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class_create(),device_create自动创建设备文件结点

2024-09-03 05:41:00   217人阅读

从linux 内核2.6的某个版本之后，devfs不复存在，udev成为devfs的替代。相比devfs，udev有很多优势，在此就不罗嗦了，提醒一 点，udev是应用层的东东，不要试图在内核的配置选项里找到它;加入对udev的支持很简单，以作者所写的一个字符设备驱动为例，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。(不太明白什么是devfs,udev,对linux中的文件系统没有什么概念呢。)
大致用法如下： struct class *myclass = class_create(THIS_MODULE, “my_device_driver”); class_device_create(myclass, NULL, MKDEV(major_num, 0), NULL, “my_device”); 这样的module被加载时，udev daemon就会自动在/dev下创建my_device设备文件。
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
 
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 function 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 function 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 <linux/module.h>     #include <linux/kernel.h>     #include <linux/init.h>     #include <linux/fs.h>     #include <linux/cdev.h>     #include <linux/device.h>
    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。
 
例子2
 
drivers/i2c/i2c-dev.c
 
/*  * module load/unload record keeping  */
static int __init i2c_dev_init(void) {      int res;
     printk(KERN_INFO "i2c /dev entries driver\n");
     res = register_chrdev(I2C_MAJOR, "i2c", &i2cdev_fops);      if (res)           goto out;
     i2c_dev_class = class_create(THIS_MODULE, "i2c-dev");  //创建一个名称为i2c-dev的class      if (IS_ERR(i2c_dev_class)) {           res = PTR_ERR(i2c_dev_class);          goto out_unreg_chrdev;      }
     res = i2c_add_driver(&i2cdev_driver);      if (res)          goto out_unreg_class;
     return 0;
out_unreg_class:     class_destroy(i2c_dev_class); out_unreg_chrdev:     unregister_chrdev(I2C_MAJOR, "i2c"); out:     printk(KERN_ERR "%s: Driver Initialisation failed\n", __FILE__);     return res; }
在 i2c_dev_init创建类i2c_dev_class
i2c_dev_class = class_create(THIS_MODULE, "i2c-dev");
 
static int i2cdev_attach_adapter(struct i2c_adapter *adap) {     struct i2c_dev *i2c_dev;     int res;
    i2c_dev = get_free_i2c_dev(adap);     if (IS_ERR(i2c_dev))         return PTR_ERR(i2c_dev);
    /* register this i2c device with the driver core */     i2c_dev->dev = device_create(i2c_dev_class, &adap->dev,          MKDEV(I2C_MAJOR, adap->nr), NULL,          "i2c-%d", adap->nr);     if (IS_ERR(i2c_dev->dev)) {          res = PTR_ERR(i2c_dev->dev);          goto error;      }      res = device_create_file(i2c_dev->dev, &dev_attr_name);      if (res)          goto error_destroy;
     pr_debug("i2c-dev: adapter [%s] registered as minor %d\n",      adap->name, adap->nr);      return 0; error_destroy:     device_destroy(i2c_dev_class, MKDEV(I2C_MAJOR, adap->nr)); error:     return_i2c_dev(i2c_dev);     return res; }
在i2cdev_attach_adapter调用device_create(i2c_dev_class, &adap->dev,          MKDEV(I2C_MAJOR, adap->nr), NULL,          "i2c-%d", adap->nr);
这样在dev目录就产生i2c-0  或i2c-1节点
 
class_device_create（）； class_device_destroy（）；
在2.6.27中变为： device_create（） device_destroy（）
本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/zhenwenxian/archive/2010/03/28/5424434.aspx

class_create(),device_create自动创建设备文件结点


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