在驱动模块初始化函数中实现设备节点的自动创建

在驱动模块初始化函数中实现设备节点的自动创建

我们在刚开始写Linux设备驱动程序的时候，很多时候都是利用mknod命令手动创建设备节点，实际上Linux内核为我们提供了一组函数，可以 用来在模块加载的时候自动在/dev目录下创建相应设备节点，并在卸载模块时删除该节点，当然前提条件是用户空间移植了udev。

内核中定义了struct class结构体，顾名思义，一个struct class结构体类型变量对应一个类，内核同时提供了class_create(…)函数，可以用它来创建一个类，这个类存放于sysfs下面，一旦创建 好了这个类，再调用device_create(…)函数来在/dev目录下创建相应的设备节点。这样，加载模块的时候，用户空间中的udev会自动响应 device_create(…)函数，去/sysfs下寻找对应的类从而创建设备节点。

注意，在2.6较早的内核版本中，device_create(…)函数名称不同，是class_device_create(…)，所以在新的内核中编译以前的模块程序有时会报错，就是因为函数名称不同，而且里面的参数设置也有一些变化。

struct class和device_create(…) 以及device_create(…)都定义在/include/linux/device.h中，使用的时候一定要包含这个头文件，否则编译器会报错。

在2.6.26.6内核版本中，struct class定义在头文件include/linux/device.h中：

/*
 * device classes
 */
    struct class {
      const char        *name;
      struct module     *owner;

  nbsp;struct kset         subsys;
      struct list_head         devices;
      struct list_head         interfaces;
      struct kset              class_dirs;
      struct semaphore sem;    /* locks children, devices, interfaces */
      struct class_attribute   *class_attrs;
      struct device_attribute      *dev_attrs;

      int (*dev_uevent)(struct device *dev, struct kobj_uevent_env *env);

      void (*class_release)(struct class *class);
      void (*dev_release)(struct device *dev);

      int (*suspend)(struct device *dev, pm_message_t state);
      int (*resume)(struct device *dev);

};

 

class_create(…)在/drivers/base/class.c中实现： 
   /*
    * 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.
    *
    * This is used to create a struct class pointer that can then be used
    * in calls to device_create().
    *
    * Note, the pointer created here is to be destroyed when finished by
    * making a call to class_destroy().
    */
   struct class *class_create(struct module *owner, const char *name)
   {
      struct class *cls;
      int retval;
      cls = kzalloc(sizeof(*cls), GFP_KERNEL);
      if (!cls) {
           retval = -ENOMEM;
           goto error;
      }

      cls->name = name;
      cls->owner = owner;
      cls->class_release = class_create_release;

      retval = class_register(cls);
      if (retval)
           goto error;

      return cls;

error:
      kfree(cls);
      return ERR_PTR(retval);
  }
    第一个参数指定类的所有者是哪个模块，第二个参数指定类名。
    在class.c中，还定义了class_destroy(…)函数，用于在模块卸载时删除类。

 

device_create(…)函数在/drivers/base/core.c中实现：
    /*
     * device_create - creates a device and registers it with sysfs
     * @class: pointer to the struct class that this device should be registered to
     * @parent: pointer to the parent struct device of this new device, if any
     * @devt: the dev_t for the char device to be added
     * @fmt: string for the device's name
     *
     * This can be used by char device classes. A struct device
     * will be created in sysfs, registered to the specified class.
     *
     * A "dev" file will be created, showing the dev_t for the device, if
     * the dev_t is not 0,0.
     * If a pointer to a parent struct device is passed in, the newly created
     * struct device will be a child of that device in sysfs.
     * The pointer to the struct device will be returned from the call.
     * Any further sysfs files that might be required can be created using this
     * pointer.
     *
     * Note: the struct class passed to this must have previously
     * been created with a call to class_create().
     */
    struct device *device_create(struct class *class, struct device *parent,
                        dev_t devt, const char *fmt, ...)
    {
         va_list vargs;
         struct device *dev;

         va_start(vargs, fmt);
         dev = device_create_vargs(class, parent, devt, NULL, fmt, vargs);
         va_end(vargs);
         return dev;
    }

