Android 车载应用开发与分析（4）- 编写基于AIDL 的 SDK

Android11+ AIDL：专为提升应用性能而生！

公众号: Android系统攻城狮

发布时间: 1970-01-01 08:33:43

原文链接: https://mp.weixin.qq.com/s?__biz=MzU2NTI3NDI5MQ==&mid=2247485515&idx=1&sn=518a69ed57f50e2a6675a8bc0410df2d&chksm=fcbf7b97cbc8f2810e7cbb013767378563937226c743baca48d671b434fc55d195ea9948b28a

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每日充电：OS+MultiMedia学习之旅

1.前言

学习理念：一次理解一个知识点

难度：★★★****★**☆**********

源码环境：Android 12

硬件环境：SDM845

阅读时间：1.5分钟

接着上一篇Android HAL发展历程：探索HAL到HIDL四个阶段的演进过程文章，我们已经介绍了HAL到HIDL发展的历程。

Android11版本开始，AIDL引入实现HAL同样的功能，可以调用HAL，也可以直接和内核驱动通信。

下面看一下HIDL和AIDL通信过程，AIDL比起传统通信方式有哪些优点？

接着实现一个AIDL实现用例，读者可以和上一篇文章HIDL实现服务做一个对比，看看它们之间的差异在哪里？

1.先看一个HIDL模式通信路线图：

图一

2.再看一个AIDL模式通信路线图：

图二

通过图一和图二比较，就能知道谷歌为什么要在Android 10以后逐渐去除HIDL通信模式。

AIDL优势很明显，它在应用端直接获取AIDL Service后，可以直接给AIDL的服务端发送IPC通信，在服务端直接调用HAL的API或者直接通过open("/dev/xxx")与驱动通信。

与传统的AIDL比起来，中间少了两三个通信环节，效率会显著提升。

下面写一个AIDL使用Binder IPC通信的例子。

2.AIDL客户端

1.创建aidl接口

# mkdir -p hardware/interfaces/invcase/aidl/android/hardware/invcase # emacs IInvcase.aidl package android.hardware.invcase; @VintfStability interface IInvcase { String getChars(); void putChars(in String msg); }

2.创建Android.bp

# cd hardware/interfaces/invcase/aidl # emacs Android.bp aidl_interface { name: "android.hardware.invcase", vendor: true, srcs: ["android/hardware/invcase/*.aidl"], stability: "vintf", owner: "vqtrong", backend: { cpp: { enabled: false, }, java: { sdk_version: "module_current", }, }, }

**3.编译与配置**

1.执行以下命令：编译报错# mmm hardware/interfaces/invcase/aidl 2.执行以下操作后，再编译aidl# m android.hardware.invcase-update-api -j12 3.再编译aidl# mmm hardware/interfaces/invcase/aidl 4.将invacase模块配置编译到系统# emacs build/make/target/product/base_vendor.mkPRODUCT_PACKAGES += android.hardware.invcase

到此AIDL客户端创建完成，接下来创建AIDL Server端。

3.AIDL Server端

1.AIDL对应Server端头文件实现

# emacs hardware/interfaces/invcase/aidl/default/Invcase.h #pragma once #include <aidl/android/hardware/invcase/BnInvcase.h> namespace aidl { namespace android { namespace hardware { namespace invcase { class Invcase : public BnInvcase { public: //AIDL：String getChars(); ndk::ScopedAStatus getChars(std::string* _aidl_return); //AIDL：void putChars(in String msg); ndk::ScopedAStatus putChars(const std::string& in_msg); }; } } } }

