我不是你想像那么勇敢：我的第一个Android 驱动程序，驱动层 到framworks层

对于未知的技术我们心里总是比较忐忑，当你走进发现原来并不是你想象中那么难，关键是我们需要勇敢迈出第一步----------Bill  2019.08.23 

      本文分两部分：一、驱动层的添加

                              二、framworks层的代码添加，以及应用层的调用。

一、驱动层的添加

         1.向内核添加我的驱动程序

             kernel-3.18\drivers\misc\mediatek\Kconfig     

                  增加:source "drivers/misc/mediatek/word_count/Kconfig"       word_count/Kconfig：我的驱动配置信息

              kernel-3.18\drivers\misc\mediatek\Kconfig\Makefile     

               增加:obj-$(CONFIG_WORD_COUNT) += word_count/     CONFIG_WORD_COUNT 在cofig文件中配置：                                                                                                                                  CONFIG_WORD_COUNT =y

         需要特别说明一下：obj-y 表示程序编译到内核，obj-c 表示只是编译驱动程序，而没有加载到内核

        2.编写驱动程序

         

#include <linux/module.h>#include <linux/init.h>#include <linux/kernel.h>#include <linux/fs.h>#include <linux/miscdevice.h>#include <asm/uaccess.h>// 定义设备文件名#define DEVICE_NAME "wordcount"static unsigned char mem[10000]; // 保存向设备文件写入的数据static int word_count = 0;#define TRUE 255#define FALSE 0// 判断指定字符是否为空格（包括空格符、制表符、回车符和换行符）static unsigned char is_spacewhite(char c){if (c == 32 || c == 9 || c == 13 || c == 10)return TRUE;elsereturn FALSE;}static int get_word_count(const char *buf){int n = 1;int i = 0;char c = ' ';char flag = 0; // 处理多个空格分隔的情况，0：正常情况，1：已遇到一个空格if (*buf == '\0')return 0;// 第1个字符是空格，从0开始计数if (is_spacewhite(*buf) == TRUE)n--;// 扫描字符串中的每一个字符for (; (c = *(buf + i)) != '\0'; i++){// 只由一个空格分隔单词的情况if (flag == 1 && is_spacewhite(c) == FALSE){flag = 0;}// 由多个空格分隔单词的情况，忽略多余的空格else if (flag == 1 && is_spacewhite(c) == TRUE){continue;}// 当前字符为空格是单词数加1if (is_spacewhite(c) == TRUE){n++;flag = 1;}}// 如果字符串以一个或多个空格结尾，不计数（单词数减1）if (is_spacewhite(*(buf + i - 1)) == TRUE)n--;return n;}static ssize_t word_count_read(struct file *file, char __user *buf, size_t count, loff_t *ppos){unsigned char temp[4];printk("xiaoshuilin word count read");temp[0] = word_count >> 24;temp[1] = word_count >> 16; temp[2] = word_count >> 8;temp[3] = word_count;//由于驱动程序是运行在内核空间，而我们的android程序是运行在用户空间，他们之间是不能直接交互的需要借助一些接口来实现数据的交互copy_to_user copy_from_user 这两个方法就linux提供的接口if (copy_to_user(buf, (void*) temp, 4)){return -EINVAL;}printk("xiaoshuilin word count read:%d", (int) count);return count;}static ssize_t word_count_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos){ssize_t written = count;printk("xiao word count write");if (copy_from_user(mem, buf, count)){return -EINVAL;}mem[count] = '\0';word_count = get_word_count(mem);printk("xiao write:word count:%d\n", (int) word_count);return written;}// 描述与设备文件触发的事件对应的回调函数指针static struct file_operations dev_fops ={ .owner = THIS_MODULE, .read = word_count_read, .write = word_count_write };// 描述设备文件的信息 static struct miscdevice misc ={ .minor = MISC_DYNAMIC_MINOR, .name = DEVICE_NAME, .fops = &dev_fops };// 初始化Linux驱动static int __init word_count_init(void){int ret; // 建立设备文件ret = misc_register(&misc);// 输出日志信息printk("xiao word_count_init_success ret=%d\n",ret);return ret;}// 卸载Linux驱动static void __exit word_count_exit(void){// 删除设备文件 misc_deregister(&misc);// 输出日志信息printk("word_count_init_exit_success\n");} // 注册初始化Linux驱动的函数，驱动程序的入口，相当于activity里面的oncreatemodule_init( word_count_init);// 注册卸载Linux驱动的函数 驱动程序的出口，相当activity里面的destroymodule_exit( word_count_exit);MODULE_AUTHOR("lining");MODULE_DESCRIPTION("statistics of word count.");MODULE_ALIAS("word count module.");MODULE_LICENSE("GPL");

