drivers/base/class.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * class.c - basic device class management
  *
  * Copyright (c) 2002-3 Patrick Mochel
  * Copyright (c) 2002-3 Open Source Development Labs
  * Copyright (c) 2003-2004 Greg Kroah-Hartman
  * Copyright (c) 2003-2004 IBM Corp.
  */

 #include <linux/device/class.h>
 #include <linux/device.h>
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/string.h>
 #include <linux/kdev_t.h>
 #include <linux/err.h>
 #include <linux/slab.h>
 #include <linux/blkdev.h>
 #include <linux/mutex.h>
 #include "base.h"

 #define to_class_attr(_attr) container_of(_attr, struct class_attribute, attr)

 static ssize_t class_attr_show(struct kobject *kobj, struct attribute *attr,
 			       char *buf)
 {
 	struct class_attribute *class_attr = to_class_attr(attr);
 	struct subsys_private *cp = to_subsys_private(kobj);
 	ssize_t ret = -EIO;

 	if (class_attr->show)
 		ret = class_attr->show(cp->class, class_attr, buf);
 	return ret;
 }

 static ssize_t class_attr_store(struct kobject *kobj, struct attribute *attr,
 				const char *buf, size_t count)
 {
 	struct class_attribute *class_attr = to_class_attr(attr);
 	struct subsys_private *cp = to_subsys_private(kobj);
 	ssize_t ret = -EIO;

 	if (class_attr->store)
 		ret = class_attr->store(cp->class, class_attr, buf, count);
 	return ret;
 }

 static void class_release(struct kobject *kobj)
 {
 	struct subsys_private *cp = to_subsys_private(kobj);
 	struct class *class = cp->class;

 	pr_debug("class '%s': release.\n", class->name);

 	if (class->class_release)
 		class->class_release(class);
 	else
 		pr_debug("class '%s' does not have a release() function, "
 			 "be careful\n", class->name);

 	kfree(cp);
 }

 static const struct kobj_ns_type_operations *class_child_ns_type(struct kobject *kobj)
 {
 	struct subsys_private *cp = to_subsys_private(kobj);
 	struct class *class = cp->class;

 	return class->ns_type;
 }

 static const struct sysfs_ops class_sysfs_ops = {
 	.show	   = class_attr_show,
 	.store	   = class_attr_store,
 };

 static struct kobj_type class_ktype = {
 	.sysfs_ops	= &class_sysfs_ops,
 	.release	= class_release,
 	.child_ns_type	= class_child_ns_type,
 };

 /* Hotplug events for classes go to the class subsys */
 static struct kset *class_kset;


 int class_create_file_ns(struct class *cls, const struct class_attribute *attr,
 			 const void *ns)
 {
 	int error;

 	if (cls)
 		error = sysfs_create_file_ns(&cls->p->subsys.kobj,
 					     &attr->attr, ns);
 	else
 		error = -EINVAL;
 	return error;
 }

 void class_remove_file_ns(struct class *cls, const struct class_attribute *attr,
 			  const void *ns)
 {
 	if (cls)
 		sysfs_remove_file_ns(&cls->p->subsys.kobj, &attr->attr, ns);
 }

 static struct class *class_get(struct class *cls)
 {
 	if (cls)
 		kset_get(&cls->p->subsys);
 	return cls;
 }

 static void class_put(struct class *cls)
 {
 	if (cls)
 		kset_put(&cls->p->subsys);
 }

 static struct device *klist_class_to_dev(struct klist_node *n)
 {
 	struct device_private *p = to_device_private_class(n);
 	return p->device;
 }

 static void klist_class_dev_get(struct klist_node *n)
 {
 	struct device *dev = klist_class_to_dev(n);

 	get_device(dev);
 }

 static void klist_class_dev_put(struct klist_node *n)
 {
 	struct device *dev = klist_class_to_dev(n);

 	put_device(dev);
 }

 static int class_add_groups(struct class *cls,
 			    const struct attribute_group **groups)
 {
 	return sysfs_create_groups(&cls->p->subsys.kobj, groups);
 }

 static void class_remove_groups(struct class *cls,
 				const struct attribute_group **groups)
 {
 	return sysfs_remove_groups(&cls->p->subsys.kobj, groups);
 }

