HIDL SIMPLE

原文：https://devarea.com/android-hidl-and-project-treble/#.XLgyn7Ejw4A

One of the problems in Android is the fact that when a new version is released only a few devices can be updated. Actually, if you want to enjoy the latest version, you need to buy a new smartphone every 6 months. Google solution is the Project trebel that separates the vendor implementation from the Android OS framework via a new vendor interface

HIDL

HAL interface definition language used to describe the interface between the framework and the vendor. All hardware interfaces are located in hardware/interfaces in .hal files

Let’s go over simple example

Create all the path

 

1 2	# cd ~/aosp # mkdir -p hardware/interfaces/simple/2.0/default

 

Create a hal file in ISimphw.hal in  hardware/interfaces/simple/2.0

 

1 2 3 4 5

package [email protected];   interface ISimphw {     simpfn(int32_t valueIn) generates (int32_t valueRet); };

 

Generate the HAL files

To generate the HAL files you need to use the hidl-gen tool run:

 

1 2 3 4 5

# [email protected] # LOC=hardware/interfaces/simple/2.0/default/ # make hidl-gen -j64 # 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

And to update all makefile (Android.mk, Android.bp) run:

 

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

Now add 2 empty files to hardware/interfaces/simple/2.0/default:

• [email protected]
• service.cpp

Now the directory hardware/interfaces/simple should look like this:

Implementing the HAL shared object:

we need to add a new static function to return the service object (usually as a singleton)

Simphw.h

 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39

#ifndef ANDROID_HARDWARE_SIMPLE_V2_0_SIMPHW_H #define ANDROID_HARDWARE_SIMPLE_V2_0_SIMPHW_H   #include #include #include   namespace android { namespace hardware { namespace simple { namespace V2_0 { namespace implementation {   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 Simphw : public ISimphw {     // Methods from ISimphw follow.     Return simpfn(int32_t valueIn) override;       // Methods from ::android::hidl::base::V1_0::IBase follow.     static ISimphw* getInstance(void); };   // FIXME: most likely delete, this is only for passthrough implementations //extern "C" ISimphw* HIDL_FETCH_ISimphw(const char* name);   }  // namespace implementation }  // namespace V2_0 }  // namespace simple }  // namespace hardware }  // namespace android   #endif  // ANDROID_HARDWARE_SIMPLE_V2_0_SIMPHW_H

Simphw.cpp

 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

#include "Simphw.h"   namespace android { namespace hardware { namespace simple { namespace V2_0 { namespace implementation {   // Methods from ISimphw follow. Return Simphw::simpfn(int32_t valueIn) {     // TODO implement     return valueIn+100; }   ISimphw *Simphw::getInstance(void){   return new Simphw(); }   // Methods from ::android::hidl::base::V1_0::IBase follow.   //ISimphw* HIDL_FETCH_ISimphw(const char* /* name */) { //    return new Simphw(); //}   }  // namespace implementation }  // namespace V2_0 }  // namespace simple }  // namespace hardware }  // namespace android

Note that if you want to support pass-through mode, you need to uncomment the HIDL_FETCH_ISimphw function

In this example, we implemented the function as simple as possible (usually we will load the hardware module here)

The generated Android.bp file build a shared library with the implementation – [email protected]

Creating the Service

To host the library we need to create a simple executable:

service.cpp

 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

#define LOG_TAG "[email protected]"   #include   #include   #include "Simphw.h"   using android::hardware::simple::V2_0::ISimphw; using android::hardware::simple::V2_0::implementation::Simphw; using android::hardware::configureRpcThreadpool; using android::hardware::joinRpcThreadpool; using android::sp;   int main() {       int res;       android::sp ser = Simphw::getInstance();       ALOGE("simp main");       configureRpcThreadpool(1, true /*callerWillJoin*/);         if (ser != nullptr) {           res = ser->registerAsService();           if(res != 0)             ALOGE("Can't register instance of SimpleHardware, nullptr");       } else {           ALOGE("Can't create instance of SimpleHardware, nullptr");        }         joinRpcThreadpool();         return 0; // should never get here }

We create an instance of our implementation, Create a thread pool for the binder and register the current process as a service

Note that the function regsiterAsService() is auto-generated by hidl-gen tool

To make this service run automatically add init file:

[email protected]

 

1 2 3 4 5

service simphwserv /vendor/bin/hw/[email protected]     class hal     user root     group root     seclabel u:r:su:s0

For testing purpose I set the security label to su , we need to set SE Linux rules (I wrote it in the init.te file):

 

1 2	allow init vendor_file:file { execute }; allow init su:process { transition };

To tell the build system to build the service add the following to Android.bp (in directory default)

 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

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

Add the following components to build/make/target/product/emulator.mk

 

1 2	[email protected] \     [email protected] \

 

Now build the ROM and run it, connect with adb and run ps -A to see all the hardware services:

The lshal tool list all the hardware services by categories:

 

1

# lshal

Writing the Client

To use the service we will write a simple client application. Usually, it will be part of the Android framework written by Google. For example, if the generic framework wants to access the vibrator service:

In file  frameworks/base/services/core/jni/com_android_server_VibratorService.cpp

 

1 2 3 4 5 6 7 8 9

static sp mHal;   ...   mHal = IVibrator::getService(); ... Status retStatus = mHal->on(timeout_ms); ... Status retStatus = mHal->off();

Add a new directory in device/generic/goldfish – simphaltest

Add the source and Android.bp files:

 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

#define LOG_TAG "[email protected]"   #include #include #include #include #include #include #include     #include     using android::hardware::simple::V2_0::ISimphw; using android::sp;     int main() {       int res;       android::sp ser = ISimphw::getService();         res = ser->simpfn(200);         printf("val=%d\n",res);         return 0; }

Android.bp

 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

cc_binary {     name: "mysimptest",     defaults: ["hidl_defaults"],     proprietary: true,     srcs: ["servtest.cpp"],       shared_libs: [         "[email protected]",         "[email protected]",         "libhidlbase",         "libhidltransport",         "liblog",         "libutils",     ], }

Add the client test to build/make/target/product/emulator.mk

 

1	mysimptest \

Add hal entry to the Manifest.xml file of your device (device/generic/goldfish/Manifest.xml in this case)

 

1 2 3 4 5 6 7 8 9

android.hardware.simple hwbinder         2.0                      ISimphw             default

Build the ROM again and test our service:

 

Google BookmarkFacebookMore

Tagged Android, Android Internals, AOSP