AndroidO Treble架构下HIDL服务查询过程

通过前面的分析我们知道，Hal进程启动时，会向hwservicemanager进程注册hidl服务，那么当Framework Server需要通过hal访问硬件设备时，首先需要查询对应的hidl服务，那么Client进程是如何查询hidl服务的呢？这篇文章将展开分析，这里再次以IComposer为例进行展开。

frameworks\native\services\surfaceflinger\DisplayHardware\ComposerHal.cpp

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1. Composer::Composer(bool useVrComposer)  
2.     : mWriter(kWriterInitialSize),  
3.       mIsUsingVrComposer(useVrComposer)  
4. {  
5.     if (mIsUsingVrComposer) {  
6.         mComposer = IComposer::getService(”vr”);  
7.     } else {  
8.         mComposer = IComposer::getService(); // use default name  
9.     }  
10.   
11.     if (mComposer == nullptr) {  
12.         LOG_ALWAYS_FATAL(”failed to get hwcomposer service”);  
13.     }  
14.   
15.     mComposer->createClient(  
16.             [&](const auto& tmpError, const auto& tmpClient)  
17.             {  
18.                 if (tmpError == Error::NONE) {  
19.                     mClient = tmpClient;  
20.                 }  
21.             });  
22.     if (mClient == nullptr) {  
23.         LOG_ALWAYS_FATAL(”failed to create composer client”);  
24.     }  
25. }  

Composer::Composer(bool useVrComposer)
    : mWriter(kWriterInitialSize),
      mIsUsingVrComposer(useVrComposer)
{
    if (mIsUsingVrComposer) {
        mComposer = IComposer::getService("vr");
    } else {
        mComposer = IComposer::getService(); // use default name
    }

    if (mComposer == nullptr) {
        LOG_ALWAYS_FATAL("failed to get hwcomposer service");
    }

    mComposer->createClient(
            [&](const auto& tmpError, const auto& tmpClient)
            {
                if (tmpError == Error::NONE) {
                    mClient = tmpClient;
                }
            });
    if (mClient == nullptr) {
        LOG_ALWAYS_FATAL("failed to create composer client");
    }
}

这里通过IComposer::getService()函数来查询IComposer这个HIDL服务，由于这里没有传递任何参数，因此函数最终会调用：

composer\2.1\[email protected]_genc++_headers\gen\android\hardware\graphics\composer\2.1\IComposer.h

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1. static ::android::sp<IComposer> getService(const std::string &serviceName=“default”, bool getStub=false);  

static ::android::sp<IComposer> getService(const std::string &serviceName="default", bool getStub=false);

注意，这里的getStub为false，说明加载hidl服务方式是由当前hidl服务的transport类型决定。

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1. <hal format=“hidl”>  
2.     <name>android.hardware.graphics.composer</name>  
3.     <transport>hwbinder</transport>  
4.     <version>2.1</version>  
5.     <interface>  
6.         <name>IComposer</name>  
7.         <instance>vr</instance>  
8.     </interface>  
9. </hal>  

    <hal format="hidl">
        <name>android.hardware.graphics.composer</name>
        <transport>hwbinder</transport>
        <version>2.1</version>
        <interface>
            <name>IComposer</name>
            <instance>vr</instance>
        </interface>
    </hal>

