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前言

接上篇Android9 HWbinder运用-注册service流程解析讲了hidl service的注册流程，这篇文章接着解析hidl service的获取流程

HwBinder框架

流程解析

废话不多说，持续以USB HAL 1.0为例，解析一下获取的流程

以vts为参阅获取的代码

获取流程

1. hardware/interfaces/usb/1.0/vts/functional/VtsHalUsbV1_0TargetTest.cpp

改一下代码，以常见的不带参数为例

usb = IUsb::getService();

getService声明在IUsb.h

2. out/soong/.intermediates/hardware/interfaces/usb/1.0/android.hardware.usb@1.0_genc++_headers/gen/android/hardware/usb/1.0/IUsb.h

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

完成在/UsbAll.cpp

3. out/soong/.intermediates/hardware/interfaces/usb/1.0/android.hardware.usb@1.0_genc++/gen/android/hardware/usb/1.0/UsbAll.cpp

::android::sp<IUsb> IUsb::getService(const std::string &serviceName, const bool getStub) {
    return ::android::hardware::details::getServiceInternal<BpHwUsb>(serviceName, true, getStub);
}

持续往下走，getServiceInternal完成在HidlTransportSupport.h

4. system/libhidl/transport/include/hidl/HidlTransportSupport.h

template <typename BpType, typename IType = typename BpType::Pure,
          typename = std::enable_if_t<std::is_same<i_tag, typename IType::_hidl_tag>::value>,
          typename = std::enable_if_t<std::is_same<bphw_tag, typename BpType::_hidl_tag>::value>>
sp<IType> getServiceInternal(const std::string& instance, bool retry, bool getStub) {
    using ::android::hidl::base::V1_0::IBase;
    sp<IBase> base = getRawServiceInternal(IType::descriptor, instance, retry, getStub);
    if (base == nullptr) {
        return nullptr;
    }
    if (base->isRemote()) {
        // getRawServiceInternal guarantees we get the proper class
        return sp<IType>(new BpType(toBinder<IBase>(base)));
    }
    return IType::castFrom(base);
}

先看getRawServiceInternal函数，完成在ServiceManagement.cpp

4.1 system/libhidl/transport/ServiceManagement.cpp

sp<::android::hidl::base::V1_0::IBase> getRawServiceInternal(const std::string& descriptor,
                                                             const std::string& instance,
                                                             bool retry, bool getStub) {
    using Transport = ::android::hidl::manager::V1_0::IServiceManager::Transport;
    using ::android::hidl::base::V1_0::IBase;
    using ::android::hidl::manager::V1_0::IServiceManager;
    sp<Waiter> waiter;
    const sp<IServiceManager1_1> sm = defaultServiceManager1_1();
    if (sm == nullptr) {
        ALOGE("getService: defaultServiceManager() is null");
        return nullptr;
    }
    Return<Transport> transportRet = sm->getTransport(descriptor, instance);
    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 ENFORCE_VINTF_MANIFEST
#ifdef LIBHIDL_TARGET_DEBUGGABLE
    const char* env = std::getenv("TREBLE_TESTING_OVERRIDE");
    const bool trebleTestingOverride = env && !strcmp(env, "true");
    const bool vintfLegacy = (transport == Transport::EMPTY) && trebleTestingOverride;
#else   // ENFORCE_VINTF_MANIFEST but not LIBHIDL_TARGET_DEBUGGABLE
    const bool trebleTestingOverride = false;
    const bool vintfLegacy = false;
#endif  // LIBHIDL_TARGET_DEBUGGABLE
#else   // not ENFORCE_VINTF_MANIFEST
    const char* env = std::getenv("TREBLE_TESTING_OVERRIDE");
    const bool trebleTestingOverride = env && !strcmp(env, "true");
    const bool vintfLegacy = (transport == Transport::EMPTY);
#endif  // ENFORCE_VINTF_MANIFEST
    for (int tries = 0; !getStub && (vintfHwbinder || vintfLegacy); tries++) {
        if (waiter == nullptr && tries > 0) {
            waiter = new Waiter(descriptor, instance, sm);
        }
        if (waiter != nullptr) {
            waiter->reset();  // don't reorder this -- see comments on reset()
        }
        Return<sp<IBase>> ret = sm->get(descriptor, instance);
        if (!ret.isOk()) {
            ALOGE("getService: defaultServiceManager()->get returns %s for %s/%s.",
                  ret.description().c_str(), descriptor.c_str(), instance.c_str());
            break;
        }
        sp<IBase> base = ret;
        if (base != nullptr) {
            Return<bool> canCastRet =
                details::canCastInterface(base.get(), descriptor.c_str(), true /* emitError */);
            if (canCastRet.isOk() && canCastRet) {
                if (waiter != nullptr) {
                    waiter->done();
                }
                return base; // still needs to be wrapped by Bp class.
            }
            if (!handleCastError(canCastRet, descriptor, instance)) break;
        }
        // In case of legacy or we were not asked to retry, don't.
        if (vintfLegacy || !retry) break;
        if (waiter != nullptr) {
            ALOGI("getService: Trying again for %s/%s...", descriptor.c_str(), instance.c_str());
            waiter->wait();
        }
    }
    if (waiter != nullptr) {
        waiter->done();
    }
    if (getStub || vintfPassthru || vintfLegacy) {
        const sp<IServiceManager> pm = getPassthroughServiceManager();
        if (pm != nullptr) {
            sp<IBase> base = pm->get(descriptor, instance).withDefault(nullptr);
            if (!getStub || trebleTestingOverride) {
                base = wrapPassthrough(base);
            }
            return base;
        }
    }
    return nullptr;
}

