AndroidO Treble架构下Hal进程启动及HIDL服务注册过程

通过前面对Treble架构的介绍,我们知道,Android Framework进程和Hal分离,每个Hal独立运行在自己的进程地址空间,那么这些Hal进程是如何启动的呢?本文以composer hal为例展开分析。
在以下路径有composer hal的rc启动脚本:
hardware/interfaces/graphics/composer/2.1/default/[email protected]

service hwcomposer-2-1 /vendor/bin/hw/android.hardware.graphics.composer@2.1-service  
    class hal animation  
    user system  
    group graphics drmrpc  
    capabilities SYS_NICE  
    onrestart restart surfaceflinger 

编译后,会将该脚本文件copy到vendor/etc/init目录,在开机时,init进程会读取并解析这个脚本,然后启动[email protected]进程:

system   661     1   32288   7832 0    0 S android.hardware.graphics.composer@2.1-service  

该进程的可执行文件是:vendor/bin/hw/[email protected]
该可执行文件对应的源码为:hardware/interfaces/graphics/composer/2.1/default/service.cpp
composer Hal启动过程
hardware/interfaces/graphics/composer/2.1/default/service.cpp

int main() {  
    // the conventional HAL might start binder services  
    android::ProcessState::initWithDriver("/dev/vndbinder");  
    android::ProcessState::self()->setThreadPoolMaxThreadCount(4);  
    android::ProcessState::self()->startThreadPool();  

    // same as SF main thread  
    struct sched_param param = {0};  
    param.sched_priority = 2;  
    if (sched_setscheduler(0, SCHED_FIFO | SCHED_RESET_ON_FORK,  
                ¶m) != 0) {  
        ALOGE("Couldn't set SCHED_FIFO: %d", errno);  
    }  

    return defaultPassthroughServiceImplementation<IComposer>(4);  
}  

前面我们分析了Treble架构下的binder通信变化,在Treble架构下,存在了3个binder设备,分别是/dev/binder、/dev/vndbinder、/dev/hwbinder,上层需要通过binder库来访问这些binder设备,而/dev/binder和/dev/vndbinder都是由libbinder来访问,因此需要指定打开的binder设备。

android::ProcessState::initWithDriver("/dev/vndbinder");

这句说明composer hal通过vndbinder来通信的,接下来就是设置binder线程个数为4,并启动binder线程池,然后调用

defaultPassthroughServiceImplementation<IComposer>(4) 

完成composer hal的启动。
system\libhidl\transport\include\hidl\LegacySupport.h

template  
__attribute__((warn_unused_result))  
status_t defaultPassthroughServiceImplementation(std::string name,  
                                            size_t maxThreads = 1) {  
    configureRpcThreadpool(maxThreads, true); //配置binder线程个数  
    status_t result = registerPassthroughServiceImplementation(name);  

    if (result != OK) {  
        return result;  
    }  

    joinRpcThreadpool();  
    return 0;  
}
template<class Interface>  
__attribute__((warn_unused_result))  
status_t registerPassthroughServiceImplementation(  
        std::string name = "default") {  
    sp<Interface> service = Interface::getService(name, true /* getStub */); //从当前进程空间中拿到IComposer接口类对象  

    if (service == nullptr) {  
        ALOGE("Could not get passthrough implementation for %s/%s.",  
            Interface::descriptor, name.c_str());  
        return EXIT_FAILURE;  
    }  

    LOG_FATAL_IF(service->isRemote(), "Implementation of %s/%s is remote!",  
            Interface::descriptor, name.c_str());  

    status_t status = service->registerAsService(name);//将IComposer注册到hwservicemanager中  

    if (status == OK) {  
        ALOGI("Registration complete for %s/%s.",  
            Interface::descriptor, name.c_str());  
    } else {  
        ALOGE("Could not register service %s/%s (%d).",  
            Interface::descriptor, name.c_str(), status);  
    }  

    return status;  
}  

这里写图片描述

Hal进程获取IComposer类对象

在composer hal进程启动时,首先调用IComposer 的getService(“default”,true)来获取IComposer的类对象。

composer\2.1\[email protected]_genc++\gen\android\hardware\graphics\composer\2.1\ComposerAll.cpp

::android::sp<IComposer> IComposer::getService(const std::string &serviceName, const bool getStub) {  
    using ::android::hardware::defaultServiceManager;  
    using ::android::hardware::details::waitForHwService;  
    using ::android::hardware::getPassthroughServiceManager;  
    using ::android::hardware::Return;  
    using ::android::sp;  
    using Transport = ::android::hidl::manager::V1_0::IServiceManager::Transport;  

    sp<IComposer> iface = nullptr;  

    const sp<::android::hidl::manager::V1_0::IServiceManager> sm = defaultServiceManager(); //获取hwservicemanager的代理  
    if (sm == nullptr) {  
        ALOGE("getService: defaultServiceManager() is null");  
        return nullptr;  
    }  

    Return<Transport> transportRet = sm->getTransport(IComposer::descriptor, serviceName);//查询IComposer的Transport  
    if (!transportRet.isOk()) {  
        ALOGE("getService: defaultServiceManager()->getTransport returns %s", transportRet.description().c_str());  
        return nullptr;  
    }  
    Transport transport = transportRet;  
    const bool vintfHwbinder = (transport == Transport::HWBINDER);  
    const bool vintfPassthru = (transport == Transport::PASSTHROUGH); //Transport类型判断  
    #ifdef __ANDROID_TREBLE__  

    #ifdef __ANDROID_DEBUGGABLE__  
    const char* env = std::getenv("TREBLE_TESTING_OVERRIDE");  
    const bool trebleTestingOverride =  env && !strcmp(env, "true");  
    const bool vintfLegacy = (transport == Transport::EMPTY) && trebleTestingOverride;  
    #else // __ANDROID_TREBLE__ but not __ANDROID_DEBUGGABLE__  
    const bool trebleTestingOverride = false;  
    const bool vintfLegacy = false;  
    #endif // __ANDROID_DEBUGGABLE__  

    #else // not __ANDROID_TREBLE__  
    const char* env = std::getenv("TREBLE_TESTING_OVERRIDE");  
    const bool trebleTestingOverride =  env && !strcmp(env, "true");  
    const bool vintfLegacy = (transport == Transport::EMPTY);  

    #endif // __ANDROID_TREBLE__  
    //hwbinder方式下获取IComposer对象  
    for (int tries = 0; !getStub && (vintfHwbinder || (vintfLegacy && tries == 0)); tries++) {  
        if (tries > 1) {  
            ALOGI("getService: Will do try %d for %s/%s in 1s...", tries, IComposer::descriptor, serviceName.c_str());  
            sleep(1);  
        }  
        if (vintfHwbinder && tries > 0) {  
            waitForHwService(IComposer::descriptor, serviceName);  
        }  
        Return<sp<::android::hidl::base::V1_0::IBase>> ret =   
                sm->get(IComposer::descriptor, serviceName);  
        if (!ret.isOk()) {  
            ALOGE("IComposer: defaultServiceManager()->get returns %s", ret.description().c_str());  
            break;  
        }  
        sp<::android::hidl::base::V1_0::IBase> base = ret;  
        if (base == nullptr) {  
            if (tries > 0) {  
                ALOGW("IComposer: found null hwbinder interface");  
            }continue;  
        }  
        Return<sp<IComposer>> castRet = IComposer::castFrom(base, true /* emitError */);  
        if (!castRet.isOk()) {  
            if (castRet.isDeadObject()) {  
                ALOGW("IComposer: found dead hwbinder service");  
                continue;  
            } else {  
                ALOGW("IComposer: cannot call into hwbinder service: %s; No permission? Check for selinux denials.", castRet.description().c_str());  
                break;  
            }  
        }  
        iface = castRet;  
        if (iface == nullptr) {  
            ALOGW("IComposer: received incompatible service; bug in hwservicemanager?");  
            break;  
        }  
        return iface;  
    }  
   //passthrough方式下获取IComposer对象  
    if (getStub || vintfPassthru || vintfLegacy) {  
        const sp<::android::hidl::manager::V1_0::IServiceManager> pm = getPassthroughServiceManager();  
        if (pm != nullptr) {  
            Return<sp<::android::hidl::base::V1_0::IBase>> ret =   
                    pm->get(IComposer::descriptor, serviceName);  
            if (ret.isOk()) {  
                sp<::android::hidl::base::V1_0::IBase> baseInterface = ret;  
                if (baseInterface != nullptr) {  
                    iface = IComposer::castFrom(baseInterface);  
                    if (!getStub || trebleTestingOverride) {  
                        iface = new BsComposer(iface);  
                    }  
                }  
            }  
        }  
    }  
    return iface;  
}  

