字符驱动【sysfs方式，支持udev】

支持udev的字符驱动。

#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/device.h>

static int major = 232;     //静态设备节点方式的默认值
static int minor = 0;         //静态设备节点方式的默认值
module_param(major, int, S_IRUGO);
module_param(minor, int, S_IRUGO);

struct cdev *char_cdev;     //cdev数据结构
static dev_t devno;        //设备编号
static struct class *char_cdev_class;

#define DEVICE_NAME     "charcdev"

static int char_cdev_open(struct inode *inode, struct file *file )
{
    try_module_get(THIS_MODULE);
    printk(KERN_INFO DEVICE_NAME "opened!\n");

    return 0;
}

static int char_cdev_release(struct inode *inode, struct file *file )
{
    printk(KERN_INFO DEVICE_NAME "closed!\n");

    module_put(THIS_MODULE);
    return 0;
}


static ssize_t char_cdev_read(struct file *file, char *buf,size_t count, loff_t *f_pos)
{
    printk(KERN_INFO DEVICE_NAME "read method!\n");

    return count;
}

static ssize_t char_cdev_write(struct file *file, const char *buf, size_t count, loff_t *f_pos)
{
    printk(KERN_INFO DEVICE_NAME "write method!\n");

    return count;
}

static int char_cdev_ioctl(struct inode *inode, struct file *file, unsigned int cmd, unsigned long arg)
{
    printk(KERN_INFO DEVICE_NAME "ioctl method!\n");

    return 0;
}

struct file_operations char_cdev_fops = {
    .owner        = THIS_MODULE,
    .read        = char_cdev_read,
    .write        = char_cdev_write,
    .open        = char_cdev_open,
    .release    = char_cdev_release,
    .ioctl        = char_cdev_ioctl
};


static int __init char_cdev_init(void)
{
    int ret;

    if (major > 0) { //静态设备节点
        devno = MKDEV(major, minor);
        ret = register_chrdev_region(devno, 1, "char_cdev");
    } else { //动态设备节点
        ret = alloc_chrdev_region(&devno, minor, 1, "char_cdev"); //从系统获取主设备号
        major = MAJOR(devno);

    }
    if (ret < 0) {
        printk(KERN_ERR "cannot get major %d \n", major);
        return -1;
    }

    char_cdev = cdev_alloc();        //分配char_cdev结构
    if (char_cdev != NULL) {
        cdev_init(char_cdev, &char_cdev_fops);        //初始化char_cdev结构
         //char_cdev->ops = &char_cdev_fops;     //可以不要
        char_cdev->owner = THIS_MODULE;
        if (cdev_add(char_cdev, devno, 1) != 0) {    //增加char_cdev到系统中
            printk(KERN_ERR "add cdev error!\n");
            goto error1;
        }

    } else {
        printk(KERN_ERR "cdev_alloc error!\n");
        goto error2;
    }

    char_cdev_class = class_create(THIS_MODULE, "char_cdev_class"); //在/sys/class/下创建char_cdev_class目录
    if (IS_ERR(char_cdev_class)) {
        printk(KERN_INFO "create class error\n");
        return -1;
    }
    //device_create(char_cdev_class, NULL, devno, NULL, "char_cdev" "%d", MINOR(devno));    //将创建/dev/char_cdev0文件
    device_create(char_cdev_class, NULL, devno, NULL, "char_cdev", NULL); //将创建/dev/char_cdev文件

    return 0;

error1:
    unregister_chrdev_region(devno, 1);     //释放已经获得的设备号
error2:
    return ret;
}

static void __exit char_cdev_exit(void)
{
    device_destroy(char_cdev_class, devno);
    class_destroy(char_cdev_class);
    cdev_del(char_cdev);            //移除字符设备
    unregister_chrdev_region(devno, 1);    //释放设备号
}

module_init(char_cdev_init);
module_exit(char_cdev_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Chenxibing,[e-mail]");

使用方法：

支持静态/动态设备节点，自动创建设备节点。

#insmod char_cdev.ko

# cat /proc/devices

  232 char_cdev

#ls /dev/char_cdev -l

crw------- 1 root root 232, 0 2011-01-16 20:43 /dev/char_cdev

#ls /sys/class/char_cdev_class/char_cdev -la

lrwxrwxrwx 1 root root 0 2011-01-16 20:58 /sys/class/char_cdev_class/char_cdev -> ../../devices/virtual/char_cdev_class/char_cdev

测试程序：

1 #include <stdio.h>
     2 #include <stdlib.h>
     3 #include <unistd.h>
     4 #include <sys/ioctl.h>
     5 #include <errno.h>
     6 #include <fcntl.h>
     7
     8 #define DEV_NAME "/dev/char_cdev"
     9
    10 int main(int argc, char *argv[])
    11 {
    12 int i;
    13 int fd = 0;
    14 int dat = 0;
    15
    16          fd = open (DEV_NAME, O_RDWR);
    17 if (fd < 0) {
    18 perror("Open "DEV_NAME" Failed!\n");
    19 exit(1);
    20 }
    21
    22          i = read(fd, &dat, 1);
    23 if (!i) {
    24 perror("read "DEV_NAME" Failed!\n");
    25 exit(1);
    26 }
    27
    28          dat = 0;
    29          i = write(fd, &dat, 1);
    30 if (!i) {
    31 perror("write "DEV_NAME" Failed!\n");
    32 exit(1);
    33 }
    34
    35          i = ioctl(fd, NULL, NULL);
    36 if (!!i) {
    37 perror("ioctl "DEV_NAME" Failed!\n");
    38 exit(1);
    39 }
    40
    41 close(fd);
    42 return 0;
    43 }