前言
今天我们来分析下AudioPolicyManager的初始化过程，以及它是如何来解析audio_policy_configuration.xml的
正文
先来看看AudioPolicyManager的初始化过程吧，说到AudioPolicyManager那么就得先说AudioPolicyService。
我们知道开机上电后会先执行init rc，audioserver就是通过init rc启动起来的，在audioserver的man函数中我摘录了几行代码
AudioFlinger::instantiate();
AudioPolicyService::instantiate();AudioPolicyService应运而生，故事就从这里开始吧，话说 AudioPolicyService::instantiate()，由于我binder学的不是很好，这里就简单说下因为AudioPolicyService :public BinderService。而BinderService的instantiate如下
static void instantiate() { publish(); }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);
}明白了instantiate的过程，其实就是向serviceManager中注册服务。我们继续看
void AudioPolicyService::onFirstRef()
{
{
Mutex::Autolock _l(mLock);
// start audio commands thread
mAudioCommandThread = new AudioCommandThread(String8("ApmAudio"), this);
// start output activity command thread
mOutputCommandThread = new AudioCommandThread(String8("ApmOutput"), this);
mAudioPolicyClient = new AudioPolicyClient(this);
mAudioPolicyManager = createAudioPolicyManager(mAudioPolicyClient);
}
// load audio processing modules
sp<AudioPolicyEffects>audioPolicyEffects = new AudioPolicyEffects();
{
Mutex::Autolock _l(mLock);
mAudioPolicyEffects = audioPolicyEffects;
}
mUidPolicy = new UidPolicy(this);
mUidPolicy->registerSelf();
mSensorPrivacyPolicy = new SensorPrivacyPolicy(this);
mSensorPrivacyPolicy->registerSelf();
}找到createAudioPolicyManager，来初始化主角 AudioPolicyManager
extern "C" AudioPolicyInterface* createAudioPolicyManager(
AudioPolicyClientInterface *clientInterface)
{
return new AudioPolicyManager(clientInterface);
}而AudioPolicyManager一般分为默认的和厂商定制的，厂商定制的一般放在hal下，但今天我们分析的default的位于frameworks/av/services/audiopolicy/managerdefault/AudioPolicyManager.cpp路径下。继续看看AudioPolicyManager的初始化
AudioPolicyManager::AudioPolicyManager(AudioPolicyClientInterface *clientInterface)
: AudioPolicyManager(clientInterface, false /*forTesting*/)
{
//加载audio_policy_configuration.xml
loadConfig();
//数据初始化
initialize();
}其中又加载了这个
AudioPolicyManager::AudioPolicyManager(AudioPolicyClientInterface *clientInterface,
bool /*forTesting*/)
:
mUidCached(AID_AUDIOSERVER), // no need to call getuid(), there's only one of us running.
mpClientInterface(clientInterface),
mLimitRingtoneVolume(false), mLastVoiceVolume(-1.0f),
mA2dpSuspended(false),
mConfig(mHwModulesAll, mAvailableOutputDevices, mAvailableInputDevices, mDefaultOutputDevice),
mAudioPortGeneration(1),
mBeaconMuteRefCount(0),
mBeaconPlayingRefCount(0),
mBeaconMuted(false),
mTtsOutputAvailable(false),
mMasterMono(false),
mMusicEffectOutput(AUDIO_IO_HANDLE_NONE)
{
}先分析 loadConfig()
void AudioPolicyManager::loadConfig() {
//解析audio_policy_configuration.xml
if (deserializeAudioPolicyXmlConfig(getConfig()) != NO_ERROR) {
ALOGE("could not load audio policy configuration file, setting defaults");
//设置默认值
getConfig().setDefault();
}
}这里的getConfig就是定义的AudioPolicyConfig
AudioPolicyConfig mConfig继续分析deserializeAudioPolicyXmlConfig
static status_t deserializeAudioPolicyXmlConfig(AudioPolicyConfig &config) {
char audioPolicyXmlConfigFile[AUDIO_POLICY_XML_CONFIG_FILE_PATH_MAX_LENGTH];
std::vector<const char*> fileNames;
status_t ret;
if (property_get_bool("ro.bluetooth.a2dp_offload.supported", false)) {
if (property_get_bool("persist.bluetooth.bluetooth_audio_hal.disabled", false) &&
property_get_bool("persist.bluetooth.a2dp_offload.disabled", false)) {
// Both BluetoothAudio@2.0 and BluetoothA2dp@1.0 (Offlaod) are disabled, and uses
// the legacy hardware module for A2DP and hearing aid.
