安卓硬件服务实例：手把手教你如何从驱动到应用添加硬件服务

序言：    

        这篇文章在安卓7.1源码添加自己的硬件访问服务，从内核驱动，hal层,jni层，application framework，最后到app调用    包装类，在内核实现简单的打印输出，通过这篇文章，会让你对安卓整个的框架有深刻的认识。

本文为原创，转载请标明原址：https://blog.csdn.net/kai_zone/article/details/81305222

系列文章：  Android硬件服务框架实例之Vibrator(驱动到应用)

                    安卓硬件访问服务框架

为了便于理解，我们从底层到上层逐个添加和修改。

1. 添加驱动，只实现一个简单的ioctl函数，驱动里打印app设置的值。

led.c代码如下：

​
​
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
static struct class *led_class;

static int led_open(struct inode *inode, struct file *file)
{
        printk(KERN_INFO "*******In  %s ***************\n", __func__);
        return 0;
}
static int led_release(struct inode *inodp, struct file *filp)
{
        printk(KERN_INFO "*******In  %s ***************\n", __func__);
        return 0;
}

static long led_ioctl
(struct file *filp, unsigned int status, unsigned long which)
{
  printk("******(%s)status:%d;which:%d********\n", __func__,(int)status,(int)which);
  return 123;
}

static struct file_operations led_fops = {
    .owner  =   THIS_MODULE,    
    .open   =   led_open,
    .release = led_release,     
    .unlocked_ioctl = led_ioctl,
};
int major;
static int led_init(void)
{
        major = register_chrdev(0, "leds", &led_fops); 
        led_class = class_create(THIS_MODULE, "leddrv");
        device_create(led_class, NULL, MKDEV(major, 0), NULL, "led"); /*dev/led */
        return 0;
}
static void led_exit(void)
{
        unregister_chrdev(major, "leds"); 
        device_destroy(led_class, MKDEV(major, 0));
        class_destroy(led_class);
}

module_init(led_init);
module_exit(led_exit);
MODULE_LICENSE("GPL");

修改Makefile直接配置到内核，增加语句obj-y    +=    led.o。编译：make bootimage -j16烧写到开发板会生成/dev/led设备节点。

2. hal层修改。

    (1). hardware/libhardware/modules/下新建目录led目录，在led目录下创建Android.mk和led_hal.c.

Android.mk代码如下：

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE := led.default

# HAL module implementation stored in
# hw/.default.so
LOCAL_MODULE_RELATIVE_PATH := hw
LOCAL_C_INCLUDES := hardware/libhardware
LOCAL_SRC_FILES := led_hal.c
LOCAL_SHARED_LIBRARIES := liblog
LOCAL_MODULE_TAGS := eng

include $(BUILD_SHARED_LIBRARY)

led_hal.c代码如下：

​
#define LOG_TAG "LedHal"
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

static int fd;
/** Close this device */
static int led_close(struct hw_device_t* device)
{
        close(fd);
        return 0;
}

static int led_open(struct led_device_t* dev)
{
        fd = open("/dev/led", O_RDWR);
        ALOGI("led_open : %d", fd);
        if (fd >= 0)
                return 0;
        else
                return -1;
}

static int led_ctrl(struct led_device_t* dev, int which, int status)
{
        if(fd < 0) {
            fd = open("/dev/led", O_RDWR);
        }
        int ret = ioctl(fd, status, which);
        ALOGI("led_ctrl : %d, %d, %d, %d", which, status, ret, fd);
        return ret;
}

static struct led_device_t led_dev = {
        .common = {
                .tag   = HARDWARE_DEVICE_TAG,
                .close = led_close,
        },
        .led_open  = led_open,
        .led_ctrl  = led_ctrl,
};

static int led_device_open(const struct hw_module_t* module, const char* id,
        struct hw_device_t** device)
{
        *device = &led_dev;
        return 0;
}

static struct hw_module_methods_t led_module_methods = {
    .open = led_device_open,
};

struct hw_module_t HAL_MODULE_INFO_SYM = {
        .tag = HARDWARE_MODULE_TAG,
    .id = LED_HARDWARE_MODULE_ID,//JNI会通过这个id获取到hal生成的库  
    .methods = &led_module_methods,
};

