drivers/base/core.c

/*
 * drivers/base/core.c - core driver model code (device registration, etc)
 *
 * Copyright (c) 2002-3 Patrick Mochel
 * Copyright (c) 2002-3 Open Source Development Labs
 * Copyright (c) 2006 Greg Kroah-Hartman <gregkh@suse.de>
 * Copyright (c) 2006 Novell, Inc.
 *
 * This file is released under the GPLv2
 *
 */

#include <linux/device.h>
#include <linux/err.h>
#include <linux/fwnode.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/kdev_t.h>
#include <linux/notifier.h>
#include <linux/of.h>
#include <linux/of_device.h>
#include <linux/genhd.h>
#include <linux/kallsyms.h>
#include <linux/mutex.h>
#include <linux/pm_runtime.h>
#include <linux/netdevice.h>
#include <linux/sched/signal.h>
#include <linux/sysfs.h>

#include "base.h"
#include "power/power.h"

#ifdef CONFIG_SYSFS_DEPRECATED
#ifdef CONFIG_SYSFS_DEPRECATED_V2
long sysfs_deprecated = 1;
#else
long sysfs_deprecated = 0;
#endif
static int __init sysfs_deprecated_setup(char *arg)
{
	return kstrtol(arg, 10, &sysfs_deprecated);
}
early_param("sysfs.deprecated", sysfs_deprecated_setup);
#endif

/* Device links support. */

#ifdef CONFIG_SRCU
static DEFINE_MUTEX(device_links_lock);
DEFINE_STATIC_SRCU(device_links_srcu);

static inline void device_links_write_lock(void)
{
	mutex_lock(&device_links_lock);
}

static inline void device_links_write_unlock(void)
{
	mutex_unlock(&device_links_lock);
}

int device_links_read_lock(void)
{
	return srcu_read_lock(&device_links_srcu);
}

void device_links_read_unlock(int idx)
{
	srcu_read_unlock(&device_links_srcu, idx);
}
#else /* !CONFIG_SRCU */
static DECLARE_RWSEM(device_links_lock);

static inline void device_links_write_lock(void)
{
	down_write(&device_links_lock);
}

static inline void device_links_write_unlock(void)
{
	up_write(&device_links_lock);
}

int device_links_read_lock(void)
{
	down_read(&device_links_lock);
	return 0;
}

void device_links_read_unlock(int not_used)
{
	up_read(&device_links_lock);
}
#endif /* !CONFIG_SRCU */

/**
 * device_is_dependent - Check if one device depends on another one
 * @dev: Device to check dependencies for.
 * @target: Device to check against.
 *
 * Check if @target depends on @dev or any device dependent on it (its child or
 * its consumer etc).  Return 1 if that is the case or 0 otherwise.
 */
static int device_is_dependent(struct device *dev, void *target)
{
	struct device_link *link;
	int ret;

	if (WARN_ON(dev == target))
		return 1;

	ret = device_for_each_child(dev, target, device_is_dependent);
	if (ret)
		return ret;

	list_for_each_entry(link, &dev->links.consumers, s_node) {
		if (WARN_ON(link->consumer == target))
			return 1;

		ret = device_is_dependent(link->consumer, target);
		if (ret)
			break;
	}
	return ret;
}

static int device_reorder_to_tail(struct device *dev, void *not_used)
{
	struct device_link *link;

	/*
	 * Devices that have not been registered yet will be put to the ends
	 * of the lists during the registration, so skip them here.
	 */
	if (device_is_registered(dev))
		devices_kset_move_last(dev);

	if (device_pm_initialized(dev))
		device_pm_move_last(dev);

	device_for_each_child(dev, NULL, device_reorder_to_tail);
	list_for_each_entry(link, &dev->links.consumers, s_node)
		device_reorder_to_tail(link->consumer, NULL);

	return 0;
}

/**
 * device_link_add - Create a link between two devices.
 * @consumer: Consumer end of the link.
 * @supplier: Supplier end of the link.
 * @flags: Link flags.
 *
 * The caller is responsible for the proper synchronization of the link creation
 * with runtime PM.  First, setting the DL_FLAG_PM_RUNTIME flag will cause the
 * runtime PM framework to take the link into account.  Second, if the
 * DL_FLAG_RPM_ACTIVE flag is set in addition to it, the supplier devices will
 * be forced into the active metastate and reference-counted upon the creation
 * of the link.  If DL_FLAG_PM_RUNTIME is not set, DL_FLAG_RPM_ACTIVE will be
 * ignored.
 *
 * If the DL_FLAG_AUTOREMOVE is set, the link will be removed automatically
 * when the consumer device driver unbinds from it.  The combination of both
 * DL_FLAG_AUTOREMOVE and DL_FLAG_STATELESS set is invalid and will cause NULL
 * to be returned.
 *
 * A side effect of the link creation is re-ordering of dpm_list and the
 * devices_kset list by moving the consumer device and all devices depending
 * on it to the ends of these lists (that does not happen to devices that have
 * not been registered when this function is called).
 *
 * The supplier device is required to be registered when this function is called
 * and NULL will be returned if that is not the case.  The consumer device need
 * not be registered, however.
 */
struct device_link *device_link_add(struct device *consumer,
				    struct device *supplier, u32 flags)
{
	struct device_link *link;

