作者：刘洪涛,华清远见嵌入式学院讲师.
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 openedn");
return 0;
}
static int hello_release (struct inode *inode, struct file *file)
{
printk (KERN_INFO "Hmmm... device closedn");
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 bytesn", count);
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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 bytesn", count);
if (count>127) return -ENOMEM;
if (count<0) return -EINVAL;
if (copy_from_user (data, buf, count)) {
ret = -EFAULT;
}
else {
data[127]='''';
printk (KERN_INFO"Received: %sn", 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(&q |
