Skip to content

Latest commit

 

History

History

hands-on_native-service

README.md

Hands-On: Implement a native example service

In the Android.bp file are two binaries defined the demo binary implementing the demoservice. And the demo-client util which connects over binder to the demoservice.

Limitations:

  • The example service ignores all permission handling.
  • No auto start over the init deamon.
  • The service needs manual deployment, it is not added to a device/product.
  • No integration of the service's git repo into the build tree with repo.

Hints

  • To format the source code run clang-format -i *.cpp *.h.

Step 1: Service setup and initial build

  1. Clone or copy the hands-on_native-service folder to system/demo in the AOSP source tree.

  2. Make sure the service demo and demo-client util builds without errors.

Verify:

If the service is build correctly you can find it's binary under: out/target/product/trout_x86_64/system/bin/demo and out/target/product/trout_x86_64/system/bin/demo-client

Hints:

  • The service is not added to a device/product.
  • Remember hmm to show option on how to build a single module.

Step 2: Run the service on a (virtual) device

As the service is not integrated into an product it is not automatically installed.

To install it by hand the system partition needs to be writable.

adb root
# Only needed once (`adb reboot` required)
adb disable-verity
adb remount system
adb sync system

And then run the service manually demo. In a new window and adb shell session test it with the demo-client hello.

Call the service with the service call ... utility See the documentation of the service utility on how the call feature works.

If you are curious on how the generated code for the AIDL file looks, you can find the relevant files in the out directory:

out/soong/.intermediates/system/demo/demo_aidl_interface-cpp-source/gen/
├── example
│   └── demo
│       ├── IDemoService.cpp
│       └── IDemoService.cpp.d
├── include
│   ├── example
│   │   └── demo
│   │       ├── BnDemoService.h
│   │       ├── BpDemoService.h
│   │       └── IDemoService.h
.   .
.   .

Verify:

  • The running service is shown in service list. (If the service list command hangs stop it with CTRL-C. As an alternative, you might want to fall back to using dumpsys -l)
  • Running demo-client hello works.
  • service call ... works.

Step 3: Log to the system log buffers (logcat)

Currently the service only logs to the standard output. But if the service is running under the init daemon these logs would not show up in the logcat.

Add logging to the system logcat buffer to the service calls.

There is a C library liblog. And the C++ logger with android-base/logging.h in the libbase.

See the readme of the liblog library /system/logging/liblog/README.md. See the readme of the libbase library /system/libbase/README.md.

Verify

The added log messages appearer in adb logcat.

Hints

  • Check how other services do the logging.
  • Logcat supports log filters see logcat on how to reduce the log output.

Step 4: Implement a new AIDL method

Add the function int calculate(int a, int b) to the AIDL interface and implement it.

This function should add the two numbers (a+b) and return the result.

Extend the client part of the service to call the new function.

Verify

With the service command you can call any service provided over the service manager. Call the new service implementation. (The service command has a help / usage message.)

Hints

  • Check other services or the AIDL documentation how to add the function.

Step 5: (Optional) Add the service to product and init system

For the init system see:

To add the service binary demo and the demo-client to the Android product see:

  • device/google/trout/ the aosp_trout_x86_64.mk and aosp_trout_common.mk.
  • And add the module to the PRODUCT_PACKAGES.

Verify:

  • Service is automatically build with m. (You can delete the service binary manually)
  • Service is started by the init daemon. Check with demo call-service