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No Pain, No Gain!

1. Introduction

Learning Philosophy: Understand one knowledge point at a time

Difficulty: ★★★☆☆

Source Code Environment: Android 9.0+

Hardware Environment: Qcom

Reading Time: 2 minutes

Some classmates in the group have raised questions about HIDL and AIDL. In response to these questions, I plan to output three articles. This article is the first one, analyzing the differences between several modes of HAL and HIDL, followed by a demo to solidify the concepts.

• First, let’s look at a diagram of the development process from HAL to HIDL

Figure 1

• What are the differences in usage between the four stages from HAL to HIDL?

• First Stage: Legacy HAL: Represents the old HAL mode.

• Second Stage: HIDL (passthrough): Also known as “passthrough mode”, it indicates using HIDL but does not require communication through the Binder IPC mechanism, and directly uses the Legacy HAL library to communicate with the driver.

• Third Stage: HIDL (binderized + dopen): Indicates using the Binder mechanism, but in this mode, the HAL library is loaded through dlopen to communicate with the driver.

• Fourth Stage: HIDL (binderized) mode: Indicates that the client communicates with the server through Binder IPC, and the server communicates directly with the driver.

• Next, let’s write an example of using HIDL in binderized mode for communication.

2. Writing .hal file

# mkdir -p hardware/interfaces/led/1.0/default

# cd hardware/interfaces/led/1.0

# emacs ILed.hal

package [email protected];

interface ILed.hal{

helloWorld(string name) generates (string result);

}

3. hidl-gen.sh generates .cpp/h from .hal

1. If the hidl-gen tool is not available, compile it

# make hidl-gen -j16

2. Switch to the outermost directory of Android

# cd ~/android

Generate Android.bp, Led.cpp, Led.h in hardware/interfaces/led/1.0/default

3. Write the hidl-gen.sh script

# emacs hidl-gen.sh

#!/bin/bash

[email protected]

LOC=./hardware/interfaces/led/1.0/default

hidl-gen -o $LOC -Lc++-impl -randroid.hidl:system/libhidl/transport $PACKAGE

4. Execute the compilation

# ./hidl-gen.sh

4. Compile and Implement HIDL Service

<1>. Update Makefile, automatically generate Android.mk, Android.bp in the hardware/interfaces/led/1.0 directory

# ./hardware/interfaces/update-makefiles.sh

# mmm hardware/interfaces/led/1.0

# touch hardware/interfaces/led/1.0/default/[email protected]

# touch hardware/interfaces/led/1.0/default/service.cpp

<2>. Implement: [email protected]

service led_hal_service /vendor/bin/hw/[email protected]

class hal

user system

group system

<3>. Implement HIDL Service: service.cpp

#define LOG_TAG “[email protected]”

#include <android/hardware/led/1.0/ILed.h>

#include <hidl/LegacySupport.h>

#include “led.h”

using android::hardware::led::V1_0::ILed;

using android::hardware::led::V1_0::implementation::led;

using android::hardware::defaultPassthroughServiceImplementation;

using android::hardware::configureRpcThreadpool;

using android::hardware::joinRpcThreadpool;

using android::sp;

int main() {

#if 0=

// Passthrough mode

return defaultPassthroughServiceImplementation<Iled>();

#else

// Binder mode

sp<ILed> service = new led();

configureRpcThreadpool(1, true /*callerWillJoin*/)

service->registerAsService();

joinRpcThreadpool();

#endif

}

<4>. Configure system/libhidl/manifiest.xml

1. Development board path: /system/manifest.xml Or /vendor/manifest.xml

# emacs system/libhidl/manifiest.xml

<hal format=”hidl”>

<name>android.hardware.led</name>

<!– hwbinder: Binder mode; passthrough: passthrough mode–>

<transport>hwbinder</transport>

<version>1.0</version>

<interface> <name>ILed</name>

<instance>default</instance>

</interface>

</hal>

2. Push to system

# adb push manifiest.xml /system

3. Restart

# adb reboot

5. HIDL Server-side Compilation

<1>. Add executable program in Android.bp

# emacs hardware/interfaces/led/1.0/default/Android.bp

cc_binary {

name: “[email protected]”,

srcs: [“service.cpp”,

“ledImpl.cpp”],

shared_libs: [

“liblog”,

“libhardware”,

“libhidlbase”

“libhidltransport”,

“libutils”,

“[email protected]”, ],

}

# mmm hardware/interfaces/led/1.0/default

system/bin/[email protected] //server-side executable program

system/lib64/[email protected] //server-side defined so

system/lib/[email protected]

vendor/lib64/hw/[email protected] //server-side implementation of hwbinder so

vendor/lib/hw/[email protected]

6. Client-side

<1>. Android.bp

# cd hardware/interfaces/led/1.0/default

# emacs Android.bp // Add

cc_binary {

relative_install_path: “hw”,

defaults: [“hidl_defaults”],

name: “led_client”,

proprietary: true,

srcs: [“led_client.cpp”],

shared_libs: [

“liblog”

“libhardware”,

“libhidlbase”,

“libhidltransport”,

“libutils”,

“[email protected]”,

],

}

#define LOG_TAG “LED_CLIENT”

#include <android/hardware/led/1.0/ILed.h>

#include <log/log.h>

using android::hardware::led::V1_0::ILed;

using android::hardware::hidl_vec;

using android::hardware::hidl_string;

using android::sp;

int main(){

sp<ILed> service = ILed::getService();

if( service == nullptr ){

ALOGE(“Can’t find ILed service…”);

return -1;

}

service->helloWorld(“HIDL!!!!”, [&](hidl_string result){

ALOGE(“%s(), line = %d, result = %s”,__FUNCTION__,__LINE__,result.c_str()); });

ALOGE(“%s(), line = %d”,__FUNCTION__,__LINE__);

return 0;

}

# mmm hardware/interfaces/led/1.0/default

vendor/bin/hw/led_client //client-side testing demo

// Push 32/64 bit so and bin to the development board

# adb push vendor_lib_hw/[email protected] /vendor/lib/hw

# adb push vendor_lib64_hw/[email protected] /vendor/lib64/hw

# adb push system_lib64/[email protected] /system/lib64

# adb push system_lib/[email protected] /system/lib

# adb push server_system_bin/[email protected] /system/bin

# adb push led_client /system/bin

# adb push manifest.xml /system // Need to restart

# adb logcat -s [email protected] LED_CLIENT led_server

// Start server-side

# /system/bin/[email protected]

// Start client-side

# /system/bin/led_client

7. Android APP as Client Configuration

# make update-api -j16

# mmm hardware/interfaces/led/1.0

# mmm hardware/interfaces/led/1.0/default

# setenforce 0

8. Conclusion