由于IComposer的transport是hwbinder类型，那么将从hwservicemanager中查询hidl服务。

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

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1. ::android::sp<IComposer> IComposer::getService(const std::string &serviceName, const bool getStub) {  
2.     using ::android::hardware::defaultServiceManager;  
3.     using ::android::hardware::details::waitForHwService;  
4.     using ::android::hardware::getPassthroughServiceManager;  
5.     using ::android::hardware::Return;  
6.     using ::android::sp;  
7.     using Transport = ::android::hidl::manager::V1_0::IServiceManager::Transport;  
8.   
9.     sp<IComposer> iface = nullptr;  
10.   
11.     const sp<::android::hidl::manager::V1_0::IServiceManager> sm = defaultServiceManager();  
12.     if (sm == nullptr) {  
13.         ALOGE(”getService: defaultServiceManager() is null”);  
14.         return nullptr;  
15.     }  
16.   
17.     Return<Transport> transportRet = sm->getTransport(IComposer::descriptor, serviceName);  
18.   
19.     if (!transportRet.isOk()) {  
20.         ALOGE(”getService: defaultServiceManager()->getTransport returns %s”, transportRet.description().c_str());  
21.         return nullptr;  
22.     }  
23.     Transport transport = transportRet;  
24.     const bool vintfHwbinder = (transport == Transport::HWBINDER);  
25.     const bool vintfPassthru = (transport == Transport::PASSTHROUGH);  
26.   
27.     #ifdef __ANDROID_TREBLE__  
28.   
29.     #ifdef __ANDROID_DEBUGGABLE__  
30.     const char* env = std::getenv(“TREBLE_TESTING_OVERRIDE”);  
31.     const bool trebleTestingOverride =  env && !strcmp(env, “true”);  
32.     const bool vintfLegacy = (transport == Transport::EMPTY) && trebleTestingOverride;  
33.     #else // __ANDROID_TREBLE__ but not __ANDROID_DEBUGGABLE__  
34.     const bool trebleTestingOverride = false;  
35.     const bool vintfLegacy = false;  
36.     #endif // __ANDROID_DEBUGGABLE__  
37.   
38.     #else // not __ANDROID_TREBLE__  
39.     const char* env = std::getenv(“TREBLE_TESTING_OVERRIDE”);  
40.     const bool trebleTestingOverride =  env && !strcmp(env, “true”);  
41.     const bool vintfLegacy = (transport == Transport::EMPTY);  
42.   
43.     #endif // __ANDROID_TREBLE__  
44.   
45.     for (int tries = 0; !getStub && (vintfHwbinder || (vintfLegacy && tries == 0)); tries++) {  
46.         if (tries > 1) {  
47.             ALOGI(”getService: Will do try %d for %s/%s in 1s…”, tries, IComposer::descriptor, serviceName.c_str());  
48.             sleep(1);  
49.         }  
50.         if (vintfHwbinder && tries > 0) {  
51.             waitForHwService(IComposer::descriptor, serviceName);  
52.         }  
53.         Return<sp<::android::hidl::base::V1_0::IBase>> ret =   
54.                 sm->get(IComposer::descriptor, serviceName);  
55.         if (!ret.isOk()) {  
56.             ALOGE(”IComposer: defaultServiceManager()->get returns %s”, ret.description().c_str());  
57.             break;  
58.         }  
59.         sp<::android::hidl::base::V1_0::IBase> base = ret;  
60.         if (base == nullptr) {  
61.             if (tries > 0) {  
62.                 ALOGW(”IComposer: found null hwbinder interface”);  
63.             }continue;  
64.         }  
65.         Return<sp<IComposer>> castRet = IComposer::castFrom(base, true /* emitError */);  
66.         if (!castRet.isOk()) {  
67.             if (castRet.isDeadObject()) {  
68.                 ALOGW(”IComposer: found dead hwbinder service”);  
69.                 continue;  
70.             } else {  
71.                 ALOGW(”IComposer: cannot call into hwbinder service: %s; No permission? Check for selinux denials.”, castRet.description().c_str());  
72.                 break;  
73.             }  
74.         }  
75.         iface = castRet;  
76.         if (iface == nullptr) {  
77.             ALOGW(”IComposer: received incompatible service; bug in hwservicemanager?”);  
78.             break;  
79.         }  
80.         return iface;  
81.     }  
82.     return iface;  
83. }  

::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();
    if (sm == nullptr) {
        ALOGE("getService: defaultServiceManager() is null");
        return nullptr;
    }

