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[luther.gliethttp]
luther@gliethttp:~$ ll /sys/class/tty/console
lrwxrwxrwx 1 root root 0 2009-06-30 09:40 /sys/class/tty/console -> ../../devices/virtual/tty/console
luther@gliethttp:~$ ll /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[luther.gliethttp]
#ifdef CONFIG_SYSFS_DEPRECATED
static struct kobject *get_device_parent(struct device *dev,
struct device *parent)
{
/* class devices without a parent live in /sys/class// */
if (dev->class && (!parent || parent->class != dev->class))
return &dev->class->subsys.kobj;
/* all other devices keep their parent */
else if (parent)
return &parent->kobj;
return NULL;
}
#else
// 在我的ubnutu 8.10中使用的如下函数
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 we have no parent, we live in "virtual".
* Class-devices with a non class-device as parent, live
* in a "glue" directory to prevent namespace collisions.
*/
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;
/* find our class-directory at the parent and reference it */
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[luther.gliethttp]
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
/* or create a new class-directory at the parent device */
k = kobject_create();
if (!k)
return NULL;
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[luther.gliethttp]
if (retval < 0) {
kobject_put(k);
return NULL;
}
/* do not emit an uevent for this simple "glue" directory */
return k;
}
if (parent)
return &parent->kobj;
return NULL;
}
#endif
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