HIDL Hal 开发笔记3----Binderized HALs 实例分析

一、整体框架

对于Binderized HALs，HAL 层以进程的形式存在，内部有一个HwBinder服务端对象，对外提供HwBinder远程调用服务。Framework 通过HwBinder远程调用到 HAL 中的函数，这些函数直接访问具体的驱动。

在源码下device/google/coral/vibrator/目录下，是 Google 为 pixel4、pixel4 xl 实现的振动器 HAL，其类型就是 Binderized HALs。本文分析其具体实现

二、HAL 层服务端实现

HAL 层表现为一个进程：

进程对应的代码位于device/google/coral/vibrator

整体结构如下：

我们从 Android.bp 下手：

cc_defaults{name:"android.hardware.vibrator@1.3-defaults.coral",defaults:["hidl_defaults"],relative_install_path:"hw",shared_libs:["libhidlbase","libcutils","libhidltransport","liblog","libhwbinder","libutils","libhardware","android.hardware.vibrator@1.0","android.hardware.vibrator@1.1","android.hardware.vibrator@1.2","android.hardware.vibrator@1.3",],}cc_defaults{name:"PtsVibratorHalFloralDefaults",defaults:["android.hardware.vibrator@1.3-defaults.coral"],static_libs:["android.hardware.vibrator@1.3-impl.coral"],test_suites:["general-tests","pts",],multilib:{lib32:{suffix:"32",},lib64:{suffix:"64",},},}cc_library{name:"android.hardware.vibrator@1.3-impl.coral",defaults:["android.hardware.vibrator@1.3-defaults.coral"],srcs:["Hardware.cpp","Vibrator.cpp",],export_include_dirs:["."],vendor_available:true,}cc_binary{name:"android.hardware.vibrator@1.3-service.coral",defaults:["android.hardware.vibrator@1.3-defaults.coral"],init_rc:["android.hardware.vibrator@1.3-service.coral.rc"],vintf_fragments:["android.hardware.vibrator@1.3-service.coral.xml"],srcs:["service.cpp"],static_libs:["android.hardware.vibrator@1.3-impl.coral"],proprietary:true,}

一个共享库android.hardware.vibrator@1.3-impl.coral，一个 native 可执行程序android.hardware.vibrator@1.3-service.coral。

• android.hardware.vibrator@1.3-impl.coral共享库中 :

• Hardware.cpp 中对振动器驱动的访问包装成了两个对象HwApi HwCal。
• Vibrator.cpp 链接了android.hardware.vibrator@1.3库，内部有一个 Vibrator类，继承自android.hardware.vibrator@1.3库中 IVibrator，IVibrator 是由hardware/interfaces/vibrator/1.3/IVibrator.hal编译出来的。Vibrator 类是一个HwBinder服务端类，对外提供了调用振动器的接口，内部实现是通过调用HwApi HwCal对象的成员函数实现的。

• android.hardware.vibrator@1.3-service.coral可执行程序：

status_tregisterVibratorService(){sp<Vibrator>vibrator=newVibrator(std::make_unique<HwApi>(),std::make_unique<HwCal>());returnvibrator->registerAsService();}intmain(){configureRpcThreadpool(1,true);status_tstatus=registerVibratorService();if(status!=OK){returnstatus;}joinRpcThreadpool();}

实现上很简单：

• 向 HwServiceManager 注册 Vibrator
• 配置 HwBinder 线程

具体振动器的操作细节就不看了，这不是我们的重点。

三、Framework 层客户端实现

对于客户端，我们只要知道 Hal 对外提供的接口即可，这个接口由hardware/interfaces/vibrator/1.3/IVibrator.hal描述：

package android.hardware.vibrator@1.3;import @1.0::EffectStrength;import @1.0::Status;import @1.2::IVibrator;interface IVibrator extends @1.2::IVibrator{supportsExternalControl()generates(bool supports);setExternalControl(bool enabled)generates(Status status);perform_1_3(Effect effect,EffectStrength strength)generates(Status status,uint32_tlengthMs);};

frameworks/base/services/core/java/com/android/server/VibratorService.java本身是一个 Binder 服务端向 App 提供服务，同时也是一个HwBinder客户端通过 JNI 访问到 HAL 服务端。

publicclassVibratorServiceextendsIVibratorService.StubimplementsInputManager.InputDeviceListener{// ......staticnativebooleanvibratorExists();staticnativevoidvibratorInit();staticnativevoidvibratorOn(longmilliseconds);staticnativevoidvibratorOff();staticnativebooleanvibratorSupportsAmplitudeControl();staticnativevoidvibratorSetAmplitude(intamplitude);staticnativelongvibratorPerformEffect(longeffect,longstrength);staticnativebooleanvibratorSupportsExternalControl();staticnativevoidvibratorSetExternalControl(booleanenabled);// ......}