    Return<Transport> transportRet = sm->getTransport(IComposer::descriptor, serviceName);

    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);

    #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__

    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;
    }
    return iface;
}

这里通过sm->get(IComposer::descriptor, serviceName)查询IComposer这个hidl服务，得到IBase对象后，在通过IComposer::castFrom转换为IComposer对象。

服务查询

[email protected]_genc++\gen\android\hidl\manager\1.0\ServiceManagerAll.cpp

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1. ::android::hardware::Return<::android::sp<::android::hidl::base::V1_0::IBase>> BpHwServiceManager::get(const ::android::hardware::hidl_string& fqName, const ::android::hardware::hidl_string& name){  
2.     ::android::hardware::Return<::android::sp<::android::hidl::base::V1_0::IBase>>  _hidl_out = ::android::hidl::manager::V1_0::BpHwServiceManager::_hidl_get(this, this, fqName, name);  
3.   
4.     return _hidl_out;  
5. }  

::android::hardware::Return<::android::sp<::android::hidl::base::V1_0::IBase>> BpHwServiceManager::get(const ::android::hardware::hidl_string& fqName, const ::android::hardware::hidl_string& name){
    ::android::hardware::Return<::android::sp<::android::hidl::base::V1_0::IBase>>  _hidl_out = ::android::hidl::manager::V1_0::BpHwServiceManager::_hidl_get(this, this, fqName, name);

