HIDL 这个机制的目的，主要是为了把框架（framework）与 HAL 进行隔离，使得框架部分可以直接被覆盖、更新，而不需要重新对 HAL 进行编译。HAL 的部分将会放在设备的 /vendor 分区中，并且是由设备供应商（vendors）或 SOC 制造商来构建。这使得框架部分可以通过 OTA 方式更新，同时不需要重新编译 HAL。

这种设计被称为Treble机制，从Android 8.0引入。在此之前framework需要调用dlopen打开HAL编译的.so才能和HAL 层通信，这样framework 与 HAL 处在同一个进程 , 两者耦合严重，导致版本升级时供应商需要做大量的适配工作。

Treble机制解决目前Android 版本之间升级麻烦的问题，将OEM适配的部分vendor与google 对android 大框架升级的部分system部分做了分离，一旦适配了一个版本的vendor信息之后，之后的版本再进行升级时，直接升级system即可，这个就不会给OEM厂商升级带来太大的工作量，直接升级最新功能，可以解决目前市面上Android版本过于凌乱的问题。

Treble机制在Vendor分区中有两种模式，直通模式(Passthrough)和绑定模式（Binderized），大致框架图如下，对于Android O之前的设备，对应图1，对于从之前的设备升级到O的版本，对应图2、图3. 对于直接基于Android O开发的设备，对应图4。

一般新增HIDL Service都是在vendor目录下新增，最好在自己的产品名下新增文件夹，创建相应的HIDL服务，假设目前要在qcom下新增HIDL服务，流程如下：

如何新增HIDL服务

1.新增hidl服务文件夹

在vendor/qcom/opensource/interfaces下新增文件夹，这里新增customizehidl文件夹

在customizehidl下新建1.0文件夹

在1.0下新增default文件夹

2. 新增.hal文件

在customizehidl下新增ICustomizehidl.hal以及types.hal文件

vendor/qcom/opensource/interfaces/ICustomizehidl.halpackage vendor.qti.hardware.customizehidl@1.0;interface ICustomizeHidl{    resetOption(int32_t side) generates (Result result);};

vendor/qcom/opensource/interfaces/types.halpackage vendor.qti.hardware.customizehidl@1.0;enum Result : int32_t {    OK = 0,    ERR,    OUT_OF_RANGE,};

3. 编译hidl-gen

source build/envsetup.sh

lunch xx

make hidl-gen

这样后面就可以用hidl-gen工具了，

4. 配置hidl的package root

PACKAGE=vendor.qti.hardware.customizehidl@1.0

LOC=vendor/qcom/opensource/interfaces/customizehidl/1.0/default/

如果有如下报错的话

ERROR: Package root not specified for vendor.qti.hardware.customizehidl@1.0

ERROR: Could not get sources for vendor.qti.hardware.customizehidl@1.0.

需要在以下目录下添加如下代码：

vendor/qcom/opensource/interfaces/Android.bphidl_package_root {    name:"vendor.qti.hardware.customizehidl",    path:"vendor/qcom/opensource/interfaces/customizehidl",}

5. 在1.0/default/下生成.cpp和.h文件

在vendor/qcom/opensource/interfaces/customizehidl/1.0/default/下生成.cpp和.h文件：

hidl-gen -o $LOC -Lc++-impl -rvendor.qti.hardware:vendor/qcom/opensource/interfaces -randroid.hidl:system/libhidl/transport $PACKAGE

或者

hidl-gen -o vendor/qcom/opensource/interfaces/customizehidl/1.0/default -Lc++-impl -rvendor.qti.hardware:vendor/qcom/opensource/interfaces –randroid.hidl:system/libhidl/transport vendor.qti.hardware.customizehidl@1.0