至此驱动程序添加完成，不过我们还需要为其添加读写权限：

system\core\rootdir\eventd.rc    ## xiao
/dev/wordcount            0666   root       root

至此驱动部分添加完成。

二、framworks层的代码添加，以及应用层的调用

     思路：添加一个类似activityManager的服务，来完成应用层调用驱动。

 1.添加服务

   frameworks\base\services\java\com\android\server\SystemServer.java

   private void startOtherServices() {

......省略不相关的代码

  WordCountManagerService WordCountManager = null;

    //add  worcountManaerService
            try{
             traceBeginAndSlog("WordCountManagerService");
             Slog.e(TAG, "start WordCountManagerService now");
            WordCountManager = new WordCountManagerService(context);
             ServiceManager.addService(Context.WORDCOUNT_SERVICE, WordCountManager);//把实例保存起来为应用层调用做准备
            traceEnd();
            }catch(Throwable e){
                Slog.e(TAG, "start WordCountManagerService fail:"+e.toString());
                 reportWtf("starting WordCountManagerService fail", e);
                }

 }

WordCountManagerService代码：

/* * Copyright (C) 2006 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package com.android.server;import android.util.Log;import android.content.Context;import android.app.IWordCountManager; //M: change default to public as DataShapingServicepublic class WordCountManagerService extends IWordCountManager.Stub {private final String TAG="XIAO-WordCountManagerService"; private final Context mContext; public WordCountManagerService(Context context){ mContext=context; Log.d(TAG,"init WordCountManagerService"); } @Override public String read(){ String readOpen=readFromEvent(); Log.d(TAG,"readOpen form jni: "+readOpen); return readOpen; } @Override public void writer(String data){ Log.d(TAG,"writer to jni: "+data); writerToEvent(data); } private native String readFromEvent(); private native void writerToEvent(String writer);}

frameworks\base\core\java\android\app\SystemServiceRegistry.java

static {............省略不相关代码//通过这个代码的实现，后续在应用层中通过getSystemService(WordCountManager.class)，就可以获取到WordCountManager registerService(Context.WORDCOUNT_SERVICE, WordCountManager.class, new CachedServiceFetcher<WordCountManager>() { @Override public WordCountManager createService(ContextImpl ctx) throws ServiceNotFoundException { IBinder b = ServiceManager.getServiceOrThrow(Context.WORDCOUNT_SERVICE); IWordCountManager service = IWordCountManager.Stub.asInterface(b); return new WordCountManager(service); }});}

frameworks\base\core\java\android\app\IWordCountManager.aidl

interface IWordCountManager { String read(); void writer(String data);

frameworks\base\core\java\android\app\WordCountManager.java

package android.app;import android.os.RemoteException;public class WordCountManager { private final String TAG = "XIAO-WordCountManager"; private final IWordCountManager mService; public WordCountManager(IWordCountManager mService) { this.mService = mService; } public String read() { String data=null; try { data= mService.read(); } catch (RemoteException ex) { ex.printStackTrace(); } return data; } public void writer(String data) { try { mService.writer(data); } catch (RemoteException ex) { ex.printStackTrace(); } } }