这里通过hwservicemanager获取当前服务的Tranport类型,Treble中定义的Tranport包括passthrough和binderized,每个hidl服务都在/system/manifest.xml或者/vendor/manifest.xml中指定了对应的Tranport类型:
这里写图片描述

manifest.xml文件的读取和解析都是由hwservicemanager来完成的,此时[email protected]作为hwservicemanager的client端,通过hwservicemanager的binder代理对象来请求hwservicemanager进程查询IComposer的Transport类型,从上图可以看出IComposer的Transport被定义为hwbinder,因此:

vintfHwbinder=true
vintfPassthru=false
vintfLegacy=false

hidl服务对象获取方式包括2中:

  1. 通过查询hwservicemanager来获取;

2.通过PassthroughServiceManager从本进程地址空间中获取;

那如何选择获取方式呢? 其实就是vintfHwbinder、vintfPassthru、vintfLegacy、getStub这4个变量值来决定hidl服务的获取方式。

  1. 当getStub为true时,不管hal属于什么传输模式,都采用PassthroughServiceManager获取接口对象;

2.当getStub为false时,则根据hal传输模式来选择接口获取方式;

   《1》 当hal模式为Hwbinder时,则从hwservicemanager中查询;

   《2》当hal传输模式为Passthru或Legacy时,则采用PassthroughServiceManager来获取;

那什么是Hwbinder,什么是Passthru及Legacy呢?下图是google提供的hal的roadmap图:
这里写图片描述

if (getStub || vintfPassthru || vintfLegacy) {  
    const sp<::android::hidl::manager::V1_0::IServiceManager> pm = getPassthroughServiceManager();  
    if (pm != nullptr) {  
        Return<sp<::android::hidl::base::V1_0::IBase>> ret =   
                pm->get(IComposer::descriptor, serviceName);  
        if (ret.isOk()) {  
            sp<::android::hidl::base::V1_0::IBase> baseInterface = ret;  
            if (baseInterface != nullptr) {  
                iface = IComposer::castFrom(baseInterface);  
                if (!getStub || trebleTestingOverride) {  
                    iface = new BsComposer(iface);  
                }  
            }  
        }  
    }  
}  

sp service = Interface::getService(name, true /* getStub */)所以getStub=true. 这里通过PassthroughServiceManager来获取IComposer对象。其实所有的Hal 进程都是通过PassthroughServiceManager来得到hidl服务对象的,而作为Hal进程的Client端Framework进程在获取hidl服务对象时,需要通过hal的Transport类型来选择获取方式。
system\libhidl\transport\ServiceManagement.cpp

sp getPassthroughServiceManager() {  
    static sp manager(new PassthroughServiceManager());  
    return manager;  
}  

这里只是简单的创建了一个PassthroughServiceManager对象。PassthroughServiceManager也实现了IServiceManager接口。然后通过PassthroughServiceManager询服务:

Return> get(const hidl_string& fqName,  
                          const hidl_string& name) override {  
        std::string stdFqName(fqName.c_str());  

        //fqName looks like [email protected]::IFoo  
        size_t idx = stdFqName.find("::");  

        if (idx == std::string::npos ||  
                idx + strlen("::") + 1 >= stdFqName.size()) {  
            LOG(ERROR) << "Invalid interface name passthrough lookup: " << fqName;  
            return nullptr;  
        }  

        std::string packageAndVersion = stdFqName.substr(0, idx);  
        std::string ifaceName = stdFqName.substr(idx + strlen("::"));  

        const std::string prefix = packageAndVersion + "-impl";  
        const std::string sym = "HIDL_FETCH_" + ifaceName;  

        const android_namespace_t* sphal_namespace = android_get_exported_namespace("sphal");  
        const int dlMode = RTLD_LAZY;  
        void *handle = nullptr;  

        // TODO: lookup in VINTF instead  
        // TODO(b/34135607): Remove HAL_LIBRARY_PATH_SYSTEM  

        dlerror(); // clear  

        for (const std::string &path : {  
            HAL_LIBRARY_PATH_ODM, HAL_LIBRARY_PATH_VENDOR, HAL_LIBRARY_PATH_SYSTEM  
        }) {  
            std::vector<std::string> libs = search(path, prefix, ".so");  

            for (const std::string &lib : libs) {  
                const std::string fullPath = path + lib;  

                // If sphal namespace is available, try to load from the  
                // namespace first. If it fails, fall back to the original  
                // dlopen, which loads from the current namespace.  
                if (sphal_namespace != nullptr && path != HAL_LIBRARY_PATH_SYSTEM) {  
                    const android_dlextinfo dlextinfo = {  
                        .flags = ANDROID_DLEXT_USE_NAMESPACE,  
                        // const_cast is dirty but required because  
                        // library_namespace field is non-const.  
                        .library_namespace = const_cast(sphal_namespace),  
                    };  
                    handle = android_dlopen_ext(fullPath.c_str(), dlMode, &dlextinfo);  
                    if (handle == nullptr) {  
                        const char* error = dlerror();  
                        LOG(WARNING) << "Failed to dlopen " << lib << " from sphal namespace:"  
                                     << (error == nullptr ? "unknown error" : error);  
                    } else {  
                        LOG(DEBUG) << lib << " loaded from sphal namespace.";  
                    }  
                }  
                if (handle == nullptr) {  
                    handle = dlopen(fullPath.c_str(), dlMode);  
                }  

                if (handle == nullptr) {  
                    const char* error = dlerror();  
                    LOG(ERROR) << "Failed to dlopen " << lib << ": "  
                               << (error == nullptr ? "unknown error" : error);  
                    continue;  
                }  

                IBase* (*generator)(const char* name);  
                *(void **)(&generator) = dlsym(handle, sym.c_str());  
                if(!generator) {  
                    const char* error = dlerror();  
                    LOG(ERROR) << "Passthrough lookup opened " << lib  
                               << " but could not find symbol " << sym << ": "  
                               << (error == nullptr ? "unknown error" : error);  
                    dlclose(handle);  
                    continue;  
                }  

