Native层HIDL服务的获取原理-Android10.0 HwBinder通信原理(七)

摘要：本节主要来讲解Android10.0 Native层HIDL服务的获取原理

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[Android取经之路] 的源码都基于Android-Q（10.0）进行分析

[Android取经之路] 系列文章：

《系统启动篇》

Android系统架构
Android是怎么启动的
Android 10.0系统启动之init进程
Android10.0系统启动之Zygote进程
Android 10.0 系统启动之SystemServer进程
Android 10.0 系统服务之ActivityMnagerService
Android10.0系统启动之Launcher(桌面)启动流程
Android10.0应用进程创建过程以及Zygote的fork流程
Android 10.0 PackageManagerService（一）工作原理及启动流程
Android 10.0 PackageManagerService（二）权限扫描
Android 10.0 PackageManagerService（三）APK扫描
Android 10.0 PackageManagerService（四）APK安装流程

《日志系统篇》

Android10.0 日志系统分析(一)-logd、logcat 指令说明、分类和属性
Android10.0 日志系统分析(二)-logd、logcat架构分析及日志系统初始化
Android10.0 日志系统分析(三)-logd、logcat读写日志源码分析
Android10.0 日志系统分析(四)-selinux、kernel日志在logd中的实现

《Binder通信原理》：

Android10.0 Binder通信原理(一)Binder、HwBinder、VndBinder概要
Android10.0 Binder通信原理(二)-Binder入门篇
Android10.0 Binder通信原理(三)-ServiceManager篇
Android10.0 Binder通信原理(四)-Native-C\C++实例分析
Android10.0 Binder通信原理(五)-Binder驱动分析
Android10.0 Binder通信原理(六)-Binder数据如何完成定向打击
Android10.0 Binder通信原理(七)-Framework binder示例
Android10.0 Binder通信原理(八)-Framework层分析
Android10.0 Binder通信原理(九)-AIDL Binder示例
Android10.0 Binder通信原理(十)-AIDL原理分析-Proxy-Stub设计模式
Android10.0 Binder通信原理(十一)-Binder总结

《HwBinder通信原理》

HwBinder入门篇-Android10.0 HwBinder通信原理(一)
HIDL详解-Android10.0 HwBinder通信原理(二)
HIDL示例-C++服务创建Client验证-Android10.0 HwBinder通信原理(三)
HIDL示例-JAVA服务创建-Client验证-Android10.0 HwBinder通信原理(四)
HwServiceManager篇-Android10.0 HwBinder通信原理(五)
Native层HIDL服务的注册原理-Android10.0 HwBinder通信原理(六)
Native层HIDL服务的获取原理-Android10.0 HwBinder通信原理(七)
JAVA层HIDL服务的注册原理-Android10.0 HwBinder通信原理(八)

上一节，我们学习了Native层 HIDL服务的注册原理，这一节我们来看看Native层HIDL服务的获取流程。

5.IDemo的服务获取

IDemo的HIDL服务获取流程如下图所示：

5.1调用栈如下

5.2 main

[\vendor\ingres\hal_demo\cpp\hal_demo_test.cpp]int main() {   //1.获取IDemo这个HIDL服务的代理对象    android::sp service = IDemo::getService();    if(service == nullptr) {        printf("Failed to get service\n");        return -1;    }   //2.调用服务的HIDL接口 getHelloString()    service->getHelloString("IngresGe", [&](hidl_string result) {                printf("%s\n", result.c_str());        });    return 0;}

主要分两步：

1.获取IDemo这个HIDL服务的代理对象

2.调用服务的HIDL接口 getHelloString()

5.3 getService()

[/out/soong/.intermediates/vendor/ingres/interfaces/demo/1.0/[email protected]_genc++/gen/vendor/ingres/demo/1.0/DemoAll.cpp]::android::sp IDemo::getService(const std::string &serviceName, const bool getStub) {    return ::android::hardware::details::getServiceInternal(serviceName, true, getStub);}

getService的调用栈如下：

根据上面的调用栈，最终进入getRawServiceInternal()

