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利用udev、sys动态创建linux设备结点


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udevsys文件系统动态创建设备结点呢?

下面通过一个实例,说明udevsys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);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。

本文永久更新链接:http://embeddedlinux.org.cn/emb-linux/file-system/200810/28-291.html



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