                IBase *interface = (*generator)(name.c_str());  

                if (interface == nullptr) {  
                    dlclose(handle);  
                    continue; // this module doesn't provide this instance name  
                }  

                registerReference(fqName, name);  

                return interface;  
            }  
        }  

        return nullptr;  
    }  

根据传入的fqName=([email protected]::IComposer”)获取当前的接口名IComposer,拼接出后面需要查找的函数名HIDL_FETCH_IComposer和库名字[email protected],然后查找”/system/lib64/hw/”、”/vendor/lib64/hw/”、”/odm/lib64/hw/”下是否有对应的so库。接着通过dlopen载入/vendor/lib/hw/[email protected],然后通过dlsym查找并调用HIDL_FETCH_IComposer函数,最后调用registerReference(fqName, name)向hwservicemanager注册。

hardware/interfaces/graphics/composer/2.1/default/Android.bp

cc_library_shared {  
    name: "[email protected]",  
    defaults: ["hidl_defaults"],  
    proprietary: true,  
    relative_install_path: "hw",  
    srcs: ["Hwc.cpp"],  
    static_libs: ["libhwcomposer-client"],  
    shared_libs: [  
        "[email protected]",  
        "[email protected]",  
        "libbase",  
        "libcutils",  
        "libfmq",  
        "libhardware",  
        "libhidlbase",  
        "libhidltransport",  
        "liblog",  
        "libsync",  
        "libutils",  
        "libhwc2on1adapter"  
    ],  
}  

从上面的编译脚本可知,[email protected]的源码文件为Hwc.cpp:
hardware/interfaces/graphics/composer/2.1/default/Hwc.cpp

IComposer* HIDL_FETCH_IComposer(const char*)  
{  
    const hw_module_t* module = nullptr;  
    int err = hw_get_module(HWC_HARDWARE_MODULE_ID, &module);  
    if (err) {  
        ALOGE("failed to get hwcomposer module");  
        return nullptr;  
    }  

    return new HwcHal(module);  
}  

hw_get_module就和AndroidO以前的Hal模式一致,这正是Passthrough复用原有hal的原理。加载hal库后,得到hw_module_t,然后使用HwcHal来包裹hw_module_t,而HwcHal实现了IComposer接口。
这里写图片描述

registerPassthroughClient

得到IComposer接口对象HwcHal后,需要注册相关信息到hwservicemanager中。
这里写图片描述
system\libhidl\transport\ServiceManagement.cpp

static void registerReference(const hidl_string &interfaceName, const hidl_string &instanceName) {  
    sp binderizedManager = defaultServiceManager();  
    if (binderizedManager == nullptr) {  
        LOG(WARNING) << "Could not registerReference for "  
                     << interfaceName << "/" << instanceName  
                     << ": null binderized manager.";  
        return;  
    }  
    auto ret = binderizedManager->registerPassthroughClient(interfaceName, instanceName);  
    if (!ret.isOk()) {  
        LOG(WARNING) << "Could not registerReference for "  
                     << interfaceName << "/" << instanceName  
                     << ": " << ret.description();  
        return;  
    }  
    LOG(VERBOSE) << "Successfully registerReference for "  
                 << interfaceName << "/" << instanceName;  
}  

这里通过hwservicemanager的代理对象跨进程调用registerPassthroughClient。
[email protected]_genc++\gen\android\hidl\manager\1.0\ServiceManagerAll.cpp

::android::hardware::Return<void> BpHwServiceManager::registerPassthroughClient(const ::android::hardware::hidl_string& fqName, const ::android::hardware::hidl_string& name){  
    ::android::hardware::Return<void>  _hidl_out = ::android::hidl::manager::V1_0::BpHwServiceManager::_hidl_registerPassthroughClient(this, this, fqName, name);  

    return _hidl_out;  
}  
::android::hardware::Return<void> BpHwServiceManager::_hidl_registerPassthroughClient(::android::hardware::IInterface *_hidl_this, ::android::hardware::details::HidlInstrumentor *_hidl_this_instrumentor, const ::android::hardware::hidl_string& fqName, const ::android::hardware::hidl_string& name) {  
    #ifdef __ANDROID_DEBUGGABLE__  
    bool mEnableInstrumentation = _hidl_this_instrumentor->isInstrumentationEnabled();  
    const auto &mInstrumentationCallbacks = _hidl_this_instrumentor->getInstrumentationCallbacks();  
    #else  
    (void) _hidl_this_instrumentor;  
    #endif // __ANDROID_DEBUGGABLE__  
    atrace_begin(ATRACE_TAG_HAL, "HIDL::IServiceManager::registerPassthroughClient::client");  
    #ifdef __ANDROID_DEBUGGABLE__  
    if (UNLIKELY(mEnableInstrumentation)) {  
        std::vector<void *> _hidl_args;  
        _hidl_args.push_back((void *)&fqName);  
        _hidl_args.push_back((void *)&name);  
        for (const auto &callback: mInstrumentationCallbacks) {  
            callback(InstrumentationEvent::CLIENT_API_ENTRY, "android.hidl.manager", "1.0", "IServiceManager", "registerPassthroughClient", &_hidl_args);  
        }  
    }  
    #endif // __ANDROID_DEBUGGABLE__  

    ::android::hardware::Parcel _hidl_data;  
    ::android::hardware::Parcel _hidl_reply;  
    ::android::status_t _hidl_err;  
    ::android::hardware::Status _hidl_status;  

    _hidl_err = _hidl_data.writeInterfaceToken(BpHwServiceManager::descriptor);  
    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    size_t _hidl_fqName_parent;  

    _hidl_err = _hidl_data.writeBuffer(&fqName, sizeof(fqName), &_hidl_fqName_parent);  
    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    _hidl_err = ::android::hardware::writeEmbeddedToParcel(  
            fqName,  
            &_hidl_data,  
            _hidl_fqName_parent,  
            0 /* parentOffset */);  

    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    size_t _hidl_name_parent;  

    _hidl_err = _hidl_data.writeBuffer(&name, sizeof(name), &_hidl_name_parent);  
    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    _hidl_err = ::android::hardware::writeEmbeddedToParcel(  
            name,  
            &_hidl_data,  
            _hidl_name_parent,  
            0 /* parentOffset */);  

    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    _hidl_err = ::android::hardware::IInterface::asBinder(_hidl_this)->transact(8 /* registerPassthroughClient */, _hidl_data, &_hidl_reply);  
    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    _hidl_err = ::android::hardware::readFromParcel(&_hidl_status, _hidl_reply);  
    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    if (!_hidl_status.isOk()) { return _hidl_status; }  

    atrace_end(ATRACE_TAG_HAL);  
    #ifdef __ANDROID_DEBUGGABLE__  
    if (UNLIKELY(mEnableInstrumentation)) {  
        std::vector<void *> _hidl_args;  
        for (const auto &callback: mInstrumentationCallbacks) {  
            callback(InstrumentationEvent::CLIENT_API_EXIT, "android.hidl.manager", "1.0", "IServiceManager", "registerPassthroughClient", &_hidl_args);  
        }  
    }  
    #endif // __ANDROID_DEBUGGABLE__  

    _hidl_status.setFromStatusT(_hidl_err);  
    return ::android::hardware::Return<void>();  

_hidl_error:  
    _hidl_status.setFromStatusT(_hidl_err);  
    return ::android::hardware::Return<void>(_hidl_status);  
} 

这里和普通binder通信相同,先就需要传输的函数参数打包到Parcel对象中,然后调用binder代理对象的transact函数将函数参数,函数调用码发送到Server端进程,这里的_hidl_this其实指向的是BpHwServiceManager,这个是与业务相关的代理对象,通过asBinder函数得到与传输相关的binder代理,那这个binder代理是什么类型呢? 其实就是BpHwBinder,关于hwservicemanager代理对象的获取,asBinder函数的实现,在后续的章节中进行分析。经过BpHwServiceManager的请求,最终位于hwservicemanager进程中的BnHwServiceManager将接收函数调用请求:
[email protected]_genc++\gen\android\hidl\manager\1.0\ServiceManagerAll.cpp

