int __init classes_init(void)
{
    class_kset = kset_create_and_add("class", NULL, NULL); ///sys/class
    if (!class_kset)
        return -ENOMEM;
    return 0;
}

#define class_create(owner, name)        \
({                        \
    static struct lock_class_key __key;    \
    __class_create(owner, name, &__key);    \
})

struct class *__class_create(struct module *owner, const char *name,
                 struct lock_class_key *key)
{
    struct class *cls;
    int retval;

    cls = kzalloc(sizeof(*cls), GFP_KERNEL);
    if (!cls) {
        retval = -ENOMEM;
        goto error;
    }

    cls->name = name;
    cls->owner = owner;
    cls->class_release = class_create_release;

    retval = __class_register(cls, key);
    if (retval)
        goto error;

    return cls;

error:
    kfree(cls);
    return ERR_PTR(retval);
}

int __class_register(struct class *cls, struct lock_class_key *key)
{
    struct subsys_private *cp;
    int error;

    pr_debug("device class '%s': registering\n", cls->name);

    cp = kzalloc(sizeof(*cp), GFP_KERNEL);
    if (!cp)
        return -ENOMEM;
    klist_init(&cp->klist_devices, klist_class_dev_get, klist_class_dev_put);
    INIT_LIST_HEAD(&cp->interfaces);
    kset_init(&cp->glue_dirs);
    __mutex_init(&cp->mutex, "subsys mutex", key);
    error = kobject_set_name(&cp->subsys.kobj, "%s", cls->name);
    if (error) {
        kfree(cp);
        return error;
    }

    /* set the default /sys/dev directory for devices of this class */
    if (!cls->dev_kobj)
        cls->dev_kobj = sysfs_dev_char_kobj;

#if defined(CONFIG_BLOCK)
    /* let the block class directory show up in the root of sysfs */
    if (!sysfs_deprecated || cls != &block_class)
        cp->subsys.kobj.kset = class_kset;
#else
    cp->subsys.kobj.kset = class_kset;
#endif
    cp->subsys.kobj.ktype = &class_ktype;
    cp->class = cls;
    cls->p = cp;

    error = kset_register(&cp->subsys);
    if (error) {
        kfree(cp);
        return error;
    }
    error = class_add_groups(class_get(cls), cls->class_groups); ///sys/class/xxxcalss
    class_put(cls);
    return error;
}