先看defaultServiceManager1_1()完成在同一个cpp

sp<IServiceManager1_1> defaultServiceManager1_1() {
    {
        AutoMutex _l(details::gDefaultServiceManagerLock);
        if (details::gDefaultServiceManager != nullptr) {
            return details::gDefaultServiceManager;
        }
        if (access("/dev/hwbinder", F_OK|R_OK|W_OK) != 0) {
            // HwBinder not available on this device or not accessible to
            // this process.
            return nullptr;
        }
        waitForHwServiceManager();
        while (details::gDefaultServiceManager == nullptr) {
            details::gDefaultServiceManager =
                    fromBinder<IServiceManager1_1, BpHwServiceManager, BnHwServiceManager>(
                        ProcessState::self()->getContextObject(nullptr));
            if (details::gDefaultServiceManager == nullptr) {
                LOG(ERROR) << "Waited for hwservicemanager, but got nullptr.";
                sleep(1);
            }
        }
    }
    return details::gDefaultServiceManager;
}

fromBinder() 是个模板函数，声明和完成都在system/libhidl/transport/include/hidl/HidlBinderSupport.h

4.1.1. system/libhidl/transport/include/hidl/HidlBinderSupport.h

template <typename IType, typename ProxyType, typename StubType>
sp<IType> fromBinder(const sp<IBinder>& binderIface) {
    using ::android::hidl::base::V1_0::IBase;
    using ::android::hidl::base::V1_0::BnHwBase;
    if (binderIface.get() == nullptr) {
        return nullptr;
    }
    if (binderIface->localBinder() == nullptr) {
        return new ProxyType(binderIface);
    }
    sp<IBase> base = static_cast<BnHwBase*>(binderIface.get())->getImpl();
    if (details::canCastInterface(base.get(), IType::descriptor)) {
        StubType* stub = static_cast<StubType*>(binderIface.get());
        return stub->getImpl();
    } else {
        return nullptr;
    }
}

binderIface便是传入的参数，反过来再看2.1传入的参数ProcessState::self()->getContextObject(nullptr)，这个完成在system/libhwbinder/ProcessState.cpp

4.1.2. system/libhwbinder/ProcessState.cpp

getContextObject(nullptr)的完成：

sp<IBinder> ProcessState::getContextObject(const sp<IBinder>& /*caller*/)
{
    return getStrongProxyForHandle(0);
}

