How to add a system service to the Android Framewo

Question

I want to add my own framework code that runs in the Android "system_server" (handles all the system level services). My service loads a JNI library that talks to a driver I have added to the kernel. The service is designed to allow an app to register a listener with it to get updates from the driver. I found a pretty good blog post (http://www.androidenea.com/2009/12/adding-system-server-to-android.html) that explains how to add a system service, but I cannot get it completely working.

First of all, the post mentions that an "appropriate" Android.mk file should be used to write the client/test application, but does not give an example of this. When I try to build it, I get build errors saying it can't find the service I have added. Could someone give an example of what this might look like?

Also, I'd like to implement this in the vendor directory (or device directory in froyo) rather than in the Android open source code. The blog post mentions that the proper place for this is the vendor directory, but does not give an example of what this should look like. Anyone know?

ANY additional information on implementing your own system service in Android would be helpful. Again my specific workflow is:

Android App -> System Service -> JNI (native) library -> Device Driver

Answer 1

Here is an example of an Android.mk used to compile a JNItest.c located at system/extras/JNITest. The Android.mk is also inside system/extras/JNITest directory.

LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)

LOCAL_SRC_FILES:= JNITest1.c

LOCAL_MODULE:= JNITest

#LOCAL_FORCE_STATIC_EXECUTABLE := true

#LOCAL_STATIC_LIBRARIES := libc
LOCAL_SHARED_LIBRARIES := libc

#LOCAL_MODULE_PATH := $(TARGET_OUT_OPTIONAL_EXECUTABLES)
LOCAL_MODULE_TAGS := eng

include $(BUILD_EXECUTABLE)

Answer 2

Follow the below steps for writing your own System Service in android framework.

1. Write your Own Service/Manager with API's exposed by inheriting the stub.
2. Create an aidl file for your service to expose & include in build.
3. Add your service in System Server, you service will start along with all core services.
4. Register your service context in context impl file.
5. Use your service in application by calling getSystemService(Context of your service)

PS; if your service get some fatal exception, device will soft reboot, as your service is running under system service.

Answer 3

There are multiply way (or 6 ways, just to be explicit) of adding a system service.

What you tried (Android App -> System Service -> JNI (native) library -> Device Driver) is one of them. You might want check out this article for an in-depth explanation regarding system service implementation patterns.

Answer 4

Texas instruments has provided a nice example:

http://processors.wiki.ti.com/index.php/Android-Adding_SystemService

Additionally, the CyanogenMod SystemServer.java has also code for dynamically loading system services as defined in the array "config_vendorServices" in config.xml (see core/res/res/values/config.xml), which I believe can be overwritten in the vendor or device directories using the overlays. This is a CyanogenMod-specific addition, added in this commit:

https://github.com/CyanogenMod/android_frameworks_base/commit/88fff90131f54d45dc496c45127ac1d16ad257df