在驅動程序中初始化入口函數中，向內核註冊一個設備後，往往要註冊一個類
例如
static int __init mydriver_init(void) //驅動程序的初始化
{
……
MYDRIVER_Major = register_chrdev(0, DEVICE_NAME,&mydriver_fops); //向內核註冊一個設備,返回值爲註冊的主設備號
if(MYDRIVER_Major < 0)
{
printk(DEVICE_NAME " can't register major number\n");
returnMYDRIVER_Major;
}
……
mydriver_class = class_create(THIS_MODULE,DEVICE_NAME); //註冊一個類，使mdev可以在"/dev/"目錄下面建立設備節點
……
//創建一個設備節點，節點名爲DEVICE_NAME
device_create(mydriver_class, NULL, MKDEV(MYDRIVER_Major, 0), NULL,DEVICE_NAME);
……
}
從linux內核2.6的某個版本之後，devfs不復存在，udev成爲devfs的替代。相比devfs，udev有很多優勢，在此就不羅嗦了，提醒一點，udev是應用層的東東，不要試圖在內核的配置選項裏找到它;加入對udev的支持很簡單，以作者所寫的一個字符設備驅動爲例，在驅動初始化的代碼裏調用class_create爲該設備創建一個class，再爲每個設備調用class_device_create創建對應的設備。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”);
這樣的module被加載時，udevdaemon就會自動在/dev下創建my_device設備文件。
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/下創建類目錄
class_device_create()
-------------------------------------------------
linux-2.6.22/include/linux/device.h
struct class_device *class_device_create(structclass *cls,
struct class_device
*parent,
dev_t devt,
structdevice *device,
constchar *fmt,
...)
class_device_create - creates a class device and registers it withsysfs
@cls:pointer to the struct class that this device should be registeredto.
@parent:pointer to the parent struct class_device of this new device, ifany.
@devt: thedev_t for the char device to be added.
@device: apointer to a struct device that is assiociated with this classdevice.
@fmt: stringfor the class device's name
對於沒有指定dev->parent的dev都將被添加到/sys/devices/virtual/tty/ 目錄下,如果指定了dev->parent,那麼同時該dev->class存在,同時parent->class存在,那麼該dev->name目錄將被添加到parent->class所在目錄下
****@*****:~$ ls-a /sys/class/tty/console
lrwxrwxrwx 1 root root 0 2009-06-3009:40 /sys/class/tty/console->../../devices/virtual/tty/console
****@*****:~$ ls-a/sys/devices/virtual/tty/console/
total 0
-rw-r--r-- 1root root 4.0K 2009-06-3010:51 uevent
drwxr-xr-x 2 root root 02009-06-30 10:51 power
lrwxrwxrwx 1 root root 0 2009-06-3010:57subsystem-> ../../../../class/tty
-r--r--r-- 1root root 4.0K 2009-06-3010:57 dev
來看看linux2.6.25內核源碼,是怎麼做得.
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將指向該目錄
#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);//獲取/sys/devices/virtual目錄對應的kobj
else if(parent->class)
return&parent->kobj;
else
parent_kobj= &parent->kobj;
spin_lock(&dev->class->class_dirs.list_lock); //class->class_dirs本身就是一個kset
//如果該kset的list鏈表上沒有掛接到/sys/devices/virtual目錄上的son,那麼說明該class_dirs還沒有在
///sys/devices/virtual目錄下創建,所以就需要創建該class名對應的目錄
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;
//創建/sys/devices/virtual/tty這個tty_class對應的目錄
k = kobject_create();
if (!k)
returnNULL;
k->kset= &dev->class->class_dirs;
//名在/sys/devices/virtual/目錄下創建以tty_class的name爲目錄名的目錄[luther.gliethttp]
retval = kobject_add(k, parent_kobj,"%s", dev->class->name);//將kobj添加到parent_kobj對應目錄下
if (retval<</SPAN> 0) {
kobject_put(k);
returnNULL;
}
return k;
}
if (parent)
return &parent->kobj;
return NULL;
}
#endif