然后会生成CustomizeHidl.cpp和CustomizeHidl.h文件。生成后需要做相关修改，修改后内容如下：

vendor/qcom/opensource/interfaces/customizehidl/1.0/default/CustomizeHidl.cpp#include "CustomizeHidl.h"#include #include #include #include #include namespace vendor {namespace qti {namespace hardware {namespace customizehidl {namespace V1_0 {namespace implementation {CustomizeHidl::CustomizeHidl() {}CustomizeHidl::~CustomizeHidl() {}Return<::vendor::qti::hardware::customizehidl::V1_0::Result> CustomizeHidl::resetOption(int32_t side) {    return ::vendor::qti::hardware::customizehidl::V1_0::Result {};}// Methods from ::android::hidl::base::V1_0::IBase follow.//ICustomizeHidl* HIDL_FETCH_ICustomizeHidl(const char* ) {//    return new CustomizeHidl();//}//}  // implementation}  // V1_0}  // customizehidl}  // hardware}  // qti}  // vendor

头文件内容如下：

vendor/qcom/opensource/interfaces/customizehidl/1.0/default/CustomizeHidl.h#include #include #include #include #include namespace vendor {namespace qti {namespace hardware {namespace customizehidl {namespace V1_0 {namespace implementation {using namespace std;using ::android::hardware::hidl_array;using ::android::hardware::hidl_memory;using ::android::hardware::hidl_string;using ::android::hardware::hidl_vec;using ::android::hardware::Return;using ::android::hardware::Void;using ::android::sp;struct CustomizeHidl : public ICustomizeHidl {    CustomizeHidl();    ~CustomizeHidl();    Return<::vendor::qti::hardware::customizehidl::V1_0::Result> resetOption(int32_t side) override;};// FIXME: most likely delete, this is only for passthrough implementations// extern "C" ICustomizeHidl* HIDL_FETCH_ICustomizeHidl(const char* name);}  // implementation}  //customizehidl}  // V1_0}  // hardware}  // qti}  // vendor

6. 在1.0/default/下面生成Android.bp

在vendor/qcom/opensource/interfaces/customizehidl/1.0/default/下面生成Android.bp：

hidl-gen -o $LOC -Landroidbp-impl -rvendor.qti.hardware:vendor/qcom/opensource/interfaces -randroid.hidl:system/libhidl/transport $PACKAGE

生成后需要做相关修改，修改后内容如下：

cc_defaults{    name: "customizehidl_defaults",    //relative_install_path: "hw",    defaults: ["hidl_defaults"],    //根据项目需求    //vendor: true,    proprietary: true,    cflags: [       "-Wno-unused-parameter",       "-Wall",    ],    shared_libs: [            "libcutils",            "liblog",            "libbase",            "libsysutils",            "libhidlbase",            "libhidltransport",            "libutils",            "vendor.qti.hardware.customizehidl@1.0",        ],}cc_library_shared {    name: "vendor.qti.hardware.customizehidl@1.0-impl",    relative_install_path: "hw",    //根据项目需求    //vendor: true,    proprietary: true,    cflags: [           "-Wno-unused-parameter",           "-Wall",           "-Wunused-variable",           "-Wunused-const-variable",           "-Wunused-variable",    ],    class="lazy" data-srcs: [        "CustomizeHidl.cpp",    ],    defaults: ["customizehidl_defaults"],}cc_binary {    name: "vendor.qti.hardware.customizehidl@1.0-service",    proprietary: true,    compile_multilib: "both",    relative_install_path: "hw",    defaults: ["customizehidl_defaults"],    //rc引用    init_rc: ["vendor.qti.hardware.customizehidl-service.rc"],    //vintf_fragments引用    vintf_fragments: ["vendor.qti.hardware.customizehidl-service.xml"],    class="lazy" data-srcs: [        "service.cpp",    ],    shared_libs: [        "libcutils",        "liblog",        "libbase",        "libsysutils",        "libhidlbase",        "libhidltransport",        "libutils",        "vendor.qti.hardware.customizehidl@1.0-impl",    ],}