::android::status_t BnHwServiceManager::onTransact(  
    uint32_t _hidl_code,  
    const ::android::hardware::Parcel &_hidl_data,  
    ::android::hardware::Parcel *_hidl_reply,  
    uint32_t _hidl_flags,  
    TransactCallback _hidl_cb) {  
::android::status_t _hidl_err = ::android::OK;  

switch (_hidl_code) {  
    case 8 /* registerPassthroughClient */:  
    {  
        _hidl_err = ::android::hidl::manager::V1_0::BnHwServiceManager::_hidl_registerPassthroughClient(this, _hidl_data, _hidl_reply, _hidl_cb);  
        break;  
    }  
    default:  
    {  
        return ::android::hidl::base::V1_0::BnHwBase::onTransact(  
                _hidl_code, _hidl_data, _hidl_reply, _hidl_flags, _hidl_cb);  
    }  
}  

BnHwServiceManager将调用_hidl_registerPassthroughClient来执行Client端的注册。

::android::status_t BnHwServiceManager::_hidl_registerPassthroughClient(  
        ::android::hidl::base::V1_0::BnHwBase* _hidl_this,  
        const ::android::hardware::Parcel &_hidl_data,  
        ::android::hardware::Parcel *_hidl_reply,  
        TransactCallback _hidl_cb) {  
    #ifdef __ANDROID_DEBUGGABLE__  
    bool mEnableInstrumentation = _hidl_this->isInstrumentationEnabled();  
    const auto &mInstrumentationCallbacks = _hidl_this->getInstrumentationCallbacks();  
    #endif // __ANDROID_DEBUGGABLE__  

    ::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;  

    _hidl_err = _hidl_data.readBuffer(sizeof(*fqName), &_hidl_fqName_parent,  reinterpret_cast<const void **>(&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;  

    _hidl_err = _hidl_data.readBuffer(sizeof(*name), &_hidl_name_parent,  reinterpret_cast<const void **>(&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::registerPassthroughClient::server");  
    #ifdef __ANDROID_DEBUGGABLE__  
    if (UNLIKELY(mEnableInstrumentation)) {  
        std::vector<void *> _hidl_args;  
        _hidl_args.push_back((void *)fqName);  
        _hidl_args.push_back((void *)name);  
        for (const auto &callback: mInstrumentationCallbacks) {  
            callback(InstrumentationEvent::SERVER_API_ENTRY, "android.hidl.manager", "1.0", "IServiceManager", "registerPassthroughClient", &_hidl_args);  
        }  
    }  
    #endif // __ANDROID_DEBUGGABLE__  

    static_cast(_hidl_this)->_hidl_mImpl->registerPassthroughClient(*fqName, *name);  

    (void) _hidl_cb;  

    atrace_end(ATRACE_TAG_HAL);  
    #ifdef __ANDROID_DEBUGGABLE__  
    if (UNLIKELY(mEnableInstrumentation)) {  
        std::vector<void *> _hidl_args;  
        for (const auto &callback: mInstrumentationCallbacks) {  
            callback(InstrumentationEvent::SERVER_API_EXIT, "android.hidl.manager", "1.0", "IServiceManager", "registerPassthroughClient", &_hidl_args);  
        }  
    }  
    #endif // __ANDROID_DEBUGGABLE__  

    ::android::hardware::writeToParcel(::android::hardware::Status::ok(), _hidl_reply);  

    return _hidl_err;  
} 

BnHwServiceManager首先读取BpHwServiceManager发送过来的函数参数,然后将registerPassthroughClient的执行转交个其成员变量的_hidl_mImpl对象,然后将执行结果返回给BpHwServiceManager,那么_hidl_mImpl保存的是什么对象呢? 其实_hidl_mImpl指向的是ServiceManager对象,这个是在构造BnHwServiceManager对象时传入的,在后续分析hwservicemanager启动过程时,会进行详细分析。
system\hwservicemanager\ServiceManager.cpp

Return<void> ServiceManager::registerPassthroughClient(const hidl_string &fqName,  
        const hidl_string &name) {  
    pid_t pid = IPCThreadState::self()->getCallingPid();  
    if (!mAcl.canGet(fqName, pid)) { //根据Client端的pid及注册接口的包名,判断是否有权限注册  
        /* We guard this function with "get", because it's typically used in 
         * the getService() path, albeit for a passthrough service in this 
         * case 
         */  
        return Void();  
    }  
    LOG(INFO) << "registerPassthroughClient " << fgName.c_str() << " of "  
                         << name.c_str()  

    PackageInterfaceMap &ifaceMap = mServiceMap[fqName];  

    if (name.empty()) {  
        LOG(WARNING) << "registerPassthroughClient encounters empty instance name for "  
                     << fqName.c_str();  
        return Void();  
    }  

    HidlService *service = ifaceMap.lookup(name);  

    if (service == nullptr) {  
        auto adding = std::make_unique(fqName, name);  
        adding->registerPassthroughClient(pid);  
        ifaceMap.insertService(std::move(adding));  
    } else {  
        service->registerPassthroughClient(pid);  
    }  
    return Void();  
}  

首先根据fqName从mServiceMap中查找对应的PackageInterfaceMap,然后根据name从PackageInterfaceMap中查找HidlService,如果找不到对应的HidlService对象,那么就调用std::make_unique(fqName,name)创建一个新的HidlService对象,并ifaceMap.insertService(std::move(adding))添加到PackageInterfaceMap中。如果查找到了HidlService对象,那么仅仅将Client进程的pid保存到HidlService的mPassthroughClients变量中。
system\hwservicemanager\HidlService.h

HidlService(const std::string &interfaceName,  
            const std::string &instanceName)  
: HidlService(  
    interfaceName,  
    instanceName,  
    nullptr,  
    static_cast(IServiceManager::PidConstant::NO_PID))  
{} 

因此registerPassthroughClient在hwservicemanager中插入一个HidlService对象而已,并没有注册对应的IBase对象。getService最后将HwcHal对象返回给registerPassthroughServiceImplementation()函数,然后再次调用registerAsService注册该IBase对象。
这里写图片描述

registerAsService注册

registerAsService用于向hwservicemanager注册IBase对象,由于前面通过PassthroughServiceManager得到的HwcHal继承于IBase,因此可以调用registerAsService函数来注册。
这里写图片描述
composer\2.1\[email protected]_genc++\gen\android\hardware\graphics\composer\2.1\ComposerAll.cpp

::android::status_t IComposer::registerAsService(const std::string &serviceName) {  
    ::android::hardware::details::onRegistration("[email protected]", "IComposer", serviceName);  

    const ::android::sp<::android::hidl::manager::V1_0::IServiceManager> sm  
            = ::android::hardware::defaultServiceManager();  
    if (sm == nullptr) {  
        return ::android::INVALID_OPERATION;  
    }  
    ::android::hardware::Return<bool> ret = sm->add(serviceName.c_str(), this);  
    return ret.isOk() && ret ? ::android::OK : ::android::UNKNOWN_ERROR;  
}  