 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);
 	class_put(cls);
 	if (error) {
 		kobject_del(&cp->subsys.kobj);
 		kfree_const(cp->subsys.kobj.name);
 		kfree(cp);
 	}
 	return error;
 }
 EXPORT_SYMBOL_GPL(__class_register);

 void class_unregister(struct class *cls)
 {
 	pr_debug("device class '%s': unregistering\n", cls->name);
 	class_remove_groups(cls, cls->class_groups);
 	kset_unregister(&cls->p->subsys);
 }

 static void class_create_release(struct class *cls)
 {
 	pr_debug("%s called for %s\n", __func__, cls->name);
 	kfree(cls);
 }

 /**
  * __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.
  * @key: the lock_class_key for this class; used by mutex lock debugging
  *
  * This is used to create a struct class pointer that can then be used
  * in calls to device_create().
  *
  * Returns &struct class pointer on success, or ERR_PTR() on error.
  *
  * Note, the pointer created here is to be destroyed when finished by
  * making a call to class_destroy().
  */
 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);
 }
 EXPORT_SYMBOL_GPL(__class_create);

 /**
  * class_destroy - destroys a struct class structure
  * @cls: pointer to the struct class that is to be destroyed
  *
  * Note, the pointer to be destroyed must have been created with a call
  * to class_create().
  */
 void class_destroy(struct class *cls)
 {
 	if (IS_ERR_OR_NULL(cls))
 		return;

 	class_unregister(cls);
 }

 /**
  * class_dev_iter_init - initialize class device iterator
  * @iter: class iterator to initialize
  * @class: the class we wanna iterate over
  * @start: the device to start iterating from, if any
  * @type: device_type of the devices to iterate over, NULL for all
  *
  * Initialize class iterator @iter such that it iterates over devices
  * of @class.  If @start is set, the list iteration will start there,
  * otherwise if it is NULL, the iteration starts at the beginning of
  * the list.
  */
 void class_dev_iter_init(struct class_dev_iter *iter, struct class *class,
 			 struct device *start, const struct device_type *type)
 {
 	struct klist_node *start_knode = NULL;

 	if (start)
 		start_knode = &start->p->knode_class;
 	klist_iter_init_node(&class->p->klist_devices, &iter->ki, start_knode);
 	iter->type = type;
 }
 EXPORT_SYMBOL_GPL(class_dev_iter_init);

 /**
  * class_dev_iter_next - iterate to the next device
  * @iter: class iterator to proceed
  *
  * Proceed @iter to the next device and return it.  Returns NULL if
  * iteration is complete.
  *
  * The returned device is referenced and won't be released till
  * iterator is proceed to the next device or exited.  The caller is
  * free to do whatever it wants to do with the device including
  * calling back into class code.
  */
 struct device *class_dev_iter_next(struct class_dev_iter *iter)
 {
 	struct klist_node *knode;
 	struct device *dev;

 	while (1) {
 		knode = klist_next(&iter->ki);
 		if (!knode)
 			return NULL;
 		dev = klist_class_to_dev(knode);
 		if (!iter->type || iter->type == dev->type)
 			return dev;
 	}
 }
 EXPORT_SYMBOL_GPL(class_dev_iter_next);

 /**
  * class_dev_iter_exit - finish iteration
  * @iter: class iterator to finish
  *
  * Finish an iteration.  Always call this function after iteration is
  * complete whether the iteration ran till the end or not.
  */
 void class_dev_iter_exit(struct class_dev_iter *iter)
 {
 	klist_iter_exit(&iter->ki);
 }
 EXPORT_SYMBOL_GPL(class_dev_iter_exit);

 /**
  * class_for_each_device - device iterator
  * @class: the class we're iterating
  * @start: the device to start with in the list, if any.
  * @data: data for the callback
  * @fn: function to be called for each device
  *
  * Iterate over @class's list of devices, and call @fn for each,
  * passing it @data.  If @start is set, the list iteration will start
  * there, otherwise if it is NULL, the iteration starts at the
  * beginning of the list.
  *
  * We check the return of @fn each time. If it returns anything
  * other than 0, we break out and return that value.
  *
  * @fn is allowed to do anything including calling back into class
  * code.  There's no locking restriction.
  */
 int class_for_each_device(struct class *class, struct device *start,
 			  void *data, int (*fn)(struct device *, void *))
 {
 	struct class_dev_iter iter;
 	struct device *dev;
 	int error = 0;

 	if (!class)
 		return -EINVAL;
 	if (!class->p) {
 		WARN(1, "%s called for class '%s' before it was initialized",
 		     __func__, class->name);
 		return -EINVAL;
 	}

 	class_dev_iter_init(&iter, class, start, NULL);
 	while ((dev = class_dev_iter_next(&iter))) {
 		error = fn(dev, data);
 		if (error)
 			break;
 	}
 	class_dev_iter_exit(&iter);

 	return error;
 }
 EXPORT_SYMBOL_GPL(class_for_each_device);