fileNames.push_back(AUDIO_POLICY_BLUETOOTH_LEGACY_HAL_XML_CONFIG_FILE_NAME);
} else if (property_get_bool("persist.bluetooth.a2dp_offload.disabled", false)) {
// A2DP offload supported but disabled: try to use special XML file
fileNames.push_back(AUDIO_POLICY_A2DP_OFFLOAD_DISABLED_XML_CONFIG_FILE_NAME);
}
} else if (property_get_bool("persist.bluetooth.bluetooth_audio_hal.disabled", false)) {
fileNames.push_back(AUDIO_POLICY_BLUETOOTH_LEGACY_HAL_XML_CONFIG_FILE_NAME);
}
fileNames.push_back(AUDIO_POLICY_XML_CONFIG_FILE_NAME);
for (const char* fileName : fileNames) {
for (int i = 0; i < kConfigLocationListSize; i++) {
snprintf(audioPolicyXmlConfigFile, sizeof(audioPolicyXmlConfigFile),
"%s/%s", kConfigLocationList[i], fileName);
// 解析 xml
ret = deserializeAudioPolicyFile(audioPolicyXmlConfigFile, &config);
if (ret == NO_ERROR) {
//最后把路径保存上：/vendor/etc/audio_policy_configuration.xml
config.setSource(audioPolicyXmlConfigFile);
return ret;
}
}
}
return ret;
}这里把要解析的xml文件名放到了vector中，最终通过遍历逐一解析，关于A2DP相关的prop的默认都是false，这里就暂不说了，这里说下 fileNames.push_back(AUDIO_POLICY_XML_CONFIG_FILE_NAME)（android7.0之后就使用了这个xml）
#define AUDIO_POLICY_XML_CONFIG_FILE_NAME "audio_policy_configuration.xml"然后抛砖引玉的就到了今天的最终主角，deserializeAudioPolicyFile位置：frameworks/av/services/audiopolicy/common/managerdefinitions/src/Serializer.cpp
status_t deserializeAudioPolicyFile(const char *fileName, AudioPolicyConfig *config)
{
PolicySerializer serializer;
return serializer.deserialize(fileName, config);
}
}这是一个解析的模板类，xml解析我们就不说了，主要说下赋值过程。先看下xml
，一般厂商也会定制这个xml到指定目录，但这里就分析frameworks/av/services/audiopolicy/config/audio_policy_configuration.xml
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<!-- Copyright (C) 2019 The Android Open Source Project
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
-->
<audioPolicyConfiguration version="1.0" xmlns:xi="http://www.w3.org/2001/XInclude">
<!-- version section contains a “version” tag in the form “major.minor” e.g version=”1.0” -->
<!-- Global configuration Decalaration -->
<globalConfiguration speaker_drc_enabled="true"/>
<!-- Modules section:
There is one section per audio HW module present on the platform.
Each module section will contains two mandatory tags for audio HAL “halVersion” and “name”.
The module names are the same as in current .conf file:
“primary”, “A2DP”, “remote_submix”, “USB”
Each module will contain the following sections:
“devicePorts”: a list of device descriptors for all input and output devices accessible via this
module.
This contains both permanently attached devices and removable devices.
“mixPorts”: listing all output and input streams exposed by the audio HAL
“routes”: list of possible connections between input and output devices or between stream and
devices.
"route": is defined by an attribute:
-"type": <mux|mix> means all sources are mutual exclusive (mux) or can be mixed (mix)
-"sink": the sink involved in this route
-"sources": all the sources than can be connected to the sink via vis route
“attachedDevices”: permanently attached devices.
The attachedDevices section is a list of devices names. The names correspond to device names
defined in <devicePorts> section.
