接下来我们仿造振动器写一个简单的 AIDL HAL 模块。
# AIDL 文件编写
首先，在 hardware/interfaces/ 路径下创建 aidl hal 项目目录：
cd hardware/interfaces
mkdir hello_aidl_hal
cd hello_aidl_hal
mkdir -p android/hardware/hello
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接着我们在 hardware/interfaces/hello_aidl_hal/aidl/android/hardware/hello 目录下创建 IHelloHal.aidl 文件：
// hardware/interfaces/hello_aidl_hal/aidl/android/hardware/hello/IHelloHal.aidl
package android.hardware.hello;
@VintfStability
interface IHelloHal {
void hello_write(String str);
String hello_read();
}
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接着编写最外层的 Android.bp：
// hardware/interfaces/hello_aidl_hal/aidl/Android.bp
aidl_interface {
name: "android.hardware.hello",
vendor_available: true,
srcs: ["android/hardware/hello/*.aidl"],
stability: "vintf",
owner:"xxx.hello",
backend: {
cpp: {
enabled: false,
},
java: {
sdk_version: "module_current",
},
},
}
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aidl 会生成 java c++ ndk rust 四种库，一般 java 和 ndk 使用会比较多。这部分内容的细节可以在 backend 中配置。
接着就可以编译了：
mmm hardware/interfaces/hello_aidl_hal/
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报错：
[ 7% 186/2361] echo "API dump for the current version of AIDL interface android.hardware.hello does not exist." && echo "Run the co
FAILED: out/soong/.intermediates/hardware/interfaces/hello_aidl_hal/aidl/android.hardware.hello-api/checkapi_current.timestamp
echo "API dump for the current version of AIDL interface android.hardware.hello does not exist." && echo "Run the command \"m android.hardware.hello-update-api\" or add \"unstable: true\" to the build rule for the interface if it does not need to be versioned" && false # hash of input list: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
API dump for the current version of AIDL interface android.hardware.hello does not exist.
Run the command "m android.hardware.hello-update-api" or add "unstable: true" to the build rule for the interface if it does not need to be versioned
15:28:12 ninja failed with: exit status 1
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按提示执行：
m android.hardware.hello-update-api
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执行完成后，生成的代码结构如下：
zzh0838@zzh0838-2204:~/Project/aosp/android-14.0.0_r15$ tree hardware/interfaces/hello_aidl_hal/
hardware/interfaces/hello_aidl_hal/
└── aidl
├── aidl_api
│ └── android.hardware.hello
│ └── current
│ └── android
│ └── hardware
│ └── hello
│ └── IHelloHal.aidl
├── android
│ └── hardware
│ └── hello
│ └── IHelloHal.aidl
└── Android.bp
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接着再编译：
mmm hardware/interfaces/hello_aidl_hal/
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执行完成后，就会在 out/soong/.intermediates/hardware/interfaces/hello_aidl_hal/aidl 目录下生成一下的一堆库：
android.hardware.hello-api android.hardware.hello-V1-java-source default
android.hardware.hello_interface android.hardware.hello-V1-ndk
android.hardware.hello-V1-java android.hardware.hello-V1-ndk-source
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# 服务端程序代码编写
接下来在 hardware/interfaces/hello_aidl_hal/aidl/default 目录下创建如下的文件：
hardware/interfaces/hello_aidl_hal/aidl/default/HelloHalImpl.h 实现如下：
#ifndef ANDROID_HARDWARE_HELLO_H
#define ANDROID_HARDWARE_HELLO_H
#include <aidl/android/hardware/hello/BnHelloHal.h>
namespace aidl::android::hardware::hello {
class HelloHalImpl : public BnHelloHal {
public:
::ndk::ScopedAStatus hello_write(const std::string& in_str) override;
::ndk::ScopedAStatus hello_read(std::string* _aidl_return) override;
};
}
#endif
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hardware/interfaces/hello_aidl_hal/aidl/default/HelloHalImpl.cpp 的实现如下：