再看getStrongProxyForHandle(0)，完成在同一个文件中

sp<IBinder> ProcessState::getStrongProxyForHandle(int32_t handle)
{
    sp<IBinder> result;
    AutoMutex _l(mLock);
    handle_entry* e = lookupHandleLocked(handle);
    if (e != NULL) {
        // We need to create a new BpHwBinder if there isn't currently one, OR we
        // are unable to acquire a weak reference on this current one.  See comment
        // in getWeakProxyForHandle() for more info about this.
        IBinder* b = e->binder;
        if (b == NULL || !e->refs->attemptIncWeak(this)) {
            b = new BpHwBinder(handle);
            e->binder = b;
            if (b) e->refs = b->getWeakRefs();
            result = b;
        } else {
            // This little bit of nastyness is to allow us to add a primary
            // reference to the remote proxy when this team doesn't have one
            // but another team is sending the handle to us.
            result.force_set(b);
            e->refs->decWeak(this);
        }
    }
    return result;
}

有代码能够看出resault和e相关，再看lookupHandleLocked(handle)，

ProcessState::handle_entry* ProcessState::lookupHandleLocked(int32_t handle)
{
    const size_t N=mHandleToObject.size();
    if (N <= (size_t)handle) {
        handle_entry e;
        e.binder = NULL;
        e.refs = NULL;
        status_t err = mHandleToObject.insertAt(e, N, handle+1-N);
        if (err < NO_ERROR) return NULL;
    }
    return &mHandleToObject.editItemAt(handle);
}

由于mHandleToObject 是成员变量，且只有此函数调用，且此函数为此进程第一次调用，所以size为0， 由此把handle_entry e 放进mHandleToObject，并回来，然后接着看上一个函数getStrongProxyForHandle(0),谈的回来值便是new BpHwBinder(0)

4.1.2.1. system/libhwbinder/BpHwBinder.cpp

BpHwBinder::BpHwBinder(int32_t handle)
    : mHandle(handle)
    , mAlive(1)
    , mObitsSent(0)
    , mObituaries(NULL)
{
    ALOGV("Creating BpHwBinder %p handle %d\n", this, mHandle);
    extendObjectLifetime(OBJECT_LIFETIME_WEAK);
    IPCThreadState::self()->incWeakHandle(handle, this);
}

4.1.2.2. system/libhwbinder/IPCThreadState.cpp

void IPCThreadState::incWeakHandle(int32_t handle, BpHwBinder *proxy)
{
    LOG_REMOTEREFS("IPCThreadState::incWeakHandle(%d)\n", handle);
    mOut.writeInt32(BC_INCREFS);
    mOut.writeInt32(handle);
    // Create a temp reference until the driver has handled this command.
    proxy->getWeakRefs()->incWeak(mProcess.get());
    mPostWriteWeakDerefs.push(proxy->getWeakRefs());
}

这里mOut终究会传给binder驱动，handle = 0 便是IHwServiceManager的Bp 这个下面会提到这里先掠过，再回到4.1. 就会知道defaultServiceManager1_1() 回来的便是BpHwServiceManager目标，然后执行sm->getTransport办法，找到完成在/out/soong/.intermediates/system/libhidl/transport/manager/1.0/android.hidl.manager@1.0_genc++/gen/android/hidl/manager/1.0/ServiceManagerAll.cpp

4.1.3. out/soong/.intermediates/system/libhidl/transport/manager/1.0/android.hidl.manager@1.0_genc++/gen/android/hidl/manager/1.1/ServiceManagerAll.cpp

::android::hardware::Return<::android::hidl::manager::V1_1::IServiceManager::Transport> BpHwServiceManager::getTransport(const ::android::hardware::hidl_string& fqName, const ::android::hardware::hidl_string& name){
    ::android::hardware::Return<::android::hidl::manager::V1_1::IServiceManager::Transport>  _hidl_out = ::android::hidl::manager::V1_0::BpHwServiceManager::_hidl_getTransport(this, this, fqName, name);
    return _hidl_out;
}

