驱动程序编写好后，还需要创建设备节点，有两种方式:
一是通过mknod命令去手动创建，例如：mknod /dev/hello c 250 0，/dev/hello为设备节点名字，c代表字符设备，250和0代表它的主次设备号。
二是使用udev或mdev来实现自动创建设备节点。
使用mknod手动创建设备节点不够灵活，如果是动态分配的设备号怎么办，难道每次加载驱动后去查看/proc/devices文件中查看它的主设备号，要是产品发布时怎么办，显然不太现实利用udev(mdev)来实现设备节点的自动创建，udev(mdev)存在于应用层。
包含头文件
#include<linux/device.h>
新建一个class结构体指针
static struct class *my_class;
在初始化函数中调用class_create()函数创建一个类，参数分别为模块所有者和class结构name字段，在/sys/class/下体现。
my_class= class_create(THIS_MODULE, "my_class");
if(IS_ERR(my_class))
{
printk("Err: failed increating class.\n");
return -1;
}
调用device_create()函数创建设备节点，参数分别为所从属类，这个设备的父设备，没有就制定NULL，设备号，设备的私有数据，最后一组参数指定设备节点名，比如这里的名为hello。函数原型：
extern struct device *device_create(struct class *cls, structdevice *parent,
dev_t devt, void *drvdata,
const char *fmt, ...)
具体实现在drivers/base/core.c中
程序中使用
device_create(my_class,NULL,dev_n,NULL,"%s","hello");
或者
device_create(my_class,NULL,dev_n,NULL,"hello");
设备卸载删除类和设备节点
device_destroy(my_class,dev_n);
class_destroy(my_class);
使用class_create()和device_create()函数可以自动创建节点。
class_create : 创建class
class_destroy : 销毁class
class_device_create : 创建device
class_device_destroy : 销毁device
class_create()
-------------------------------------------------
linux-2.6.22/include/linux/device.h
struct class *class_create(struct module *owner, const char *name)
class_create - create a struct class structure
@owner: pointer to the module that is to "own" this struct class
@name: pointer to a string for the name of this class.
在/sys/class/下创建类目录
class_device_create()
-------------------------------------------------
linux-2.6.22/include/linux/device.h
struct class_device *class_device_create(struct class *cls,
struct class_device *parent,
dev_t devt,
struct device *device,
const char *fmt, ...)
class_device_create - creates a class device and registers it with sysfs
@cls: pointer to the struct class that this device should be registered to.
@parent: pointer to the parent struct class_device of this new device, if any.
@devt: the dev_t for the char device to be added.
@device: a pointer to a struct device that is assiociated with this class device.
@fmt: string for the class device's name
在驱动模块初始化函数中实现设备节点的自动创建
设备驱动文件char01.c
#include <linux/init.h>
#include <linux/module.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/kdev_t.h>
#include <linux/fs.h>
/////////////////////////////////////////////////
int char01_open(struct inode *inode, struct file *filp)
{
printk("char01 open!/n");
return 0;
}
int char01_release(struct inode *inode, struct file *filp)
{
printk("char01 release!/n");
return 0;
}
ssize_t char01_read(struct file *filp, char *buf,
size_t count, loff_t *fpos)
{
printk("char01 read!/n");
return 0;
}
ssize_t char01_write(struct file *filp, const char *buf,
size_t count, loff_t *fpos)
{
printk("char01 write!/n");
return 0;
}
int char01_ioctl(struct inode *inode, struct file *filp,
unsigned int cmd, unsigned long param)
{
printk("char01 ioctl!/n");
printk("cmd:%d param:%ld/n", cmd, param);
return 0;
}
/////////////////////////////////////////////////
struct file_operations fops =
{
.owner = THIS_MODULE,
.open = char01_open,
.release = char01_release,
.read = char01_read,
.write = char01_write,
.ioctl = char01_ioctl
};
dev_t devno;
struct class *pclass;
struct cdev dev;
int char01_dev_init(void)
{
int result;
result = alloc_chrdev_region(&devno, 0, 1, "char01");
if (result != 0)
{
printk("alloc_chrdev_region failed!/n");
goto ERR1;
}
cdev_init(&dev, &fops);
dev.owner = THIS_MODULE;
dev.ops = &fops;
result = cdev_add(&dev, devno, 1);
if (result != 0)
{
printk("cdev_add failed!/n");
goto ERR2;
}
pclass = class_create(THIS_MODULE, "char01");
if (IS_ERR(pclass))
{
printk("class_create failed!/n");
goto ERR3;
}
device_create(pclass, NULL, devno, NULL, "char01");
return 0;
ERR3:
cdev_del(&dev);
ERR2:
unregister_chrdev_region(devno, 1);
ERR1:
return -1;
}
/////////////////////////////////////////////////
/////////////////////////////////////////////////
/////////////////////////////////////////////////
static int __init char01_init(void)
{
printk("module char01 init!/n");
return char01_dev_init();
}
static void __exit char01_exit(void)
{
printk("module char01 exit!/n");
class_destroy(pclass);
device_destroy(pclass,devno);
cdev_del(&dev);
unregister_chrdev_region(devno, 1);
}
/////////////////////////////////////////////////
MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Yao.GUET");
module_init(char01_init);
module_exit(char01_exit);
/////////////////////////////////////////////////
测试文件char01_test.c
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/stat.h>
/////////////////////////////////////////////////
int main(int argc, char *argv)
{
int fd;
fd = open("/dev/char01", O_RDWR);
if (fd<0)
{
printf("open /dev/char01 failed!/n");
printf("%s/n", strerror(errno));
return -1;
}
printf("open /dev/char01 ok!/n");
ioctl(fd, 0);
close(fd);
}