    return _hidl_out;
}

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1. ::android::hardware::Return<::android::sp<::android::hidl::base::V1_0::IBase>> BpHwServiceManager::_hidl_get(::android::hardware::IInterface *_hidl_this, ::android::hardware::details::HidlInstrumentor *_hidl_this_instrumentor, const ::android::hardware::hidl_string& fqName, const ::android::hardware::hidl_string& name) {  
2.     #ifdef __ANDROID_DEBUGGABLE__  
3.     bool mEnableInstrumentation = _hidl_this_instrumentor->isInstrumentationEnabled();  
4.     const auto &mInstrumentationCallbacks = _hidl_this_instrumentor->getInstrumentationCallbacks();  
5.     #else  
6.     (void) _hidl_this_instrumentor;  
7.     #endif // __ANDROID_DEBUGGABLE__  
8.     atrace_begin(ATRACE_TAG_HAL, ”HIDL::IServiceManager::get::client”);  
9.     #ifdef __ANDROID_DEBUGGABLE__  
10.     if (UNLIKELY(mEnableInstrumentation)) {  
11.         std::vector<void *> _hidl_args;  
12.         _hidl_args.push_back((void *)&fqName);  
13.         _hidl_args.push_back((void *)&name);  
14.         for (const auto &callback: mInstrumentationCallbacks) {  
15.             callback(InstrumentationEvent::CLIENT_API_ENTRY, ”android.hidl.manager”, “1.0”, “IServiceManager”, “get”, &_hidl_args);  
16.         }  
17.     }  
18.     #endif // __ANDROID_DEBUGGABLE__  
19.   
20.     ::android::hardware::Parcel _hidl_data;  
21.     ::android::hardware::Parcel _hidl_reply;  
22.     ::android::status_t _hidl_err;  
23.     ::android::hardware::Status _hidl_status;  
24.   
25.     ::android::sp<::android::hidl::base::V1_0::IBase> _hidl_out_service;  
26.   
27.     _hidl_err = _hidl_data.writeInterfaceToken(BpHwServiceManager::descriptor);  
28.     if (_hidl_err != ::android::OK) { goto _hidl_error; }  
29.   
30.     size_t _hidl_fqName_parent;  
31.   
32.     _hidl_err = _hidl_data.writeBuffer(&fqName, sizeof(fqName), &_hidl_fqName_parent);  
33.     if (_hidl_err != ::android::OK) { goto _hidl_error; }  
34.   
35.     _hidl_err = ::android::hardware::writeEmbeddedToParcel(  
36.             fqName,  
37.             &_hidl_data,  
38.             _hidl_fqName_parent,  
39.             0 /* parentOffset */);  
40.   
41.     if (_hidl_err != ::android::OK) { goto _hidl_error; }  
42.   
43.     size_t _hidl_name_parent;  
44.   
45.     _hidl_err = _hidl_data.writeBuffer(&name, sizeof(name), &_hidl_name_parent);  
46.     if (_hidl_err != ::android::OK) { goto _hidl_error; }  
47.   
48.     _hidl_err = ::android::hardware::writeEmbeddedToParcel(  
49.             name,  
50.             &_hidl_data,  
51.             _hidl_name_parent,  
52.             0 /* parentOffset */);  
53.   
54.     if (_hidl_err != ::android::OK) { goto _hidl_error; }  
55.   
56.     _hidl_err = ::android::hardware::IInterface::asBinder(_hidl_this)->transact(1 /* get */, _hidl_data, &_hidl_reply);  
57.     if (_hidl_err != ::android::OK) { goto _hidl_error; }  
58.   
59.     _hidl_err = ::android::hardware::readFromParcel(&_hidl_status, _hidl_reply);  
60.     if (_hidl_err != ::android::OK) { goto _hidl_error; }  
61.   
62.     if (!_hidl_status.isOk()) { return _hidl_status; }  
63.   
64.     {  
65.         ::android::sp<::android::hardware::IBinder> _hidl__hidl_out_service_binder;  
66.         _hidl_err = _hidl_reply.readNullableStrongBinder(&_hidl__hidl_out_service_binder);  
67.         if (_hidl_err != ::android::OK) { goto _hidl_error; }  
68.   
69.         _hidl_out_service = ::android::hardware::fromBinder<::android::hidl::base::V1_0::IBase,::android::hidl::base::V1_0::BpHwBase,::android::hidl::base::V1_0::BnHwBase>(_hidl__hidl_out_service_binder);  
70.     }  
71.   
72.     atrace_end(ATRACE_TAG_HAL);  
73.     #ifdef __ANDROID_DEBUGGABLE__  
74.     if (UNLIKELY(mEnableInstrumentation)) {  
75.         std::vector<void *> _hidl_args;  
76.         _hidl_args.push_back((void *)&_hidl_out_service);  
77.         for (const auto &callback: mInstrumentationCallbacks) {  
78.             callback(InstrumentationEvent::CLIENT_API_EXIT, ”android.hidl.manager”, “1.0”, “IServiceManager”, “get”, &_hidl_args);  
79.         }  
80.     }  
81.     #endif // __ANDROID_DEBUGGABLE__  
82.   
83.     _hidl_status.setFromStatusT(_hidl_err);  
84.     return ::android::hardware::Return<::android::sp<::android::hidl::base::V1_0::IBase>>(_hidl_out_service);  
85.   
86. _hidl_error:  
87.     _hidl_status.setFromStatusT(_hidl_err);  
88.     return ::android::hardware::Return<::android::sp<::android::hidl::base::V1_0::IBase>>(_hidl_status);  
89. }  

::android::hardware::Return<::android::sp<::android::hidl::base::V1_0::IBase>> BpHwServiceManager::_hidl_get(::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::get::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", "get", &_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;

    ::android::sp<::android::hidl::base::V1_0::IBase> _hidl_out_service;

    _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(1 /* get */, _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; }

    {
        ::android::sp<::android::hardware::IBinder> _hidl__hidl_out_service_binder;
        _hidl_err = _hidl_reply.readNullableStrongBinder(&_hidl__hidl_out_service_binder);
        if (_hidl_err != ::android::OK) { goto _hidl_error; }

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

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

    _hidl_status.setFromStatusT(_hidl_err);
    return ::android::hardware::Return<::android::sp<::android::hidl::base::V1_0::IBase>>(_hidl_out_service);

