Android 11 Audio strategy配置解析

在启动AudioPolicyService时，通过EngineBase的loadAudioPolicyEngineConfig函数去解析strategy配置。其调用流程如下

接下来就对loadAudioPolicyEngineConfig展开分析
1，解析volume标签

engineConfig::ParsingResult EngineBase::loadAudioPolicyEngineConfig()
{//省略auto result = engineConfig::parse();//1if (result.parsedConfig == nullptr) {engineConfig::Config config = gDefaultEngineConfig;//2android::status_t ret = engineConfig::parseLegacyVolumes(config.volumeGroups);//3result = {std::make_unique<engineConfig::Config>(config),static_cast<size_t>(ret == NO_ERROR ? 0 : 1)};} else {//省略}//省略
}

注释1处，parse函数会去解析/vendor/etc/audio_policy_engine_configuration.xml 文件，我的Android 11 源码环境没有这个文件,所以会进入if分支。注释2处设置默认配置为gDefaultEngineConfig。注释3处调用parseLegacyVolumes去解析audio_policy_configuration.xml文件下的volume标签。

parseLegacyVolumes找到audio_policy_configuration.xml文件后，调用到deserializeLegacyVolumeCollection函数继续解析

//frameworks/av/services/audiopolicy/engine/config/src/EngineConfig.cpp
static status_t deserializeLegacyVolumeCollection(_xmlDoc *doc, const _xmlNode *cur,VolumeGroups &volumeGroups,size_t &nbSkippedElement)
{std::map<std::string, VolumeCurves> legacyVolumeMap;for (cur = cur->xmlChildrenNode; cur != NULL; cur = cur->next) {if (xmlStrcmp(cur->name, (const xmlChar *)legacyVolumecollectionTag)) {//legacyVolumecollectionTag:volumescontinue;}const xmlNode *child = cur->xmlChildrenNode;for (; child != NULL; child = child->next) {if (!xmlStrcmp(child->name, (const xmlChar *)legacyVolumeTag)) {//legacyVolumeTag：volumestatus_t status = deserializeLegacyVolume(doc, child, legacyVolumeMap);//1if (status != NO_ERROR) {nbSkippedElement += 1;}}}}for (const auto &volumeMapIter : legacyVolumeMap) {//省略int indexMin = streamType >= AUDIO_STREAM_PUBLIC_CNT ? 0 : -1;int indexMax = streamType >= AUDIO_STREAM_PUBLIC_CNT ? 100 : -1;volumeGroups.push_back({ volumeMapIter.first, indexMin, indexMax, volumeMapIter.second });//2}return NO_ERROR;
}

注释1处，对volumes标签下的每个volume,调用deserializeLegacyVolume处理，解析的结果放在legacyVolumeMap这个容器中。注释2处将map容器的内容保存到volumeGroups中

deserializeLegacyVolume

//frameworks/av/services/audiopolicy/engine/config/src/EngineConfig.cpp
status_t deserializeLegacyVolume(_xmlDoc *doc, const _xmlNode *cur,std::map<std::string, VolumeCurves> &legacyVolumes)
{std::string streamTypeLiteral = getXmlAttribute(cur, "stream");//解析streamstd::string deviceCategoryLiteral = getXmlAttribute(cur, "deviceCategory");//解析deviceCategorystd::string referenceName = getXmlAttribute(cur, "ref");//引用其它文件的内容，解析过程是一样的const xmlNode *ref = NULL;if (!referenceName.empty()) {getReference(xmlDocGetRootElement(doc), ref, referenceName, legacyVolumecollectionTag);}CurvePoints curvePoints;for (const xmlNode *child = referenceName.empty() ?cur->xmlChildrenNode : ref->xmlChildrenNode; child != NULL; child = child->next) {if (!xmlStrcmp(child->name, (const xmlChar *)VolumeTraits::volumePointTag)) {xmlCharUnique pointXml(xmlNodeListGetString(doc, child->xmlChildrenNode, 1), xmlFree);std::vector<int> point;collectionFromString<DefaultTraits<int>>(reinterpret_cast<const char*>(pointXml.get()), point, ",");curvePoints.push_back({point[0], point[1]});//将解析point标签的结果保存在curvePoints中}}legacyVolumes[streamTypeLiteral].push_back({ deviceCategoryLiteral, curvePoints });//保存到legacyVolumes中return NO_ERROR;
}