 /**
  * class_find_device - device iterator for locating a particular device
  * @class: the class we're iterating
  * @start: Device to begin with
  * @data: data for the match function
  * @match: function to check device
  *
  * This is similar to the class_for_each_dev() function above, but it
  * returns a reference to a device that is 'found' for later use, as
  * determined by the @match callback.
  *
  * The callback should return 0 if the device doesn't match and non-zero
  * if it does.  If the callback returns non-zero, this function will
  * return to the caller and not iterate over any more devices.
  *
  * Note, you will need to drop the reference with put_device() after use.
  *
  * @match is allowed to do anything including calling back into class
  * code.  There's no locking restriction.
  */
 struct device *class_find_device(struct class *class, struct device *start,
 				 const void *data,
 				 int (*match)(struct device *, const void *))
 {
 	struct class_dev_iter iter;
 	struct device *dev;

 	if (!class)
 		return NULL;
 	if (!class->p) {
 		WARN(1, "%s called for class '%s' before it was initialized",
 		     __func__, class->name);
 		return NULL;
 	}

 	class_dev_iter_init(&iter, class, start, NULL);
 	while ((dev = class_dev_iter_next(&iter))) {
 		if (match(dev, data)) {
 			get_device(dev);
 			break;
 		}
 	}
 	class_dev_iter_exit(&iter);

 	return dev;
 }
 EXPORT_SYMBOL_GPL(class_find_device);

 int class_interface_register(struct class_interface *class_intf)
 {
 	struct class *parent;
 	struct class_dev_iter iter;
 	struct device *dev;

 	if (!class_intf || !class_intf->class)
 		return -ENODEV;

 	parent = class_get(class_intf->class);
 	if (!parent)
 		return -EINVAL;

 	mutex_lock(&parent->p->mutex);
 	list_add_tail(&class_intf->node, &parent->p->interfaces);
 	if (class_intf->add_dev) {
 		class_dev_iter_init(&iter, parent, NULL, NULL);
 		while ((dev = class_dev_iter_next(&iter)))
 			class_intf->add_dev(dev, class_intf);
 		class_dev_iter_exit(&iter);
 	}
 	mutex_unlock(&parent->p->mutex);

 	return 0;
 }

 void class_interface_unregister(struct class_interface *class_intf)
 {
 	struct class *parent = class_intf->class;
 	struct class_dev_iter iter;
 	struct device *dev;

 	if (!parent)
 		return;

 	mutex_lock(&parent->p->mutex);
 	list_del_init(&class_intf->node);
 	if (class_intf->remove_dev) {
 		class_dev_iter_init(&iter, parent, NULL, NULL);
 		while ((dev = class_dev_iter_next(&iter)))
 			class_intf->remove_dev(dev, class_intf);
 		class_dev_iter_exit(&iter);
 	}
 	mutex_unlock(&parent->p->mutex);

 	class_put(parent);
 }

 ssize_t show_class_attr_string(struct class *class,
 			       struct class_attribute *attr, char *buf)
 {
 	struct class_attribute_string *cs;

 	cs = container_of(attr, struct class_attribute_string, attr);
 	return sysfs_emit(buf, "%s\n", cs->str);
 }

 EXPORT_SYMBOL_GPL(show_class_attr_string);

 struct class_compat {
 	struct kobject *kobj;
 };

 /**
  * class_compat_register - register a compatibility class
  * @name: the name of the class
  *
  * Compatibility class are meant as a temporary user-space compatibility
  * workaround when converting a family of class devices to a bus devices.
  */
 struct class_compat *class_compat_register(const char *name)
 {
 	struct class_compat *cls;

 	cls = kmalloc(sizeof(struct class_compat), GFP_KERNEL);
 	if (!cls)
 		return NULL;
 	cls->kobj = kobject_create_and_add(name, &class_kset->kobj);
 	if (!cls->kobj) {
 		kfree(cls);
 		return NULL;
 	}
 	return cls;
 }
 EXPORT_SYMBOL_GPL(class_compat_register);

