android hal学习——aidl，java service，jni编写

一、参考

二、代码
1、aidl相关
1）aidl文件定义
位置：
frameworks/base/core/java/android/os/IExampleService.aidl

package android.os;interface IExampleService {    void setVal(int val);    int getVal();}

2）、修改相应的Android.mk
vim frameworks/base/Android.mk
找到下面的这句话：

## READ ME: ############################################################ When updating this list of aidl files, consider if that aidl is## part of the SDK API.  If it is, also add it to the list below that## is preprocessed and distributed with the SDK.  This list should## not contain any aidl files for parcelables, but the one below should## if you intend for 3rd parties to be able to send those objects## across process boundaries.#### READ ME: ########################################################LOCAL_SRC_FILES += \

在这个LOCAL_SRC_FILES后面增加：

    。。。            core/java/android/os/IExampleService.aidl \

3）、编译aidl

mmm frameworks/base/...n Runtime shutdown[100% 8/8] Install: out/target/product/generic/system/framework/framework.jarmake: Leaving directory `/home/zzz/opensource/android-src'#### make completed successfully (03:34 (mm:ss)) ####

2、服务端service相关
1）实现服务端service功能
参考文章提到是在frameworks/base/services/java/com/android/server建立ExampleService.java来实现aidl接口，应该是版本不同，我这边需要则在以下目录下实现：
frameworks/base/services/core/java/com/android/server。
代码照旧copy：

package com.android.server;import android.content.Context;import android.os.IExampleService;import android.util.Slog;public class ExampleService extends IExampleService.Stub {    private static final String TAG = "ExampleService";    private int mPtr = 0;    ExampleService() {        mPtr = init_native();        if(mPtr == 0) {            Slog.e(TAG, "Failed to initialize example service.");        }    }    public void setVal(int val) {        if(mPtr == 0) {            Slog.e(TAG, "Example service is not initialized.");            return;        }        setVal_native(mPtr, val);    }    public int getVal() {        if(mPtr == 0) {            Slog.e(TAG, "Example service is not initialized.");            return 0;        }        return getVal_native(mPtr);    }    private static native int init_native();    private static native void setVal_native(int ptr, int val);    private static native int getVal_native(int ptr);};

2）、编译该service

 mmm frameworks/base/services/core/ 。。。 ============================================Starting build with ninjaninja: Entering directory `.'[100% 5/5] build out/target/product/ge...rvices.core_intermediates/classes.jackmake: Leaving directory `/home/zzz/opensource/android-src'#### make completed successfully (01:11 (mm:ss)) ####

3、jni相关
1）定义jni cpp文件
位置：frameworks/base/services/core/jni/com_android_server_ExampleService.cpp

#define LOG_TAG "ExampleServiceJNI"#include "jni.h"#include "JNIHelp.h"#include "android_runtime/AndroidRuntime.h"#include <utils/misc.h>#include <utils/Log.h>#include <hardware/hardware.h>#include <hardware/example.h>#include <stdio.h>namespace android{    static void example_setVal(JNIEnv* env, jobject clazz, jint ptr, jint value) {        example_device_t* device = (example_device_t*)ptr;        if(!device) {            LOGE("Device example is not open.");            return;        }        int val = value;        LOGI("Set value %d to device example.", val);        device->set_val(device, val);    }    static jint example_getVal(JNIEnv* env, jobject clazz, jint ptr) {        example_device_t* device = (example_device_t*)ptr;        if(!device) {            LOGE("Device example is not open.");            return 0;        }        int val = 0;        device->get_val(device, &val);        LOGI("Get value %d from device example.", val);        return val;    }    static inline int example_device_open(const hw_module_t* module, struct example_device_t** device) {        return module->methods->open(module, EXAMPLE_HARDWARE_DEVICE_ID, (struct hw_device_t**)device);    }    static jint example_init(JNIEnv* env, jclass clazz) {        example_module_t* module;        example_device_t* device;        LOGI("Initializing HAL stub example......");        if(hw_get_module(EXAMPLE_HARDWARE_MODULE_ID, (const struct hw_module_t**)&module) == 0) {            LOGI("Device example found.");            if(example_device_open(&(module->common), &device) == 0) {                LOGI("Device example is open.");                return (jint)device;            }            LOGE("Failed to open device example.");            return 0;        }        LOGE("Failed to get HAL stub example.");        return 0;    }    static const JNINativeMethod method_table[] = {        {"init_native", "()I", (void*)example_init},        {"setVal_native", "(II)V", (void*)example_setVal},        {"getVal_native", "(I)I", (void*)example_getVal},    };    int register_android_server_ExampleService(JNIEnv *env) {            return jniRegisterNativeMethods(env, "com/android/server/ExampleService", method_table, NELEM(method_table));    }};

