class_create，device_create ()详解

在驱动程序中初始化入口函数中，向内核注册一个设备后，往往要注册一个类

例如

static int __init mydriver_init(void) //驱动程序的初始化

{

……

MYDRIVER_Major = register_chrdev(0, DEVICE_NAME, &mydriver_fops); //向内核注册一个设备,返回值为注册的主设备号

if (MYDRIVER_Major < 0)

{

printk(DEVICE_NAME " can't register major number\n");

return MYDRIVER_Major;

}

……

mydriver_class = class_create(THIS_MODULE, DEVICE_NAME); //注册一个类，使mdev可以在"/dev/"目录下 面建立设备节点

……

//创建一个设备节点，节点名为DEVICE_NAME

device_create(mydriver_class, NULL, MKDEV(MYDRIVER_Major, 0), NULL, DEVICE_NAME);

……

}

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。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

对于没有指定dev->parent的dev都将被添加到/sys/devices/virtual/tty/ 目录下,如果指定了dev->parent,那么同时该dev->class存在,同时parent->class存在,那么该dev->name目录将被添加到parent->class所在目录下

****@*****:~$ ls -a /sys/class/tty/console

lrwxrwxrwx 1 root root 0 2009-06-30 09:40
/sys/class/tty/console->../../devices/virtual/tty/console

****@*****:~$ ls -a/sys/devices/virtual/tty/console/

total 0

-rw-r--r-- 1 root root 4.0K 2009-06-30 10:51 uevent

drwxr-xr-x 2 root root 0 2009-06-30 10:51 power

lrwxrwxrwx 1 root root 0 2009-06-30 10:57 subsystem->../../../../class/tty

-r--r--r-- 1 root root 4.0K 2009-06-30 10:57 dev

来看看linux2.6.25内核源码,是怎么做得.

device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 1),"console");

==>device_register

==>device_add

==>setup_parent

==>get_device_parent

==>dev->kobj.parent= kobj("/sys/devices/virtual/tty");//所以所有的文件添加都将指向该目录

#ifdef CONFIG_SYSFS_DEPRECATED

static struct kobject *get_device_parent(struct device*dev,

struct device*parent)

{

if (dev->class&&(!parent
|| parent->class!= dev->class))

return &dev->class->subsys.kobj;

else if (parent)

return &parent->kobj;

return NULL;

}

#else

static struct kobject*get_device_parent(struct device*dev,

struct device*parent)

{

int retval;

if (dev->class){

struct kobject
*kobj = NULL;

struct kobject
*parent_kobj;

struct kobject
*k;

if (parent==NULL)

parent_kobj= virtual_device_parent(dev);// 获取/sys/devices/virtual目录对应的kobj

else if(parent->class)

return&parent->kobj;

else

parent_kobj=&parent->kobj;

spin_lock(&dev->class->class_dirs.list_lock); //
class->class_dirs本身就是一个kset

// 如果该kset的list链表上没有挂接到/sys/devices/virtual目录上的son,那么说明该class_dirs还没有在

// /sys/devices/virtual目录下创建,所以就需要创建该class名对应的目录

list_for_each_entry(k,&dev->class->class_dirs.list, entry)

if(k->parent== parent_kobj){

kobj= kobject_get(k);

break;

}

spin_unlock(&dev->class->class_dirs.list_lock);

if (kobj)

return kobj;

// 创建/sys/devices/virtual/tty这个tty_class对应的目录

k = kobject_create();

if (!k)

returnNULL;

k->kset=&dev->class->class_dirs;

// 名在/sys/devices/virtual/目录下创建以tty_class的name为目录名的目录[luther.gliethttp]

retval = kobject_add(k, parent_kobj,"%s", dev->class->name);//
将kobj添加到parent_kobj对应目录下

if (retval< 0){

kobject_put(k);

returnNULL;

}

return k;

}

if (parent)

return &parent->kobj;

return NULL;

}

#endif