首先执行onRegistration函数,然后调用hwservicemanager的代理对象的add函数。
system\libhidl\transport\ServiceManagement.cpp

void onRegistration(const std::string &packageName,  
                    const std::string& /* interfaceName */,  
                    const std::string& /* instanceName */) {  
    tryShortenProcessName(packageName);  
} 
void tryShortenProcessName(const std::string &packageName) {  
    std::string processName = binaryName();  

    if (!startsWith(processName, packageName)) {  
        return;  
    }  

    // e.x. android.hardware.module.foo@1.0 -> foo@1.0  
    size_t lastDot = packageName.rfind('.');  
    size_t secondDot = packageName.rfind('.', lastDot - 1);  

    if (secondDot == std::string::npos) {  
        return;  
    }  

    std::string newName = processName.substr(secondDot + 1,  
            16 /* TASK_COMM_LEN */ - 1);  
    ALOGI("Removing namespace from process name %s to %s.",  
            processName.c_str(), newName.c_str());  

    int rc = pthread_setname_np(pthread_self(), newName.c_str());  
    ALOGI_IF(rc != 0, "Removing namespace from process name %s failed.",  
            processName.c_str());  
}  

这里只是简单的修改了当前进程的名称。
[email protected]_genc++\gen\android\hidl\manager\1.0\ServiceManagerAll.cpp

::android::hardware::Return<bool> BpHwServiceManager::add(const ::android::hardware::hidl_string& name, const ::android::sp<::android::hidl::base::V1_0::IBase>& service){  
    ::android::hardware::Return<bool>  _hidl_out = ::android::hidl::manager::V1_0::BpHwServiceManager::_hidl_add(this, this, name, service);  

    return _hidl_out;  
}  
::android::hardware::Return<bool> BpHwServiceManager::_hidl_add(::android::hardware::IInterface *_hidl_this, ::android::hardware::details::HidlInstrumentor *_hidl_this_instrumentor, const ::android::hardware::hidl_string& name, const ::android::sp<::android::hidl::base::V1_0::IBase>& service) {  
    #ifdef __ANDROID_DEBUGGABLE__  
    bool mEnableInstrumentation = _hidl_this_instrumentor->isInstrumentationEnabled();  
    const auto &mInstrumentationCallbacks = _hidl_this_instrumentor->getInstrumentationCallbacks();  
    #else  
    (void) _hidl_this_instrumentor;  
    #endif // __ANDROID_DEBUGGABLE__  
    atrace_begin(ATRACE_TAG_HAL, "HIDL::IServiceManager::add::client");  
    #ifdef __ANDROID_DEBUGGABLE__  
    if (UNLIKELY(mEnableInstrumentation)) {  
        std::vector<void *> _hidl_args;  
        _hidl_args.push_back((void *)&name);  
        _hidl_args.push_back((void *)&service);  
        for (const auto &callback: mInstrumentationCallbacks) {  
            callback(InstrumentationEvent::CLIENT_API_ENTRY, "android.hidl.manager", "1.0", "IServiceManager", "add", &_hidl_args);  
        }  
    }  
    #endif // __ANDROID_DEBUGGABLE__  

    ::android::hardware::Parcel _hidl_data;  
    ::android::hardware::Parcel _hidl_reply;  
    ::android::status_t _hidl_err;  
    ::android::hardware::Status _hidl_status;  

    bool _hidl_out_success;  

    _hidl_err = _hidl_data.writeInterfaceToken(BpHwServiceManager::descriptor);  
    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    size_t _hidl_name_parent;  

    _hidl_err = _hidl_data.writeBuffer(&name, sizeof(name), &_hidl_name_parent);  
    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    _hidl_err = ::android::hardware::writeEmbeddedToParcel(  
            name,  
            &_hidl_data,  
            _hidl_name_parent,  
            0 /* parentOffset */);  

    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    if (service == nullptr) {  
        _hidl_err = _hidl_data.writeStrongBinder(nullptr);  
    } else {  
        ::android::sp<::android::hardware::IBinder> _hidl_binder = ::android::hardware::toBinder<  
                ::android::hidl::base::V1_0::IBase>(service);  
        if (_hidl_binder.get() != nullptr) {  
            _hidl_err = _hidl_data.writeStrongBinder(_hidl_binder);  
        } else {  
            _hidl_err = ::android::UNKNOWN_ERROR;  
        }  
    }  
    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    ::android::hardware::ProcessState::self()->startThreadPool();  
    _hidl_err = ::android::hardware::IInterface::asBinder(_hidl_this)->transact(2 /* add */, _hidl_data, &_hidl_reply);  
    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    _hidl_err = ::android::hardware::readFromParcel(&_hidl_status, _hidl_reply);  
    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    if (!_hidl_status.isOk()) { return _hidl_status; }  

    _hidl_err = _hidl_reply.readBool(&_hidl_out_success);  
    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    atrace_end(ATRACE_TAG_HAL);  
    #ifdef __ANDROID_DEBUGGABLE__  
    if (UNLIKELY(mEnableInstrumentation)) {  
        std::vector<void *> _hidl_args;  
        _hidl_args.push_back((void *)&_hidl_out_success);  
        for (const auto &callback: mInstrumentationCallbacks) {  
            callback(InstrumentationEvent::CLIENT_API_EXIT, "android.hidl.manager", "1.0", "IServiceManager", "add", &_hidl_args);  
        }  
    }  
    #endif // __ANDROID_DEBUGGABLE__  

    _hidl_status.setFromStatusT(_hidl_err);  
    return ::android::hardware::Return<bool>(_hidl_out_success);  

_hidl_error:  
    _hidl_status.setFromStatusT(_hidl_err);  
    return ::android::hardware::Return<bool>(_hidl_status);  
}  

这里的步骤和前面的registerPassthroughClient基本一致,唯一不同的是,此时需要向Server端hwservicemanager传输一个IBase对象

::android::sp<::android::hardware::IBinder> _hidl_binder = ::android::hardware::toBinder<  
        ::android::hidl::base::V1_0::IBase>(service);  
if (_hidl_binder.get() != nullptr) {  
    _hidl_err = _hidl_data.writeStrongBinder(_hidl_binder);  
}  

这里首先通过toBinder函数将IBase对象,其实就是HwcHal对象转换为IBinder对象,然后通过writeStrongBinder将IBinder对象序列化到Parcel中,toBinder函数在后续进行分析,我们这里只需要知道经过toBinder函数后,在Hal进程端会创建一个BnHwComposer本地binder对象,然后通过IPC调用发送给hwservicemanager。
[email protected]_genc++\gen\android\hidl\manager\1.0\ServiceManagerAll.cpp

