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/[email protected]
    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 [email protected]

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(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(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
__attribute__((warn_unused_result))
status_t registerPassthroughServiceImplementation(
        std::string name = "default") {
    sp 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;
}

AndroidO Treble架构下Hal进程启动及HIDL服务注册过程_第1张图片

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::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 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 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> 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> 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> 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:

AndroidO Treble架构下Hal进程启动及HIDL服务注册过程_第2张图片

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:

AndroidO Treble架构下Hal进程启动及HIDL服务注册过程_第3张图片

    if (getStub || vintfPassthru || vintfLegacy) {
        const sp<::android::hidl::manager::V1_0::IServiceManager> pm = getPassthroughServiceManager();
        if (pm != nullptr) {
            Return> 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 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。
AndroidO Treble架构下Hal进程启动及HIDL服务注册过程_第4张图片

registerPassthroughClient

得到IComposer接口对象HwcHal后,需要注册相关信息到hwservicemanager中。

AndroidO Treble架构下Hal进程启动及HIDL服务注册过程_第5张图片

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

    return _hidl_out;
}
::android::hardware::Return 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 _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 _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();

_hidl_error:
    _hidl_status.setFromStatusT(_hidl_err);
    return ::android::hardware::Return(_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(&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(&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 _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 _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 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。
AndroidO Treble架构下Hal进程启动及HIDL服务注册过程_第6张图片

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。
AndroidO Treble架构下Hal进程启动及HIDL服务注册过程_第7张图片
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 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. [email protected] -> [email protected]
    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 BpHwServiceManager::add(const ::android::hardware::hidl_string& name, const ::android::sp<::android::hidl::base::V1_0::IBase>& service){
    ::android::hardware::Return  _hidl_out = ::android::hidl::manager::V1_0::BpHwServiceManager::_hidl_add(this, this, name, service);

    return _hidl_out;
}
::android::hardware::Return 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 _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 _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(_hidl_out_success);

_hidl_error:
    _hidl_status.setFromStatusT(_hidl_err);
    return ::android::hardware::Return(_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::_hidl_add(
        ::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* name;
    ::android::sp<::android::hidl::base::V1_0::IBase> service;

    size_t _hidl_name_parent;

    _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; }

    {
        ::android::sp<::android::hardware::IBinder> _hidl_service_binder;
        _hidl_err = _hidl_data.readNullableStrongBinder(&_hidl_service_binder);
        if (_hidl_err != ::android::OK) { return _hidl_err; }

        service = ::android::hardware::fromBinder<::android::hidl::base::V1_0::IBase,::android::hidl::base::V1_0::BpHwBase,::android::hidl::base::V1_0::BnHwBase>(_hidl_service_binder);
    }

    atrace_begin(ATRACE_TAG_HAL, "HIDL::IServiceManager::add::server");
    #ifdef __ANDROID_DEBUGGABLE__
    if (UNLIKELY(mEnableInstrumentation)) {
        std::vector _hidl_args;
        _hidl_args.push_back((void *)name);
        _hidl_args.push_back((void *)&service);
        for (const auto &callback: mInstrumentationCallbacks) {
            callback(InstrumentationEvent::SERVER_API_ENTRY, "android.hidl.manager", "1.0", "IServiceManager", "add", &_hidl_args);
        }
    }
    #endif // __ANDROID_DEBUGGABLE__

    bool _hidl_out_success = static_cast(_hidl_this)->_hidl_mImpl->add(*name, service);

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

    _hidl_err = _hidl_reply->writeBool(_hidl_out_success);
    /* _hidl_err ignored! */

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

    _hidl_cb(*_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:
AndroidO Treble架构下Hal进程启动及HIDL服务注册过程_第8张图片
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 BpHwBase::interfaceChain(interfaceChain_cb _hidl_cb){
    ::android::hardware::Return  _hidl_out = ::android::hidl::base::V1_0::BpHwBase::_hidl_interfaceChain(this, this, _hidl_cb);

    return _hidl_out;
}
::android::hardware::Return 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 _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;

    _hidl_err = _hidl_data.writeInterfaceToken(BpHwBase::descriptor);
    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(&_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,
AndroidO Treble架构下Hal进程启动及HIDL服务注册过程_第9张图片
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 _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 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;

	::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 _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。
AndroidO Treble架构下Hal进程启动及HIDL服务注册过程_第10张图片
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 &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;

    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。

AndroidO Treble架构下Hal进程启动及HIDL服务注册过程_第11张图片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。AndroidO Treble架构下Hal进程启动及HIDL服务注册过程_第12张图片

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(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。

AndroidO Treble架构下Hal进程启动及HIDL服务注册过程_第13张图片


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