开始学习驱动的时候，是将驱动程序编译成模块然后用mknod命令手动建立设备节点以提供给应用程序调用。这对于刚开始调试驱动程序的时候常用的一种方法。但是，当有种需要必须在系统启动的时候就将驱动程序就绪，来供应用层程序调用。这时就不能再手动的建立设备节点了，而必须自动的创建设备节点(不需要人为的操作)。
★注册类
注册类的目的是为了使mdev可以在/dev/目录下建立设备节点。
首先要定义一个类，利用struct class结构体。这个结构体定义在头文件include/linux/device.h中
struct class {
const char* name;
struct module* owner;
struct subsystemsubsys;
struct list_headchildren;
struct list_headdevices;
struct list_headinterfaces;
struct semaphoresem;/* locks both the children and interfaces lists */
struct kobject*virtual_dir;
struct class_attribute* class_attrs;
struct class_device_attribute* class_dev_attrs;
struct device_attribute* dev_attrs;
int(*uevent)(struct class_device *dev, char **envp,
int num_envp, char *buffer, int buffer_size);
int(*dev_uevent)(struct device *dev, char **envp, int num_envp,
char *buffer, int buffer_size);
void(*release)(struct class_device *dev);
void(*class_release)(struct class *class);
void(*dev_release)(struct device *dev);
int(*suspend)(struct device *, pm_message_t state);
int(*resume)(struct device *);
}
然后使用
完成对类的注册。其中第一个参数一般为：THIS_MODULE。第二个参数为：设备节点的名称
举个例子：
★创建设备节点
创建设备节点的函数：
struct device *device_create(struct class *class, struct device *parent,dev_t devt, const char *fmt, ...)
{
va_list args;
struct device *dev = NULL;
int retval = -ENODEV;
if (class == NULL || IS_ERR(class))
goto error;
dev = kzalloc(sizeof(*dev), GFP_KERNEL);
if (!dev) {
retval = -ENOMEM;
goto error;
}
dev->devt = devt;
dev->class = class;
dev->parent = parent;
dev->release = device_create_release;
va_start(args, fmt);
vsnprintf(dev->bus_id, BUS_ID_SIZE, fmt, args);
va_end(args);
retval = device_register(dev);
if (retval)
goto error;
return dev;
error:
kfree(dev);
return ERR_PTR(retval);
}
该函数的四个参数从左到右以此为：创建设备节点所属的类、该设备的父节点(若果没有就指定为NULL)、设备号、设备名称、次设备号。
★销毁类和设备节点
注意不要忘记了还要销毁类和销毁设备节点。
销毁类：参数为用struct class结构体定义的变量
void class_destroy(struct class *cls)
{
if ((cls == NULL) || (IS_ERR(cls)))
return;
class_unregister(cls);
}销毁设备节点：
void device_destroy(struct class *class, dev_t devt)
{
struct device *dev = NULL;
struct device *dev_tmp;
down(&class->sem);
list_for_each_entry(dev_tmp, &class->devices, node) {
if (dev_tmp->devt == devt) {
dev = dev_tmp;
break;
}
}
up(&class->sem);
if (dev)
device_unregister(dev);
}
★例子(自己写的延时驱动)
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define NAME"ralink_drive_delay"
#define RALINK_GPIO_DEVNAME "my_delay"
#define delay_us 0 //most least is 10 US
#define delay_ms 1 //Ms
int delay_MAJOR = 109;
MODULE_LICENSE("Dual BSD/GPL");
static long Ralink_delay_ioctl(struct inode * inode, struct file * file, unsigned int cmd,unsigned long arg)
{
switch(cmd)
{
case delay_us:
udelay(10 * arg);
return 0;
case delay_ms:
udelay(1000);
return 0;
default:
return -1;
}
}
static struct file_operations My_delay_fops =
{
.owner = THIS_MODULE,
.ioctl = Ralink_delay_ioctl,
};
static struct class *delay_class;
static int __init my_delay_init(void)
{
int ret = 0;
ret = register_chrdev(delay_MAJOR, RALINK_GPIO_DEVNAME,&My_delay_fops);
if(ret < 0)
{
printk("unable to register character device\n");
return ret;
}
if (delay_MAJOR == 0)
{
delay_MAJOR = ret;
printk(KERN_DEBUG NAME ": got dynamic major %d\n", ret);
}
//注册一个类，使mdev可以在"/dev/目录下建立设备节点"
delay_class = class_create(THIS_MODULE, RALINK_GPIO_DEVNAME);
if(IS_ERR(delay_class))
{
printk("failed in My_led class.\n");
return -1;
}
device_create(delay_class, NULL, MKDEV(delay_MAJOR, 0),RALINK_GPIO_DEVNAME 0);//
//第一个参数是所要创建的设备所从属的类
//第二个参数是这个设备的父节点，没有指定就是NULL
//第三个参数是设备号
//第四个参数是设备名称
//第五个参数是从设备号
printk("my_delay driver initialized\n");
return 0;
}
void __exit my_delay_exit(void)
{
unregister_chrdev(delay_MAJOR,RALINK_GPIO_DEVNAME);
device_destroy(delay_class,MKDEV(delay_MAJOR,0));//注销设备节点
class_destroy(delay_class);//销毁类
printk("my_delay driver exited\n");
}
module_init(my_delay_init);
module_exit(my_delay_exit);
原文：/xgsilence/article/details/35650849