(2) 添加led_hal.h：hardware/libhardware/include/hardware/led_hal.h；led_hal.h代码如下：

#ifndef ANDROID_LED_INTERFACE_H
#define ANDROID_LED_INTERFACE_H
#include 
#include 
#include 
#include 

#define LED_HARDWARE_MODULE_ID "led"

__BEGIN_DECLS
struct led_device_t {
    struct hw_device_t common;

        int (*led_open)(struct led_device_t* dev);
        int (*led_ctrl)(struct led_device_t* dev,int which, int status);
};

__END_DECLS

#endif  // ANDROID_LED_INTERFACE_H

3. JNI层：

(1) 创建文件：frameworks/base/services/core/jni/com_android_server_LedService.cpp，代码如下：

​
#define LOG_TAG "LedService"

#include "jni.h"
#include "JNIHelp.h"
#include "android_runtime/AndroidRuntime.h"
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

namespace android
{

static led_device_t* led_device;

jint ledOpen(JNIEnv *env, jobject cls)
{
        jint err;
    hw_module_t* module;
        hw_device_t* device;
        ALOGI("native ledOpen ...");

        /* 1. hw_get_module 通过"led"(这是hal的id)找到对应的库.*/
    err = hw_get_module("led", (hw_module_t const**)&module);
    if (err == 0) {
                /* 2. get device : module->methods->open */
            err = module->methods->open(module, NULL, &device);
            if (err == 0) {
                        /* 3. call led_open */
                led_device = (led_device_t *)device;
                        return led_device->led_open(led_device);
            } else {
                return -1;
        }
    }
    return -1;
}

void ledClose(JNIEnv *env, jobject cls)
{
        //ALOGI("native ledClose ...");
        //close(fd);
}

jint ledCtrl(JNIEnv *env, jobject cls, jint which, jint status)
{
        ALOGI("native ledCtrl %d, %d", which, status);
        return led_device->led_ctrl(led_device, which, status);
}
//注册本地方法。
static const JNINativeMethod methods[] = {
        {"native_ledOpen", "()I", (void *)ledOpen},
        {"native_ledClose", "()V", (void *)ledClose},
        {"native_ledCtrl", "(II)I", (void *)ledCtrl},
};
int register_android_server_LedService(JNIEnv *env)
{//本地方法对应的java类LedService
    return jniRegisterNativeMethods(env, "com/android/server/LedService",
            methods, NELEM(methods));
}
}

​

(2) 修改frameworks/base/services/core/jni/onload.cpp，修改如下：

+int register_android_server_LedService(JNIEnv* env);
 int register_android_server_connectivity_Vpn(JNIEnv* env);
@@ -74,6 +75,7 @@ extern "C" jint JNI_OnLoad(JavaVM* vm, void* /* reserved */)
     register_android_server_VibratorService(env);
+    register_android_server_LedService(env);

​

(3) 修改：frameworks/base/services/core/jni/Android.mk；添加如下：

     $(LOCAL_REL_DIR)/com_android_server_VibratorService.cpp \
+    $(LOCAL_REL_DIR)/com_android_server_LedService.cpp \

至此，c/c++代码已经修改完成了。下面进入java程序的修改。

4. framework层：

(1) 增加文件：frameworks/base/core/java/android/os/ILedService.aidl。代码如下：

package android.os;

/** {@hide} */
interface ILedService
{
        int ledCtrl(int which, int status);
}

(2) 创建文件： frameworks/base/services/core/java/com/android/server/LedService.java。代码如下：

package com.android.server;
import android.os.ILedService;

public class LedService extends ILedService.Stub {
    private static final String TAG = "LedService";

        /* call native c function to access hardware */
        public int ledCtrl(int which, int status) throws android.os.RemoteException
        {
                return native_ledCtrl(which, status);
        }
        public LedService() {
                native_ledOpen();
        }

        public static native int native_ledOpen();
        public static native void native_ledClose();
        public static native int native_ledCtrl(int which, int status);
}

LedService.java通过JNI,调用本地函数，

(3) 修改：frameworks/base/Android.mk：

        core/java/android/os/IVibratorService.aidl \
+       core/java/android/os/ILedService.aidl \
        core/java/android/security/IKeystoreService.aidl \