VibratorService 中有多个 native 方法，这些方法用于远程调用 Hal 层。

对应的 JNI 函数实现在frameworks/base/services/core/jni/com_android_server_VibratorService.cpp：

#defineLOG_TAG"VibratorService"#include<android/hardware/vibrator/1.0/IVibrator.h>#include<android/hardware/vibrator/1.0/types.h>#include<android/hardware/vibrator/1.0/IVibrator.h>#include<android/hardware/vibrator/1.1/types.h>#include<android/hardware/vibrator/1.2/IVibrator.h>#include<android/hardware/vibrator/1.2/types.h>#include<android/hardware/vibrator/1.3/IVibrator.h>#include"jni.h"#include<nativehelper/JNIHelp.h>#include"android_runtime/AndroidRuntime.h"#include<utils/misc.h>#include<utils/Log.h>#include<hardware/vibrator.h>#include<inttypes.h>#include<stdio.h>using android::hardware::Return;using android::hardware::vibrator::V1_0::EffectStrength;using android::hardware::vibrator::V1_0::Status;using android::hardware::vibrator::V1_1::Effect_1_1;namespace V1_0=android::hardware::vibrator::V1_0;namespace V1_1=android::hardware::vibrator::V1_1;namespace V1_2=android::hardware::vibrator::V1_2;namespace V1_3=android::hardware::vibrator::V1_3;namespace android{staticconstexprintNUM_TRIES=2;// Creates a Return<R> with STATUS::EX_NULL_POINTER.template<class R>inlineReturn<R>NullptrStatus(){using::android::hardware::Status;returnReturn<R>{Status::fromExceptionCode(Status::EX_NULL_POINTER)};}// Helper used to transparently deal with the vibrator HAL becoming unavailable.template<class R,class I,class...Args0,class...Args1>Return<R>halCall(Return<R>(I::*fn)(Args0...),Args1&&...args1){// Assume that if getService returns a nullptr, HAL is not available on the// device.staticsp<I>sHal=I::getService();staticbool sAvailable=sHal!=nullptr;if(!sAvailable){returnNullptrStatus<R>();}// Return<R> doesn't have a default constructor, so make a Return<R> with// STATUS::EX_NONE.using::android::hardware::Status;Return<R>ret{Status::fromExceptionCode(Status::EX_NONE)};// Note that ret is guaranteed to be changed after this loop.for(inti=0;i<NUM_TRIES;++i){ret=(sHal==nullptr)?NullptrStatus<R>():(*sHal.*fn)(std::forward<Args1>(args1)...);if(ret.isOk()){break;}ALOGE("Failed to issue command to vibrator HAL. Retrying.");// Restoring connection to the HAL.sHal=I::tryGetService();}returnret;}template<class R>boolisValidEffect(jlong effect){if(effect<0){returnfalse;}R val=static_cast<R>(effect);autoiter=hardware::hidl_enum_range<R>();returnval>=*iter.begin()&&val<=*std::prev(iter.end());}staticvoidvibratorInit(JNIEnv/* env */,jobject/* clazz */){halCall(&V1_0::IVibrator::ping).isOk();}staticjbooleanvibratorExists(JNIEnv*/* env */,jobject/* clazz */){returnhalCall(&V1_0::IVibrator::ping).isOk()?JNI_TRUE:JNI_FALSE;}staticvoidvibratorOn(JNIEnv*/* env */,jobject/* clazz */,jlong timeout_ms){Status retStatus=halCall(&V1_0::IVibrator::on,timeout_ms).withDefault(Status::UNKNOWN_ERROR);if(retStatus!=Status::OK){ALOGE("vibratorOn command failed (%"PRIu32").",static_cast<uint32_t>(retStatus));}}staticvoidvibratorOff(JNIEnv*/* env */,jobject/* clazz */){Status retStatus=halCall(&V1_0::IVibrator::off).withDefault(Status::UNKNOWN_ERROR);if(retStatus!=Status::OK){ALOGE("vibratorOff command failed (%"PRIu32").",static_cast<uint32_t>(retStatus));}}staticjlongvibratorSupportsAmplitudeControl(JNIEnv*,jobject){returnhalCall(&V1_0::IVibrator::supportsAmplitudeControl).withDefault(false);}staticvoidvibratorSetAmplitude(JNIEnv*,jobject,jint amplitude){Status status=halCall(&V1_0::IVibrator::setAmplitude,static_cast<uint32_t>(amplitude)).withDefault(Status::UNKNOWN_ERROR);if(status!