[/system/libhidl/transport/ServiceManagement.cpp]sp<::android::hidl::base::V1_0::IBase> getRawServiceInternal(const std::string& descriptor,                                                             const std::string& instance,                                                             bool retry, bool getStub) {    using Transport = ::android::hidl::manager::V1_0::IServiceManager::Transport;    using ::android::hidl::manager::V1_0::IServiceManager;    sp waiter;    sp sm;    Transport transport = Transport::EMPTY;    if (kIsRecovery) {        transport = Transport::PASSTHROUGH;    } else {            //拿到HwServiceManager的对象，参考[5.4]        sm = defaultServiceManager1_1();        if (sm == nullptr) {            ALOGE("getService: defaultServiceManager() is null");            return nullptr;        }            //获取IDemo服务的transport，确认是直通式PASSTHROUGH，还是绑定式：HWBINDER            //transport可以在/vendor/etc/vintf/manifest.xml中查看hwbinder        Return transportRet = sm->getTransport(descriptor, instance);        if (!transportRet.isOk()) {            ALOGE("getService: defaultServiceManager()->getTransport returns %s",                  transportRet.description().c_str());            return nullptr;        }        transport = transportRet;    }    const bool vintfHwbinder = (transport == Transport::HWBINDER); //绑定式服务    const bool vintfPassthru = (transport == Transport::PASSTHROUGH); //直通式服务        ...    for (int tries = 0; !getStub && (vintfHwbinder || vintfLegacy); tries++) {        if (waiter == nullptr && tries > 0) {            waiter = new Waiter(descriptor, instance, sm);        }        if (waiter != nullptr) {            waiter->reset();  // don't reorder this -- see comments on reset()        }            //如果是绑定式的服务，调用 BpHwServiceManager::get()        Return> ret = sm->get(descriptor, instance);        if (!ret.isOk()) {            ALOGE("getService: defaultServiceManager()->get returns %s for %s/%s.",                  ret.description().c_str(), descriptor.c_str(), instance.c_str());            break;        }        sp base = ret;        if (base != nullptr) {            Return canCastRet =                details::canCastInterface(base.get(), descriptor.c_str(), true /* emitError */);            if (canCastRet.isOk() && canCastRet) {                if (waiter != nullptr) {                    waiter->done();                }                return base; // still needs to be wrapped by Bp class.            }            if (!handleCastError(canCastRet, descriptor, instance)) break;        }        // In case of legacy or we were not asked to retry, don't.        if (vintfLegacy || !retry) break;        if (waiter != nullptr) {            ALOGI("getService: Trying again for %s/%s...", descriptor.c_str(), instance.c_str());            waiter->wait(true /* timeout */);        }    }    if (waiter != nullptr) {        waiter->done();    }    if (getStub || vintfPassthru || vintfLegacy) {            //如果是直通式的hidl服务，获取直通式的HwServiceManager对象来获取服务        const sp pm = getPassthroughServiceManager();        if (pm != nullptr) {            sp base = pm->get(descriptor, instance).withDefault(nullptr);            if (!getStub || trebleTestingOverride) {                base = wrapPassthrough(base);            }            return base;        }    }    return nullptr;}

getRawServiceInternal()步骤如下：

1.获取HwServiceManager的代理对象

2.获取IDemo 这个hidl服务的transport，来确认是绑定式服务，还是直通式服务

3.根据transport类型，调用不同的接口来获取服务对象 (我们设计的IDemo是绑定式hidl服务)

5.4 defaultServiceManager1_1

[/system/libhidl/transport/ServiceManagement.cpp]sp defaultServiceManager1_1() {    return defaultServiceManager1_2();}[/system/libhidl/transport/ServiceManagement.cpp]defaultServiceManager1_2()是用来拿到HwServiceManager的代理对象--BpHwServiceManagersp defaultServiceManager1_2() {    using android::hidl::manager::V1_2::BnHwServiceManager;    using android::hidl::manager::V1_2::BpHwServiceManager;    static std::mutex gDefaultServiceManagerLock;    static sp gDefaultServiceManager;    {        std::lock_guard _l(gDefaultServiceManagerLock);        if (gDefaultServiceManager != nullptr) {            return gDefaultServiceManager;        }        //1.检查hwbinder的节点是否存在，如果不存在说明不支持hwbinder        if (access("/dev/hwbinder", F_OK|R_OK|W_OK) != 0) {            // HwBinder not available on this device or not accessible to            // this process.            return nullptr;        }        //2.等待属性"hwservicemanager.ready" 变为true，表明hwservicemanager已经启动好        waitForHwServiceManager();        while (gDefaultServiceManager == nullptr) {            //3.拿到HwServiceManager的代理对象            gDefaultServiceManager =                fromBinder(                    ProcessState::self()->getContextObject(nullptr));            if (gDefaultServiceManager == nullptr) {                LOG(ERROR) << "Waited for hwservicemanager, but got nullptr.";                sleep(1);            }        }    }    return gDefaultServiceManager;}