此处服务添加完成，不过还需要Android.mk上做修改否则会出现找不到类的情况。

frameworks\base\Android.mk 

LOCAL_SRC_FILES += \

                                 core/java/android/app/IWordCountManager.aidl 

2.增加服务与驱动的交互，服务是java层代码，驱动是C/C++。所以我们需要增加一个JNI。

   frameworks\base\services\core\jni\com_android_server_WordCountManagerService.cpp

/* //device/libs/android_runtime/android_server_AlarmManagerService.cpp**** Copyright 2006, The Android Open Source Project**** Licensed under the Apache License, Version 2.0 (the "License");** you may not use this file except in compliance with the License.** You may obtain a copy of the License at**** http://www.apache.org/licenses/LICENSE-2.0**** Unless required by applicable law or agreed to in writing, software** distributed under the License is distributed on an "AS IS" BASIS,** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.** See the License for the specific language governing permissions and** limitations under the License.*/#define LOG_TAG "WordCountManagerService"#include <nativehelper/JNIHelp.h>#include "jni.h"#include <utils/Log.h>#include <utils/misc.h>#include <utils/String8.h>#include <dirent.h>#include <fcntl.h>#include <stdio.h>#include <string.h>#include <sys/epoll.h>#include <sys/timerfd.h>#include <sys/types.h>#include <sys/socket.h>#include <arpa/inet.h>#include <netinet/in.h>#include <stdlib.h>#include <errno.h>#include <unistd.h>#include <sys/stat.h>namespace android {char* jstring_to_pchar(JNIEnv* env, jstring str){char* pstr = NULL;jclass clsstring = env->FindClass("java/lang/String");jstring strencode = env->NewStringUTF("utf-8");jmethodID mid = env->GetMethodID(clsstring, "getBytes", "(Ljava/lang/String;)[B");jbyteArray byteArray = (jbyteArray)( (env)->CallObjectMethod(str, mid, strencode));jsize size = (env)->GetArrayLength( byteArray);jbyte* pbyte = (env)->GetByteArrayElements(byteArray, JNI_FALSE);if (size > 0){pstr = (char*) malloc(size);memcpy(pstr, pbyte, size);} env->DeleteLocalRef(clsstring);return pstr;}static void android_server_WordCountManagerService_writerToEvent(JNIEnv* env, jobject obj, jstring data){ int dev;dev = open("/dev/wordcount", O_WRONLY);char* pstr = jstring_to_pchar(env, data);ALOGD("XIAO-android_server_WordCountManagerService_writerToEvent dev=%d ,pstr=%s\n",dev,pstr);//const char* pstr = env->GetStringUTFChars(data, NULL);if (pstr != NULL){ssize_t write_size=write(dev,pstr, strlen(pstr));ALOGD("XIAO-android_server_WordCountManagerService_writerToEvent write_size=%d \n",write_size);}close(dev); }static jstring android_server_WordCountManagerService_readFromEvent(JNIEnv* env, jobject obj){ int dev; int size;char* buf=NULL; struct stat statbuf;dev = open("/dev/wordcount", O_RDONLY);if(dev!=-1){ fstat(dev,&statbuf); size=statbuf.st_size;}else{size=50;}size=50;char bufs[size]; buf=bufs; ssize_t read_size=read(dev, buf, size); ALOGD("XIAO-android_server_WordCountManagerService_readFromEvent dev=%d ,size=%d\n",dev,size);ALOGD("XIAO-android_server_WordCountManagerService_readForEvent buf=%s, read_size=%d \n",buf,read_size);if(buf!=NULL){jstring data=env->NewStringUTF(buf);ALOGD("XIAO-android_server_WordCountManagerService_readForEvent data=%s \n",data);close(dev);return data; }close(dev);return NULL;}/// M: added for powerOffAlarm feature @{static const JNINativeMethod sMethods[] = { /* name, signature, funcPtr */ {"writerToEvent", "(Ljava/lang/String;)V", (void*)android_server_WordCountManagerService_writerToEvent}, {"readFromEvent", "()Ljava/lang/String;", (void*)android_server_WordCountManagerService_readFromEvent},};int register_android_server_WordCountManagerServic(JNIEnv* env){ return jniRegisterNativeMethods(env, "com/android/server/WordCountManagerService", sMethods, NELEM(sMethods));}} /* namespace android */

frameworks\base\services\core\jni\Android.mk

LOCAL_SRC_FILES += \ 

                                       $(LOCAL_REL_DIR)/com_android_server_WordCountManagerService.cpp

 

frameworks\base\services\core\jni\onload.cpp

 namespace android {
int register_android_server_WordCountManagerServic(JNIEnv* env);//添加动态注销JNI的方法。

}

extern "C" jint JNI_OnLoad(JavaVM* vm, void* /* reserved */)
{
    JNIEnv* env = NULL;
    jint result = -1;

    if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) {
        ALOGE("GetEnv failed!");
        return result;
    }
    ALOG_ASSERT(env, "Could not retrieve the env!");

    register_android_server_WordCountManagerServic(env);//调用注册方法

}