=Status::OK){ALOGE("Failed to set vibrator amplitude (%"PRIu32").",static_cast<uint32_t>(status));}}staticjbooleanvibratorSupportsExternalControl(JNIEnv*,jobject){returnhalCall(&V1_3::IVibrator::supportsExternalControl).withDefault(false);}staticvoidvibratorSetExternalControl(JNIEnv*,jobject,jboolean enabled){Status status=halCall(&V1_3::IVibrator::setExternalControl,static_cast<uint32_t>(enabled)).withDefault(Status::UNKNOWN_ERROR);if(status!=Status::OK){ALOGE("Failed to set vibrator external control (%"PRIu32").",static_cast<uint32_t>(status));}}staticjlongvibratorPerformEffect(JNIEnv*,jobject,jlong effect,jint strength){Status status;uint32_tlengthMs;autocallback=[&status,&lengthMs](Status retStatus,uint32_tretLengthMs){status=retStatus;lengthMs=retLengthMs;};EffectStrengtheffectStrength(static_cast<EffectStrength>(strength));Return<void>ret;if(isValidEffect<V1_0::Effect>(effect)){ret=halCall(&V1_0::IVibrator::perform,static_cast<V1_0::Effect>(effect),effectStrength,callback);}elseif(isValidEffect<Effect_1_1>(effect)){ret=halCall(&V1_1::IVibrator::perform_1_1,static_cast<Effect_1_1>(effect),effectStrength,callback);}elseif(isValidEffect<V1_2::Effect>(effect)){ret=halCall(&V1_2::IVibrator::perform_1_2,static_cast<V1_2::Effect>(effect),effectStrength,callback);}elseif(isValidEffect<V1_3::Effect>(effect)){ret=halCall(&V1_3::IVibrator::perform_1_3,static_cast<V1_3::Effect>(effect),effectStrength,callback);}else{ALOGW("Unable to perform haptic effect, invalid effect ID (%"PRId32")",static_cast<int32_t>(effect));return-1;}if(!ret.isOk()){ALOGW("Failed to perform effect (%"PRId32")",static_cast<int32_t>(effect));return-1;}if(status==Status::OK){returnlengthMs;}elseif(status!=Status::UNSUPPORTED_OPERATION){// Don't warn on UNSUPPORTED_OPERATION, that's a normal event and just means the motor// doesn't have a pre-defined waveform to perform for it, so we should just give the// opportunity to fall back to the framework waveforms.ALOGE("Failed to perform haptic effect: effect=%"PRId64", strength=%"PRId32", error=%"PRIu32").",static_cast<int64_t>(effect),static_cast<int32_t>(strength),static_cast<uint32_t>(status));}return-1;}staticconstJNINativeMethod method_table[]={{"vibratorExists","()Z",(void*)vibratorExists},{"vibratorInit","()V",(void*)vibratorInit},{"vibratorOn","(J)V",(void*)vibratorOn},{"vibratorOff","()V",(void*)vibratorOff},{"vibratorSupportsAmplitudeControl","()Z",(void*)vibratorSupportsAmplitudeControl},{"vibratorSetAmplitude","(I)V",(void*)vibratorSetAmplitude},{"vibratorPerformEffect","(JJ)J",(void*)vibratorPerformEffect},{"vibratorSupportsExternalControl","()Z",(void*)vibratorSupportsExternalControl},{"vibratorSetExternalControl","(Z)V",(void*)vibratorSetExternalControl},};intregister_android_server_VibratorService(JNIEnv*env){returnjniRegisterNativeMethods(env,"com/android/server/VibratorService",method_table,NELEM(method_table));}};

所有的函数都通过halcall来实现，halcall中会去从 HwServiceManager 中去获取Vibrator Hal的代理对象，然后通过这个代理对象发起远程调用，从而调用到 HAL 层。

最后我们再来看 HAL 端的 VINTF 配置文件/Project/android-10.0.0_r41/device/google/coral/vibrator/android.hardware.vibrator@1.3-service.coral.xml：

<manifest version="1.0"type="device"><hal format="hidl"><name>android.hardware.vibrator</name><transport>hwbinder</transport><version>1.3</version><interface><name>IVibrator</name><instance>default</instance></interface></hal></manifest>

注意这里 transport 指定了 hal 的类型为 hwbinder，也就是我们说的Binderized hal。