5.4.1 BpHwBinder::transact()

[/system/libhwbinder/BpHwBinder.cpp]status_t BpHwBinder::transact(    uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags, TransactCallback /*callback*/){    // Once a binder has died, it will never come back to life.    if (mAlive) {        //拿到IPCThreadState的对象，调用transact()执行        status_t status = IPCThreadState::self()->transact(            mHandle, code, data, reply, flags);        if (status == DEAD_OBJECT) mAlive = 0;        return status;    }    return DEAD_OBJECT;}

BpBinder::transact()就是调用IPCThreadState::self()->transact() 进行处理

根据如下调用栈所示，BpHwBinder::transact()最终会转到BnHwServiceManager::_hidl_get()，实现流程和注册服务类似，相关源码分析参考上一节《Native层HIDL服务的注册原理》的[4.7.1] - [4.8]

5.5 BnHwServiceManager::_hidl_get()

[/out/soong/.intermediates/system/libhidl/transport/manager/1.2/[email protected]_genc++/gen/android/hidl/manager/1.2/ServiceManagerAll.cpp]::android::status_t BnHwServiceManager::_hidl_get(        ::android::hidl::base::V1_0::BnHwBase* _hidl_this,        const ::android::hardware::Parcel &_hidl_data,        ::android::hardware::Parcel *_hidl_reply,        TransactCallback _hidl_cb) {        ...    ::android::status_t _hidl_err = ::android::OK;    if (!_hidl_data.enforceInterface(BnHwServiceManager::Pure::descriptor)) {        _hidl_err = ::android::BAD_TYPE;        return _hidl_err;    }    const ::android::hardware::hidl_string* fqName;    const ::android::hardware::hidl_string* name;    size_t _hidl_fqName_parent;        //1.获取hidl服务的fqName    _hidl_err = _hidl_data.readBuffer(sizeof(*fqName), &_hidl_fqName_parent,  reinterpret_cast(&fqName));    if (_hidl_err != ::android::OK) { return _hidl_err; }    _hidl_err = ::android::hardware::readEmbeddedFromParcel(            const_cast<::android::hardware::hidl_string &>(*fqName),            _hidl_data,            _hidl_fqName_parent,            0 /* parentOffset */);    if (_hidl_err != ::android::OK) { return _hidl_err; }    size_t _hidl_name_parent;        //2.获取hidl服务的name    _hidl_err = _hidl_data.readBuffer(sizeof(*name), &_hidl_name_parent,  reinterpret_cast(&name));    if (_hidl_err != ::android::OK) { return _hidl_err; }    _hidl_err = ::android::hardware::readEmbeddedFromParcel(            const_cast<::android::hardware::hidl_string &>(*name),            _hidl_data,            _hidl_name_parent,            0 /* parentOffset */);    if (_hidl_err != ::android::OK) { return _hidl_err; }    atrace_begin(ATRACE_TAG_HAL, "HIDL::IServiceManager::get::server");        ...        //3.根据hidl服务的fqName和name，从HwServiceManager的hidl service的map中拿到服务对象    ::android::sp<::android::hidl::base::V1_0::IBase> _hidl_out_service = static_cast(_hidl_this->getImpl().get())->get(*fqName, *name);        //4.把reply信息写入Parcel    ::android::hardware::writeToParcel(::android::hardware::Status::ok(), _hidl_reply);    if (_hidl_out_service == nullptr) {        _hidl_err = _hidl_reply->writeStrongBinder(nullptr);    } else {            //5.把获取的hidl服务转成IBinder对象        ::android::sp<::android::hardware::IBinder> _hidl_binder = ::android::hardware::getOrCreateCachedBinder(_hidl_out_service.get());        if (_hidl_binder.get() != nullptr) {                  //6.把转换后的IBinder对象，写入reply的Parcel数据中            _hidl_err = _hidl_reply->writeStrongBinder(_hidl_binder);        } else {            _hidl_err = ::android::UNKNOWN_ERROR;        }    }    /* _hidl_err ignored! */    atrace_end(ATRACE_TAG_HAL);         ..     //7.通过回调，把reply的Parcel数据给发给client    _hidl_cb(*_hidl_reply);    return _hidl_err;}