::android::hardware::Return<::android::hidl::manager::V1_1::IServiceManager::Transport> BpHwServiceManager::_hidl_getTransport(::android::hardware::IInterface *_hidl_this, ::android::hardware::details::HidlInstrumentor *_hidl_this_instrumentor, const ::android::hardware::hidl_string& fqName, const ::android::hardware::hidl_string& name) {
.......
    ::android::hardware::Parcel _hidl_data;
    ::android::hardware::Parcel _hidl_reply;
    ::android::status_t _hidl_err;
    ::android::hardware::Status _hidl_status;
    ::android::hidl::manager::V1_1::IServiceManager::Transport _hidl_out_transport;
    _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(3 /* getTransport */, _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.readUint8((uint8_t *)&_hidl_out_transport);
    if (_hidl_err != ::android::OK) { goto _hidl_error; }
......
    _hidl_status.setFromStatusT(_hidl_err);
    return ::android::hardware::Return<::android::hidl::manager::V1_1::IServiceManager::Transport>(_hidl_out_transport);
_hidl_error:
    _hidl_status.setFromStatusT(_hidl_err);
    return ::android::hardware::Return<::android::hidl::manager::V1_1::IServiceManager::Transport>(_hidl_status);
}

接着看这个函数 _hidl_err = ::android::hardware::IInterface::asBinder(_hidl_this)->transact(3 /* getTransport */, _hidl_data, &_hidl_reply);通过上一篇文章【Android9 HWbinder运用-注册service流程解析】 能够知道asBinder回来BpHwBinder，然后看transact函数

4.1.3.1. BpHwBinder.cpp

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

接着调用到了system/libhwbinder/IPCThreadState.cpp

4.1.3.2. system/libhwbinder/IPCThreadState.cpp

status_t IPCThreadState::transact(int32_t handle,
                                  uint32_t code, const Parcel& data,
                                  Parcel* reply, uint32_t flags)
{
    status_t err;
    flags |= TF_ACCEPT_FDS;
    ...
    err = writeTransactionData(BC_TRANSACTION_SG, flags, handle, code, data, NULL);
    if (err != NO_ERROR) {
        if (reply) reply->setError(err);
        return (mLastError = err);
    }
    if ((flags & TF_ONE_WAY) == 0) {
    ...
        if (reply) {
            err = waitForResponse(reply);
        } else {
            Parcel fakeReply;
            err = waitForResponse(&fakeReply);
        }
      ...
    } else {
        err = waitForResponse(NULL, NULL);
    }
    return err;
}

通过上一篇文章【Android9 HWbinder运用-注册service流程解析】第3.第4节可知终究接着便是走system/libhwbinder/IPCThreadState.cpp收到通知，调用BHwBinder的transact，回调非Bn端的onTransact

4.1.3.3. system/libhwbinder/Binder.cpp

status_t BHwBinder::transact(
    uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags, TransactCallback callback)
{
    data.setDataPosition(0);
    status_t err = NO_ERROR;
    switch (code) {
        default:
            err = onTransact(code, data, reply, flags,
                    [&](auto &replyParcel) {
                        replyParcel.setDataPosition(0);
                        if (callback != NULL) {
                            callback(replyParcel);
                        }
                    });
            break;
    }
    return err;
}

4.1.3.4. out/soong/.intermediates/system/libhidl/transport/manager/1.0/android.hidl.manager@1.0_genc++/gen/android/hidl/manager/1.1/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 3 /* getTransport */:
        {
            bool _hidl_is_oneway = _hidl_flags & 1 /* oneway */;
            if (_hidl_is_oneway != false) {
                return ::android::UNKNOWN_ERROR;
            }
            _hidl_err = ::android::hidl::manager::V1_0::BnHwServiceManager::_hidl_getTransport(this, _hidl_data, _hidl_reply, _hidl_cb);
            break;
        }
......
    }
    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;
}

