利用udev、sys动态创建linux设备结点(宋宝华)

在Linux 2.6内核中，devfs被认为是过时的方法，并最终被抛弃，udev取代了它。Devfs的一个很重要的特点就是可以动态创建设备结点。那我们现在如何通过udev和sys文件系统动态创建设备结点呢？

下面通过一个实例，说明udev、sys动态创建设备结点的方法。注意代码中红色的部分是为了实现动态创建设备结点添加的。

 

#include

#include

#include

#include

#include

#include

#include

MODULE_LICENSE ("GPL");

 

int hello_major = 252;

int hello_minor = 0;

int number_of_devices = 1;

char data[50]="foobar not equal to barfoo";

 

struct cdev cdev;

dev_t dev = 0;

static int hello_open (struct inode *inode, struct file *file)

{

 printk (KERN_INFO "Hey! device opened\n");

 return 0;

}

 

static int hello_release (struct inode *inode, struct file *file)

{

 printk (KERN_INFO "Hmmm... device closed\n");

 return 0;

}

ssize_t hello_read (struct file *filp, char *buff, size_t count, loff_t *offp)

{

 ssize_t result = 0;

 if (copy_to_user (buff, data, sizeof(data)-1))

    result = -EFAULT;

 else

    printk (KERN_INFO "wrote %d bytes\n", count);

   return result;

}

 

ssize_t hello_write (struct file *filp, const char *buf, size_t count, loff_t *f_pos)

{

 ssize_t ret = 0;

 printk (KERN_INFO "Writing %d bytes\n", count);

 if (count>127) return -ENOMEM;

 if (count<0) return -EINVAL;

 if (copy_from_user (data, buf, count)) {

    ret = -EFAULT;

 }

 else {

    data[127]='\0';

    printk (KERN_INFO"Received: %s\n", data);

    ret = count;

 }

 return ret;

}

struct file_operations hello_fops = {

 .owner = THIS_MODULE,

 .open = hello_open,

 .release = hello_release,

 .read = hello_read,

 .write = hello_write

};

struct class *my_class;

static void char_reg_setup_cdev (void)

{

 int error, devno = MKDEV (hello_major, hello_minor);

 cdev_init (&cdev, &hello_fops);

 cdev.owner = THIS_MODULE;

 cdev.ops = &hello_fops;

 error = cdev_add (&cdev, devno , 1);

 if (error)

     printk (KERN_NOTICE "Error %d adding char_reg_setup_cdev", error);

       /* creating your own class */

 my_class =class_create(THIS_MODULE, "farsight_class");//add by lht

 if(IS_ERR(my_class)) {

         printk("Err: failed in creating class.\n");

         return ;

 }

   /* register your own device in sysfs, and this will cause udevd to create corresponding device node */

 class_device_create(my_class,NULL, devno, NULL,"farsight_dev");

    // device_create(my_class,NULL, devno,"farsight_dev");

}

 

static int __init hello_2_init (void)

{

 int result;

 dev = MKDEV (hello_major, hello_minor);

 result = register_chrdev_region (dev, number_of_devices, "test");

 if (result<0) {

    printk (KERN_WARNING "hello: can't get major number %d\n", hello_major);

    return result;

 }

 char_reg_setup_cdev ();

 printk (KERN_INFO "char device registered\n");

 return 0;

}

static void __exit hello_2_exit (void)

{

  dev_t devno = MKDEV (hello_major, hello_minor);

  cdev_del (&cdev);

  unregister_chrdev_region (devno, number_of_devices);

   class_device_destroy(my_class, devno);

   class_destroy(my_class);

}

module_init (hello_2_init);

module_exit (hello_2_exit);v

在编译了驱动后，可以查看/dev/farsight_dev设备结点，和 /sys/class/farsight_class/farsight_dev/

 本代码的测试环境是Ubantu7.04，内核版本是2.6.20-15-generi。在不同版本的内核中，有些系统函数的参数可能不太一样。