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");
returnMYDRIVER_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，udevdaemon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(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
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 2009-06-3009:40 /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
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<</SPAN> 0) {
kobject_put(k);
returnNULL;
}
return k;
}
if (parent)
return &parent->kobj;
return NULL;
}
#endif