Cubietruck---29.AudioFlinger与AudioPolicyServer初始化分析

《深入理解android》卷1第七章深入理解audio系统的笔记
1.AudioFlinger的启动
./frameworks/av/media/mediaserver/main_mediaserver.cpp

int main(int argc, char** argv)
{
    AudioFlinger::instantiate();           //audioFlinger
    AudioPolicyService::instantiate();       //与audioFlingerService的启动
    ProcessState::self()->startThreadPool();
    IPCThreadState::self()->joinThreadPool();
}

调用了instantiate来启动AF与APS,但是在AudioFlinger.cpp与AudioPolicyServer.cpp中是找不到instantiate这个函数的，
为什么呢？
因为看AudioFlinger的定义

class AudioFlinger :
    public BinderService<AudioFlinger>,
    public BnAudioFlinger

AF是继承自BinderService,BinderService会创建AudioFlinger这个服务.并调用AudioFlinger的onFirstRef
onFirstRef(它也没有干什么事)，执行完成后，AudioFlinger就启动起来了，服务嘛只有别人调它时才会起作用。


2.APS的启动

AudioPolicyService::AudioPolicyService() : BnAudioPolicyService() , mpAudioPolicyDev(NULL) , mpAudioPolicy(NULL)
{
    char value[PROPERTY_VALUE_MAX];
    const struct hw_module_t *module;
    Mutex::Autolock _l(mLock);
    mTonePlaybackThread = new AudioCommandThread(String8(""));
    mAudioCommandThread = new AudioCommandThread(String8("ApmCommand"));
    hw_get_module(AUDIO_POLICY_HARDWARE_MODULE_ID, &module);       //找到库./hardware/libhardware_legacy/audio下的句柄
    audio_policy_dev_open(module, &mpAudioPolicyDev);              //打开库，库指针放在mpAudioPolicyDev中
    //重要这时mpAudioPolicy就是legacy_audio_policy->policy的一堆函数指针
    mpAudioPolicyDev->create_audio_policy(mpAudioPolicyDev, &aps_ops, this, &mpAudioPolicy);
    mpAudioPolicy->init_check(mpAudioPolicy);
    if (access(AUDIO_EFFECT_VENDOR_CONFIG_FILE, R_OK) == 0) {
        loadPreProcessorConfig(AUDIO_EFFECT_VENDOR_CONFIG_FILE);
    } else if (access(AUDIO_EFFECT_DEFAULT_CONFIG_FILE, R_OK) == 0) {
        loadPreProcessorConfig(AUDIO_EFFECT_DEFAULT_CONFIG_FILE);
    }
}

2.1 APS调用audio_policy.default的create
在./hardware/libhardware_legacy/audio/audio_policy_hal.cpp中(即库audio_policy.default.so)

static int create_legacy_ap(const struct audio_policy_device *device,
                            struct audio_policy_service_ops *aps_ops,
                            void *service,
                            struct audio_policy **ap)
{
    struct legacy_audio_policy *lap;
    lap = (struct legacy_audio_policy *)calloc(1, sizeof(*lap));
    //以下初始化lap结构体
    lap->policy.init_check = ap_init_check;
     .....一堆lap->policy的函数指针的初始化
    lap->service = service;
    lap->aps_ops = aps_ops;
    //下面这两行看出，以后经常看到的mpClientInterface就是下面的lap->service_client
    lap->service_client = new AudioPolicyCompatClient(aps_ops, service);
    lap->apm = createAudioPolicyManager(lap->service_client);

    *ap = &lap->policy;    //将lap->policy赋给了mpAudioPolicy，这样fw中的APS就可以调用库中的函数了
    return 0;
}

注1.关于下面这两句
lap->service_client = new AudioPolicyCompatClient(aps_ops, service);
lap->apm = createAudioPolicyManager(lap->service_client);  
  --> new AudioPolicyManagerDefault
   --> 在构造函数中AudioPolicyManagerBase::AudioPolicyManagerBase
   -->  mpClientInterface = lap->service_client;
所以这个mpClientInterface就是一个AudioPolicyCompatClient
注2.捋一下层次结构
AudioPolicyService-->set_force_use    //在fw层的调用
    mpAudioPolicy->setForce_use      //mpAudioPolicy就是audio_policy.default.so的接口
ap_set_force_use   //由此进入库audio_policy.default.so
   lap->apm->setForceUse  (lap->apm 就是AudioPolicyManager 即AudioPolicyManagerBase)
       AudioPolicyManagerBase-->setForceUse
          mpClientInterface->setParameters       //这个mpClientInterface就是AudioPolicyCompatClient
              AudioPolicyCompatClient::setParameters
                 mServiceOps->set_parameters       //这个mServiceOps初始化是传入的fw层的APS
aps_set_parameters                          //再次回到fw层
   audioPolicyService->setParameters
       mAudioCommandThread->parametersCommand