::android::status_t BnHwServiceManager::onTransact(  
        uint32_t _hidl_code,  
        const ::android::hardware::Parcel &_hidl_data,  
        ::android::hardware::Parcel *_hidl_reply,  
        uint32_t _hidl_flags,  
        TransactCallback _hidl_cb) {  
    ::android::status_t _hidl_err = ::android::OK;  
    switch (_hidl_code) {  
        case 2 /* add */:  
        {  
            _hidl_err = ::android::hidl::manager::V1_0::BnHwServiceManager::_hidl_add(this, _hidl_data, _hidl_reply, _hidl_cb);  
            break;  
        }  
        default:  
        {  
            return ::android::hidl::base::V1_0::BnHwBase::onTransact(  
                    _hidl_code, _hidl_data, _hidl_reply, _hidl_flags, _hidl_cb);  
        }  
    }  
    if (_hidl_err == ::android::UNEXPECTED_NULL) {  
        _hidl_err = ::android::hardware::writeToParcel(  
                ::android::hardware::Status::fromExceptionCode(::android::hardware::Status::EX_NULL_POINTER),  
                _hidl_reply);  
    }return _hidl_err;  
}  
::android::status_t BnHwServiceManager::onTransact(  
        uint32_t _hidl_code,  
        const ::android::hardware::Parcel &_hidl_data,  
        ::android::hardware::Parcel *_hidl_reply,  
        uint32_t _hidl_flags,  
        TransactCallback _hidl_cb) {  
    ::android::status_t _hidl_err = ::android::OK;  
    switch (_hidl_code) {  
        case 2 /* add */:  
        {  
            _hidl_err = ::android::hidl::manager::V1_0::BnHwServiceManager::_hidl_add(this, _hidl_data, _hidl_reply, _hidl_cb);  
            break;  
        }  
        default:  
        {  
            return ::android::hidl::base::V1_0::BnHwBase::onTransact(  
                    _hidl_code, _hidl_data, _hidl_reply, _hidl_flags, _hidl_cb);  
        }  
    }  
    if (_hidl_err == ::android::UNEXPECTED_NULL) {  
        _hidl_err = ::android::hardware::writeToParcel(  
                ::android::hardware::Status::fromExceptionCode(::android::hardware::Status::EX_NULL_POINTER),  
                _hidl_reply);  
    }return _hidl_err;  
}  

hwservicemanager进程通过_hidl_err = _hidl_data.readNullableStrongBinder(&_hidl_service_binder);拿到client进程发送过来的BnHwComposer对象,binder实体到达目的端进程将变为binder代理对象,然后通过fromBinder函数将binder代理对象转换为业务代理对象BpHwBase,这个过程在后续进行详细分析,接下来继续调用_hidl_mImpl的add函数,而我们知道_hidl_mImpl其实就是ServiceManager:
这里写图片描述
system\hwservicemanager\ServiceManager.cpp

Return ServiceManager::add(const hidl_string& name, const sp& service) {  
    bool isValidService = false;  

    if (service == nullptr) {  
        return false;  
    }  
    LOG(INFO) << "register service " << name;  

    // TODO(b/34235311): use HIDL way to determine this  
    // also, this assumes that the PID that is registering is the pid that is the service  
    pid_t pid = IPCThreadState::self()->getCallingPid();  

    auto ret = service->interfaceChain([&](const auto &interfaceChain) {  
        if (interfaceChain.size() == 0) {  
            return;  
        }  
        ...  
    });  

    if (!ret.isOk()) {  
        LOG(ERROR) << "Failed to retrieve interface chain.";  
        return false;  
    }  

    return isValidService;  
}  

接着调用interfaceChain函数并传入一个函数回调,由于此时service是BpHwBase对象,BpHwBase的interfaceChain函数实现如下:
[email protected]_genc++\gen\android\hidl\base\1.0\BaseAll.cpp

::android::hardware::Return<void> BpHwBase::interfaceChain(interfaceChain_cb _hidl_cb){  
    ::android::hardware::Return<void>  _hidl_out = ::android::hidl::base::V1_0::BpHwBase::_hidl_interfaceChain(this, this, _hidl_cb);  

    return _hidl_out;  
}  
::android::hardware::Return<void> BpHwBase::_hidl_interfaceChain(::android::hardware::IInterface *_hidl_this, ::android::hardware::details::HidlInstrumentor *_hidl_this_instrumentor, interfaceChain_cb _hidl_cb) {  
    #ifdef __ANDROID_DEBUGGABLE__  
    bool mEnableInstrumentation = _hidl_this_instrumentor->isInstrumentationEnabled();  
    const auto &mInstrumentationCallbacks = _hidl_this_instrumentor->getInstrumentationCallbacks();  
    #else  
    (void) _hidl_this_instrumentor;  
    #endif // __ANDROID_DEBUGGABLE__  
    if (_hidl_cb == nullptr) {  
        return ::android::hardware::Status::fromExceptionCode(  
                ::android::hardware::Status::EX_ILLEGAL_ARGUMENT,  
                "Null synchronous callback passed.");  
    }  

    atrace_begin(ATRACE_TAG_HAL, "HIDL::IBase::interfaceChain::client");  
    #ifdef __ANDROID_DEBUGGABLE__  
    if (UNLIKELY(mEnableInstrumentation)) {  
        std::vector<void *> _hidl_args;  
        for (const auto &callback: mInstrumentationCallbacks) {  
            callback(InstrumentationEvent::CLIENT_API_ENTRY, "android.hidl.base", "1.0", "IBase", "interfaceChain", &_hidl_args);  
        }  
    }  
    #endif // __ANDROID_DEBUGGABLE__  

    ::android::hardware::Parcel _hidl_data;  
    ::android::hardware::Parcel _hidl_reply;  
    ::android::status_t _hidl_err;  
    ::android::hardware::Status _hidl_status;  

    const ::android::hardware::hidl_vec<::android::hardware::hidl_string>* _hidl_out_descriptors;  

<span style="color:#FF0000;">   <span style="color:#000000;"> _hidl_err = _hidl_data.writeInterfaceToken(BpHwBase::descriptor);</span></span>  
    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    _hidl_err = ::android::hardware::IInterface::asBinder(_hidl_this)->transact(256067662 /* interfaceChain */, _hidl_data, &_hidl_reply);  
    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    _hidl_err = ::android::hardware::readFromParcel(&_hidl_status, _hidl_reply);  
    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    if (!_hidl_status.isOk()) { return _hidl_status; }  

    size_t _hidl__hidl_out_descriptors_parent;  

    _hidl_err = _hidl_reply.readBuffer(sizeof(*_hidl_out_descriptors), &_hidl__hidl_out_descriptors_parent,  reinterpret_cast<const void **>(&_hidl_out_descriptors));  

    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    size_t _hidl__hidl_out_descriptors_child;  

    _hidl_err = ::android::hardware::readEmbeddedFromParcel(  
            const_cast<::android::hardware::hidl_vec<::android::hardware::hidl_string> &>(*_hidl_out_descriptors),  
            _hidl_reply,  
            _hidl__hidl_out_descriptors_parent,  
            0 /* parentOffset */, &_hidl__hidl_out_descriptors_child);  

    if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    for (size_t _hidl_index_0 = 0; _hidl_index_0 < _hidl_out_descriptors->size(); ++_hidl_index_0) {  
        _hidl_err = ::android::hardware::readEmbeddedFromParcel(  
                const_cast<::android::hardware::hidl_string &>((*_hidl_out_descriptors)[_hidl_index_0]),  
                _hidl_reply,  
                _hidl__hidl_out_descriptors_child,  
                _hidl_index_0 * sizeof(::android::hardware::hidl_string));  

        if (_hidl_err != ::android::OK) { goto _hidl_error; }  

    }  

    _hidl_cb(*_hidl_out_descriptors);  

    atrace_end(ATRACE_TAG_HAL);  
    #ifdef __ANDROID_DEBUGGABLE__  
    if (UNLIKELY(mEnableInstrumentation)) {  
        std::vector _hidl_args;  
        _hidl_args.push_back((void *)_hidl_out_descriptors);  
        for (const auto &callback: mInstrumentationCallbacks) {  
            callback(InstrumentationEvent::CLIENT_API_EXIT, "android.hidl.base", "1.0", "IBase", "interfaceChain", &_hidl_args);  
        }  
    }  
    #endif // __ANDROID_DEBUGGABLE__  

    _hidl_status.setFromStatusT(_hidl_err);  
    return ::android::hardware::Return();  

_hidl_error:  
    _hidl_status.setFromStatusT(_hidl_err);  
    return ::android::hardware::Return(_hidl_status);  
}

