Android13 CameraServer启动流程

代码入口

frameworks/av/camera/cameraserver

里面包含了四个文件

我们先来看看Android.bp的内容

package {
    // See: http://go/android-license-faq
    // A large-scale-change added 'default_applicable_licenses' to import
    // all of the 'license_kinds' from "frameworks_av_camera_license"
    // to get the below license kinds:
    //   SPDX-license-identifier-Apache-2.0
    default_applicable_licenses: ["frameworks_av_camera_license"],
}

cc_binary {
    name: "cameraserver",

    srcs: ["main_cameraserver.cpp"],

    header_libs: [
        "libmedia_headers",
    ],

    shared_libs: [
        "libcameraservice",
        "liblog",
        "libutils",
        "libui",
        "libgui",
        "libbinder",
        "libhidlbase",
        "android.hardware.camera.common@1.0",
        "android.hardware.camera.provider@2.4",
        "android.hardware.camera.provider@2.5",
        "android.hardware.camera.provider@2.6",
        "android.hardware.camera.provider@2.7",
        "android.hardware.camera.provider-V1-ndk",
        "android.hardware.camera.device@1.0",
        "android.hardware.camera.device@3.2",
        "android.hardware.camera.device@3.4",
    ],
    compile_multilib: "first",
    cflags: [
        "-Wall",
        "-Wextra",
        "-Werror",
        "-Wno-unused-parameter",
    ],

    init_rc: ["cameraserver.rc"],

    vintf_fragments: [
        "manifest_android.frameworks.cameraservice.service@2.2.xml",
    ],
}

我们注意到

init_rc: ["cameraserver.rc"],

由此可知系统在编译时会将cameraserver.rc放到system/etc/init目录下，
init进程启动的时候会解析这个目录下的所有.rc文件。

solid/android13/amdroid13_ntls/out/target/product/hpg2_24/system/etc/init$ ll cameraserver.rc
-rw-rw-r-- 1 wancg wancg 214 3月 7 14:59 cameraserver.rc

接下来我们来探探cameraserver.rc的庐山真面目：

service cameraserver /system/bin/cameraserver
    class main
    user cameraserver
    group audio camera input drmrpc
    ioprio rt 4
    task_profiles CameraServiceCapacity MaxPerformance
    rlimit rtprio 10 10

开机时/system/bin/cameraserver启动一个名称为cameraserver的服务

再来看看main_cameraserver.cpp 的内容

#define LOG_TAG "cameraserver"
//#define LOG_NDEBUG 0

#include "CameraService.h"
#include <hidl/HidlTransportSupport.h>

using namespace android;

int main(int argc __unused, char** argv __unused)
{
    signal(SIGPIPE, SIG_IGN);

    // Set 5 threads for HIDL calls. Now cameraserver will serve HIDL calls in
    // addition to consuming them from the Camera HAL as well.
    hardware::configureRpcThreadpool(5, /*willjoin*/ false);

    sp<ProcessState> proc(ProcessState::self());
    sp<IServiceManager> sm = defaultServiceManager();
    ALOGI("ServiceManager: %p", sm.get());
    CameraService::instantiate();
    //下面我们就从CameraService继续分析。
    ALOGI("ServiceManager: %p done instantiate", sm.get());
    ProcessState::self()->startThreadPool();
    IPCThreadState::self()->joinThreadPool();
}

CarmeraServer.cpp

CameraService继承了BinderService.h.这个:instantiate()调用到了BinderService.h里的代码

frameworks/native/libs/binder/include/binder/BinderService.h
class BinderService
{
public:
    static status_t publish(bool allowIsolated = false,
                            int dumpFlags = IServiceManager::DUMP_FLAG_PRIORITY_DEFAULT) {
        sp<IServiceManager> sm(defaultServiceManager());
        return sm->addService(String16(SERVICE::getServiceName()), new SERVICE(), allowIsolated,
                              dumpFlags);
    }

    static void publishAndJoinThreadPool(
            bool allowIsolated = false,
            int dumpFlags = IServiceManager::DUMP_FLAG_PRIORITY_DEFAULT) {
        publish(allowIsolated, dumpFlags);
        joinThreadPool();
    }

    static void instantiate() { publish(); }

    static status_t shutdown() { return NO_ERROR; }

private:
    static void joinThreadPool() {
        sp<ProcessState> ps(ProcessState::self());
        ps->startThreadPool();
        ps->giveThreadPoolName();
        IPCThreadState::self()->joinThreadPool();
    }
};

在回过头来看看上面提到的CameraService方法

// frameworks/av/services/camera/libcameraservice/CameraService.h
class CameraService :
    // 继承BinderService指定泛型类型为CameraService
    public BinderService<CameraService>,
    public virtual ::android::hardware::BnCameraService,
    public virtual IBinder::DeathRecipient,
    public virtual CameraProviderManager::StatusListener
{
    ...
public:
    ...
    // 注册的binder服务名称为“media.camera”
    static char const* getServiceName() { 
      return "media.camera"; 
    }
    ...
}

接下来我们看下frameworks/native/libs/binder/include/binder/BinderService.h 中提到addService方法

// frameworks/native/libs/binder/include/binder/IServiceManager.h
// 第一个参数是字符串media.camera
// 第二个参数是new的CameraService对象
// 这里相当于const sp<IBinder>& service = new CameraService()
virtual status_t addService(const String16& name, const sp<IBinder>& service,
                            bool allowIsolated = false,
                            int dumpsysFlags = DUMP_FLAG_PRIORITY_DEFAULT) = 0;