_hidl_error:
    _hidl_status.setFromStatusT(_hidl_err);
    return ::android::hardware::Return<::android::sp<::android::hidl::base::V1_0::IBase>>(_hidl_status);
}

整个调用过程和hidl服务过程完全一致，就是一个从BpHwServiceManager –> BnHwServiceManager –> ServiceManager的过程。但需要注意，BpHwServiceManager得到BnHwServiceManager返回过来的binder代理后，会通过fromBinder函数进行对象转换：

::android::hardware::fromBinder<::android::hidl::base::V1_0::IBase,::android::hidl::base::V1_0::BpHwBase,::android::hidl::base::V1_0::BnHwBase>(_hidl__hidl_out_service_binder)

hwservicemanager将IComposer的binder代理BpHwBinder发给Framework Server进程，Framework Server进程拿到的依然是IComposer的binder代理BpHwBinder对象，因此在fromBinder函数中将创建BpHwBase对象来封装BpHwBinder。

[cpp] view plain copy

print ?

1. ::android::status_t BnHwServiceManager::_hidl_get(  
2.         ::android::hidl::base::V1_0::BnHwBase* _hidl_this,  
3.         const ::android::hardware::Parcel &_hidl_data,  
4.         ::android::hardware::Parcel *_hidl_reply,  
5.         TransactCallback _hidl_cb) {  
6.     #ifdef __ANDROID_DEBUGGABLE__  
7.     bool mEnableInstrumentation = _hidl_this->isInstrumentationEnabled();  
8.     const auto &mInstrumentationCallbacks = _hidl_this->getInstrumentationCallbacks();  
9.     #endif // __ANDROID_DEBUGGABLE__  
10.   
11.     ::android::status_t _hidl_err = ::android::OK;  
12.     if (!_hidl_data.enforceInterface(BnHwServiceManager::Pure::descriptor)) {  
13.         _hidl_err = ::android::BAD_TYPE;  
14.         return _hidl_err;  
15.     }  
16.   
17.     const ::android::hardware::hidl_string* fqName;  
18.     const ::android::hardware::hidl_string* name;  
19.   
20.     size_t _hidl_fqName_parent;  
21.   
22.     _hidl_err = _hidl_data.readBuffer(sizeof(*fqName), &_hidl_fqName_parent,  reinterpret_cast<const void **>(&fqName));  
23.   
24.     if (_hidl_err != ::android::OK) { return _hidl_err; }  
25.   
26.     _hidl_err = ::android::hardware::readEmbeddedFromParcel(  
27.             const_cast<::android::hardware::hidl_string &>(*fqName),  
28.             _hidl_data,  
29.             _hidl_fqName_parent,  
30.             0 /* parentOffset */);  
31.   
32.     if (_hidl_err != ::android::OK) { return _hidl_err; }  
33.   
34.     size_t _hidl_name_parent;  
35.   
36.     _hidl_err = _hidl_data.readBuffer(sizeof(*name), &_hidl_name_parent,  reinterpret_cast<const void **>(&name));  
37.   
38.     if (_hidl_err != ::android::OK) { return _hidl_err; }  
39.   
40.     _hidl_err = ::android::hardware::readEmbeddedFromParcel(  
41.             const_cast<::android::hardware::hidl_string &>(*name),  
42.             _hidl_data,  
43.             _hidl_name_parent,  
44.             0 /* parentOffset */);  
45.   
46.     if (_hidl_err != ::android::OK) { return _hidl_err; }  
47.   
48.     atrace_begin(ATRACE_TAG_HAL, ”HIDL::IServiceManager::get::server”);  
49.     #ifdef __ANDROID_DEBUGGABLE__  
50.     if (UNLIKELY(mEnableInstrumentation)) {  
51.         std::vector<void *> _hidl_args;  
52.         _hidl_args.push_back((void *)fqName);  
53.         _hidl_args.push_back((void *)name);  
54.         for (const auto &callback: mInstrumentationCallbacks) {  
55.             callback(InstrumentationEvent::SERVER_API_ENTRY, ”android.hidl.manager”, “1.0”, “IServiceManager”, “get”, &_hidl_args);  
56.         }  
57.     }  
58.     #endif // __ANDROID_DEBUGGABLE__  
59.   
60.     ::android::sp<::android::hidl::base::V1_0::IBase> _hidl_out_service = static_cast<BnHwServiceManager*>(_hidl_this)->_hidl_mImpl->get(*fqName, *name);  
61.   
62.     ::android::hardware::writeToParcel(::android::hardware::Status::ok(), _hidl_reply);  
63.   
64.     if (_hidl_out_service == nullptr) {  
65.         _hidl_err = _hidl_reply->writeStrongBinder(nullptr);  
66.     } else {  
67.         ::android::sp<::android::hardware::IBinder> _hidl_binder = ::android::hardware::toBinder<  
68.                 ::android::hidl::base::V1_0::IBase>(_hidl_out_service);  
69.         if (_hidl_binder.get() != nullptr) {  
70.             _hidl_err = _hidl_reply->writeStrongBinder(_hidl_binder);  
71.         } else {  
72.             _hidl_err = ::android::UNKNOWN_ERROR;  
73.         }  
74.     }  
75.     /* _hidl_err ignored! */  
76.   
77.     atrace_end(ATRACE_TAG_HAL);  
78.     #ifdef __ANDROID_DEBUGGABLE__  
79.     if (UNLIKELY(mEnableInstrumentation)) {  
80.         std::vector<void *> _hidl_args;  
81.         _hidl_args.push_back((void *)&_hidl_out_service);  
82.         for (const auto &callback: mInstrumentationCallbacks) {  
83.             callback(InstrumentationEvent::SERVER_API_EXIT, ”android.hidl.manager”, “1.0”, “IServiceManager”, “get”, &_hidl_args);  
84.         }  
85.     }  
86.     #endif // __ANDROID_DEBUGGABLE__  
87.   
88.     _hidl_cb(*_hidl_reply);  
89.     return _hidl_err;  
90. }  