 /**
  * class_compat_unregister - unregister a compatibility class
  * @cls: the class to unregister
  */
 void class_compat_unregister(struct class_compat *cls)
 {
 	kobject_put(cls->kobj);
 	kfree(cls);
 }
 EXPORT_SYMBOL_GPL(class_compat_unregister);

 /**
  * class_compat_create_link - create a compatibility class device link to
  *			      a bus device
  * @cls: the compatibility class
  * @dev: the target bus device
  * @device_link: an optional device to which a "device" link should be created
  */
 int class_compat_create_link(struct class_compat *cls, struct device *dev,
 			     struct device *device_link)
 {
 	int error;

 	error = sysfs_create_link(cls->kobj, &dev->kobj, dev_name(dev));
 	if (error)
 		return error;

 	/*
 	 * Optionally add a "device" link (typically to the parent), as a
 	 * class device would have one and we want to provide as much
 	 * backwards compatibility as possible.
 	 */
 	if (device_link) {
 		error = sysfs_create_link(&dev->kobj, &device_link->kobj,
 					  "device");
 		if (error)
 			sysfs_remove_link(cls->kobj, dev_name(dev));
 	}

 	return error;
 }
 EXPORT_SYMBOL_GPL(class_compat_create_link);

 /**
  * class_compat_remove_link - remove a compatibility class device link to
  *			      a bus device
  * @cls: the compatibility class
  * @dev: the target bus device
  * @device_link: an optional device to which a "device" link was previously
  * 		 created
  */
 void class_compat_remove_link(struct class_compat *cls, struct device *dev,
 			      struct device *device_link)
 {
 	if (device_link)
 		sysfs_remove_link(&dev->kobj, "device");
 	sysfs_remove_link(cls->kobj, dev_name(dev));
 }
 EXPORT_SYMBOL_GPL(class_compat_remove_link);

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

 EXPORT_SYMBOL_GPL(class_create_file_ns);
 EXPORT_SYMBOL_GPL(class_remove_file_ns);
 EXPORT_SYMBOL_GPL(class_unregister);
 EXPORT_SYMBOL_GPL(class_destroy);

 EXPORT_SYMBOL_GPL(class_interface_register);
 EXPORT_SYMBOL_GPL(class_interface_unregister);
	// SPDX-License-Identifier: GPL-2.0
	/*
	* class.c - basic device class management
	*
	* Copyright (c) 2002-3 Patrick Mochel
	* Copyright (c) 2002-3 Open Source Development Labs
	* Copyright (c) 2003-2004 Greg Kroah-Hartman
	* Copyright (c) 2003-2004 IBM Corp.
	*/

	#include <linux/device/class.h>
	#include <linux/device.h>
	#include <linux/module.h>
	#include <linux/init.h>
	#include <linux/string.h>
	#include <linux/kdev_t.h>
	#include <linux/err.h>
	#include <linux/slab.h>
	#include <linux/blkdev.h>
	#include <linux/mutex.h>
	#include "base.h"

	#define to_class_attr(_attr) container_of(_attr, struct class_attribute, attr)

	static ssize_t class_attr_show(struct kobject kobj, struct attribute attr,
	char *buf)
	{
	struct class_attribute *class_attr = to_class_attr(attr);
	struct subsys_private *cp = to_subsys_private(kobj);
	ssize_t ret = -EIO;

	if (class_attr->show)
	ret = class_attr->show(cp->class, class_attr, buf);
	return ret;
	}

	static ssize_t class_attr_store(struct kobject kobj, struct attribute attr,
	const char *buf, size_t count)
	{
	struct class_attribute *class_attr = to_class_attr(attr);
	struct subsys_private *cp = to_subsys_private(kobj);
	ssize_t ret = -EIO;

	if (class_attr->store)
	ret = class_attr->store(cp->class, class_attr, buf, count);
	return ret;
	}

	static void class_release(struct kobject *kobj)
	{
	struct subsys_private *cp = to_subsys_private(kobj);
	struct class *class = cp->class;

	pr_debug("class '%s': release.\n", class->name);

	if (class->class_release)
	class->class_release(class);
	else
	pr_debug("class '%s' does not have a release() function, "
	"be careful\n", class->name);

	kfree(cp);
	}

	static const struct kobj_ns_type_operations class_child_ns_type(struct kobject kobj)
	{
	struct subsys_private *cp = to_subsys_private(kobj);
	struct class *class = cp->class;

	return class->ns_type;
	}

	static const struct sysfs_ops class_sysfs_ops = {
	.show = class_attr_show,
	.store = class_attr_store,
	};

	static struct kobj_type class_ktype = {
	.sysfs_ops = &class_sysfs_ops,
	.release = class_release,
	.child_ns_type = class_child_ns_type,
	};