2）修改onload.cpp代码，增加相关的函数：
vim frameworks/base/services/core/jni/onload.cpp

namespace android {...int register_android_server_ExampleService(JNIEnv* env);};extern "C" jint JNI_OnLoad(JavaVM* vm, void* /* reserved */){...   register_android_server_ExampleService(env);    return JNI_VERSION_1_4;}

3）修改Android.mk文件
vim frameworks/base/services/core/jni/Android.mk
增加LOCAL_SRC_FILES的内容：

LOCAL_SRC_FILES += \...    $(LOCAL_REL_DIR)/com_android_server_ExampleService.cpp \    $(LOCAL_REL_DIR)/onload.cpp \

4）编译
mmm frameworks/base/services/core/jni/

...============================================Starting build with ninjaninja: Entering directory `.'ninja: no work to do.make: Leaving directory `/home/zzz/opensource/android-src'#### make completed successfully (4 seconds) ####

4、将ExampleService加入到系统进程中
vim frameworks/base/services/java/com/android/server/SystemServer.java
增加：

 814  815  816 //-----------begin-----------------// 817 try { 818                 Slog.i(TAG, "Example Service");   819                 ServiceManager.addService("example", new ExampleService());      820             } catch (Throwable e) { 821                 Slog.e(TAG, "Failure starting Example Service", e); 822             }   823 //---------end---------//

5、重新编译frameworks/base/services模块：
mmm frameworks/base/services/
第一次编译出了点错误：

frameworks/base/services/core/jni/com_android_server_ExampleService.cpp:66:9: error: use of undeclared identifier 'LOGE'        LOGE("Failed to get HAL stub example.");        ^9 errors generated.ninja: build stopped: subcommand failed.make: *** [ninja_wrapper] Error 1make: Leaving directory `/home/zzz/opensource/android-src'#### make failed to build some targets (01:32 (mm:ss)) ####

将com_android_server_ExampleService.cpp里面的LOGE改为ALOGE，LOGI改为ALOGI，再编译：
mmm frameworks/base/services/

No need to regenerate ninja fileStarting build with ninjaninja: Entering directory `.'[100% 19/19] build out/target/product/...interaction_intermediates/classes.jackmake: Leaving directory `/home/gumh/opensource/android-src'#### make completed successfully (6 seconds) ####

6、修改权限
为了避免无权访问/dev/example，修改以下文件：
vim system/core/rootdir/ueventd.rc
在最后面增加：
/dev/example 0666 root root

7、重新生成system.img
make snod

。。。make_ext4fs -T -1 -S out/target/product/generic/root/file_contexts.bin -L system -l 1610612736 -a system out/target/product/generic/system.img out/target/product/generic/system out/target/product/generic/systemCreating filesystem with parameters:    Size: 1610612736    Block size: 4096    Blocks per group: 32768    Inodes per group: 8192    Inode size: 256    Journal blocks: 6144    Label: system    Blocks: 393216    Block groups: 12    Reserved block group size: 95Created filesystem with 1751/98304 inodes and 146362/393216 blocksout/target/product/generic/system.img maxsize=1644333504 blocksize=2112 total=1610612736 reserve=16610880#### make completed successfully (19 seconds) ####