	if (!consumer || !supplier ||
	    ((flags & DL_FLAG_STATELESS) && (flags & DL_FLAG_AUTOREMOVE)))
		return NULL;

	device_links_write_lock();
	device_pm_lock();

	/*
	 * If the supplier has not been fully registered yet or there is a
	 * reverse dependency between the consumer and the supplier already in
	 * the graph, return NULL.
	 */
	if (!device_pm_initialized(supplier)
	    || device_is_dependent(consumer, supplier)) {
		link = NULL;
		goto out;
	}

	list_for_each_entry(link, &supplier->links.consumers, s_node)
		if (link->consumer == consumer)
			goto out;

	link = kzalloc(sizeof(*link), GFP_KERNEL);
	if (!link)
		goto out;

	if (flags & DL_FLAG_PM_RUNTIME) {
		if (flags & DL_FLAG_RPM_ACTIVE) {
			if (pm_runtime_get_sync(supplier) < 0) {
				pm_runtime_put_noidle(supplier);
				kfree(link);
				link = NULL;
				goto out;
			}
			link->rpm_active = true;
		}
		pm_runtime_new_link(consumer);
	}
	get_device(supplier);
	link->supplier = supplier;
	INIT_LIST_HEAD(&link->s_node);
	get_device(consumer);
	link->consumer = consumer;
	INIT_LIST_HEAD(&link->c_node);
	link->flags = flags;

	/* Determine the initial link state. */
	if (flags & DL_FLAG_STATELESS) {
		link->status = DL_STATE_NONE;
	} else {
		switch (supplier->links.status) {
		case DL_DEV_DRIVER_BOUND:
			switch (consumer->links.status) {
			case DL_DEV_PROBING:
				/*
				 * Balance the decrementation of the supplier's
				 * runtime PM usage counter after consumer probe
				 * in driver_probe_device().
				 */
				if (flags & DL_FLAG_PM_RUNTIME)
					pm_runtime_get_sync(supplier);

				link->status = DL_STATE_CONSUMER_PROBE;
				break;
			case DL_DEV_DRIVER_BOUND:
				link->status = DL_STATE_ACTIVE;
				break;
			default:
				link->status = DL_STATE_AVAILABLE;
				break;
			}
			break;
		case DL_DEV_UNBINDING:
			link->status = DL_STATE_SUPPLIER_UNBIND;
			break;
		default:
			link->status = DL_STATE_DORMANT;
			break;
		}
	}

	/*
	 * Move the consumer and all of the devices depending on it to the end
	 * of dpm_list and the devices_kset list.
	 *
	 * It is necessary to hold dpm_list locked throughout all that or else
	 * we may end up suspending with a wrong ordering of it.
	 */
	device_reorder_to_tail(consumer, NULL);

	list_add_tail_rcu(&link->s_node, &supplier->links.consumers);
	list_add_tail_rcu(&link->c_node, &consumer->links.suppliers);

	dev_info(consumer, "Linked as a consumer to %s\n", dev_name(supplier));

 out:
	device_pm_unlock();
	device_links_write_unlock();
	return link;
}
EXPORT_SYMBOL_GPL(device_link_add);

static void device_link_free(struct device_link *link)
{
	put_device(link->consumer);
	put_device(link->supplier);
	kfree(link);
}

#ifdef CONFIG_SRCU
static void __device_link_free_srcu(struct rcu_head *rhead)
{
	device_link_free(container_of(rhead, struct device_link, rcu_head));
}

static void __device_link_del(struct device_link *link)
{
	dev_info(link->consumer, "Dropping the link to %s\n",
		 dev_name(link->supplier));

	if (link->flags & DL_FLAG_PM_RUNTIME)
		pm_runtime_drop_link(link->consumer);

	list_del_rcu(&link->s_node);
	list_del_rcu(&link->c_node);
	call_srcu(&device_links_srcu, &link->rcu_head, __device_link_free_srcu);
}
#else /* !CONFIG_SRCU */
static void __device_link_del(struct device_link *link)
{
	dev_info(link->consumer, "Dropping the link to %s\n",
		 dev_name(link->supplier));

	list_del(&link->s_node);
	list_del(&link->c_node);
	device_link_free(link);
}
#endif /* !CONFIG_SRCU */