“defaultOutputDevice”: device to be used by default when no policy rule applies
-->
<modules>
<!-- Primary Audio HAL -->
<module name="primary" halVersion="3.0">
<attachedDevices>
<item>Speaker</item>
<item>Built-In Mic</item>
<item>Built-In Back Mic</item>
</attachedDevices>
<defaultOutputDevice>Speaker</defaultOutputDevice>
<mixPorts>
<mixPort name="primary output" role="source" flags="AUDIO_OUTPUT_FLAG_PRIMARY">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/>
</mixPort>
<mixPort name="deep_buffer" role="source"
flags="AUDIO_OUTPUT_FLAG_DEEP_BUFFER">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/>
</mixPort>
<mixPort name="compressed_offload" role="source"
flags="AUDIO_OUTPUT_FLAG_DIRECT|AUDIO_OUTPUT_FLAG_COMPRESS_OFFLOAD|AUDIO_OUTPUT_FLAG_NON_BLOCKING">
<profile name="" format="AUDIO_FORMAT_MP3"
samplingRates="8000,11025,12000,16000,22050,24000,32000,44100,48000"
channelMasks="AUDIO_CHANNEL_OUT_STEREO,AUDIO_CHANNEL_OUT_MONO"/>
<profile name="" format="AUDIO_FORMAT_AAC"
samplingRates="8000,11025,12000,16000,22050,24000,32000,44100,48000"
channelMasks="AUDIO_CHANNEL_OUT_STEREO,AUDIO_CHANNEL_OUT_MONO"/>
<profile name="" format="AUDIO_FORMAT_AAC_LC"
samplingRates="8000,11025,12000,16000,22050,24000,32000,44100,48000"
channelMasks="AUDIO_CHANNEL_OUT_STEREO,AUDIO_CHANNEL_OUT_MONO"/>
</mixPort>
<mixPort name="voice_tx" role="source">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_OUT_MONO"/>
</mixPort>
<mixPort name="primary input" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,11025,12000,16000,22050,24000,32000,44100,48000"
channelMasks="AUDIO_CHANNEL_IN_MONO,AUDIO_CHANNEL_IN_STEREO,AUDIO_CHANNEL_IN_FRONT_BACK"/>
</mixPort>
<mixPort name="voice_rx" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_IN_MONO"/>
</mixPort>
</mixPorts>
<devicePorts>
<!-- Output devices declaration, i.e. Sink DEVICE PORT -->
<devicePort tagName="Earpiece" type="AUDIO_DEVICE_OUT_EARPIECE" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="48000" channelMasks="AUDIO_CHANNEL_IN_MONO"/>
</devicePort>
<devicePort tagName="Speaker" role="sink" type="AUDIO_DEVICE_OUT_SPEAKER" address="">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/>
<gains>
<gain name="gain_1" mode="AUDIO_GAIN_MODE_JOINT"
minValueMB="-8400"
maxValueMB="4000"
defaultValueMB="0"
stepValueMB="100"/>
</gains>
</devicePort>
<devicePort tagName="Wired Headset" type="AUDIO_DEVICE_OUT_WIRED_HEADSET" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/>
</devicePort>
<devicePort tagName="Wired Headphones" type="AUDIO_DEVICE_OUT_WIRED_HEADPHONE" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/>
</devicePort>
<devicePort tagName="BT SCO" type="AUDIO_DEVICE_OUT_BLUETOOTH_SCO" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_OUT_MONO"/>
</devicePort>
<devicePort tagName="BT SCO Headset" type="AUDIO_DEVICE_OUT_BLUETOOTH_SCO_HEADSET" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_OUT_MONO"/>
</devicePort>
<devicePort tagName="BT SCO Car Kit" type="AUDIO_DEVICE_OUT_BLUETOOTH_SCO_CARKIT" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_OUT_MONO"/>
</devicePort>
<devicePort tagName="Telephony Tx" type="AUDIO_DEVICE_OUT_TELEPHONY_TX" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_OUT_MONO"/>
</devicePort>
<devicePort tagName="Built-In Mic" type="AUDIO_DEVICE_IN_BUILTIN_MIC" role="source">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,11025,12000,16000,22050,24000,32000,44100,48000"