::android::status_t BnHwServiceManager::_hidl_get(
        ::android::hidl::base::V1_0::BnHwBase* _hidl_this,
        const ::android::hardware::Parcel &_hidl_data,
        ::android::hardware::Parcel *_hidl_reply,
        TransactCallback _hidl_cb) {
    #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::get::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", "get", &_hidl_args);
        }
    }
    #endif // __ANDROID_DEBUGGABLE__

    ::android::sp<::android::hidl::base::V1_0::IBase> _hidl_out_service = static_cast<BnHwServiceManager*>(_hidl_this)->_hidl_mImpl->get(*fqName, *name);

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

    if (_hidl_out_service == nullptr) {
        _hidl_err = _hidl_reply->writeStrongBinder(nullptr);
    } else {
        ::android::sp<::android::hardware::IBinder> _hidl_binder = ::android::hardware::toBinder<
                ::android::hidl::base::V1_0::IBase>(_hidl_out_service);
        if (_hidl_binder.get() != nullptr) {
            _hidl_err = _hidl_reply->writeStrongBinder(_hidl_binder);
        } else {
            _hidl_err = ::android::UNKNOWN_ERROR;
        }
    }
    /* _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_service);
        for (const auto &callback: mInstrumentationCallbacks) {
            callback(InstrumentationEvent::SERVER_API_EXIT, "android.hidl.manager", "1.0", "IServiceManager", "get", &_hidl_args);
        }
    }
    #endif // __ANDROID_DEBUGGABLE__

    _hidl_cb(*_hidl_reply);
    return _hidl_err;
}

BnHwServiceManager通过ServiceManager对象查询到对应的hidl服务，返回IBase对象后，会调用toBinder函数转换为IBinder类型对象：

::android::hardware::toBinder< ::android::hidl::base::V1_0::IBase>(_hidl_out_service)

由于在hwservicemanager这边，保存的是IComposer的BpHwBase对象，因此在toBinder函数中将调用IInterface::asBinder来得到BpHwBase的成员变量中的BpHwBinder对象。

[cpp] view plain copy

print ?

