2-安卓底层-java实现调用linux系统调用

java实现调用linux系统调用流程：

java --》 jni ---》 driver

java 实现的是native方法

jni 实现的是调用linux 系统调用

java_open = method结构体 ==> Jopen == jni里调用 => open(系统调用) ==> driver_open

驱动：ibo.c

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/cdev.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <asm/uaccess.h>
#include <asm/io.h>

#define     IBO_MAJOR   505
#define     IBO_MINOR   0
#define     IBO_NUM     1
#define     IBO_NAME    "ibo"
#define     CLS_NAME    "ibo_cls"
#define     DEV_NAME    "ibo"

dev_t devno;
struct cdev ibo_cdev;
struct class * cls;

static int ibo_open(struct inode *inode,struct file *filp){
    printk("ibo_open success\n");
    return 0;
}

static int ibo_release(struct inode *inode,struct file *filp){
    printk("ibo_release success\n");
    return 0;
}

static long ibo_ioctl(struct file *filp,unsigned int cmd,unsigned long arg){
    printk("ibo_ioctl success %d\n",cmd);
    return 0;
}

struct file_operations ibo_fops={
     .owner          = THIS_MODULE,
     .open           = ibo_open,
     .release        = ibo_release,
     .unlocked_ioctl = ibo_ioctl,
};

static int ibo_init(void){
    int ret;
    devno = MKDEV(IBO_MAJOR,IBO_MINOR);
    ret = register_chrdev_region(devno,IBO_NUM,IBO_NAME);
    if (ret < 0){
        return -EFAULT;
    }

    cdev_init(&ibo_cdev,&ibo_fops);
    ibo_cdev.owner = THIS_MODULE;

    cdev_add(&ibo_cdev,devno,IBO_NUM);

    cls = class_create(THIS_MODULE,CLS_NAME);
    if (IS_ERR(cls)){
        printk("class_create fail!!!\n");
        return -EFAULT;
    }

    device_create(cls,NULL,devno,NULL,DEV_NAME);

    printk("ibo_init success\n");
    return 0;
}

static void ibo_exit(void){
    device_destroy(cls,devno);
    class_destroy(cls);
    cdev_del(&ibo_cdev);
    unregister_chrdev_region(devno,IBO_NUM);

    printk("ibo_exit success\n");
    return;
}

module_init(ibo_init);
module_exit(ibo_exit);

MODULE_LICENSE("GPL");

驱动:Makefile

ifeq ($(KERNELRELEASE),)

KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)

modules:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) 

clean:
    rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions Module* modules*

.PHONY: modules clean

else
    obj-m := ibo.o
endif

1.输入make编译生成 .ko 文件

2.sudo insmod ibo.ko 把模块插入到内核中

• 输出 ibo_init success 表示成功插入到内核中

---

JAVA : Ibo.java

class Ibo{
    static{
        System.loadLibrary("native");
    }
    private native void open();
    private native void ioctl(int cmd);
    private native void release();


    public static void main(String[] args) {

        Ibo m=new Ibo();
        m.open();
        m.ioctl(525);
        m.release();
    }
}

3.javac Ibo.java生成 class文件

4.javah Ibo生成 h文件

---

JNI : native.c

#include <jni.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/ioctl.h>

int fd;

void Jopen(JNIEnv *env,jobject obj){
    fd = open("/dev/ibo",O_RDWR);
    return;
}
void Jioctl(JNIEnv *env,jobject obj,jint cmd){
    ioctl(fd,cmd);
    return;
}
void Jrelease(JNIEnv *env,jobject obj){
    close(fd);
    return;
}

JNINativeMethod methods[]={
    "open","()V",(void *)Jopen,
    "ioctl","(I)V",(void *)Jioctl,
    "release","()V",(void *)Jrelease,
};

JNIEXPORT jint JNICALL
JNI_OnLoad(JavaVM *vm, void *reserved){
    JNIEnv *env;
    jclass cls;

    system("sudo chmod 777 /dev/ibo");

    (*vm)->GetEnv(vm, (void **)&env, JNI_VERSION_1_2);
    if(env == NULL) return JNI_ERR;

    cls = (*env)->FindClass(env, "Ibo");
    if(cls == NULL) return JNI_ERR;

    (*env)->RegisterNatives(env, cls,methods, sizeof(methods)/sizeof(JNINativeMethod));

    return JNI_VERSION_1_2;
}

5.gcc -shared -fPIC native.c -o libnative.so -I /usr/lib/jvm/java-7-openjdk-amd64/include/ 编译生成 libnative.so 文件

6.export LD_LIBRARY_PATH=:

7.java Ibo 运行

成功调用.PNG