前言
之前通过代码说了 audio_policy_configuration 的解析过程，代码确实需要一定耐心来看，那么今天结合具体 xml 再来说明下 audio_policy_configuration 的解析过程
正文
audio_policy_configuration.xml 位于 frameworks/av/services/audiopolicy/config/ 目录下
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<!-- Copyright (C) 2015 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 -->
<!-- 从 module 标签开始，module 即对应的 HwModule，对应初始化 module 的 name 和 halVersion，解析完 module 会通过 AudioPolicyConfig 的 -->
<module name="primary" halVersion="3.0">
<!--attachedDevices 是最后解析的，通过 AudioPolicyConfig 赋值 mAvailableOutputDevices(DeviceDescriptor 集合) 和 mAvailableInputDevices(DeviceDescriptor 集合) -->
<attachedDevices>
<item>Speaker</item>
<item>Built-In Mic</item>
<item>Built-In Back Mic</item>
</attachedDevices>
<!--defaultOutputDevice 也是最后解析的，通过 AudioPolicyConfig 赋值 mDefaultOutputDevices(DeviceDescriptor) -->
<defaultOutputDevice>Speaker</defaultOutputDevice>
<!-- 找到 module 标签后便首先开始解析 mixport，将所有的 mixport 作为集合赋值给 module 下的 mInputProfiles(IOProfile 集合) 和 mOutputProfiles(IOProfile 集合)
和 mPorts(AudioPort 集合)-->
<mixPorts>
<!-- 每一个 mixrort 就是一个 IOProfile 即 AudioPort，对应初始化 name 和 falgs 属性，以及根据 role 属性判断是加入 mInputProfiles 或 mOutputProfiles 中
将所有的 profile 作为集合赋值给 mixPort 下的 mProfiles-->
<mixPort name="primary output" role="source" flags="AUDIO_OUTPUT_FLAG_PRIMARY">
<!-- 每一个 profile 就是一个 IOProfile 即 AudioProfile，对应初始化 format samplingRates 和 channelMasks-->
<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>
<!-- 解析 devicePort 标签通过 HwModule 初始化 mDeclaredDevices(DeviceDescriptor 集合) 和 mPorts(AudioPort 集合)-->
<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 -->
<!-- 解析 route 标签赋值给 HwModule 的 mRoutes(AudioRoute 集合) 并对应初始化 mixport 即 IOProfile 的 mSupportedDevices，这个对应规则可以参照
[Android9.0AudioPolicy 之 audio_policy_configuration.xml 解析 ( 一)][1]-->
<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="Telephony Tx"
sources="voice_tx"/>
<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"/>
<route type="mix" sink="voice_rx"
sources="Telephony Rx"/>
</routes>
</module>
<!-- HDMI Audio HAL -->
<module description="HDMI Audio HAL" name="hdmi" version="2.0">
<mixPorts>
<mixPort name="hdmi output" role="source">
<profile name=""format="AUDIO_FORMAT_PCM_16_BIT"samplingRates="48000"/>
</mixPort>
</mixPorts>
<devicePorts>
<devicePort tagName="HDMI Out" type="AUDIO_DEVICE_OUT_AUX_DIGITAL" role="sink">
<profile name=""format="AUDIO_FORMAT_PCM_16_BIT"samplingRates="48000"channelMasks="AUDIO_CHANNEL_OUT_STEREO"/>
</devicePort>
</devicePorts>
<routes>
<route type="mix" sink="HDMI Out"
sources="hdmi output"/>
</routes>
</module>
<!-- A2dp Audio HAL -->
<xi:include href="a2dp_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"/>
</modules>
<!-- End of Modules section -->
<!-- Volume section -->
<xi:include href="audio_policy_volumes.xml"/>
<xi:include href="default_volume_tables.xml"/>
<!-- End of Volume section -->
</audioPolicyConfiguration>
总结
这样整个 policy 的 xml 就解析完成了。有点需要注意这里有个
<!-- A2dp Audio HAL -->
<xi:include href="a2dp_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"/> 其实在解析时这些 include 的文件也会放到一起解析的，下一张分享下解析完 audio_policy_configuration 后 AudioPolicyManager 又做了什么，
如有任何问题，欢迎指正