_hidl_get流程如下：

1.获取hidl服务的fqName

2.获取hidl服务的name

3.根据hidl服务的fqName和name，从HwServiceManager的hidl service的map中拿到服务对象

4.把reply信息写入Parcel

5.把获取的hidl服务转成IBinder对象

6.把转换后的IBinder对象，写入reply的Parcel数据中

7.通过回调，把reply的Parcel数据给发给client

5.5.1 ServiceManager::get()

[/system/hwservicemanager/ServiceManager.cpp]Return> ServiceManager::get(const hidl_string& hidlFqName,                                      const hidl_string& hidlName) {    const std::string fqName = hidlFqName;    const std::string name = hidlName;    if (!mAcl.canGet(fqName, getBinderCallingContext())) {        return nullptr;    }        //1.根据fqName和name找到对应的hidlService    HidlService* hidlService = lookup(fqName, name);    if (hidlService == nullptr) {        tryStartService(fqName, name);        return nullptr;    }    //2.根据hidlService 拿到IBase的对象    sp service = hidlService->getService();    if (service == nullptr) {        tryStartService(fqName, name);        return nullptr;    }    hidlService->guaranteeClient();    hardware::addPostCommandTask([hidlService] {        hidlService->handleClientCallbacks(false /* isCalledOnInterval */);    });    return service;}

5.7.3 ServiceManager::lookup()

主要是根据fqName和name从 HwServiceManager的服务map：mServiceMap 中找到对应的hidlservice。

[/system/hwservicemanager/ServiceManager.cpp]HidlService* ServiceManager::lookup(const std::string& fqName, const std::string& name) {        //1.根据fqName从 mServiceMap 中 找到一个节点    auto ifaceIt = mServiceMap.find(fqName);    if (ifaceIt == mServiceMap.end()) {        return nullptr;    }        //2.从找到的map节点中，拿到PackageInterfaceMap的内容    PackageInterfaceMap &ifaceMap = ifaceIt->second;        //3.从PackageInterfaceMap中根据name找到hidlService    HidlService *hidlService = ifaceMap.lookup(name);    return hidlService;}

5.5.2 HidlService::getService()

获取HidlService对象的mService

[/system/hwservicemanager/HidlService.cpp]sp HidlService::getService() const {    return mService;}

6. 协议码的转换流程

Binder通信协议是基于Command-Reply的方式的。

7.IDemo Client\Server交互流程

在IDemo的服务注册和获取的过程中，IDemo的服务和Client都是作为Client端，HwServiceManager作为Server端。

在IDemo的服务和client调用过程中，IDemo的服务为Server端，Client为客户端。

8.代码路径

/system/libhwbinder/BpHwBinder.cpp/system/libhwbinder/IPCThreadState.cpp/system/libhidl/transport/ServiceManagement.cpp/system/libhidl/transport/include/hidl/HidlTransportSupport.h/vendor/ingres/hal_demo/cpp/hal_demo_test.cpp/out/soong/.intermediates/vendor/ingres/interfaces/demo/1.0/[email protected]_genc++/gen/vendor/ingres/demo/1.0/DemoAll.cpp/out/soong/.intermediates/system/libhidl/transport/manager/1.2/[email protected]_genc++/gen/android/hidl/manager/1.2/ServiceManagerAll.cpp

9. 总结

至此，Native层的HIDL服务注册和获取就梳理完了，主要就是进程和HwBinder驱动、HwServiceManager的交互流程，下一节我们再一起看看JAVA层的hidl服务注册和获取流程。

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