channelMasks="AUDIO_CHANNEL_IN_MONO,AUDIO_CHANNEL_IN_STEREO,AUDIO_CHANNEL_IN_FRONT_BACK"/>
</devicePort>
<devicePort tagName="Built-In Back Mic" type="AUDIO_DEVICE_IN_BACK_MIC" role="source">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,11025,12000,16000,22050,24000,32000,44100,48000"
channelMasks="AUDIO_CHANNEL_IN_MONO,AUDIO_CHANNEL_IN_STEREO,AUDIO_CHANNEL_IN_FRONT_BACK"/>
</devicePort>
<devicePort tagName="Wired Headset Mic" type="AUDIO_DEVICE_IN_WIRED_HEADSET" role="source">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,11025,12000,16000,22050,24000,32000,44100,48000"
channelMasks="AUDIO_CHANNEL_IN_MONO,AUDIO_CHANNEL_IN_STEREO,AUDIO_CHANNEL_IN_FRONT_BACK"/>
</devicePort>
<devicePort tagName="BT SCO Headset Mic" type="AUDIO_DEVICE_IN_BLUETOOTH_SCO_HEADSET" role="source">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_IN_MONO"/>
</devicePort>
<devicePort tagName="Telephony Rx" type="AUDIO_DEVICE_IN_TELEPHONY_RX" role="source">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_IN_MONO"/>
</devicePort>
</devicePorts>
<!-- route declaration, i.e. list all available sources for a given sink -->
<routes>
<route type="mix" sink="Earpiece"
sources="primary output,deep_buffer,BT SCO Headset Mic"/>
<route type="mix" sink="Speaker"
sources="primary output,deep_buffer,compressed_offload,BT SCO Headset Mic,Telephony Rx"/>
<route type="mix" sink="Wired Headset"
sources="primary output,deep_buffer,compressed_offload,BT SCO Headset Mic,Telephony Rx"/>
<route type="mix" sink="Wired Headphones"
sources="primary output,deep_buffer,compressed_offload,BT SCO Headset Mic,Telephony Rx"/>
<route type="mix" sink="primary input"
sources="Built-In Mic,Built-In Back Mic,Wired Headset Mic,BT SCO Headset Mic"/>
<route type="mix" sink="Telephony Tx"
sources="Built-In Mic,Built-In Back Mic,Wired Headset Mic,BT SCO Headset Mic, voice_tx"/>
<route type="mix" sink="voice_rx"
sources="Telephony Rx"/>
</routes>
</module>
<!-- A2dp Input Audio HAL -->
<xi:include href="a2dp_in_audio_policy_configuration.xml"/>
<!-- Usb Audio HAL -->
<xi:include href="usb_audio_policy_configuration.xml"/>
<!-- Remote Submix Audio HAL -->
<xi:include href="r_submix_audio_policy_configuration.xml"/>
<!-- Bluetooth Audio HAL -->
<xi:include href="bluetooth_audio_policy_configuration.xml"/>
<!-- MSD Audio HAL (optional) -->
<xi:include href="msd_audio_policy_configuration.xml"/>
</modules>
<!-- End of Modules section -->
<!-- Volume section:
IMPORTANT NOTE: Volume tables have been moved to engine configuration.
Keep it here for legacy.
Engine will fallback on these files if none are provided by engine.
-->
<xi:include href="audio_policy_volumes.xml"/>
<xi:include href="default_volume_tables.xml"/>
<!-- End of Volume section -->
<!-- Surround Sound configuration -->
<xi:include href="surround_sound_configuration_5_0.xml"/>
<!-- End of Surround Sound configuration -->
</audioPolicyConfiguration>我们来看看如何把xml里这些标签解析出来初始化的。也就是initialize()，代码太长我们还是一点一点分析吧
audio_policy::EngineInstance *engineInstance = audio_policy::EngineInstance::getInstance();
if (!engineInstance) {
ALOGE("%s: Could not get an instance of policy engine", __FUNCTION__);
return NO_INIT;
}
// Retrieve the Policy Manager Interface
mEngine = engineInstance->queryInterface<AudioPolicyManagerInterface>();
if (mEngine == NULL) {