	/* Hotplug events for classes go to the class subsys */
	static struct kset *class_kset;


	int class_create_file_ns(struct class cls, const struct class_attribute attr,
	const void *ns)
	{
	int error;

	if (cls)
	error = sysfs_create_file_ns(&cls->p->subsys.kobj,
	&attr->attr, ns);
	else
	error = -EINVAL;
	return error;
	}

	void class_remove_file_ns(struct class cls, const struct class_attribute attr,
	const void *ns)
	{
	if (cls)
	sysfs_remove_file_ns(&cls->p->subsys.kobj, &attr->attr, ns);
	}

	static struct class class_get(struct class cls)
	{
	if (cls)
	kset_get(&cls->p->subsys);
	return cls;
	}

	static void class_put(struct class *cls)
	{
	if (cls)
	kset_put(&cls->p->subsys);
	}

	static struct device klist_class_to_dev(struct klist_node n)
	{
	struct device_private *p = to_device_private_class(n);
	return p->device;
	}

	static void klist_class_dev_get(struct klist_node *n)
	{
	struct device *dev = klist_class_to_dev(n);

	get_device(dev);
	}

	static void klist_class_dev_put(struct klist_node *n)
	{
	struct device *dev = klist_class_to_dev(n);

	put_device(dev);
	}

	static int class_add_groups(struct class *cls,
	const struct attribute_group **groups)
	{
	return sysfs_create_groups(&cls->p->subsys.kobj, groups);
	}

	static void class_remove_groups(struct class *cls,
	const struct attribute_group **groups)
	{
	return sysfs_remove_groups(&cls->p->subsys.kobj, groups);
	}

	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);
	class_put(cls);
	if (error) {
	kobject_del(&cp->subsys.kobj);
	kfree_const(cp->subsys.kobj.name);
	kfree(cp);
	}
	return error;
	}
	EXPORT_SYMBOL_GPL(__class_register);

	void class_unregister(struct class *cls)
	{
	pr_debug("device class '%s': unregistering\n", cls->name);
	class_remove_groups(cls, cls->class_groups);
	kset_unregister(&cls->p->subsys);
	}

	static void class_create_release(struct class *cls)
	{
	pr_debug("%s called for %s\n", __func__, cls->name);
	kfree(cls);
	}

	/**
	* __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.
	* @key: the lock_class_key for this class; used by mutex lock debugging
	*
	* This is used to create a struct class pointer that can then be used
	* in calls to device_create().
	*
	* Returns &struct class pointer on success, or ERR_PTR() on error.
	*
	* Note, the pointer created here is to be destroyed when finished by
	* making a call to class_destroy().
	*/
	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);
	}
	EXPORT_SYMBOL_GPL(__class_create);

	/**
	* class_destroy - destroys a struct class structure
	* @cls: pointer to the struct class that is to be destroyed
	*
	* Note, the pointer to be destroyed must have been created with a call
	* to class_create().
	*/
	void class_destroy(struct class *cls)
	{
	if (IS_ERR_OR_NULL(cls))
	return;

	class_unregister(cls);
	}

	/**
	* class_dev_iter_init - initialize class device iterator
	* @iter: class iterator to initialize
	* @class: the class we wanna iterate over
	* @start: the device to start iterating from, if any
	* @type: device_type of the devices to iterate over, NULL for all
	*
	* Initialize class iterator @iter such that it iterates over devices
	* of @class. If @start is set, the list iteration will start there,
	* otherwise if it is NULL, the iteration starts at the beginning of
	* the list.
	*/
	void class_dev_iter_init(struct class_dev_iter iter, struct class class,
	struct device start, const struct device_type type)
	{
	struct klist_node *start_knode = NULL;

	if (start)
	start_knode = &start->p->knode_class;
	klist_iter_init_node(&class->p->klist_devices, &iter->ki, start_knode);
	iter->type = type;
	}
	EXPORT_SYMBOL_GPL(class_dev_iter_init);

