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
     
      #include
      
       #include
       
        #include
        
         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;}