本文中Helloworld 位于hardware/interfaces中，所以目录路径为hardware/interfaces/helloworld/1.0。

cd ./hardware/interfaces/helloworld/1.0

创建文件IHelloWorld.hal

package [email protected];
 
interface IHelloWorld {
    justTest(string name) generates (string result, HelloTest value);
 
    justTest1(HelloTest name);
};
创建文件：types.hal

package [email protected];
 
enum HelloTest : uint8_t {
    V_TEST1 = 0,
    V_TEST2 = 1,
};

自动生成.bp文件的命令：

source ./build/envsetup.sh 
lunch
./hardware/interfaces/update-makefiles.sh 

用hidl-gen生成空.cpp文件，

#! /bin/bash
 
[email protected]
LOC=hardware/interfaces/helloworld/1.0/default/
 
hidl-gen -o $LOC -Lc++-impl -randroid.hardware:hardware/interfaces \
        -randroid.hidl:system/libhidl/transport $PACKAGE
hidl-gen -o $LOC -Landroidbp-impl -randroid.hardware:hardware/interfaces \
        -randroid.hidl:system/libhidl/transport $PACKAGE

保存文件gen_cpp.sh，运行gen_cpp.sh后产生default目录和.cpp .h .bp文件，其中cpp文件就是我们需要实现的。
  
编辑.cpp文件，修改如下：

#define LOG_TAG "HelloWorldImpl"

#include <log/log.h>

#include "HelloWorld.h"

namespace android {
namespace hardware {
namespace helloworld {
namespace V1_0 {
namespace implementation {

// Methods from ::android::hardware::helloworld::V1_0::IHelloWorld follow.
Return<void> HelloWorld::justTest(const hidl_string& name, justTest_cb _hidl_cb) {
ALOGD("justTest, name = %s", name.c_str());

    _hidl_cb(name, HelloTest::V_TEST2);
    ALOGD("justTest end.");
        return Void();
}

Return<void> HelloWorld::justTest1(::android::hardware::helloworld::V1_0::HelloTest name) {
    ALOGD("justTest1, name = %hhu", name);
        return Void();
}


// Methods from ::android::hidl::base::V1_0::IBase follow.

IHelloWorld* HIDL_FETCH_IHelloWorld(const char* name) {
    ALOGD("FETCH IHelloWorld: %s", name);
    if (name != nullptr)
        return new HelloWorld();
    else
        return nullptr;
}
//
}  // namespace implementation
}  // namespace V1_0
}  // namespace helloworld
}  // namespace hardware
}  // namespace android

创建service.cpp

#define LOG_TAG "[email protected]"
 
#include <android/hardware/helloworld/1.0/IHelloWorld.h>
 
#include <hidl/LegacySupport.h>
#include "HelloWorld.h"
 
// Generated HIDL files
using android::hardware::helloworld::V1_0::IHelloWorld;
using android::hardware::helloworld::V1_0::implementation::HelloWorld;
 
using android::hardware::defaultPassthroughServiceImplementation;
using android::hardware::configureRpcThreadpool;
using android::hardware::joinRpcThreadpool;
 
int main() {
#if 1
    return defaultPassthroughServiceImplementation<IHelloWorld>();
#else
    sp<IHelloWorld> service = new HelloWorld();
    configureRpcThreadpool(1, true /*callerWillJoin*/);
    if(android::OK !=  service->registerAsService())
        return 1;
    joinRpcThreadpool();
#endif
} 

修改Android.bp

cc_library_shared {
    name: "[email protected]",
    relative_install_path: "hw",
    proprietary: true,
    srcs: [
        "HelloWorld.cpp",
    ],
    shared_libs: [
        "liblog",
        "libhidlbase",
        "libhidltransport",
        "libutils",
        "[email protected]",
    ],
}

cc_binary {
    name: "[email protected]",
    defaults: ["hidl_defaults"],
    relative_install_path: "hw",
    vendor: true,
    init_rc: ["[email protected]"],
    srcs: [
        "HelloWorld.cpp",
        "service.cpp"
    ],
    shared_libs: [
        "liblog",
        "libhidlbase",
        "libhidltransport",
        "libutils",
        "libhardware",
        "[email protected]",
    ],
}

创建[email protected]

service helloworld-hal-1-0 /vendor/bin/hw/[email protected]
    class hal
    user system
    group system

编译可执行二进制：
mmm hardware/interfaces/helloworld/1.0/default/

生成.so文件：
out/target/product/lime/system/lib64/vndk-29/[email protected]
out/target/product/lime/vendor/lib64/hw/[email protected]

生成可执行文件：
out/target/product/lime/vendor/bin/hw/[email protected]
启动脚本：
out/target/product/lime/vendor/etc/init/[email protected]

--------------------------------------------------------------------------------------------------

到此，服务、.so库文件、都已经编译完成，下面开始客户端的调用的实现

---------------------------------------------------------------------------------------------------
创建直通模式客户端 client.cpp：（default目录）

#include <android/hardware/helloworld/1.0/IHelloWorld.h>
#include <hidl/Status.h>
#include <hidl/LegacySupport.h>
#include <utils/misc.h>
#include <hidl/HidlSupport.h>
#include <stdio.h>

using android::hardware::helloworld::V1_0::IHelloWorld;
using android::sp;
using android::hardware::hidl_string;

int main()
{
    int ret = 0;
    android::sp<IHelloWorld> service = IHelloWorld::getService();
    if(service == nullptr) {
        printf("Failed to get service\n");
        ret = -1;
        return ret;
    }
    ::android::hardware::helloworld::V1_0::HelloTest name = {};
    service->justTest1(name);

    return ret;
}

创建Android.mk

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)
LOCAL_PROPRIETARY_MODULE := true
LOCAL_MODULE := helloworld_client
LOCAL_SRC_FILES := \
    client.cpp \
 
LOCAL_SHARED_LIBRARIES := \
   liblog \
   libhidlbase \
   libutils \
   an[email protected] \
 
include $(BUILD_EXECUTABLE)

编译可执行二进制：
mmm hardware/interfaces/helloworld/1.0/default/
生成文件：
out/target/product/lime/vendor/bin/helloworld_client

将vendor烧到手机上后,可直接运行helloworld_client。

参考文章：

Android HIDL 实例_私房菜-程序员宅基地_hidl_interface