第一个参数指定所要创建的设备所从属的类，第二个参数是这个设备的父设备，如果没有就指定为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。

 

下面以一个简单字符设备驱动来展示如何使用这几个函数
    ＃include
    ＃include
    ＃include
    ＃include
    ＃include
    ＃include

MODULE_LICENSE ("GPL");

int hello_major = 555;
int hello_minor = 0;
int number_of_devices = 1;

struct cdev cdev;
dev_t dev = 0;

struct file_operations hello_fops = {
      .owner = THIS_MODULE
};

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);

}

struct class *my_class;

static int __init hello_2_init (void)
{
       int result;
       dev = MKDEV (hello_major, hello_minor);
       result = register_chrdev_region (dev, number_of_devices, "hello");
       if (result<0) {
           printk (KERN_WARNING "hello: can't get major number %d\n", hello_major);
           return result;
      }

     char_reg_setup_cdev ();

     /* create your own class under /sysfs */
     my_class = class_create(THIS_MODULE, "my_class");
     if(IS_ERR(my_class))
     {
          printk("Err: failed in creating class.\n");
          return -1;
      }

      /* register your own device in sysfs, and this will cause udev to create corresponding device node */
      device_create( my_class, NULL, MKDEV(hello_major, 0), "hello" "%d", 0 );

      printk (KERN_INFO "Registered character driver\n");
      return 0;
}

static void __exit hello_2_exit (void)
{
       dev_t devno = MKDEV (hello_major, hello_minor);

       cdev_del (&cdev);

       device_destroy(my_class, MKDEV(adc_major, 0));         //delete device node under /dev
       class_destroy(my_class);                               //delete class created by us

       unregister_chrdev_region (devno, number_of_devices);

       printk (KERN_INFO "char driver cleaned up\n");
}

module_init (hello_2_init);
module_exit (hello_2_exit);

这样，模块加载后，就能在/dev目录下找到hello0这个设备节点了。

 

 

 

 

下面是我写的LED简单驱动代码，Arm平台(lpc3250)如下实现功能：
1>把代码编译后，添加到内核模块使LED灭10秒，然后亮10秒
2>在/dev目录自动挂载LED设备节点，可以“Echo "1" >/dev/led”控制LED
3>再实现在开机自动运行，自动添加到内核中。当然是修改启动代码实现的。
4>最后我编译进内核中，下面我先把代码贴出来。

DE>/**
 * @：0xf4028004和0xf4028008是GPIO端口3输出与输出寄存器虚拟地址
 * 地址是我直接算出来的，可以用io_p2v()函数实现
 * @: __raw_writel()向地址写数据
 * @: class_create()创建总线，class_destroy()删除
 * @: device_create()创建设备节点,device_destroy()删除
 */

#include <linux/init.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/errno.h>
#include <linux/device.h>
#include <linux/miscdevice.h>
#include <linux/platform_device.h>
#include <linux/types.h>
#include <linux/io.h>
#include <linux/delay.h>
#include <linux/irq.h>
#include <linux/interrupt.h>

#include <asm/uaccess.h>
#include <mach/irq.h>
#include <asm/io.h>
#include <asm/pgtable.h>
#include <asm/page.h>
#include <mach/hardware.h>
#include <mach/platform.h>
#include <mach/lpc32xx_gpio.h>