这里再次回到Hal进程空间,调用BnHwComposer的interfaceChain函数查询_hidl_out_descriptors,
这里写图片描述
然后调用传递进来的回调函数_hidl_cb。因此BnHwComposer的onTransact将接收请求:
composer\2.1\[email protected]_genc++\gen\android\hardware\graphics\composer\2.1\ComposerAll.cpp

::android::status_t BnHwComposer::onTransact(  
        uint32_t _hidl_code,  
        const ::android::hardware::Parcel &_hidl_data,  
        ::android::hardware::Parcel *_hidl_reply,  
        uint32_t _hidl_flags,  
        TransactCallback _hidl_cb) {  
    ::android::status_t _hidl_err = ::android::OK;  

    switch (_hidl_code) {  
        case 256067662 /* interfaceChain */:  
        {  
            _hidl_err = ::android::hidl::base::V1_0::BnHwBase::_hidl_interfaceChain(this, _hidl_data, _hidl_reply, _hidl_cb);  
            break;  
        }  
        default:  
        {  
            return ::android::hidl::base::V1_0::BnHwBase::onTransact(  
                    _hidl_code, _hidl_data, _hidl_reply, _hidl_flags, _hidl_cb);  
        }  
    }  

    if (_hidl_err == ::android::UNEXPECTED_NULL) {  
        _hidl_err = ::android::hardware::writeToParcel(  
                ::android::hardware::Status::fromExceptionCode(::android::hardware::Status::EX_NULL_POINTER),  
                _hidl_reply);  
    }return _hidl_err;  
} 

注意,onTransact的最后一个参数是一个回调函数,是由IPCThreadState传递进来的,该回调函数将传入BnHwBase的interfaceChain中执行。这个实现由其父类BnHwBase来完成:
[email protected]_genc++\gen\android\hidl\base\1.0\BaseAll.cpp

::android::status_t BnHwBase::_hidl_interfaceChain(  
        BnHwBase* _hidl_this,  
        const ::android::hardware::Parcel &_hidl_data,  
        ::android::hardware::Parcel *_hidl_reply,  
        TransactCallback _hidl_cb) {  
    #ifdef __ANDROID_DEBUGGABLE__  
    bool mEnableInstrumentation = _hidl_this->isInstrumentationEnabled();  
    const auto &mInstrumentationCallbacks = _hidl_this->getInstrumentationCallbacks();  
    #endif // __ANDROID_DEBUGGABLE__  

    ::android::status_t _hidl_err = ::android::OK;  
    if (!_hidl_data.enforceInterface(BnHwBase::Pure::descriptor)) {  
        _hidl_err = ::android::BAD_TYPE;  
        return _hidl_err;  
    }  

    atrace_begin(ATRACE_TAG_HAL, "HIDL::IBase::interfaceChain::server");  
    #ifdef __ANDROID_DEBUGGABLE__  
    if (UNLIKELY(mEnableInstrumentation)) {  
        std::vector<void *> _hidl_args;  
        for (const auto &callback: mInstrumentationCallbacks) {  
            callback(InstrumentationEvent::SERVER_API_ENTRY, "android.hidl.base", "1.0", "IBase", "interfaceChain", &_hidl_args);  
        }  
    }  
    #endif // __ANDROID_DEBUGGABLE__  

    bool _hidl_callbackCalled = false;  

    static_cast(_hidl_this)->_hidl_mImpl->interfaceChain([&](const auto &_hidl_out_descriptors) {  
         ...  
     });  

    if (!_hidl_callbackCalled) {  
        LOG_ALWAYS_FATAL("interfaceChain: _hidl_cb not called, but must be called once.");  
    }  

    return _hidl_err;  
} 

BnHwBase的interfaceChain实现又转交给_hidl_mImpl,同时也传入一个匿名的回调函数,而BnHwBase的_hidl_mImpl保存的是HwcHal对象,HwcHal并没有实现该函数,该函数由其父类IComposer类实现。
composer\2.1\[email protected]_genc++\gen\android\hardware\graphics\composer\2.1\ComposerAll.cpp

::android::hardware::Return<void> IComposer::interfaceChain(interfaceChain_cb _hidl_cb){  
    _hidl_cb({  
        IComposer::descriptor,  
        ::android::hidl::base::V1_0::IBase::descriptor,  
    });  
    return ::android::hardware::Void();}  

这里只是回调由BnHwBase传进来的回调函数,且函数参数是IComposer::descriptor, IBase::descriptor。回调函数实现如下:

{  
    if (_hidl_callbackCalled) {  
        LOG_ALWAYS_FATAL("interfaceChain: _hidl_cb called a second time, but must be called once.");  
    }  
    _hidl_callbackCalled = true;  

"color:#FF0000;">   "color:#000000;">::android::hardware::writeToParcel(::android::hardware::Status::ok(), _hidl_reply);  

    size_t _hidl__hidl_out_descriptors_parent;  

    _hidl_err = _hidl_reply->writeBuffer(&_hidl_out_descriptors, sizeof(_hidl_out_descriptors), &_hidl__hidl_out_descriptors_parent);  
    /* _hidl_err ignored! */  

    size_t _hidl__hidl_out_descriptors_child;  

    _hidl_err = ::android::hardware::writeEmbeddedToParcel(  
            _hidl_out_descriptors,  
            _hidl_reply,  
            _hidl__hidl_out_descriptors_parent,  
            0 /* parentOffset */, &_hidl__hidl_out_descriptors_child);  

    /* _hidl_err ignored! */  

    for (size_t _hidl_index_0 = 0; _hidl_index_0 < _hidl_out_descriptors.size(); ++_hidl_index_0) {  
        _hidl_err = ::android::hardware::writeEmbeddedToParcel(  
                _hidl_out_descriptors[_hidl_index_0],  
                _hidl_reply,  
                _hidl__hidl_out_descriptors_child,  
                _hidl_index_0 * sizeof(::android::hardware::hidl_string));  

        /* _hidl_err ignored! */  

    }  

    atrace_end(ATRACE_TAG_HAL);  
    #ifdef __ANDROID_DEBUGGABLE__  
    if (UNLIKELY(mEnableInstrumentation)) {  
        std::vector<void *> _hidl_args;  
        _hidl_args.push_back((void *)&_hidl_out_descriptors);  
        for (const auto &callback: mInstrumentationCallbacks) {  
            callback(InstrumentationEvent::SERVER_API_EXIT, "android.hidl.base", "1.0", "IBase", "interfaceChain", &_hidl_args);  
        }  
    }  
    #endif // __ANDROID_DEBUGGABLE__  

    _hidl_cb(*_hidl_reply);  
}  

这里只是将回调函数的参数IComposer::descriptor,IBase::descriptor打包到Parcel对象中,然后继续调用由IPCThreadState传进入的回调函数,该回调实现如下:
system\libhwbinder\IPCThreadState.cpp

auto reply_callback = [&] (auto &replyParcel) {  
    if (reply_sent) {  
        // Reply was sent earlier, ignore it.  
        ALOGE("Dropping binder reply, it was sent already.");  
        return;  
    }  
    reply_sent = true;  
    if ((tr.flags & TF_ONE_WAY) == 0) {  
        replyParcel.setError(NO_ERROR);  
        sendReply(replyParcel, 0);  
    } else {  
        ALOGE("Not sending reply in one-way transaction");  
    }  
}; 

该回调函数只是将打包后的Parcel发送给hwservicemanager进程。
这里写图片描述
也就是说,hwservicemanager将得到IComposer::descriptor,IBase::descriptor,BpHwBase读取到这些数据后,接着会回调由ServiceManager传入进来的回调函数:
system\hwservicemanager\ServiceManager.cpp