我们看下class sp的实现

// system/core/libutils/include/utils/StrongPointer.h
// 下面的T就是CameraService*
template <typename T>
sp<T>& sp<T>::operator=(T* other) {
    T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
    if (other) {
        check_not_on_stack(other);
        // 可以看到如果指针不为空的话
        // 会调用自身的incStrong方法
        other->incStrong(this);
    }
    if (oldPtr) oldPtr->decStrong(this);
    if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
    m_ptr = other;
    return *this;
}

但是我们发现CameraService里并没有incStrong方法，那么一定
是它的父类的方法，由此引出了一个非常重要的类RefBase。
RefBase是Android中所有C++对象的基类。

从这个文件可以看出,instantiate最终还是调用到了IServiceManager里的addService, 将我们的cameraService注册到了系统的服务管理器里去了.

这里调用到CameraService后, 因为是开机第一次调用,它的引用计数为1,所以会调用到CameraService::onFirstRef()这个函数. 这个函数是从CameraService的父类RefBase里继承过来的.该函数在强引用sp新增引用计数时调用，什么意思？就是当有sp包装的类初始化的时候调用.我们再看看cameraService::onFirstRef()

frameworks\av\services\camera\libcameraservice\CameraService.cpp
void CameraService::onFirstRef()
{

    ALOGI("CameraService process starting");

    BnCameraService::onFirstRef();

    // Update battery life tracking if service is restarting
    BatteryNotifier& notifier(BatteryNotifier::getInstance());
    notifier.noteResetCamera();
    notifier.noteResetFlashlight();

    status_t res = INVALID_OPERATION;

    res = enumerateProviders();
    if (res == OK) {
        mInitialized = true;
    }

    mUidPolicy = new UidPolicy(this);
    mUidPolicy->registerSelf();
    mSensorPrivacyPolicy = new SensorPrivacyPolicy(this);
    mSensorPrivacyPolicy->registerSelf();
    mInjectionStatusListener = new InjectionStatusListener(this);
    mAppOps.setCameraAudioRestriction(mAudioRestriction);
    sp<HidlCameraService> hcs = HidlCameraService::getInstance(this);
    if (hcs->registerAsService() != android::OK) {
        ALOGE("%s: Failed to register default android.frameworks.cameraservice.service@1.0",
              __FUNCTION__);
    }

    // This needs to be last call in this function, so that it's as close to
    // ServiceManager::addService() as possible.
    CameraServiceProxyWrapper::pingCameraServiceProxy();
    ALOGI("CameraService pinged cameraservice proxy");
}

在这个函数里,我们只关注enumerateProviders(),这里就到了列出所有cameraProvider.

status_t CameraService::enumerateProviders() {
    status_t res;

    std::vector<std::string> deviceIds;
    std::unordered_map<std::string, std::set<std::string>> unavailPhysicalIds;
    {
        Mutex::Autolock l(mServiceLock);

        if (nullptr == mCameraProviderManager.get()) {
            mCameraProviderManager = new CameraProviderManager();
            res = mCameraProviderManager->initialize(this);
            if (res != OK) {
                ALOGE("%s: Unable to initialize camera provider manager: %s (%d)",
                        __FUNCTION__, strerror(-res), res);
                logServiceError(String8::format("Unable to initialize camera provider manager"),
                ERROR_DISCONNECTED);
                return res;
            }
        }


        // Setup vendor tags before we call get_camera_info the first time
        // because HAL might need to setup static vendor keys in get_camera_info
        // TODO: maybe put this into CameraProviderManager::initialize()?
        mCameraProviderManager->setUpVendorTags();

        if (nullptr == mFlashlight.get()) {
            mFlashlight = new CameraFlashlight(mCameraProviderManager, this);
        }

        res = mFlashlight->findFlashUnits();
        if (res != OK) {
            ALOGE("Failed to enumerate flash units: %s (%d)", strerror(-res), res);
        }

        deviceIds = mCameraProviderManager->getCameraDeviceIds(&unavailPhysicalIds);
    }


    for (auto& cameraId : deviceIds) {
        String8 id8 = String8(cameraId.c_str());
        if (getCameraState(id8) == nullptr) {
            onDeviceStatusChanged(id8, CameraDeviceStatus::PRESENT);
        }
        if (unavailPhysicalIds.count(cameraId) > 0) {
            for (const auto& physicalId : unavailPhysicalIds[cameraId]) {
                String8 physicalId8 = String8(physicalId.c_str());
                onDeviceStatusChanged(id8, physicalId8, CameraDeviceStatus::NOT_PRESENT);
            }
        }
    }

    // Derive primary rear/front cameras, and filter their charactierstics.
    // This needs to be done after all cameras are enumerated and camera ids are sorted.
    if (SessionConfigurationUtils::IS_PERF_CLASS) {
        // Assume internal cameras are advertised from the same
        // provider. If multiple providers are registered at different time,
        // and each provider contains multiple internal color cameras, the current
        // logic may filter the characteristics of more than one front/rear color
        // cameras.
        Mutex::Autolock l(mServiceLock);
        filterSPerfClassCharacteristicsLocked();
    }

    return OK;
}

这个函数里,创建了一个CameraProviderManager对象,并调进行了初始化.具体如下：