linux内核驱动知识三，自动创建设备文件devfs与udev

Linux  2.4内核中devfs

创建设备目录：

    devfs_handle_t devfs_mk_dir(devfs_handle_t dir, const char *name, void info);

创建设备文件：

devfs_handle_t devfs_register(devfs_handle_t dir, const char * name.

 unsigned int flags, unsigned int major,

 unsigned int minor, umode_t mode,

 void *ops, void *info) ;        

    在指定的目录中创建设备文件：dir 目录名，为空表示在/dev/目录下创建；name  文件名；flags  创建标志；major 主设备号；minor 次设备号；mode创建模式；ops 操作函数集；info  通常为空

撤销设备文件：

void devfs_unregister(devfs_handlle_t de);

使用实例：

Static devfs_handle_t devfs_handle ;

 

Devfs_handle = devfs-register(NULL, DEVICE_NAME, DEVFS_FL_DEFAULT, major, 0 , S_IFCHR | S_IRUSR | S_IWUSR, &XXX_fops);

 

Devfs_unregister(devfs_handle);

此方法在linux 2.6任然被支持，但是是一种过时的做法

 

 Linux  2.6内核中udev

从linux 2.6.13开始，devfs不复存在，udev 成为devfs的替代品。相比devfs,udev(mdev)存在于应用层。利用udev(mdev)来实现设备文件的自动创建 很简单，在驱动代码里调用class_create 为该设备创建一个class,在为每个设备调用device_create创建对应的设备。

 

例1：

struct class *myclass ；

static struct device *dev;
myclass =  class_create(THIS_MODULE, “my_device_driver”);

if (IS_ERR(my_class)) {
printk("Err: failed in creating class.\n");
return ;

}

dev = device_create(myclass, NULL, MKDEV(major_num, minor_num), NULL, “my_device”); 

 

device_destroy(my_class, MKDEV(major_num, minor_num));
class_destroy(my_class);

 

例2：

现在，好使的是device_create ，从2.6.18开始可用

struct device *device_create(struct class *class, struct device *parent,
dev_t devt, const char *fmt, ...)

 

从2.6.26起又多了一个参数drvdata： the data to be added to the device for callbacks不会用就给个NULL吧.

struct device *device_create(struct class *class, struct device *parent,
dev_t devt, void *drvdata, const char *fmt, ...)

 

dev=device_create(usb_class, NULL, test_usb_devno, shortname);
//2.6.26以上
// dev=device_create(usb_class, NULL, test_usb_devno, NULL,shortname);

 

  device_create( my_class, NULL, MKDEV(hello_major, 0), "hello" "%d", 0 );

如果成功，它将会在/dev目录下产生/dev/hello0设备。

 

当驱动被加载时，udev(mdev)就会自动在/dev下创建my_device设备文件。

 

#include // device_create()

 

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

 

PS:

2.6.15中的函数：

       Class_device_create(struct class *cls,  struct class_device *parent,  dev_t devt, struct device *device, const  char *fmt, ...);

       Class_devcie_destroy(struct class *class, dev_t devt);

      

在2.6.27中变为：

       Device_create(struct class *class, struct device *parent,

                          dev_t devt, void *drvdata, const char *fmt, ..);

       Device_destroy(struct class *class, dev_t devt);