以以下内容场景为例

<volumes><volume stream="AUDIO_STREAM_VOICE_CALL" deviceCategory="DEVICE_CATEGORY_HEADSET"><point>0,-4200</point><point>33,-2800</point><point>66,-1400</point><point>100,0</point></volume><volume stream="AUDIO_STREAM_VOICE_CALL" deviceCategory="DEVICE_CATEGORY_SPEAKER"><point>0,-2400</point><point>33,-1600</point><point>66,-800</point><point>100,0</point></volume><volume stream="AUDIO_STREAM_SYSTEM" deviceCategory="DEVICE_CATEGORY_HEADSET"><point>1,-3000</point><point>33,-2600</point><point>66,-2200</point><point>100,-1800</point></volume>//省略
<volumes>

最后的解析结果为

再来看一下图中各结构体的定义。源码路径：frameworks/av/services/audiopolicy/engine/config/include/EngineConfig.h

VolumeCurve

struct VolumeCurve {std::string deviceCategory;//volume标签下的deviceCategory字段CurvePoints curvePoints;//volume标签下的point字段的集合
};

VolumeGroup

struct VolumeGroup {std::string name;//来自于volume标签下的stream字段int indexMin;int indexMax;VolumeCurves volumeCurves;//VolumeCurve 的集合
};

2，遍历volumeGroups，结果保存到EngineBase的mVolumeGroups集合中

engineConfig::ParsingResult EngineBase::loadAudioPolicyEngineConfig()
{//省略for (auto &volumeConfig : result.parsedConfig->volumeGroups) {//遍历// save default volume config for streams not defined in configurationif (volumeConfig.name.compare("AUDIO_STREAM_MUSIC") == 0) {defaultVolumeConfig = volumeConfig;}if (volumeConfig.name.compare("AUDIO_STREAM_PATCH") == 0) {defaultSystemVolumeConfig = volumeConfig;}loadVolumeConfig(mVolumeGroups, volumeConfig);}//省略
}

loadVolumeConfig

engineConfig::ParsingResult EngineBase::loadAudioPolicyEngineConfig()
{auto loadVolumeConfig = [](auto &volumeGroups, auto &volumeConfig) {//省略sp<VolumeGroup> volumeGroup = new VolumeGroup(volumeConfig.name, volumeConfig.indexMin,volumeConfig.indexMax);//创建VolumeGroup对象volumeGroups[volumeGroup->getId()] = volumeGroup;//放入mVolumeGroups集合中for (auto &configCurve : volumeConfig.volumeCurves) {device_category deviceCat = DEVICE_CATEGORY_SPEAKER;//省略sp<VolumeCurve> curve = new VolumeCurve(deviceCat);//创建VolumeCurve对象for (auto &point : configCurve.curvePoints) {curve->add({point.index, point.attenuationInMb});}volumeGroup->add(curve);//添加到volumeGroup对象中}return volumeGroup;};

可以看出，最后，EngineBase的mVolumeGroups保存了配置文件中volume字段的信息。

3,解析ProductStrategies，保存在EngineBase的mProductStrategies集合中
在分析之前，需要先了解几个结构体
ProductStrategy

struct ProductStrategy {std::string name;AttributesGroups attributesGroups;
};

AttributesGroup

struct AttributesGroup {std::string name;audio_stream_type_t stream;std::string volumeGroup;AttributesVector attributesVect;//using AttributesVector = std::vector<audio_attributes_t>;
};

audio_attributes_t

typedef struct {audio_content_type_t content_type;audio_usage_t        usage;audio_source_t       source;audio_flags_mask_t   flags;char                 tags[AUDIO_ATTRIBUTES_TAGS_MAX_SIZE]; /* UTF8 */
} __attribute__((packed)) audio_attributes_t; // sent through Binder;

gDefaultEngineConfig

//frameworks/av/services/audiopolicy/engine/common/src/EngineDefaultConfig.h
const engineConfig::Config gDefaultEngineConfig = {1.0,gOrderedStrategies,{},{},{}
};

