Android HAL实例解析(2)

4、第一种方法：直接调用service方法的实现过程

    下面分析第一种方法中，各层的关键代码。

（1）HAL层

    一般来说HAL moudle需要涉及的是三个关键结构体：

struct hw_module_t;

struct hw_module_methods_t;

struct hw_device_t;

    下面结合代码说明这3个结构的用法。部分代码经过修改，后面的章节会给出修改的原因。

文件：mokoid-read-only/hardware/modules/include/mokoid/led.h 

struct led_module_t {
   struct hw_module_t common;
};
//HAL 规定不能直接使用hw_module_t结构，因此需要做这么一个继承。
struct led_control_device_t {
//自定义的一个针对Led控制的结构，包含hw_device_t和支持的API操作
   struct hw_device_t common;
   /* attributes */
   int fd;  //可用于具体的设备描述符
   /* supporting control APIs go here */
   int (*set_on)(struct led_control_device_t *dev, int32_t led);
   int (*set_off)(struct led_control_device_t *dev, int32_t led);
};
#define LED_HARDWARE_MODULE_ID "led"
//定义一个MODULE_ID，HAL层可以根据这个ID找到我们这个HAL stub

文件：mokoid-read-only/hardware/modules/led/led.c

#define LOG_TAG "MokoidLedStub"
#include <hardware/hardware.h>
#include <fcntl.h>
#include <errno.h>
#include <cutils/log.h>
#include <cutils/atomic.h>
//#include <mokoid/led.h>
#include "../include/mokoid/led.h"
/*****************************************************************************/
int fd;             //硬件led的设备描述符 。你也可以用led_control_device_t结构中定义的fd
#define GPG3DAT2_ON 0x4800                 //ioctl控制命令
#define GPG3DAT2_OFF 0x4801
int led_device_close(struct hw_device_t* device)
{
    struct led_control_device_t* ctx = (struct led_control_device_t*)device;
    if (ctx) {
        free(ctx);
    }
    close(fd);
    return 0;
}
int led_on(struct led_control_device_t *dev, int32_t led)
{
    LOGI("LED Stub: set %d on.", led);
    ioctl(fd,GPG3DAT2_ON,NULL);           //控制Led亮灭，和硬件相关
    return 0;
}
int led_off(struct led_control_device_t *dev, int32_t led)
{
    LOGI("LED Stub: set %d off.", led);
    return 0;
}
static int led_device_open(const struct hw_module_t* module, const char* name,
        struct hw_device_t** device)
{
    struct led_control_device_t *dev;
    dev = (struct led_control_device_t *)malloc(sizeof(*dev));
    memset(dev, 0, sizeof(*dev));
    dev->common.tag =  HARDWARE_DEVICE_TAG;
    dev->common.version = 0;
    dev->common.module = module;
    dev->common.close = led_device_close;
    dev->set_on = led_on;        //实例化支持的操作
    dev->set_off = led_off;
    *device = &dev->common;     //将实例化后的led_control_device_t地址返回给jni层
                    //这样jni层就可以直接调用led_on、led_off、led_device_close方法了。
    if((fd=open("/dev/led",O_RDWR))==-1)      //打开硬件设备
    {
        LOGE("LED open error");
    }
    else
        LOGI("open ok");
success:
    return 0;
}
static struct hw_module_methods_t led_module_methods = {
    open: led_device_open
};
const struct led_module_t HAL_MODULE_INFO_SYM = {
//定义这个对象等于向系统注册了一个ID为LED_HARDWARE_MODULE_ID的stub。注意这里HAL_MODULE_INFO_SYM的名称不能改。
    common: {
        tag: HARDWARE_MODULE_TAG,
        version_major: 1,
        version_minor: 0,
        id: LED_HARDWARE_MODULE_ID,
        name: "Sample LED Stub",
        author: "The Mokoid Open Source Project",
        methods: &led_module_methods,  //实现了一个open的方法供jni层调用，
                                       //从而实例化led_control_device_t
    }
    /* supporting APIs go here */
};

（2）JNI层

文件：mokoid-read-only/frameworks/base/service/jni/com_mokoid_server_LedService.cpp

struct led_control_device_t *sLedDevice = NULL;

static jboolean mokoid_setOn(JNIEnv* env, jobject thiz, jint led)
{
    LOGI("LedService JNI: mokoid_setOn() is invoked.");

    if (sLedDevice == NULL) {
        LOGI("LedService JNI: sLedDevice was not fetched correctly.");
        return -1;
    } else {
        return sLedDevice->set_on(sLedDevice, led);//调用hal层的注册的方法
    }
}

static jboolean mokoid_setOff(JNIEnv* env, jobject thiz, jint led)
{
    LOGI("LedService JNI: mokoid_setOff() is invoked.");


    if (sLedDevice == NULL) {
        LOGI("LedService JNI: sLedDevice was not fetched correctly.");
        return -1;
    } else {
        return sLedDevice->set_off(sLedDevice, led); //调用hal层的注册的方法
    }
}