在hardware/libhardware_legacy/audio/AudioPolicyManagerBase.cpp中

AudioPolicyManagerBase::AudioPolicyManagerBase(AudioPolicyClientInterface *clientInterface)
    :
    mPrimaryOutput((audio_io_handle_t)0),
    mAvailableOutputDevices(AUDIO_DEVICE_NONE),
    mPhoneState(AudioSystem::MODE_NORMAL),
    mLimitRingtoneVolume(false), mLastVoiceVolume(-1.0f),
    mTotalEffectsCpuLoad(0), mTotalEffectsMemory(0),
    mA2dpSuspended(false), mHasA2dp(false), mHasUsb(false), mHasRemoteSubmix(false)
{
    mpClientInterface = clientInterface;                   //这一句就把APS传来的ops保存在了成员变量中了
    for (int i = 0; i < AudioSystem::NUM_FORCE_USE; i++) {
        mForceUse[i] = AudioSystem::FORCE_NONE;
    }
    initializeVolumeCurves();
    //在这两个路径下面找auido_policy.conf文件，没有找到的话就用默认的
    // #define AUDIO_POLICY_CONFIG_FILE "/system/etc/audio_policy.conf"
    //#define AUDIO_POLICY_VENDOR_CONFIG_FILE "/vendor/etc/audio_policy.conf"
    //分别把global_configuration与audio_hw_modules加载进来
    if (loadAudioPolicyConfig(AUDIO_POLICY_VENDOR_CONFIG_FILE) != NO_ERROR) {
        if (loadAudioPolicyConfig(AUDIO_POLICY_CONFIG_FILE) != NO_ERROR) {
            defaultAudioPolicyConfig();
        }
    }

    for (size_t i = 0; i < mHwModules.size(); i++) {
        mHwModules[i]->mHandle = mpClientInterface->loadHwModule(mHwModules[i]->mName);
        for (size_t j = 0; j < mHwModules[i]->mOutputProfiles.size(); j++)
        {
            const IOProfile *outProfile = mHwModules[i]->mOutputProfiles[j];

            if (outProfile->mSupportedDevices & mAttachedOutputDevices) {
                AudioOutputDescriptor *outputDesc = new AudioOutputDescriptor(outProfile);
                outputDesc->mDevice = (audio_devices_t)(mDefaultOutputDevice & outProfile->mSupportedDevices);
                audio_io_handle_t output = mpClientInterface->openOutput(...);
                if (output == 0) {
                    delete outputDesc;
                } else {
                    mAvailableOutputDevices = (audio_devices_t)(mAvailableOutputDevices | (outProfile->mSupportedDevices & mAttachedOutputDevices));
                    if (mPrimaryOutput == 0 && outProfile->mFlags & AUDIO_OUTPUT_FLAG_PRIMARY) {
                        mPrimaryOutput = output;
                    }
                    addOutput(output, outputDesc);
                    setOutputDevice(output, (audio_devices_t)(mDefaultOutputDevice &outProfile->mSupportedDevices), true);
                }
            }
        }
    }
    updateDevicesAndOutputs();
}

循环调用以下函数加载音频设备的库
mpClientInterface->loadHwModule
   aps_load_hw_module(在fw: APS中)
      af->loadHwModule (在AudioFlinger中)
        af->loadHwModule_l (在AudioFlinger中)
            通过调用hw_get_module_by_class把audio.primary.exDroid.so与audio.a2dp.default.so加载进来
            注意虽然audio.primary.exDroid.so与audio.a2dp.default.so的id相同都是AUDIO_HARDWARE_MODULE_ID，
            但hw_get_module_by_class是通过名字加载的，所以不会冲突
音频库的具体加载过程
./frameworks/av/services/audioflinger/AudioFlinger.cpp

audio_module_handle_t AudioFlinger::loadHwModule_l(const char *name)
{
    audio_hw_device_t *dev;
    //将audio.primary.exDroid.so与audio.a2dp.default.so通过名字加载进来，因为这儿没有usb的，所以不考虑
    //有几个库就说明有几个设备，这儿说明在板子上有primary与a2dp两个音频设备
    int rc = load_audio_interface(name, &dev);     //库的接口放在dev中
    mAudioHwDevs.add(handle, new AudioHwDevice(name, dev, flags));  //然后把dev(即库的接口)保存在成员变量mAudioHwDevs中
    return handle;
}

注3. AF、APS、audio_policy.default.so与audio.hw.so之间的相互调用
a. fw中的APS调用AF
sp af = AudioSystem::get_audio_flinger();
这就获取了AF，然后就可以通过af调用AudioFilinger的函数接口

b. fw中的APS调用库audio_policy.default.so
   在AudioPolicyService的构造函数中，就通过hw_get_module打开了库audio_policy.default.so，
   并把接口保存在mpAudioPolicy中，所以就可以通过mpAudioPolicy调用

c. audio_policy.default.so如何调用APS(fw中的AudioPolicyServer)
    a. AudioPolicyCompatClient的成员函数audio_policy_service_ops* mServiceOps在构造函数中被初始化为APS的接口指针
    b. 这样就可以调用mServiceOps->load_hw_module来访问APS中的函数

d. AF与audio.hw.so之间的调用
  在板子上audio.hw.so包括两个： audio.primary.exDroid.so与audio.a2dp.default.so
   AF通过loadHwMoudle_l加载了这两个库，然后分别把库的函数指针保存在mAudioHwDevs中，
   这样就可以通过mAudioHwDevs来调用