#define LOG_TAG "HelloHalImpl"
#define LOG_NDEBUG 0
#include "HelloHalImpl.h"
#include <log/log.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
namespace aidl::android::hardware::hello {
::ndk::ScopedAStatus HelloHalImpl::hello_write(const std::string& in_str) {
ALOGD("write %s", in_str.c_str());
int fd;
int len = in_str.size();
fd = open("/dev/hello", O_RDWR);
write(fd, in_str.c_str(), len);
close(fd);
return ::ndk::ScopedAStatus::ok();
}
::ndk::ScopedAStatus HelloHalImpl::hello_read(std::string* _aidl_return) {
int fd;
char buf[1024];
fd = open("/dev/hello", O_RDWR);
read(fd, buf, 1024);
*_aidl_return = buf;
return ::ndk::ScopedAStatus::ok();
}
::ndk::ScopedAStatus HelloHalImpl::hello_init() {
ALOGD("Hello hal init");
return ::ndk::ScopedAStatus::ok();
}
}
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可以看出，这里的 HelloHalImpl 就是 binder 服务端类的具体实现。
接着写一个主程序，来注册这个 binder 服务:
hardware/interfaces/hello_aidl_hal/aidl/default/main.cpp
#include "HelloHalImpl.h"
#define LOG_TAG "HelloHalImpl"
#define LOG_NDEBUG 0
#include <iostream>
#include <android-base/logging.h>
#include <android/binder_manager.h>
#include <android/binder_process.h>
#include <stdio.h>
#include <log/log.h>
using aidl::android::hardware::hello::HelloHalImpl;
int main() {
ABinderProcess_setThreadPoolMaxThreadCount(0);
std::shared_ptr<HelloHalImpl> hello = ::ndk::SharedRefBase::make<HelloHalImpl>();
const std::string instance = std::string() + HelloHalImpl::descriptor + "/default";
ALOGD("HelloHalImpl instance =%s sde =%p \n", instance.c_str(), hello->asBinder().get());
binder_status_t status =
AServiceManager_addService(hello->asBinder().get(), instance.c_str());
CHECK_EQ(status, STATUS_OK);
ALOGD("HelloHalImpl AServiceManager_addService status=%d \n", status);
fflush(stdout);
ABinderProcess_joinThreadPool();
return EXIT_FAILURE; // should not reach
}
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接着还要写一个 hal 的 vintf：
hardware/interfaces/hello_aidl_hal/aidl/default/hellohal-default.xml
<manifest version="1.0" type="device">
<hal format="aidl" optional="true">
<name>android.hardware.hello</name>
<version>1</version>
<interface>
<name>IHelloHal</name>
<instance>default</instance>
</interface>
</hal>
</manifest>
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需要开机启动，添加:
hardware/interfaces/hello_aidl_hal/aidl/default/android.hardware.hello.rc
service vendor.hellohal-default /vendor/bin/hw/android.hardware.hello.example
class hal
user root
group root
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接着编写 hardware/interfaces/hello_aidl_hal/aidl/default/Android.bp
cc_binary {
name: "android.hardware.hello.example",
relative_install_path: "hw",
vendor: true,
init_rc: ["android.hardware.hello.rc"],
vintf_fragments: ["hellohal-default.xml"],
shared_libs: [
"android.hardware.hello-V1-ndk",
"liblog",
"libbase",
"libcutils",
"libutils",
"libbinder_ndk",
],
srcs: [
"main.cpp",
"HelloHalImpl.cpp",
],
}
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接着还需要将 hal 加入到兼容性矩阵中：
hardware/interfaces/compatibility_matrices/compatibility_matrix.8.xml
<hal format="aidl" optional="true">
<name>android.hardware.hello</name>
<version>1</version>
<interface>
<name>IHelloHal</name>
<instance>default</instance>
</interface>
</hal>
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在 Android14 中还会多一个叫 fuzzer 的东西，暂时还没搞清楚作用，看源码大部分 hal 都没有做支持，这里我们写的 hal 也不做支持，修改 system/sepolicy/build/soong/service_fuzzer_bindings.go :
"android.hardware.vibrator.IVibrator/default": EXCEPTION_NO_FUZZER,
"android.hardware.vibrator.IVibratorManager/default": []string{"android.hardware.vibrator-service.example_fuzzer"},
