设备驱动-----自动创建节点

#include <linux/module.h>#include <linux/init.h>#include <linux/fs.h>#include <linux/device.h>MODULE_LICENSE("GPL");#define DEVICE_NAME ("my_dev")int MAJOR_NUM = 666;int g_val;struct device *dev;struct class *myclass;static ssize_t global_read(struct file *filp, char __user *buf, size_t len, loff_t *off){int ret;char val[20];printk(KERN_ERR "###### global_read \n");sprintf(val, "%d\n", g_val);//ssize_t simple_read_from_buffer(void __user *to, size_t count,loff_t *ppos, const void *from, size_t available);ret = simple_read_from_buffer(buf, len, off, val, strlen(val));return ret;}static ssize_t global_write(struct file *filp, const char __user *buf, size_t len, loff_t *off){int  ret, temp;char val[20];//simple_write_to_buffer(void *to, size_t available, loff_t *ppos,const void __user *from, size_t count);ret = simple_write_to_buffer(val, strlen(val), off, buf, len);sscanf(val, "%d", &temp);g_val = temp;return ret;}struct file_operations fileops = {.read = global_read,.write = global_write,};static int __init globalvar_init(void){int ret;g_val = 0;printk(KERN_ERR "golabvar_init \n");ret = register_chrdev(MAJOR_NUM, "my_driver", &fileops);if(ret){printk(KERN_ERR "register_chrdev fail \n");}else{printk(KERN_ERR "register_chrdev sucess \n");//注册一个类，使mdev可以在"/dev/"目录下 面建立设备节点myclass = class_create(THIS_MODULE, DEVICE_NAME);//创建一个设备节点，节点名为DEVICE_NAMEdev = device_create(myclass, NULL, MKDEV(MAJOR_NUM, 0), NULL, DEVICE_NAME);if(!dev){printk(KERN_ERR "device_create faile \n");}}return 0;} static void __exit globalvar_exit(void){printk("golabvar_exit \n");device_destroy(myclass, MKDEV(MAJOR_NUM, 0));class_destroy(myclass);unregister_chrdev(MAJOR_NUM, "globalvar");}module_init(globalvar_init);module_exit(globalvar_exit);

makefile

obj-m := mknode.o    mknode-objs := auto_mknode.o       KID :=/lib/modules/`uname -r`/build    PWD := $(shell pwd)        all:    make -C $(KID) M=${PWD} modules        clean:    rm -rf *.o .cmd *.ko *.mod.c .tmp_versions

参考：

在2.6里已经用udev取代devfs，为解决上面那样手动创建节点的麻烦，我们可以在程序里加上创建节点这项，如下：

以字符设备char_dev为例，在驱动初始化的代码里调用class_create为该设备创建一个class，再为每个设备调用 class_device_create创建对应的设备，这样的module被加载时，undev daemon就会自动在/dev下创建char_dev设备文件。大概方法如下：

struct class *myclass = class_create(THIS_MODULE, “char_dev”);
class_device_create(myclass, NULL, MKDEV(major_num, 0), NULL, “char_dev”);

当然，在exit函数中要把创建的class移除：
class_destory(&xxx_dev->cdev);
class_device_desotry(my_class,MKDEV(major_num,0));

下面介绍下函数class_creat和class_device_creat的原型：

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_creat(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

void class_destroy(struct class *cls);/*销毁/sys/class下的类   */

void class_device_destroy(struct class *cls, dev_t devt);   /*销毁一个类设备*/

参数含义同上

补充：

在Linux2.6中，针对上面的这个问题不同的版本有些修改，使用前要先查看下/.../include/linux/device.h里的函数声明，如我用的是Linux2.6.29，里面就没有class_device_create函数，而直接使用device_create就可以了，而在之前的版本如Linux2.6.15，里面就要用class_device_create函数