(4) 在文件frameworks/base/services/java/com/android/server/SystemServer.java添加如下内容：

+          
+            traceBeginAndSlog("StartLedService");
+            LedService led = new LedService();
+            ServiceManager.addService("led", led);
+            Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
+
             if (!disableConsumerIr) {

到这里，LedService服务就已经注册添加到系统里了。下面是使用服务。

5. application framework:

(1)创建文件: frameworks/base/core/java/android/os/SystemLed.java,这个类供app获取，

    通过getSystemService(Context.LED_SERVICE);

package android.os;

import android.content.Context;
import android.media.AudioAttributes;
import android.util.Log;

/**
 * Led implementation that controls the main system led.
 *
 * @hide
 */
public class SystemLed {
    private static final String TAG = "Led";

    private final ILedService mService;
    public SystemLed() {
        mService = ILedService.Stub.asInterface(
                ServiceManager.getService("led"));
    }

    public SystemLed(Context context) {
        mService = ILedService.Stub.asInterface(
                ServiceManager.getService("led"));
    }

   public void ledCtrl(int which,int status)
        {
                try{
                mService.ledCtrl(which, status);
                }catch(Exception e){}
        }
}

 

(2) 修改文件：frameworks/base/core/java/android/content/Context.java

     public static final String VIBRATOR_SERVICE = "vibrator";
+    public static final String LED_SERVICE = "led";

(3) 最后修改文件：frameworks/base/core/java/android/app/SystemServiceRegistry.java

+import android.os.SystemLed;
 import android.os.UserHandle;
 import android.os.UserManager;
 import android.os.Vibrator;
@@ -486,6 +487,13 @@ final class SystemServiceRegistry {
             public Vibrator createService(ContextImpl ctx) {
                 return new SystemVibrator(ctx);
             }});
+        registerService(Context.LED_SERVICE, SystemLed.class,
+                new CachedServiceFetcher() {
+            @Override
+            public SystemLed createService(ContextImpl ctx) {
+                return new SystemLed(ctx);
+            }});

安卓源码的修改已全部完成。

make update-api  更新api;

make systemimage -j16  编译system.img 并烧写到开发板。

6. APP应用：

由于源码里怎加了很多类，而在安卓sdk中是没有这些类的，解决这个办法就是eclipse或者android studio关联下面这个文件：

out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/classes.jar。

eclipse关联方法：https://blog.csdn.net/mazhaojuan/article/details/21403717

android studio关联：https://www.jetbrains.com/idea/help/configuring-module-dependencies-and-libraries.html

APP主要代码如下：

 

​
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;
import android.os.SystemLed;
import android.os.RemoteException;
import android.os.ServiceManager;

public class MainActivity extends Activity {
	
    private SystemLed ledservice = null;
    private static int STATUS = 0,WHICH =1 ;
    private TextView text= null;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);	
		text = (TextView) findViewById(R.id.text);
		text.setText("STATUS:"+STATUS+";WHICH:"+WHICH);
        //通过getSystemService()来获取SystemLed.
		ledservice = (SystemLed) getSystemService(Context.LED_SERVICE);				
	}
	
	public void add(View view)
	{
			ledservice.ledCtrl(++WHICH, ++STATUS);
			text.setText("STATUS:"+STATUS+";WHICH:"+WHICH);
	}
	public void reduce(View view)
	{
			ledservice.ledCtrl(--WHICH, --STATUS);
			text.setText("STATUS:"+STATUS+";WHICH:"+WHICH);
	}

​

7. 效果图：

(1)APP界面（比较简单，凑合看吧，嘿嘿...）：

(2)内核打印： 命令：cat /dev/kmsg | grep led,点击自增或者自减按钮，会看到输出变化。

APP代码下载：https://download.csdn.net/download/kai_zone/10575497

本文涉及的代码：https://download.csdn.net/download/kai_zone/10575551

容易出现的问题：

a .设备节点权限问题，没有权限，open设备节点会失败，chmod 777 dev/led给权限，也可以在.rc文件。

b. classes.jar导包问题，如果app没有你添加的类，肯定是类还没编译到classes.jar文件，重新编译再次导入。