接着来看解析ProductStrategies的过程

engineConfig::ParsingResult EngineBase::loadAudioPolicyEngineConfig()
{//省略for (auto& strategyConfig : result.parsedConfig->productStrategies) {//1,,result.parsedConfig指向前面说的默认配置gDefaultEngineConfigsp<ProductStrategy> strategy = new ProductStrategy(strategyConfig.name);//1，创建ProductStrategy类对象for (const auto &group : strategyConfig.attributesGroups) {//遍历const auto &iter = std::find_if(begin(mVolumeGroups), end(mVolumeGroups),[&group](const auto &volumeGroup) {return group.volumeGroup == volumeGroup.second->getName(); });//3，根据名字查找sp<VolumeGroup> volumeGroup = nullptr;if (iter == end(mVolumeGroups)) {//没有找到的//省略} else {volumeGroup = iter->second;//找到了}addSupportedAttributesToGroup(group, volumeGroup, strategy);//4，将支持的属性添加到volumeGroup和strategy中}product_strategy_t strategyId = strategy->getId();mProductStrategies[strategyId] = strategy;//5,保存在mProductStrategies中
}

注释1处遍历的就是gOrderedStrategies 集合。注释2处，创建ProductStrategy对象时，传入的名字就是gOrderedStrategies中各元素的名字，如：“STRATEGY_PHONE”，“STRATEGY_SONIFICATION” 。注释3处，遍历前面得到的mVolumeGroups集合，根据名字进行匹配（用volumeGroup 的名字和“AUDIO_STREAM_VOICE_CALL”，“AUDIO_STREAM_BLUETOOTH_SCO”等进行匹配），找到匹配的volumeGroup 。注释4处将支持的属性添加到volumeGroup和strategy中，注释5处将该strategy保存到EngineBase的mProductStrategies集合中

//frameworks/av/services/audiopolicy/engine/common/src/EngineDefaultConfig.h
const engineConfig::ProductStrategies gOrderedStrategies = {{"STRATEGY_PHONE",{{"phone", AUDIO_STREAM_VOICE_CALL, "AUDIO_STREAM_VOICE_CALL",{{AUDIO_CONTENT_TYPE_UNKNOWN, AUDIO_USAGE_VOICE_COMMUNICATION, AUDIO_SOURCE_DEFAULT, 0,""}},},{"sco", AUDIO_STREAM_BLUETOOTH_SCO, "AUDIO_STREAM_BLUETOOTH_SCO",{{AUDIO_CONTENT_TYPE_UNKNOWN, AUDIO_USAGE_UNKNOWN, AUDIO_SOURCE_DEFAULT, AUDIO_FLAG_SCO,""}},}},},{"STRATEGY_SONIFICATION",{{"ring", AUDIO_STREAM_RING, "AUDIO_STREAM_RING",{{AUDIO_CONTENT_TYPE_UNKNOWN, AUDIO_USAGE_NOTIFICATION_TELEPHONY_RINGTONE,AUDIO_SOURCE_DEFAULT, 0, ""}}},{"alarm", AUDIO_STREAM_ALARM, "AUDIO_STREAM_ALARM",{{AUDIO_CONTENT_TYPE_UNKNOWN, AUDIO_USAGE_ALARM, AUDIO_SOURCE_DEFAULT, 0, ""}},}},},//省略

继续来看一下addSupportedAttributesToGroup函数

engineConfig::ParsingResult EngineBase::loadAudioPolicyEngineConfig()
{//省略auto addSupportedAttributesToGroup = [](auto &group, auto &volumeGroup, auto &strategy) {for (const auto &attr : group.attributesVect) {strategy->addAttributes({group.stream, volumeGroup->getId(), attr});//保存在strategy的mAttributesVector中volumeGroup->addSupportedAttributes(attr);//保存在volumeGroup中}};//省略
}

总结一下上面得到的结果

除了保存在ProductStrategy中之外，还会将attr保存到匹配的volumeGroup中（根据名字匹配）