7. 在1.0下生成Android.bp

在vendor/qcom/opensource/interfaces/customizehidl/1.0下生成Android.bp

source system/tools/hidl/update-makefiles-helper.sh

do_makefiles_update vendor.qti.hardware:vendor/qcom/opensource/interfaces android.hardware:hardware/interfaces android.hidl:system/libhidl/transport

生成后需要做相关修改，修改后内容如下：

hidl_interface {    name: "vendor.qti.hardware.customizehidl@1.0",    root: "vendor.qti.hardware.customizehidl",    //根据需求进行设置    //product_specific: true,    system_ext_specific: true,    class="lazy" data-srcs: [        "types.hal",        "ICustomizeHidl.hal",    ],    interfaces: [        "android.hidl.base@1.0",    ],    gen_java: true,}

8. 在主目录android下执行如下命令生成current.txt

hidl-gen -Lhash -rvendor.qti.hardware:vendor/qcom/opensource/interfaces -randroid.hidl:system/libhidl/transport vendor.qti.hardware.customizehidl@1.0 > vendor/qcom/opensource/interfaces/customizehidl/current.txt

9. 在1.0/default/下添加vendor.qti.hardware.customizehidl-service.rc

添加如下内容

service vendor.qti.hardware.customizehidl-1-0 /vendor/bin/hw/vendor.qti.hardware.customizehidl@1.0-serviceclass haluser systemgroup system

10. 在1.0/default/下添加vendor.qti.hardware.customizehidl-service.xml

            vendor.qti.hardware.customizehidl        hwbinder        1.0                    ICustomizeHidl            default

11. 在device/qcom/common/vendor_compatibility_matrix.xml中添加如下内容

            vendor.qti.hardware.customizehidl        hwbinder        1.0                    ICustomizeHidl            default

12. 在1.0/default/下添加service.cpp

如果采用Binderized方式，如下

#include #include #include "CustomizeHidl.h"#include #include using namespace android;using vendor::qti::hardware::customizehidl::V1_0::ICustomizeHidl;using vendor::qti::hardware::customizehidl::V1_0::implementation::CustomizeHidl;using android::hardware::configureRpcThreadpool;using android::hardware::joinRpcThreadpool;using android::sp;int main(int , char ** ) {    sp service = new CustomizeHidl();    configureRpcThreadpool(1, true );    if (::android::OK != service->registerAsService()) {        return -1;    }    joinRpcThreadpool();    return 0;}

如果要采用Passthrough方式的话，则需要按如下方法写main,但同时需要将CustomizeHidl.cpp以及CustomizeHidl.h中的HIDL_FETCH_ICustomizeHidl方法放开才可以。

#include #include #include "CustomizeHidl.h"#include #include using namespace android;using vendor::qti::hardware::customizehidl::V1_0::ICustomizeHidl;using android::hardware::configureRpcThreadpool;using android::hardware::joinRpcThreadpool;using android::hardware::defaultPassthroughServiceImplementation;using android::hardware::registerPassthroughServiceImplementation;int main() {android::status_t status;configureRpcThreadpool(10, false);status = registerPassthroughServiceImplementation();LOG_ALWAYS_FATAL_IF(status != OK, "Error while registering ICustomizeHidl: %d", status);joinRpcThreadpool();return status;}

13. 编写测试bin程序

vendor/qcom/opensource/interfaces/customizehidl/下新增hidl_test_bin目录，并添加Android.bp

cc_binary {    name: "hidl_test_bin",                     class="lazy" data-srcs: [        "hidl_test_bin.cpp",    ],      shared_libs: [        "libcutils",        "libutils",        "liblog",//以下so一定要添加，否则可能会有报错        "libbinder",        "libhidlbase",        "libbase",        "libhidltransport",        "vendor.qti.hardware.customizehidl@1.0",    ],      cflags: [        "-Werror",        "-Wno-error=deprecated-declarations",        "-Wno-unused-parameter",        "-Wall",    ],  }