1. if (ifacePtr->isRemote()) {  
2.     return ::android::hardware::IInterface::asBinder(static_cast<ProxyType *>(ifacePtr));  
3. }  

if (ifacePtr->isRemote()) {
    return ::android::hardware::IInterface::asBinder(static_cast<ProxyType *>(ifacePtr));
}

fromBinder和toBinder函数在之前的文章中已经详细分析了，这里就不再展开。

服务查询过程其实就是根据接口包名及服务名称，从hwservicemanager管理的表中查询对应的IBase服务对象，然后在Client进程空间分别创建BpHwBinder和BpHwBase对象。

接口转换

Framework Server进程通过上述hidl服务查询，得到了BpHwBase对象后，需要将其转换为与业务相关的代理对象，这就是通过：Return<sp<IComposer>> castRet = IComposer::castFrom(base, true /* emitError */);

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

[cpp] view plain copy

print ?

1. ::android::hardware::Return<::android::sp<IComposer>> IComposer::castFrom(const ::android::sp<::android::hidl::base::V1_0::IBase>& parent, bool emitError) {  
2.     return ::android::hardware::details::castInterface<IComposer, ::android::hidl::base::V1_0::IBase, BpHwComposer>(  
3.             parent, ”[email protected]::IComposer”, emitError);  
4. }  

::android::hardware::Return<::android::sp<IComposer>> IComposer::castFrom(const ::android::sp<::android::hidl::base::V1_0::IBase>& parent, bool emitError) {
    return ::android::hardware::details::castInterface<IComposer, ::android::hidl::base::V1_0::IBase, BpHwComposer>(
            parent, "[email protected]::IComposer", emitError);
}

system\libhidl\transport\include\hidl\HidlTransportSupport.h

[cpp] view plain copy

print ?

1. // cast the interface IParent to IChild.  
2. // Return nonnull if cast successful.  
3. // Return nullptr if:  
4. // 1. parent is null  
5. // 2. cast failed because IChild is not a child type of IParent.  
6. // 3. !emitError, calling into parent fails.  
7. // Return an error Return object if:  
8. // 1. emitError, calling into parent fails.  
9. template<typename IChild, typename IParent, typename BpChild, typename BpParent>  
10. Return<sp<IChild>> castInterface(sp<IParent> parent, const char *childIndicator, bool emitError) {  
11.     if (parent.get() == nullptr) {  
12.         // casts always succeed with nullptrs.  
13.         return nullptr;  
14.     }  
15.     Return<bool> canCastRet = details::canCastInterface(parent.get(), childIndicator, emitError);  
16.     if (!canCastRet.isOk()) {  
17.         // call fails, propagate the error if emitError  
18.         return emitError  
19.                 ? details::StatusOf<bool, sp<IChild>>(canCastRet)  
20.                 : Return<sp<IChild>>(sp<IChild>(nullptr));  
21.     }  
22.   
23.     if (!canCastRet) {  
24.         return sp<IChild>(nullptr); // cast failed.  
25.     }  
26.     // TODO b/32001926 Needs to be fixed for socket mode.  
27.     if (parent->isRemote()) {  
28.         // binderized mode. Got BpChild. grab the remote and wrap it.  
29.         return sp<IChild>(new BpChild(toBinder<IParent, BpParent>(parent)));  
30.     }  
31.     // Passthrough mode. Got BnChild and BsChild.  
32.     return sp<IChild>(static_cast<IChild *>(parent.get()));  
33. }  
34.   
35. }  // namespace details  

