利用udev、sys动态创建linux设备结点

在Linux2.6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 <linux/module.h>          #include <linux/kernel.h>         #include <linux/init.h>          #include <linux/fs.h>          #include <linux/cdev.h>          #include <asm/uaccess.h>          #include <linux/device.h>         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);

 

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。