字符设备的另一种注册方法

代码如下：

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/irq.h>
#include <asm/uaccess.h>
#include <asm/irq.h>
#include <asm/io.h>
#include <asm/arch/regs-gpio.h>
#include <asm/hardware.h>
#include <linux/poll.h>
#include <linux/cdev.h>

/* 确定主设备号 */
static int major;
static struct class *cls;
static struct cdev my_cdev;

static int open(struct inode *inode, struct file *file)
{
    printk(" In ‘open‘ \n");
    return 0;
}


/* 构造file_operations */
static struct file_operations fops = {
    .owner = THIS_MODULE,
    .open  = open,
};

static int cdev_init(void)
{
    dev_t devid;
    
    if (major) {
        devid = MKDEV(major, 0);
        register_chrdev_region(devid, 1, "cdev");  
    } else {
        /* 动态申请设备编号 */
        alloc_chrdev_region(&devid, 0, 1, "cdev"); 
        major = MAJOR(devid);                     
    }
    
    cdev_init(&my_cdev, &fops);
    cdev_add(&my_cdev, devid, 1);

    /* 创建类 */
    cls = class_create(THIS_MODULE, "cdev");
    /* 创建节点 /dev/cdev0 */
    class_device_create(cls, NULL, MKDEV(major, 0), NULL, "cdev0"); 
    
    return 0;
}

static void cdev_exit(void)
{
    class_device_destroy(cls, MKDEV(major, 0));
    class_destroy(cls);

    cdev_del(&my_cdev);
    unregister_chrdev_region(MKDEV(major, 0), 1);
}

module_init(cdev_init);
module_exit(cdev_exit);

MODULE_LICENSE("GPL");