顺着_hidl_getTransport函数往下看

::android::status_t BnHwServiceManager::_hidl_getTransport(
        ::android::hidl::base::V1_0::BnHwBase* _hidl_this,
        const ::android::hardware::Parcel &_hidl_data,
        ::android::hardware::Parcel *_hidl_reply,
        TransactCallback _hidl_cb) {
......
    ::android::status_t _hidl_err = ::android::OK;
    if (!_hidl_data.enforceInterface(BnHwServiceManager::Pure::descriptor)) {
        _hidl_err = ::android::BAD_TYPE;
        return _hidl_err;
    }
    const ::android::hardware::hidl_string* fqName;
    const ::android::hardware::hidl_string* name;
    size_t _hidl_fqName_parent;
    _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; }
......
    ::android::hidl::manager::V1_0::IServiceManager::Transport _hidl_out_transport = static_cast<IServiceManager*>(_hidl_this->getImpl().get())->getTransport(*fqName, *name);
    ::android::hardware::writeToParcel(::android::hardware::Status::ok(), _hidl_reply);
    _hidl_err = _hidl_reply->writeUint8((uint8_t)_hidl_out_transport);
    /* _hidl_err ignored! */
   ......
    _hidl_cb(*_hidl_reply);
    return _hidl_err;
}

接着便是IServiceManager完成类的getTransport办法,完成/system/hwservicemanager/ServiceManager.cpp

4.1.3.5. system/hwservicemanager/ServiceManager.cpp

Return<ServiceManager::Transport> ServiceManager::getTransport(const hidl_string& fqName,
                                                               const hidl_string& name) {
    using ::android::hardware::getTransport;
    pid_t pid = IPCThreadState::self()->getCallingPid();
    if (!mAcl.canGet(fqName, pid)) {
        return Transport::EMPTY;
    }
    switch (getTransport(fqName, name)) {
        case vintf::Transport::HWBINDER:
             return Transport::HWBINDER;
        case vintf::Transport::PASSTHROUGH:
             return Transport::PASSTHROUGH;
        case vintf::Transport::EMPTY:
        default:
             return Transport::EMPTY;
    }
}

getTransport的完成在Vintf.cpp

4.1.3.6 system/hwservicemanager/Vintf.cpp

vintf::Transport getTransport(const std::string &interfaceName, const std::string &instanceName) {
    FQName fqName(interfaceName);
    if (!fqName.isValid()) {
        LOG(ERROR) << __FUNCTION__ << ": " << interfaceName
                   << " is not a valid fully-qualified name ";
        return vintf::Transport::EMPTY;
    }
    if (!fqName.hasVersion()) {
        LOG(ERROR) << __FUNCTION__ << ": " << fqName.string()
                   << " does not specify a version.";
        return vintf::Transport::EMPTY;
    }
    if (fqName.name().empty()) {
        LOG(ERROR) << __FUNCTION__ << ": " << fqName.string()
                   << " does not specify an interface name.";
        return vintf::Transport::EMPTY;
    }
    vintf::Transport tr = getTransportFromManifest(fqName, instanceName,
            vintf::VintfObject::GetFrameworkHalManifest());
    if (tr != vintf::Transport::EMPTY) {
        return tr;
    }
    tr = getTransportFromManifest(fqName, instanceName,
            vintf::VintfObject::GetDeviceHalManifest());
    if (tr != vintf::Transport::EMPTY) {
        return tr;
    }
    LOG(WARNING) << __FUNCTION__ << ": Cannot find entry "
                 << fqName.string() << "/" << instanceName
                 << " in either framework or device manifest.";
    return vintf::Transport::EMPTY;
}

getTransportFromManifest这个函数就代表是从manifest.xml拿到的Transport，详细的解析有爱好的能够持续跟一下，IUusb相关的xml如下，能够看到Transport 是 HWBINDER

    <hal format="hidl">
        <name>android.hardware.usb</name>
        <transport>hwbinder</transport>
        <version>1.0</version>
        <interface>
            <name>IUsb</name>
            <instance>default</instance>
        </interface>
    </hal>

