如何通過udev和sys文件系統(tǒng)動態(tài)創(chuàng)建設備結點

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在Linux2.6內核中，devfs被認為是過時的方法，并最終被拋棄，udev取代了它。Devfs的一個很重要的特點就是可以動態(tài)創(chuàng)建設備結點。那我們現在如何通過udev和sys文件系統(tǒng)動態(tài)創(chuàng)建設備結點呢？

??????? 下面通過一個實例，說明udev、sys動態(tài)創(chuàng)建設備結點的方法。注意代碼中紅色的部分是為了實現動態(tài)創(chuàng)建設備結點添加的。?
#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

??????? 在編譯了驅動后，可以查看/dev/farsight_dev設備結點，和 /sys/class/farsight_class/farsight_dev/ 本代碼的測試環(huán)境是Ubantu7.04，內核版本是2.6.20-15-generi。在不同版本的內核中，有些系統(tǒng)函數的參數可能不太一樣。