{  
    if (interfaceChain.size() == 0) {  
        return;  
    }  

    // First, verify you're allowed to add() the whole interface hierarchy  
    for(size_t i = 0; i < interfaceChain.size(); i++) {  
        std::string fqName = interfaceChain[i];  
        if (!mAcl.canAdd(fqName, pid)) {  
            return;  
        }  
    }  

    for(size_t i = 0; i < interfaceChain.size(); i++) {  
        std::string fqName = interfaceChain[i];  
        LOG(INFO) << "add service of " << fqName;  

        PackageInterfaceMap &ifaceMap = mServiceMap[fqName];  
        HidlService *hidlService = ifaceMap.lookup(name);  

        if (hidlService == nullptr) {  
            LOG(INFO) << "insertService " << name << " of " << fgName ;  
            ifaceMap.insertService(  
                std::make_unique(fqName, name, service, pid));  
        } else {  
            if (hidlService->getService() != nullptr) {  
                auto ret = hidlService->getService()->unlinkToDeath(this);  
                ret.isOk(); // ignore  
            }  
            LOG(INFO) << "setService " << " of " << fgName ;  
            hidlService->setService(service, pid);  
        }  

        ifaceMap.sendPackageRegistrationNotification(fqName, name);  
    }  

    auto linkRet = service->linkToDeath(this, 0 /*cookie*/);  
    linkRet.isOk(); // ignore  

    isValidService = true;  
}  

该回调函数的参数值其实就是从Hal进程传递过来的IComposer::descriptor,IBase::descriptor,这时就开始完成服务注册了,整个服务注册过程分为三个步骤:
1. 服务校验过程
2. 服务添加过程
3. 死亡通知注册过程

服务校验

AccessControl类主要负责权限检查,包括SELinux权限。
system\hwservicemanager\AccessControl.cpp

AccessControl::AccessControl() {  
    mSeHandle = selinux_android_hw_service_context_handle();  
    LOG_ALWAYS_FATAL_IF(mSeHandle == NULL, "Failed to acquire SELinux handle.");  

    if (getcon(&mSeContext) != 0) {  
        LOG_ALWAYS_FATAL("Failed to acquire hwservicemanager context.");  
    }  

    selinux_status_open(true);  

    mSeCallbacks.func_audit = AccessControl::auditCallback;  
    selinux_set_callback(SELINUX_CB_AUDIT, mSeCallbacks);  

    mSeCallbacks.func_log = selinux_log_callback; /* defined in libselinux */  
    selinux_set_callback(SELINUX_CB_LOG, mSeCallbacks);  
} 

判断是否有权限添加过程如下:

bool AccessControl::canAdd(const std::string& fqName, pid_t pid) {  
    FQName fqIface(fqName);  

    if (!fqIface.isValid()) {  
        return false;  
    }  
    const std::string checkName = fqIface.package() + "::" + fqIface.name();  
    return checkPermission(pid, kPermissionAdd, checkName.c_str());  
} 

system\tools\hidl\utils\FQName.cpp

FQName::FQName(const std::vector<std::string> &names)  
    : mValid(false),  
      mIsIdentifier(false) {  
    setTo(StringHelper::JoinStrings(names, "."));  
} 
bool FQName::setTo(const std::string &s) {  
    clearVersion();  
    mPackage.clear();  
    mName.clear();  

    mValid = true;  

    std::smatch match;  
    if (std::regex_match(s, match, kRE1)) {  
        CHECK_EQ(match.size(), 5u);  

        mPackage = match.str(1);  
        parseVersion(match.str(2), match.str(3));  
        mName = match.str(4);  
    } else if (std::regex_match(s, match, kRE2)) {  
        CHECK_EQ(match.size(), 4u);  

        parseVersion(match.str(1), match.str(2));  
        mName = match.str(3);  
    } else if (std::regex_match(s, match, kRE3)) {  
        CHECK_EQ(match.size(), 4u);  

        mPackage = match.str(1);  
        parseVersion(match.str(2), match.str(3));  
    } else if (std::regex_match(s, match, kRE4)) {  
        mName = match.str(0);  
    } else if (std::regex_match(s, match, kRE5)) {  
        mIsIdentifier = true;  
        mName = match.str(0);  
    } else if (std::regex_match(s, match, kRE6)) {  
        CHECK_EQ(match.size(), 6u);  

        mPackage = match.str(1);  
        parseVersion(match.str(2), match.str(3));  
        mName = match.str(4);  
        mValueName = match.str(5);  
    } else if (std::regex_match(s, match, kRE7)) {  
        CHECK_EQ(match.size(), 5u);  

        parseVersion(match.str(1), match.str(2));  
        mName = match.str(3);  
        mValueName = match.str(4);  
    } else if (std::regex_match(s, match, kRE8)) {  
        CHECK_EQ(match.size(), 3u);  

        mName = match.str(1);  
        mValueName = match.str(2);  
    } else {  
        mValid = false;  
    }  

    // mValueName must go with mName.  
    CHECK(mValueName.empty() || !mName.empty());  

    // package without version is not allowed.  
    CHECK(mPackage.empty() || !version().empty());  

    return isValid();  
}  

setTo函数其实就是使用正则表达式从[email protected]::IServiceManager字符串中取出包名,版本号,及服务类名,从而检查包名是否符合命名规则,如果包名有效,则继续调用checkPermission函数来检查selinux权限。

bool AccessControl::checkPermission(pid_t sourcePid, const char *targetContext,  
                                    const char *perm, const char *interface) {  
    char *sourceContext = NULL;  
    bool allowed = false;  
    struct audit_data ad;  

    if (getpidcon(sourcePid, &sourceContext) < 0) {  
        ALOGE("SELinux: failed to retrieved process context for pid %d", sourcePid);  
        return false;  
    }  

    ad.pid = sourcePid;  
    ad.interfaceName = interface;  

 "color:#FF0000;"> "color:#000000;">  allowed = (selinux_check_access(sourceContext, targetContext, "hwservice_manager",  
                                    perm, (void *) &ad) == 0);  

    freecon(sourceContext);  

    return allowed;  
}  

服务注册

如果服务注册进程有权限向hwservicemanager注册服务,接下来将完成服务添加。
这里写图片描述

每个服务接口对应多个实例,比如[email protected]::IServiceManager可以注册多个实例,每个实例名称不同
这里写图片描述

PackageInterfaceMap &ifaceMap = mServiceMap[fqName];  
HidlService *hidlService = ifaceMap.lookup(name);  

const HidlService *ServiceManager::PackageInterfaceMap::lookup(  
        const std::string &name) const {  
    auto it = mInstanceMap.find(name);  

    if (it == mInstanceMap.end()) {  
        return nullptr;  
    }  
    return it->second.get();  
}  

根据名称查找HidlService,如果找不到,则新增一个HidlService,如果已经存在,则更新service。

if (hidlService == nullptr) {  
    LOG(INFO) << "insertService " << name << " of " << fgName ;  
    ifaceMap.insertService(  
        std::make_unique<HidlService>(fqName, name, service, pid));  
} else {  
    if (hidlService->getService() != nullptr) {  
        auto ret = hidlService->getService()->unlinkToDeath(this);  
        ret.isOk(); // ignore  
    }  
    LOG(INFO) << "setService " << " of " << fgName ;  
    hidlService->setService(service, pid);  
} 

到此就完成了hidl服务注册。
这里写图片描述

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