser(), null);
                doFingerprintCleanupForUser(ActivityManager.getCurrentUser());
            } else {
                Slog.w(TAG, "Failed to open Fingerprint HAL!");
                MetricsLogger.count(mContext, "fingerprintd_openhal_error", 1);
                mDaemon = null;
            }
 
 
 
 
 
//************************************************************************************//
 
 
 
 private final class FingerprintServiceWrapper extends IFingerprintService.Stub {
        @Override // Binder call
        public long preEnroll(IBinder token) {
            checkPermission(MANAGE_FINGERPRINT);
            return startPreEnroll(token);
        }
 
        @Override // Binder call
        public int postEnroll(IBinder token) {
            checkPermission(MANAGE_FINGERPRINT);
            return startPostEnroll(token);
        }
 
        @Override // Binder call
        public void enroll(final IBinder token, final byte[] cryptoToken, final int userId,
                final IFingerprintServiceReceiver receiver, final int flags,
                final String opPackageName) {
            checkPermission(MANAGE_FINGERPRINT);
            final int limit = mContext.getResources().getInteger(
                    com.android.internal.R.integer.config_fingerprintMaxTemplatesPerUser);
 
            final int enrolled = FingerprintService.this.getEnrolledFingerprints(userId).size();
            if (enrolled >= limit) {
                Slog.w(TAG, "Too many fingerprints registered");
                return;
            }
        }
        return mDaemon;
    }

对FingerprintService再往上一层的封装是FingerprintManager，应用app可以直接和它通信

frameworks/base/core/java/android/hardware/fingerprint/FingerprintManager.java （以下为搜索mService的代码，大家可以自己去看看）

    private IFingerprintService mService;
        if (mService != null) try {
            mService.authenticate(mToken, sessionId, userId, mServiceReceiver, flags,
 
        if (mService != null) {
                mService.authenticate(mToken, sessionId, userId, mServiceReceiver,
               
        if (mService != null) try {
            mService.enroll(mToken, token, userId, mServiceReceiver, flags,
            
        if (mService != null) try {
            result = mService.preEnroll(mToken);
        if (mService != null) try {
            result = mService.postEnroll(mToken);
        if (mService != null) try {
            mService.setActiveUser(userId);
        if (mService != null) try {
            mService.remove(mToken, fp.getFingerId(), fp.getGroupId(), userId, mServiceReceiver);
            mService.remove(mToken, fp.getFingerId(), fp.getGroupId(), userId, mServiceReceiver);
        if (mService != null) try {
            mService.enumerate(mToken, userId, mServiceReceiver);
            
        if (mService != null) {
                mService.rename(fpId, userId, newName);
        if (mService != null) try {
            return mService.getEnrolledFingerprints(userId, mContext.getOpPackageName());
        if (mService != null) try {
            return mService.hasEnrolledFingerprints(
        if (mService != null) try {
            return mService.hasEnrolledFingerprints(userId, mContext.getOpPackageName());
        if (mService != null) {
                return mService.isHardwareDetected(deviceId, mContext.getOpPackageName());
        if (mService != null) {
                return mService.getAuthenticatorId(mContext.getOpPackageName());
        if (mService != null) {
                mService.resetTimeout(token);
        if (mService == null) {
        if (mService != null) try {
            mService.cancelEnrollment(mToken);
        if (mService != null) try {
            mService.cancelAuthentication(mToken, mContext.getOpPackageName());

以上代码大家可以发现FingerprintManager其实并没有真正实现什么接口，都是调用的IFingerprintService，这里就用到aidl了，FingerprintManager通过aidl的Stub获取了Fingerprintservice，然后在这里去调用这个service的方法，以操作service，这就是aidl的作用。

frameworks/base/core/java/android/hardware/fingerprint/IFingerprintService.aidl （大家如果去看完整的代码，这里的接口是和FingerprintManager中调用的完全一致的）

interface IFingerprintService {
    // Authenticate the given sessionId with a fingerprint
    void authenticate(IBinder token, long sessionId, int userId,
            IFingerprintServiceReceiver receiver, int flags, String opPackageName,
            in Bundle bundle, IBiometricPromptReceiver dialogReceiver);
 
    // Cancel authentication for the given sessionId
    void cancelAuthentication(IBinder token, String opPackageName);
 
    // Start fingerprint enrollment
    void enroll(IBinder token, in byte [] cryptoToken, int groupId, IFingerprintServiceReceiver receiver,
            int flags, String opPackageName);
 
    // Cancel enrollment in progress
    void cancelEnrollment(IBinder token);
 
    // Any errors resulting from this call will be returned to the listener
    void remove(IBinder token, int fingerId, int groupId, int userId,
            IFingerprintServiceReceiver receiver);
 
    // Rename the fingerprint specified by fingerId and groupId to the given name
    void rename(int fingerId, int groupId, String name);
 
    // Get a list of enrolled fingerprints in the given group.
    List<Fingerprint> getEnrolledFingerprints(int groupId, String opPackageName);
 
    // Determine if HAL is loaded and ready
    boolean isHardwareDetected(long deviceId, String opPackageName);
 
    // Get a pre-enrollment authentication token
    long preEnroll(IBinder token);
 
    // Finish an enrollment sequence and invalidate the authentication token
    int postEnroll(IBinder token);

五.总结

根据以上可以画出这样一张流程图（以下以汇顶指纹为例，流程上都是一样的）

System APP下发注册命令->FingerprintManager收到命令->FingerprintService收到命令->（2.1 service）BiometricsFingerprint收到命令->(fingerprint.default.so)Fingerprint.cpp收到命令->指纹CA收到命令->指纹TA收到命令->SPI采集数据\算法进行注册等