添加hidl_test_bin.cpp文件

#define LOG_TAG "hidl_test_bin"#include #include #include #include #include #include #include #include #include using namespace android;using namespace std;using vendor::qti::hardware::customizehidl::V1_0::ICustomizeHidl;using vendor::qti::hardware::customizehidl::V1_0::Result;using android::hardware::Return;using android::hardware::details::return_status;using android::hardware::Void;sp halService;int main(int argc, char* argv[]) {    halService = ICustomizeHidl::getService();    if (halService == NULL){        cout << "get hal service failed" <resetOption(value);    return 0;}

14. 测试

14.1 单编方法：

source build/envsetup.sh

lunch xxx

cd vendor/qcom/opensource/interfaces/customizehidl

mma(编译hidl服务相关)

cd vendor/qcom/opensource/interfaces/customizehidl/hidl_test_bin

mma(编译test bin相关)

14.2 测试方法：

1. adb pull vendor/etc/vintf/compatibility_matrix.xml

在最后增加

        vendor.qti.hardware.customizehidl
        hwbinder
        1.0

            ICustomizeHidl
            default

2. 再push回去

adb root
adb remount

adb push compatibility_matrix.xml vendor/etc/vintf/compatibility_matrix.xml

3. 在out/target/product/qssi下执行

adb push ./product/lib/vendor.qti.hardware.customizehidl@1.0.so product/lib/
adb push ./product/lib64/vendor.qti.hardware.customizehidl@1.0.so product/lib64/
adb push ./vendor/lib/hw/vendor.qti.hardware.customizehidl@1.0-impl.so vendor/lib/hw/
adb push ./vendor/lib/vendor.qti.hardware.customizehidl@1.0.so vendor/lib/
adb push ./vendor/lib64/hw/vendor.qti.hardware.customizehidl@1.0-impl.so vendor/lib64/hw/
adb push ./vendor/lib64/vendor.qti.hardware.customizehidl@1.0.so vendor/lib64/
adb push ./vendor/etc/vintf/manifest/vendor.qti.hardware.customizehidl-service.xml vendor/etc/vintf/manifest
adb push ./vendor/bin/hw/vendor.qti.hardware.customizehidl@1.0-service vendor/bin/hw/
adb push ./system_ext/lib/vendor.qti.hardware.customizehidl@1.0.so system_ext/lib/
adb push ./system_ext/lib64/vendor.qti.hardware.customizehidl@1.0.so system_ext/lib64/
adb push system/bin/hidl_test_bin system/bin(测试的bin程序)
然后执行
adb reboot
重启后
关闭selinux: adb shell setenforce 0
窗口1：起hidl服务
adb shell
cd vendor/bin/hw
./vendor.qti.hardware.customizehidl@1.0-service

窗口2：起test bin程序
adb shell
hidl_test_bin 100

然后观察窗口2输出什么
如果输出如下则代表两者通信成功
get hal service scuess
value is 100

15. 可能碰到的问题

15.1 错误1

04-14 12:27:02.103 599 599 I hwservicemanager: getTransport: Cannot find entry vendor.qti.hardware.customizehidl@1.0::ICustomizeHidl/default in either framework or device VINTF manifest.
04-14 12:27:02.104 4169 4169 E HidlServiceManagement: Service vendor.qti.hardware.customizehidl@1.0::ICustomizeHidl/default must be in VINTF manifest in order to register/get

那就是vintf manifest相关的配置出现问题，可以检查下是否有push相应的manifest文件，接口的内容是否书写正确等。

15.2 新增目录放hal服务

如遇到新建的目录编译不出来相关hidl的out下相关文件，需要添加update-makefiles.sh文件，可以从其他hidl的目录中拷贝过来，修改其中的目录即可

set -e

if [ -z "$ANDROID_BUILD_TOP" ]; then
echo "Missing ANDROID_BUILD_TOP env variable. Run 'lunch' first."
exit 1
fi

source $ANDROID_BUILD_TOP/system/tools/hidl/update-makefiles-helper.sh

do_makefiles_update \
"vendor/newname/interfaces/customizehidl"