ALOGE("%s: Failed to get Policy Engine Interface", __FUNCTION__);
return NO_INIT;
}
mEngine->setObserver(this);
status_t status = mEngine->initCheck();
if (status != NO_ERROR) {
LOG_FATAL("Policy engine not initialized(err=%d)", status);
return status;
}这块代码主要初始化Engine ，Engine 主要做strategy用的，后面再细说。
for (const auto& hwModule : mHwModulesAll) {
hwModule->setHandle(mpClientInterface->loadHwModule(hwModule->getName()));
if (hwModule->getHandle() == AUDIO_MODULE_HANDLE_NONE) {
ALOGW("could not open HW module %s", hwModule->getName());
continue;
}
mHwModules.push_back(hwModule);一个很长的for循环，我们从头开始梳理，首先涉及了mHwModulesAl
mHwModulesAll
类型：HwModuleCollection: public Vector<sp< HwModule > >
还记得通过AudioPolicyManager的初始化时mConfig(mHwModulesAll, mAvailableOutputDevices, mAvailableInputDevices, mDefaultOutputDevice)，mHwModulesAll，其实它对应的就是 < module name=“primary” halVersion=“3.0”>包括那几个include的集合，仅参照本文是 primary 、a2dp、usb、r_submix、bluetooth和msd。
那么我们回到initialize()中继续往下看，又有一个mHwModules
mHwModules
类型：HwModuleCollection: public Vector<sp< HwModule > >
比起mHwModulesAll，mHwModules多初始化了一个handle，我们继续看
for (const auto& outProfile : hwModule->getOutputProfiles()) {
//canOpenNewIo默认 true（maxOpenCount(1),curOpenCount(0)）
if (!outProfile->canOpenNewIo()) {
ALOGE("Invalid Output profile max open count %u for profile %s",
outProfile->maxOpenCount, outProfile->getTagName().c_str());
continue;
}
if (!outProfile->hasSupportedDevices()) {
ALOGW("Output profile contains no device on module %s", hwModule->getName());
continue;
}
if ((outProfile->getFlags() & AUDIO_OUTPUT_FLAG_TTS) != 0) {
mTtsOutputAvailable = true;
}
if ((outProfile->getFlags() & AUDIO_OUTPUT_FLAG_DIRECT) != 0) {
continue;
}
const DeviceVector &supportedDevices = outProfile->getSupportedDevices();
//在supportdevice中过滤出availablededevice
DeviceVector availProfileDevices = supportedDevices.filter(mAvailableOutputDevices);
sp<DeviceDescriptor> supportedDevice = 0;
//过滤完如果包含defaultdevice 则使用defaultOutputDevice
if (supportedDevices.contains(mDefaultOutputDevice)) {
supportedDevice = mDefaultOutputDevice;
} else {
// choose first device present in profile's SupportedDevices also part of
// mAvailableOutputDevices.
if (availProfileDevices.isEmpty()) {
continue;
}
// 如果不包含mDefaultOutputDevice则取availProfileDevices的第一个元素
supportedDevice = availProfileDevices.itemAt(0);
}
// 个人觉得这个判断有点奇怪，supportedDevice就是从mAvailableOutputDevices里过滤出来的，这里不如直接来个判null更好理解
if (!mAvailableOutputDevices.contains(supportedDevice)) {
continue;
}
//构建我们outputDesc，也就是我们要输出声音的通过
sp<SwAudioOutputDescriptor> outputDesc = new SwAudioOutputDescriptor(outProfile,
mpClientInterface);
audio_io_handle_t output = AUDIO_IO_HANDLE_NONE;
//最终通过audioflinger打开一个通道，这个通道的output在audioflinger中会被重新计算一个值并赋值给它，而它对应的device（supportedDevice）
// 又会映射到audio hal下对应真正的device
status_t status = outputDesc->open(nullptr, DeviceVector(supportedDevice),
AUDIO_STREAM_DEFAULT,
AUDIO_OUTPUT_FLAG_NONE, &output);
if (status != NO_ERROR) {
ALOGW("Cannot open output stream for devices %s on hw module %s",
supportedDevice->toString().c_str(), hwModule->getName());
continue;
}
for (const auto &device : availProfileDevices) {
// give a valid ID to an attached device once confirmed it is reachable
if (!device->isAttached()) {
device->attach(hwModule);
}
}
//mixPort中falg为AUDIO_OUTPUT_FLAG_PRIMARY赋值给了mPrimaryOutput
if (mPrimaryOutput == 0 &&
outProfile->getFlags() & AUDIO_OUTPUT_FLAG_PRIMARY) {