	/**
	* class_dev_iter_next - iterate to the next device
	* @iter: class iterator to proceed
	*
	* Proceed @iter to the next device and return it. Returns NULL if
	* iteration is complete.
	*
	* The returned device is referenced and won't be released till
	* iterator is proceed to the next device or exited. The caller is
	* free to do whatever it wants to do with the device including
	* calling back into class code.
	*/
	struct device class_dev_iter_next(struct class_dev_iter iter)
	{
	struct klist_node *knode;
	struct device *dev;

	while (1) {
	knode = klist_next(&iter->ki);
	if (!knode)
	return NULL;
	dev = klist_class_to_dev(knode);
	if (!iter->type \|\| iter->type == dev->type)
	return dev;
	}
	}
	EXPORT_SYMBOL_GPL(class_dev_iter_next);

	/**
	* class_dev_iter_exit - finish iteration
	* @iter: class iterator to finish
	*
	* Finish an iteration. Always call this function after iteration is
	* complete whether the iteration ran till the end or not.
	*/
	void class_dev_iter_exit(struct class_dev_iter *iter)
	{
	klist_iter_exit(&iter->ki);
	}
	EXPORT_SYMBOL_GPL(class_dev_iter_exit);

	/**
	* class_for_each_device - device iterator
	* @class: the class we're iterating
	* @start: the device to start with in the list, if any.
	* @data: data for the callback
	* @fn: function to be called for each device
	*
	* Iterate over @class's list of devices, and call @fn for each,
	* passing it @data. If @start is set, the list iteration will start
	* there, otherwise if it is NULL, the iteration starts at the
	* beginning of the list.
	*
	* We check the return of @fn each time. If it returns anything
	* other than 0, we break out and return that value.
	*
	* @fn is allowed to do anything including calling back into class
	* code. There's no locking restriction.
	*/
	int class_for_each_device(struct class class, struct device start,
	void data, int (fn)(struct device , void ))
	{
	struct class_dev_iter iter;
	struct device *dev;
	int error = 0;

	if (!class)
	return -EINVAL;
	if (!class->p) {
	WARN(1, "%s called for class '%s' before it was initialized",
	__func__, class->name);
	return -EINVAL;
	}

	class_dev_iter_init(&iter, class, start, NULL);
	while ((dev = class_dev_iter_next(&iter))) {
	error = fn(dev, data);
	if (error)
	break;
	}
	class_dev_iter_exit(&iter);

	return error;
	}
	EXPORT_SYMBOL_GPL(class_for_each_device);

	/**
	* class_find_device - device iterator for locating a particular device
	* @class: the class we're iterating
	* @start: Device to begin with
	* @data: data for the match function
	* @match: function to check device
	*
	* This is similar to the class_for_each_dev() function above, but it
	* returns a reference to a device that is 'found' for later use, as
	* determined by the @match callback.
	*
	* The callback should return 0 if the device doesn't match and non-zero
	* if it does. If the callback returns non-zero, this function will
	* return to the caller and not iterate over any more devices.
	*
	* Note, you will need to drop the reference with put_device() after use.
	*
	* @match is allowed to do anything including calling back into class
	* code. There's no locking restriction.
	*/
	struct device class_find_device(struct class class, struct device *start,
	const void *data,
	int (match)(struct device , const void *))
	{
	struct class_dev_iter iter;
	struct device *dev;

	if (!class)
	return NULL;
	if (!class->p) {
	WARN(1, "%s called for class '%s' before it was initialized",
	__func__, class->name);
	return NULL;
	}

	class_dev_iter_init(&iter, class, start, NULL);
	while ((dev = class_dev_iter_next(&iter))) {
	if (match(dev, data)) {
	get_device(dev);
	break;
	}
	}
	class_dev_iter_exit(&iter);

	return dev;
	}
	EXPORT_SYMBOL_GPL(class_find_device);

	int class_interface_register(struct class_interface *class_intf)
	{
	struct class *parent;
	struct class_dev_iter iter;
	struct device *dev;

	if (!class_intf \|\| !class_intf->class)
	return -ENODEV;

	parent = class_get(class_intf->class);
	if (!parent)
	return -EINVAL;

