linux 2.6 驱动笔记（二）

字符设备驱动

linux 2.6的字符驱动由cdev结构体描述，具体参考globalmem例子，代码主要分以下几部分：

1. 定义一个字符类型设备驱动的结构体

struct globalmem_dev{

    struct cdev cdev; /*linux 2.6 内核表示一个字符设备结构体 */

    unsigned char mem[200];

};

其中cdev在cdev.h文件中定义如下：

struct cdev {

    struct kobject kobj;

    struct module *owner;

    struct file_operations *ops; //文件操作结构体

    struct list_head list;

    dev_t dev; //设备号 unsigned long

    unsigned int count;

};

2. 在驱动模块的加载、卸载函数中注册设备，同时绑定文件操作结构体

static const struct file_operations globalmem_fops = {

    .owner     = THIS_MODULE,

    .llseek    = globalmem_llseek,

    .read   = globalmem_read,

    .write  = globalmem_write,

    .open   = globalmem_open,

    .release= globalmem_release};



//设备驱动加载

int globalmem_init(void){

    int result;

    dev_t devno = MKDEV(200, 0);



    result = register_chrdev_region(devno, 1, "globalmem");//注册字符设备编号

    globalmem_devp= kmalloc(sizeof(struct globalmem_dev), GFP_KERNEL);

    memset(globalmem_devp, 0, sizeof(struct globalmem_dev));



    cdev_init(&globalmem_devp->cdev, &globalmem_fops);

    globalmem_devp->cdev.owner = THIS_MODULE;



    int err = cdev_add(&globalmem_devp->cdev, devno, 1);



    return result;

}

3. 实现文件操作的具体接口，以文件写为例：

 

static ssize_t globalmem_read(struct file *flip, char __user *buf, size_t size, loff_t *ppos){

       //....

    

    struct globalmem_dev *dev = flip->private_data;

    copy_to_user(buf, (void*)(dev->mem+p), count); //内核空间拷贝至用户空间

    *ppos += count;

 

测试用应用代码如下：

#include<sys/types.h>

#include<sys/stat.h>

#include<stdio.h>

#include<fcntl.h>



void main(){

    int fd,num;



    fd = open("/dev/globalmem", O_RDWR);



    if(fd != -1){

        read(fd, &num, sizeof(int));

        printf("the globalmem is %d\n", num);



        scanf("%d", &num);

        printf("the input is %d\n", num);

        write(fd, &num, sizeof(int));



        read(fd, &num, sizeof(int));

        printf("the new globalmem is %d/n", num);

    

        close(fd);

        

    }else{

        printf("device err!");

    }

    return;

}