mPrimaryOutput = outputDesc;
}
//将output和outputDesc一起放到了mOutputs中统一维护
addOutput(output, outputDesc);
//这个后续在说
setOutputDevices(outputDesc,
DeviceVector(supportedDevice),
true,
0,
NULL);
}看的头生疼，首先hwModule->getOutputProfiles()其实拿到的是HwModule中的mOutputProfiles
mOutputProfiles
类型： Vector<sp< IOProfile> > OutputProfileCollection而IOProfile又继承了AudioPort，我们可以简单理解一个outputProfile其实就是一个IOProfile也就一个是 AudioPort。他是解析 < mixPort>标签来的，并根据 role="source"还是 role="sink"决add到mOutputProfiles还是add到mInputProfiles中，因此我们粗暴的认为一个outProfile就是一个mixPort（ role="source"的mixPort）继续往下看outProfile->hasSupportedDevices()，函数原型
!mSupportedDevices.isEmpty()mSupportedDevices
类型：DeviceVector : public SortedVector<sp< DeviceDescriptor> >而DeviceDescriptor : public AudioPort, public AudioPortConfig，那么mSupportedDevices怎么来的呢？这块就涉及到< route >标签的解析了，route的解析相比mixPort与device标签的解析要复杂一点，首先一个route一定包含一个sink和一组source就像下面这样
<route type="mix" sink="Earpiece"
sources="primary output,deep_buffer,BT SCO Headset Mic"/>其次route的sink可以是device，也可以是一个mixPort，route里的source也是一样。然后一个sink对应一个route（一般都是这样的），一个source可以对应多个route。那么SupportedDevices是怎么来的呢？先遍历mixport找到role=“sink”（即inputProfile）然后在遍历route找到route中sink与inputProfile一样的那条route，这样我们就定位到此route下的sources，然后把sources里是device的source过滤出来就组成了inputProfile的SupportedDevices。然后再看outputProfile的SupportedDevices。也是先找mixport找到role=“source”（即outputProfile）然后遍历route，在每个route的sources中找name与mixport中的outputProfile相等的，定位到对应route后，然后把此route的sink存起来，因为一个source对应多个route，那么存起来的route的sink也就又是一个集合，然后也是过滤出是device的组成了outputProfile的SupportedDevices。举个例子比如我们primary output它的SupportedDevices就是Earpiece、Speaker、Wired Headset和Wired Headphones，primary input的SupportedDevices是Built-In Mic、Built-In Back Mic、Wired Headset Mic、BT SCO Headset Mic。结合上边的xml理解起来就容易多了。继续看又有一个mAvailableOutputDevices，
mAvailableInputDevices
类型 ：DeviceVector : public SortedVector<sp< DeviceDescriptor> >
mAvailableOutputDevices和mAvailableInputDevices主要对应xml中 < attachedDevices>标签中的元素针，对本文xml主要有
<attachedDevices>
<item>Speaker</item>
<item>Built-In Mic</item>
<item>Built-In Back Mic</item>
</attachedDevices>具体的流程就是先找到item然后在找对应device根据type计算出是outdevice还是inputdevice，这个计算方式也简单，因为作为inputdevice都是与BIT_IN | 运算的，因此判断的逻辑就是用device的type和BIT_IN 做&运算，这样inputdevice的结果是1，outputdevice的结果是0，在把区分这些放进vector中就成了mAvailableOutputDevices和mAvailableInputDevices。其实我们也可以参照< devicePort >中role="source"即为input的device用，role="source"为output的device。如下源码位置定义了所有的device的type
system/media/audio/include/system/audio-base.h
然后在SupportedDevices中过滤出mAvailableInputDevices
mDefaultOutputDevice
类型： sp< DeviceDescriptor>
这个很好理解对应xml中
<defaultOutputDevice>Speaker</defaultOutputDevice>这块逻辑就是从supportDevice中过滤出availableDevice，如果这里有defaultDevice就用default如果没有，则在过滤完的devices中选第一个来构造我们的outputDesc
outputDesc
类型：SwAudioOutputDescriptor: public AudioOutputDescriptor，
AudioOutputDescriptor: public AudioPortConfig, public AudioIODescriptorInterface, public ClientMapHandler< TrackClientDescriptor>
这个就是输出通道的描述符，这里包含了对应mixPort的全部信息。然后将output作为key，outputDesc作为value存入mOutputs中统一管理。
mOutputs
类型：SwAudioOutputCollection : public DefaultKeyedVector< audio_io_handle_t, sp< SwAudioOutputDescriptor> >
真是层层递进呀，那mOutputs到这里我们也知道是是什么了。
initialize()后续代码分析input的原理跟out的相同，这里就不多说了。
总结
关于AudioPolicyManager的audio_policy_configuration.xml解析，我们主要分析的是解析module，具体又分了 mixPort devicePort和route三部分。其中route理解起来可能会复杂一些。但audio_policy_configuration.xml解析这个很重要，因为所有的内容都是从这个XML中解析来的，而且这个XML的解析又涉及很多类，需要耐心去分析。