// cast the interface IParent to IChild.
// Return nonnull if cast successful.
// Return nullptr if:
// 1. parent is null
// 2. cast failed because IChild is not a child type of IParent.
// 3. !emitError, calling into parent fails.
// Return an error Return object if:
// 1. emitError, calling into parent fails.
template<typename IChild, typename IParent, typename BpChild, typename BpParent>
Return<sp<IChild>> castInterface(sp<IParent> parent, const char *childIndicator, bool emitError) {
    if (parent.get() == nullptr) {
        // casts always succeed with nullptrs.
        return nullptr;
    }
    Return<bool> canCastRet = details::canCastInterface(parent.get(), childIndicator, emitError);
    if (!canCastRet.isOk()) {
        // call fails, propagate the error if emitError
        return emitError
                ? details::StatusOf<bool, sp<IChild>>(canCastRet)
                : Return<sp<IChild>>(sp<IChild>(nullptr));
    }

    if (!canCastRet) {
        return sp<IChild>(nullptr); // cast failed.
    }
    // TODO b/32001926 Needs to be fixed for socket mode.
    if (parent->isRemote()) {
        // binderized mode. Got BpChild. grab the remote and wrap it.
        return sp<IChild>(new BpChild(toBinder<IParent, BpParent>(parent)));
    }
    // Passthrough mode. Got BnChild and BsChild.
    return sp<IChild>(static_cast<IChild *>(parent.get()));
}

}  // namespace details

这个模板函数展开后如下：

[cpp] view plain copy

print ?

1. Return<sp<IComposer>> castInterface(sp<IBase> parent, const char *childIndicator, bool emitError) {  
2.     if (parent.get() == nullptr) {  
3.         // casts always succeed with nullptrs.  
4.         return nullptr;  
5.     }  
6.     Return<bool> canCastRet = details::canCastInterface(parent.get(), childIndicator, emitError);  
7.     if (!canCastRet.isOk()) {  
8.         // call fails, propagate the error if emitError  
9.         return emitError  
10.                 ? details::StatusOf<bool, sp<IComposer>>(canCastRet)  
11.                 : Return<sp<IComposer>>(sp<IComposer>(nullptr));  
12.     }  
13.   
14.     if (!canCastRet) {  
15.         return sp<IComposer>(nullptr); // cast failed.  
16.     }  
17.     // TODO b/32001926 Needs to be fixed for socket mode.  
18.     if (parent->isRemote()) {  
19.         // binderized mode. Got BpChild. grab the remote and wrap it.  
20.         return sp<IComposer>(new BpHwComposer(toBinder<IBase, BpParent>(parent)));  
21.     }  
22.     // Passthrough mode. Got BnChild and BsChild.  
23.     return sp<IComposer>(static_cast<IComposer *>(parent.get()));  
24. }  

Return<sp<IComposer>> castInterface(sp<IBase> parent, const char *childIndicator, bool emitError) {
    if (parent.get() == nullptr) {
        // casts always succeed with nullptrs.
        return nullptr;
    }
    Return<bool> canCastRet = details::canCastInterface(parent.get(), childIndicator, emitError);
    if (!canCastRet.isOk()) {
        // call fails, propagate the error if emitError
        return emitError
                ? details::StatusOf<bool, sp<IComposer>>(canCastRet)
                : Return<sp<IComposer>>(sp<IComposer>(nullptr));
    }

    if (!canCastRet) {
        return sp<IComposer>(nullptr); // cast failed.
    }
    // TODO b/32001926 Needs to be fixed for socket mode.
    if (parent->isRemote()) {
        // binderized mode. Got BpChild. grab the remote and wrap it.
        return sp<IComposer>(new BpHwComposer(toBinder<IBase, BpParent>(parent)));
    }
    // Passthrough mode. Got BnChild and BsChild.
    return sp<IComposer>(static_cast<IComposer *>(parent.get()));
}

因此最终会创建一个BpHwComposer对象。

new BpHwComposer(toBinder<IBase, BpParent>(parent))

            </div>