字符设备驱动（二）

mycdev.c

/*字符驱动模块程序 2017年04月21日 星期五*/#include <linux/init.h>     //模块所需的大量符号和函数定义#include <linux/module.h>   //指定初始化和清除函数#include <linux/types.h>    //dev_t 是用来在内核里代表设备号的类型.#include <linux/fs.h>           //"文件系统"头文件是编写设备驱动需要的头文件. 许多重要的函数和数据结构在此定义#include <linux/sched.h>#include <linux/cdev.h>     //cdev 结构管理的函数, 它代表内核中的字符设备#include <linux/mm.h>#include <linux/kernel.h>   //printk()一个传统宏定义, 可用来获取一个结构指针, 从它里面包含的某个其他结构的指#include <asm/io.h>//#include <asm.current.h>              //#include <asm/uaccess.h>    //在内核和用户空间中移动数据的函数copy_to_user和copy_from_user MODULE_LICENSE("leo BSD/GPL");  //许可证#define MYCDEV_MAJOB 231 /*给定的主设备号*/#define MYCDEV_SIZE 2048//open 方法提供给驱动来做任何的初始化来准备后续的操作.static int mycdev_open(struct inode *inode, struct file *fp){    return 0;}//释放 open 分配在 filp->private_data 中的任何东西,在最后的 close 关闭设备static int mycdev_release(struct inode *inode, struct file *fp){    return 0;}//文件操作static ssize_t mycdev_read(struct file *fp, char __user *buf, size_t size, loff_t *pos){    unsigned long p = *pos;    unsigned int count = size;    char kernel_buf[MYCDEV_SIZE]="This is mycdev!";    if(p >= MYCDEV_SIZE)            return -1;    if(count > MYCDEV_SIZE)            count = MYCDEV_SIZE-p;    if(copy_to_user(buf,kernel_buf,count)!=0){            printk("read error!\n");            return -1;    }    printk("reader: %d bytes was read...\n",count);    return count;}static ssize_t mycdev_write(struct file *fp, const char __user *buf, size_t size, loff_t *pos){    return size;}/*填充mycdev的file_operation结构*/static const struct file_operations mycdev_fops = {.owner = THIS_MODULE,//.llseek = mycdev_llseek,.read = mycdev_read,.write = mycdev_write,//.ioctl = mycdev_ioctl,.open = mycdev_open,.release = mycdev_release,};/*模块初始化函数*/static int __init mycdev_init(void){    int ret;    printk("mycdev module is starting..\n");//此处打印成功    ret = register_chrdev(MYCDEV_MAJOB, "my_cdev", &mycdev_fops); //注册驱动程序    if(ret < 0)    {        printk("register failed..\n");    }    else    {        printk("register success..\n");//此处打印成功    }    return 0;};/*模块卸载函数*/static void __exit mycdev_exit(void){    printk("mycdev module is leaving..\n");    unregister_chrdev(MYCDEV_MAJOB, "my_cdev");//注销驱动程序}module_init(mycdev_init);module_exit(mycdev_exit);

test.c

#include <stdio.h>#include <string.h>int main(){    FILE *fp0 = NULL;    char Buf[4096];    /*初始化Buf*/    strcpy(Buf,"Mem is char dev!"); //此处打印    printf("BUF: %s\n",Buf);    /*打开设备文件*/    fp0 = fopen("/dev/my_cdev","r+");    if (fp0 == NULL)    {        printf("Open my_cdev Error!\n");//此处打印        return -1;    }    /*写入设备*/    fwrite(Buf, sizeof(Buf), 1, fp0);    /*重新定位文件位置（思考没有该指令，会有何后果)*/    fseek(fp0,0,SEEK_SET);    /*清除Buf*/    strcpy(Buf,"Buf is NULL!");    printf("BUF: %s\n",Buf);    /*读出设备*/    fread(Buf, sizeof(Buf), 1, fp0);    /*检测结果*/    printf("BUF: %s\n",Buf);    return 0;    }