	mutex_lock(&parent->p->mutex);
	list_add_tail(&class_intf->node, &parent->p->interfaces);
	if (class_intf->add_dev) {
	class_dev_iter_init(&iter, parent, NULL, NULL);
	while ((dev = class_dev_iter_next(&iter)))
	class_intf->add_dev(dev, class_intf);
	class_dev_iter_exit(&iter);
	}
	mutex_unlock(&parent->p->mutex);

	return 0;
	}

	void class_interface_unregister(struct class_interface *class_intf)
	{
	struct class *parent = class_intf->class;
	struct class_dev_iter iter;
	struct device *dev;

	if (!parent)
	return;

	mutex_lock(&parent->p->mutex);
	list_del_init(&class_intf->node);
	if (class_intf->remove_dev) {
	class_dev_iter_init(&iter, parent, NULL, NULL);
	while ((dev = class_dev_iter_next(&iter)))
	class_intf->remove_dev(dev, class_intf);
	class_dev_iter_exit(&iter);
	}
	mutex_unlock(&parent->p->mutex);

	class_put(parent);
	}

	ssize_t show_class_attr_string(struct class *class,
	struct class_attribute attr, char buf)
	{
	struct class_attribute_string *cs;

	cs = container_of(attr, struct class_attribute_string, attr);
	return sysfs_emit(buf, "%s\n", cs->str);
	}

	EXPORT_SYMBOL_GPL(show_class_attr_string);

	struct class_compat {
	struct kobject *kobj;
	};

	/**
	* class_compat_register - register a compatibility class
	* @name: the name of the class
	*
	* Compatibility class are meant as a temporary user-space compatibility
	* workaround when converting a family of class devices to a bus devices.
	*/
	struct class_compat class_compat_register(const char name)
	{
	struct class_compat *cls;

	cls = kmalloc(sizeof(struct class_compat), GFP_KERNEL);
	if (!cls)
	return NULL;
	cls->kobj = kobject_create_and_add(name, &class_kset->kobj);
	if (!cls->kobj) {
	kfree(cls);
	return NULL;
	}
	return cls;
	}
	EXPORT_SYMBOL_GPL(class_compat_register);

	/**
	* class_compat_unregister - unregister a compatibility class
	* @cls: the class to unregister
	*/
	void class_compat_unregister(struct class_compat *cls)
	{
	kobject_put(cls->kobj);
	kfree(cls);
	}
	EXPORT_SYMBOL_GPL(class_compat_unregister);

	/**
	* class_compat_create_link - create a compatibility class device link to
	* a bus device
	* @cls: the compatibility class
	* @dev: the target bus device
	* @device_link: an optional device to which a "device" link should be created
	*/
	int class_compat_create_link(struct class_compat cls, struct device dev,
	struct device *device_link)
	{
	int error;

	error = sysfs_create_link(cls->kobj, &dev->kobj, dev_name(dev));
	if (error)
	return error;

	/*
	* Optionally add a "device" link (typically to the parent), as a
	* class device would have one and we want to provide as much
	* backwards compatibility as possible.
	*/
	if (device_link) {
	error = sysfs_create_link(&dev->kobj, &device_link->kobj,
	"device");
	if (error)
	sysfs_remove_link(cls->kobj, dev_name(dev));
	}

	return error;
	}
	EXPORT_SYMBOL_GPL(class_compat_create_link);

	/**
	* class_compat_remove_link - remove a compatibility class device link to
	* a bus device
	* @cls: the compatibility class
	* @dev: the target bus device
	* @device_link: an optional device to which a "device" link was previously
	* created
	*/
	void class_compat_remove_link(struct class_compat cls, struct device dev,
	struct device *device_link)
	{
	if (device_link)
	sysfs_remove_link(&dev->kobj, "device");
	sysfs_remove_link(cls->kobj, dev_name(dev));
	}
	EXPORT_SYMBOL_GPL(class_compat_remove_link);

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

	EXPORT_SYMBOL_GPL(class_create_file_ns);
	EXPORT_SYMBOL_GPL(class_remove_file_ns);
	EXPORT_SYMBOL_GPL(class_unregister);
	EXPORT_SYMBOL_GPL(class_destroy);

	EXPORT_SYMBOL_GPL(class_interface_register);
	EXPORT_SYMBOL_GPL(class_interface_unregister);