/** helper APIs */
static inline int led_control_open(const struct hw_module_t* module,
        struct led_control_device_t** device) {
    return module->methods->open(module,
            LED_HARDWARE_MODULE_ID, (struct hw_device_t**)device);
//这个过程非常重要，jni通过LED_HARDWARE_MODULE_ID找到对应的stub
}

static jboolean mokoid_init(JNIEnv *env, jclass clazz)
{
    led_module_t* module;
     LOGI("jni init-----------------------.");
if (hw_get_module(LED_HARDWARE_MODULE_ID, (const hw_module_t**)&module) == 0) {
//根据LED_HARDWARE_MODULE_ID找到hw_module_t，参考hal层的实现
        LOGI("LedService JNI: LED Stub found.");
        if (led_control_open(&module->common, &sLedDevice) == 0) {
    //通过hw_module_t找到led_control_device_t
            LOGI("LedService JNI: Got Stub operations.");
            return 0;
        }
    }

    LOGE("LedService JNI: Get Stub operations failed.");
    return -1;
}

/*
 * Array of methods.
* Each entry has three fields: the name of the method, the method
 * signature, and a pointer to the native implementation.
 */
static const JNINativeMethod gMethods[] = {
    { "_init",      "()Z",  (void *)mokoid_init },//Framework层调用_init时促发
    { "_set_on",        "(I)Z", (void *)mokoid_setOn },
    { "_set_off",       "(I)Z", (void *)mokoid_setOff },
};
/*
*JNINativeMethod是jni层注册的方法，Framework层可以使用这些方法
*_init 、_set_on、_set_off是在Framework中调用的方法名称，函数的类型及返回值如下：
*（）Z   无参数    返回值为bool型
* (I)Z   整型参数  返回值为bool型
*/
static int registerMethods(JNIEnv* env) {
        static const char* const kClassName =
        "com/mokoid/server/LedService";//注意：必须和你Framework层的service类名相同
        jclass clazz;
      /* look up the class */
        clazz = env->FindClass(kClassName);
        if (clazz == NULL) {
                    LOGE("Can't find class %s/n", kClassName);
                    return -1;
        }
    /* register all the methods */
        if (env->RegisterNatives(clazz, gMethods,
                        sizeof(gMethods) / sizeof(gMethods[0])) != JNI_OK)
        {
            LOGE("Failed registering methods for %s/n", kClassName);
            return -1;
        }
    /* fill out the rest of the ID cache */
        return 0;
}
jint JNI_OnLoad(JavaVM* vm, void* reserved) {//Framework层加载jni库时调用
        JNIEnv* env = NULL;
        jint result = -1;
        LOGI("JNI_OnLoad LED");
            if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) {
            LOGE("ERROR: GetEnv failed/n");
            goto fail;
        }
            assert(env != NULL);
        if (registerMethods(env) != 0) { //注册你的JNINativeMethod
            LOGE("ERROR: PlatformLibrary native registration failed/n");
            goto fail;
        }
        /* success -- return valid version number */
        result = JNI_VERSION_1_4;
fail:
        return result;
}

（3）service  （属于Framework层）

文件：frameworks/base/service/java/com/mokoid/server/LedService.java

package com.mokoid.server;
import Android.util.Config;
import Android.util.Log;
import Android.content.Context;
import Android.os.Binder;
import Android.os.Bundle;
import Android.os.RemoteException;
import Android.os.IBinder;
import mokoid.hardware.ILedService;
public final class LedService extends ILedService.Stub {
//对于这种直接模式不需要进程通讯，所以可以不加extends ILedService.Stub，此处加上主要是为了后面的第二种模式.
    static {
        System.load("/system/lib/libmokoid_runtime.so");//加载jni的动态库
    }
    public LedService() {
        Log.i("LedService", "Go to get LED Stub...");
    _init();
    }
    /*
     * Mokoid LED native methods.
     */
    public boolean setOn(int led) {
        Log.i("MokoidPlatform", "LED On");
    return _set_on(led);
    }
    public boolean setOff(int led) {
        Log.i("MokoidPlatform", "LED Off");
    return _set_off(led);
    }
    private static native boolean _init();          //声明jni库可以提供的方法
    private static native boolean _set_on(int led);
    private static native boolean _set_off(int led);
}

（4）APP 测试程序 （属于APP层）

文件：apps/LedClient/src/com/mokoid/LedClient/LedClient.java

package com.mokoid.LedClient;
import com.mokoid.server.LedService;// 导入Framework层的LedService
import Android.app.Activity;
import Android.os.Bundle;
import Android.widget.TextView;

public class LedClient extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // Call an API on the library.
    LedService ls = new LedService();  //实例化LedService
    ls.setOn(1);                       //通过LedService提供的方法，控制底层硬件
    ls.setOff(2);

        TextView tv = new TextView(this);
        tv.setText("LED 1 is on. LED 2 is off.");
        setContentView(tv);
    }
}