#define DEVNAME "LED"
#define LED_MAJOR 251

#define P3_SET ((volatile unsigned int) 0xf4028004)
#define P3_CLR ((volatile unsigned int) 0xf4028008)

struct led_dev
{
    struct cdev cdev;
    unsigned int value;
};

struct led_dev *led_dev;

int led_open(struct inode *inode, struct file *filp)
{
    struct led_dev *dev;
    dev = container_of(inode->i_cdev, struct led_dev, cdev);
    filp->private_data = dev;
    try_module_get(THIS_MODULE);
    return 0;
}

int led_release(struct inode *inode, struct file *filp)
{
    module_put(THIS_MODULE);
    return 0;
}

static int led_write(struct file *filp, const char __user *buf, size_t count, loff_t *ppos)
{
    struct led_dev *dev = filp->private_data;
    if(copy_from_user(&(dev->value), buf , 1))
    {
        return -EFAULT;
    }
    if(dev->value == 1)
        __raw_writel(1 << 5, P3_SET);
    else
        __raw_writel(1 << 5, P3_CLR);
    return 1;
}

int led_ioctl(struct inode *inode, struct file *filp, unsigned int cmd, unsigned long arg)
{
    struct led_dev *dev = filp->private_data;
    switch (cmd)
    {
        case 0:
            dev->value = 0;
            __raw_writel(1 << 5, P3_CLR);
            break;
        case 1:
            dev->value = 1;
            __raw_writel(1 << 5, P3_SET);
            break;
        default :
            dev->value = 1;
            __raw_writel(1 << 5, P3_SET);
            break;
    }
    return 0;
}

struct file_operations led_fops =
{
    .owner = THIS_MODULE,
    .write = led_write,
    .ioctl = led_ioctl,
    .open = led_open,
    .release = led_release,
};

static void led_setup_cdev(struct led_dev *dev, int index)
{
    int err, devno = MKDEV(LED_MAJOR, 0);
    cdev_init(&dev->cdev, &led_fops);
    dev->cdev.owner = THIS_MODULE;
    dev->cdev.ops = &led_fops;
    err = cdev_add(&dev->cdev, devno, 1);
    if(err)
        printk(KERN_NOTICE "Error adding LED");
}

struct class *led_class;
static int __init led_init(void)
{
    int i,result;    
    dev_t dev = MKDEV(LED_MAJOR, 0);
    result = register_chrdev_region(dev, 1, DEVNAME);
    if(result < 0)
        return result;
    led_dev = kmalloc(sizeof(struct led_dev), GFP_KERNEL);
    if(!led_dev)
    {
        result = ~ENOMEM;
        goto fail;
    }
    memset(led_dev, 0, sizeof(struct led_dev));
    led_setup_cdev(led_dev, 0);
    led_class = class_create(THIS_MODULE, "led_class");
    device_create(led_class, NULL, MKDEV(LED_MAJOR, 0), "LED","LED%d", 0);
    __raw_writel(1 << 5, P3_SET);
    for(i = 0; i< 5; i++)
    {
        msleep(1000);
    }
    __raw_writel(1 << 5, P3_CLR);
    for(i = 0; i < 10; i++)
    {    
        msleep(1000);        
    }
    __raw_writel(1 << 5, P3_SET);
    return 0;
fail:
    unregister_chrdev_region(dev, 1);
    return result;
}

static void __exit led_exit(void)
{
    cdev_del(&led_dev->cdev);
    device_destroy(led_class, MKDEV(LED_MAJOR, 0));
    class_destroy(led_class);
    kfree(led_dev);
    unregister_chrdev_region(MKDEV(LED_MAJOR, 0), 1);
}

module_init(led_init);
module_exit(led_exit);

MODULE_LICENSE("GPL");DE>

内核模块在开机自动添加到内核中：
在/etc/rc.d/rc.local文件中，添加插入内核模块的命令就行了
insmod led.ko

内核模块编译进内核中，下面以LED驱动为例子：
第一：将您写的led.c 文档添加到/driver/mtd/maps/ 目录下。
第二：修改/driver/mtd/maps目录下的kconfig文档：
config MTD_LED
tristate “LED driver"
第三：修改该目录下makefile文档。
添加如下内容：obj-$(CONFIG_MTD_LED)    += led.o

然后make menuconfig，在device drivers该选项下面找到LED驱动模块，选中M直接编译成内核模块。