2.AIDL对应Server端c++实现

# emacs hardware/interfaces/invcase/aidl/default/Invcase.cpp #define LOG_TAG "Invcase" #include <utils/Log.h> #include <iostream> #include <fstream> #include "Invcase.h" namespace aidl { namespace android { namespace hardware { namespace invcase { //String getChars(); ndk::ScopedAStatus Invcase::getChars(__unused std::string* _aidl_return) { std::string str = "I am from HAL layer"; *_aidl_return = str; ALOGE("%s, %s(), line = %d, HAL: send_to_app: %s",__FILE__,__FUNCTION__,__LINE__,str.c_str()); return ndk::ScopedAStatus::ok(); } //void putChars(in String msg); ndk::ScopedAStatus Invcase::putChars(__unused const std::string& in_msg) { ALOGE("%s, %s(), line = %d, HAL: recive_from_app = %s",__FILE__,__FUNCTION__,__LINE__,in_msg.c_str()); return ndk::ScopedAStatus::ok(); } } } } }

在Invcase::getChars和Invcase::putChars函数中添加对驱动程序的访问即可。在这里我只是写了打印语句。

到这里AIDL的Server端也实现完成，我们要将实现的内容注册成一个AIDL服务，可以通过Binder完成IPC通信。

4.创建AIDL IPC通信

1.注册AIDL服务

# emacs hardware/interfaces/invcase/aidl/default/service.cpp #define LOG_TAG "Invcase" #include <android-base/logging.h> #include <android/binder_manager.h> #include <android/binder_process.h> #include <binder/ProcessState.h> #include <binder/IServiceManager.h> #include "Invcase.h" using aidl::android::hardware::invcase::Invcase; using std::string_literals::operator""s; int main() { android::ProcessState::initWithDriver("/dev/vndbinder"); ABinderProcess_setThreadPoolMaxThreadCount(0); ABinderProcess_startThreadPool(); std::shared_ptr<Invcase> invcase = ndk::SharedRefBase::make<Invcase>(); const std::string name = Invcase::descriptor + "/default"s; ALOGE("%s, %s(), line = %d, descriptor = %s, name = %s,",__FILE__,__FUNCTION__,__LINE__,Invcase::descriptor,name.c_str()); if(AServiceManager_addService(invcase->asBinder().get(), name.c_str()) != STATUS_OK) { ALOGE("Failed to register IInvcase service"); return -1; } ALOGE("IInvcase service starts to join service pool"); ABinderProcess_joinThreadPool(); return EXIT_FAILURE; }

其中name就是AIDL服务名，它启动起来以后，我们通过service命令看到它。

**2.创建Android.bp**

# emacs hardware/interfaces/invcase/aidl/default/Android.bp cc_binary { name: "android.hardware.invcase-service", vendor: true, relative_install_path: "hw", init_rc: ["android.hardware.invcase-service.rc"], vintf_fragments: ["android.hardware.invcase-service.xml"], srcs: [ "Invcase.cpp", "service.cpp", ], cflags: [ "-Wall", "-Werror", ], shared_libs: [ "libbase", "liblog", "libhardware", "libbinder_ndk", "libbinder", "libutils", "android.hardware.invcase-V1-ndk_platform", ], }

****3.编译、添加到系统设置****

1.编译 # mmm hardware/interfaces/invcase/aidl/default # adb push out/target/product/xxx/vendor/lib64/android.hardware.invcase-V1-ndk_platform.so /vendor/lib64 # adb push out/target/product/xxx/vendor/bin/hw/android.hardware.invcase-service /vendor/bin/hw 2.将hal服务添加到系统编译 # emacs build/make/target/product/base_vendor.mk PRODUCT_PACKAGES += \ android.hardware.invcase \ android.hardware.invcase-service \ 3.将hal服务增加到init.rc并启动 # emacs hardware/interfaces/invcase/aidl/default/android.hardware.invcase-service.rc service android.hardware.invcase-service /vendor/bin/hw/android.hardware.invcase-service interface aidl android.hardware.invcase.IInvcase/default class hal user system group system .对外公开AIDL接口 # emacs hardware/interfaces/invcase/aidl/default/android.hardware.invcase-service.xml <manifest version="1.0" type="device"> <hal format="aidl"> <name>android.hardware.invcase</name> <version>1</version> <fqname>IInvcase/default</fqname> </hal> </manifest> 5..将新的包增加到框架兼容性矩阵中 # emacs hardware/interfaces/compatibility_matrices/compatibility_matrix.6.xml # emacs hardware/interfaces/compatibility_matrices/compatibility_matrix.current.xml <hal format="aidl" optional="true"> <name>android.hardware.invcase</name> <version>1</version> <interface> <name>IInvcase</name> <instance>default</instance> </interface> </hal>