// 添加的内容
"android.hardware.hello.IHelloHal/default": EXCEPTION_NO_FUZZER,
"android.hardware.weaver.IWeaver/default": EXCEPTION_NO_FUZZER,
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# Selinux
接下来配置 Selinux 权限：
添加 system/sepolicy/vendor/hal_hello.te：
hal_attribute(hellohal);
type hal_hellohal_default, domain, mlstrustedsubject;
hal_server_domain(hal_hellohal_default, hal_hellohal);
type hal_hellohal_default_exec, exec_type, vendor_file_type, file_type;
init_daemon_domain(hal_hellohal_default);
binder_call(hal_hellohal_client, hal_hellohal_default)
type hal_hellohal_service, service_manager_type;
add_service(hal_hellohal_default, hal_hellohal_service)
allow hal_hellohal_client hal_hellohal_service:service_manager find;
hal_client_domain(system_server, hal_hellohal)
allow hal_hellohal_default servicemanager:binder { call transfer };
allow { platform_app shell } hal_hellohal:binder {call};
allow hal_hellohal_default hello_dev_t:chr_file { open read write };
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在 system/sepolicy/vendor/file_contexts 中添加：
/(vendor|system/vendor)/bin/hw/android\.hardware\.hello\.example u:object_r:hal_hellohal_default_exec:s0
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修改 system/sepolicy/private/service_contexts 和 system/sepolicy/prebuilts/api/34.0/private/service_contexts，注意保持两个文件一致：
android.hardware.hello.IHelloHal/default u:object_r:hal_hellohal_service:s0
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# 编写测试程序
在 hardware/interfaces/hello_aidl_hal 目录下创建：
hardware/interfaces/hello_aidl_hal/test_aidl_hal/main.cpp:
#define LOG_TAG "Test-HAL"
#define LOG_NDEBUG 0
#include <iostream>
#include <log/log.h>
#include <android/binder_manager.h>
#include <android/binder_process.h>
#include <aidl/android/hardware/hello/IHelloHal.h>
#include <stdio.h>
using aidl::android::hardware::hello::IHelloHal;
int main() {
std::shared_ptr<IHelloHal> service = IHelloHal::fromBinder(ndk::SpAIBinder(AServiceManager_getService("android.hardware.hello.IHelloHal/default")));
ALOGD("get service = %p\n",service.get());
if (service == nullptr) {
return -1;
}
service->hello_write("hello");
fflush(stdout);
return EXIT_FAILURE; // should not reach
}
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hardware/interfaces/hello_aidl_hal/test_aidl_hal/Android.bp:
cc_binary {
name: "test_aidl_hal",
vendor: true,
shared_libs: [
"android.hardware.hello-V1-ndk",
"liblog",
"libbase",
"libcutils",
"libutils",
"libbinder_ndk",
],
srcs: [
"main.cpp",
],
}
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# 编译与测试
# 编译
source build/envsetup.sh
lunch aosp_cf_x86_phone-eng
m
# 启动模拟器
cvd start -kernel_path=/home/zzh0838/Project/aosp/kernel/out/virtual_device_x86_64/dist/bzImage -initramfs_path=/home/zzh0838/Project/aosp/kernel/out/virtual_device_x86_64/dist/initramfs.img
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最后测试，
运行测试程序：
adb shell
test_aidl_hal
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查看 log：
adb logcat | grep hello
04-11 11:13:31.414 0 0 W : drivers/char/hello_driver.c hello_init line 69
04-11 11:13:32.803 0 0 I init : Parsing file /vendor/etc/init/android.hardware.hello.rc...
04-11 11:13:37.533 0 0 I init : starting service 'vendor.hellohal-default'...
04-11 11:13:37.537 0 0 I init : ... started service 'vendor.hellohal-default' has pid 339
04-11 11:13:37.604 0 0 I servicemanager: Found android.hardware.hello.IHelloHal/default in device VINTF manifest.
04-11 11:20:11.512 339 339 D HelloHalImpl: write hello
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