然后回到4.1章节，持续往下看就走到sm->get(descriptor, instance);函数

4.1.4 out/soong/.intermediates/system/libhidl/transport/manager/1.1/android.hidl.manager@1.1_genc++/gen/android/hidl/manager/1.1/ServiceManagerAll.cpp

// Methods from ::android::hidl::manager::V1_0::IServiceManager follow.
::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;
}

// Methods from ::android::hidl::manager::V1_0::IServiceManager follow.
::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) {
......
    ::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_binder;
        _hidl_err = _hidl_reply.readNullableStrongBinder(&_hidl_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_binder);
    }
......
    _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);
}

由4.1.3可知终究hidl_err = ::android::hardware::IInterface::asBinder(_hidl_this)->transact(1 /* get */, _hidl_data, &_hidl_reply);会走到system/libhwbinder/IPCThreadState.cpp收到通知，调用BHwBinder的transact，回调非Bn端的onTransact

4.1.4.1. out/soong/.intermediates/system/libhidl/transport/manager/1.0/android.hidl.manager@1.0_genc++/gen/android/hidl/manager/1.1/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 1 /* get */:
        {
            bool _hidl_is_oneway = _hidl_flags & 1 /* oneway */;
            if (_hidl_is_oneway != false) {
                return ::android::UNKNOWN_ERROR;
            }
            _hidl_err = ::android::hidl::manager::V1_0::BnHwServiceManager::_hidl_get(this, _hidl_data, _hidl_reply, _hidl_cb);
            break;
        }
     ......
    }
    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;
}

顺着_hidl_get持续往下看

// Methods from ::android::hidl::manager::V1_0::IServiceManager follow.
::android::status_t BnHwServiceManager::_hidl_get(
        ::android::hidl::base::V1_0::BnHwBase* _hidl_this,
        const ::android::hardware::Parcel &_hidl_data,
        ::android::hardware::Parcel *_hidl_reply,
        TransactCallback _hidl_cb) {
  ......
    ::android::status_t _hidl_err = ::android::OK;
    if (!_hidl_data.enforceInterface(BnHwServiceManager::Pure::descriptor)) {
        _hidl_err = ::android::BAD_TYPE;
        return _hidl_err;
    }
    const ::android::hardware::hidl_string* fqName;
    const ::android::hardware::hidl_string* name;
    size_t _hidl_fqName_parent;
    _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; }
......
    ::android::sp<::android::hidl::base::V1_0::IBase> _hidl_out_service = static_cast<IServiceManager*>(_hidl_this->getImpl().get())->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! */
......
    _hidl_cb(*_hidl_reply);
    return _hidl_err;
}

接着看IServiceManager完成类的get办法

4.1.4.2. system/hwservicemanager/ServiceManager.cpp

// Methods from ::android::hidl::manager::V1_0::IServiceManager follow.
Return<sp<IBase>> ServiceManager::get(const hidl_string& hidlFqName,
                                      const hidl_string& hidlName) {
    const std::string fqName = hidlFqName;
    const std::string name = hidlName;
    pid_t pid = IPCThreadState::self()->getCallingPid();
    if (!mAcl.canGet(fqName, pid)) {
        return nullptr;
    }
    auto ifaceIt = mServiceMap.find(fqName);
    if (ifaceIt == mServiceMap.end()) {
        tryStartService(fqName, hidlName);
        return nullptr;
    }
    const PackageInterfaceMap &ifaceMap = ifaceIt->second;
    const HidlService *hidlService = ifaceMap.lookup(name);
    if (hidlService == nullptr) {
        tryStartService(fqName, hidlName);
        return nullptr;
    }
    sp<IBase> service = hidlService->getService();
    if (service == nullptr) {
        tryStartService(fqName, hidlName);
        return nullptr;
    }
    return service;
}

这里就从Android9 HWbinder运用-注册service流程解析讲到的map里边拿到bp，再回到4.1.4.1 就把bp转化为bpbinder写入parcel回来给client 至此获取的流程基本完毕