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");
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。