到这一步，基本设置已经完成，下面将它Run起来跑一下试试。

5.调试运行

push编译出来依赖的so、.rc、xml、bin等 1.invcase启动服务 # adb push out/target/product/xxx/vendor/etc/init/android.hardware.invcase-service.rc /vendor/etc/init 2.invcase hal添加到系统 # adb push out/target/product/xxx/vendor/etc/vintf/manifest/android.hardware.invcase-service.xml /vendor/etc/vintf/manifest 3.hal调用aidl生成的api，实现服务 # adb push out/target/product/xxx/vendor/bin/hw/android.hardware.invcase-service /vendor/bin/hw 4.aidl生成cpp的api，提供给HAL服务使用 # adb push out/target/product/xxx/vendor/lib64/android.hardware.invcase-V1-ndk_platform.so /vendor/lib64 5.运行hal服务 # setenforce 0 # /vendor/bin/hw/android.hardware.invcase-service 6.运行hal服务 # start android.hardware.invcase-service 注意：使用start的方式启动失败，需要配置sepolicy，自行配置即可。

到这一步，我们的AIDL服务已经可以跑起来，毕竟Android默认开启了SeLinux策略，那么我们怎么添加SeLinux Policy？

6.增加Selinux Policy策略

1.定义一个新类型 # emacs system/sepolicy/prebuilts/api/32.0/public/hwservice.te # emacs system/sepolicy/public/hwservice.te type hal_invcase_hwservice, hwservice_manager_type; 2.设置兼容性忽略api为31，及以下的。 # emacs system/sepolicy/prebuilts/api/32.0/private/compat/31.0/31.0.ignore.cil # emacs system/sepolicy/private/compat/31.0/31.0.ignore.cil (type new_objects) (typeattribute new_objects) (typeattributeset new_objects ( new_objects hal_invcase_hwservice ) ) 3.添加服务路径 # emacs system/sepolicy/vendor/file_contexts /(vendor|system/vendor)/bin/hw/android\.hardware\.invcase-service u:object_r:hal_invcase_service_exec:s0 4.设置服务上下文接口 # emacs system/sepolicy/prebuilts/api/32.0/private/hwservice_contexts # emacs system/sepolicy/private/hwservice_contexts android.hardware.invcase::IInvcase u:object_r:hal_invcase_hwservice:s0 5.声明属性 # emacs system/sepolicy/prebuilts/api/32.0/public/attributes # emacs system/sepolicy/public/attributes hal_attribute(invcase); attribute hal_invcase; attribute hal_invcase_client; attribute hal_invcase_server; 6.定义默认域 # emacs system/sepolicy/vendor/hal_invcase_service.te type hal_invcase_service, domain; hal_server_domain(hal_invcase_service, hal_invcase) type hal_invcase_service_exec, exec_type, vendor_file_type, vendor_file_type, file_type; init_daemon_domain(hal_invcase_service) 7.设置binder策略 # emacs system/sepolicy/prebuilts/api/32.0/public/hal_invcase.te # emacs system/sepolicy/public/hal_invcase.te binder_call(hal_invcase_client, hal_invcase_server) binder_call(hal_invcase_server, hal_invcase_client) hal_attribute_hwservice(hal_invcase, hal_invcase_hwservice) 8.将system_server声明为HAL服务的客户端 # emacs system/sepolicy/prebuilts/api/32.0/private/system_server.te # emacs system/sepolicy/private/system_server.te hal_client_domain(system_server, hal_invcase) 9.将invcase hal服务添加系统编译中 # emacs build/target/product/base_vendor.mk + PRODUCT_PACKAGES += \ + android.hardware.invcase-service \ 注意：vendor ndk的so库被编译到system.img中。