/**
 * device_link_del - Delete a link between two devices.
 * @link: Device link to delete.
 *
 * The caller must ensure proper synchronization of this function with runtime
 * PM.
 */
void device_link_del(struct device_link *link)
{
	device_links_write_lock();
	device_pm_lock();
	__device_link_del(link);
	device_pm_unlock();
	device_links_write_unlock();
}
EXPORT_SYMBOL_GPL(device_link_del);

static void device_links_missing_supplier(struct device *dev)
{
	struct device_link *link;

	list_for_each_entry(link, &dev->links.suppliers, c_node)
		if (link->status == DL_STATE_CONSUMER_PROBE)
			WRITE_ONCE(link->status, DL_STATE_AVAILABLE);
}

/**
 * device_links_check_suppliers - Check presence of supplier drivers.
 * @dev: Consumer device.
 *
 * Check links from this device to any suppliers.  Walk the list of the device's
 * links to suppliers and see if all of them are available.  If not, simply
 * return -EPROBE_DEFER.
 *
 * We need to guarantee that the supplier will not go away after the check has
 * been positive here.  It only can go away in __device_release_driver() and
 * that function  checks the device's links to consumers.  This means we need to
 * mark the link as "consumer probe in progress" to make the supplier removal
 * wait for us to complete (or bad things may happen).
 *
 * Links with the DL_FLAG_STATELESS flag set are ignored.
 */
int device_links_check_suppliers(struct device *dev)
{
	struct device_link *link;
	int ret = 0;

	device_links_write_lock();

	list_for_each_entry(link, &dev->links.suppliers, c_node) {
		if (link->flags & DL_FLAG_STATELESS)
			continue;

		if (link->status != DL_STATE_AVAILABLE) {
			device_links_missing_supplier(dev);
			ret = -EPROBE_DEFER;
			break;
		}
		WRITE_ONCE(link->status, DL_STATE_CONSUMER_PROBE);
	}
	dev->links.status = DL_DEV_PROBING;

	device_links_write_unlock();
	return ret;
}

/**
 * device_links_driver_bound - Update device links after probing its driver.
 * @dev: Device to update the links for.
 *
 * The probe has been successful, so update links from this device to any
 * consumers by changing their status to "available".
 *
 * Also change the status of @dev's links to suppliers to "active".
 *
 * Links with the DL_FLAG_STATELESS flag set are ignored.
 */
void device_links_driver_bound(struct device *dev)
{
	struct device_link *link;

	device_links_write_lock();

	list_for_each_entry(link, &dev->links.consumers, s_node) {
		if (link->flags & DL_FLAG_STATELESS)
			continue;

		WARN_ON(link->status != DL_STATE_DORMANT);
		WRITE_ONCE(link->status, DL_STATE_AVAILABLE);
	}

	list_for_each_entry(link, &dev->links.suppliers, c_node) {
		if (link->flags & DL_FLAG_STATELESS)
			continue;

		WARN_ON(link->status != DL_STATE_CONSUMER_PROBE);
		WRITE_ONCE(link->status, DL_STATE_ACTIVE);
	}

	dev->links.status = DL_DEV_DRIVER_BOUND;

	device_links_write_unlock();
}

/**
 * __device_links_no_driver - Update links of a device without a driver.
 * @dev: Device without a drvier.
 *
 * Delete all non-persistent links from this device to any suppliers.
 *
 * Persistent links stay around, but their status is changed to "available",
 * unless they already are in the "supplier unbind in progress" state in which
 * case they need not be updated.
 *
 * Links with the DL_FLAG_STATELESS flag set are ignored.
 */
static void __device_links_no_driver(struct device *dev)
{
	struct device_link *link, *ln;

	list_for_each_entry_safe_reverse(link, ln, &dev->links.suppliers, c_node) {
		if (link->flags & DL_FLAG_STATELESS)
			continue;

		if (link->flags & DL_FLAG_AUTOREMOVE)
			__device_link_del(link);
		else if (link->status != DL_STATE_SUPPLIER_UNBIND)
			WRITE_ONCE(link->status, DL_STATE_AVAILABLE);
	}

	dev->links.status = DL_DEV_NO_DRIVER;
}

void device_links_no_driver(struct device *dev)
{
	device_links_write_lock();
	__device_links_no_driver(dev);
	device_links_write_unlock();
}

/**
 * device_links_driver_cleanup - Update links after driver removal.
 * @dev: Device whose driver has just gone away.
 *
 * Update links to consumers for @dev by changing their status to "dormant" and
 * invoke %__device_links_no_driver() to update links to suppliers for it as
 * appropriate.
 *
 * Links with the DL_FLAG_STATELESS flag set are ignored.
 */
void device_links_driver_cleanup(struct device *dev)
{
	struct device_link *link;

	device_links_write_lock();

	list_for_each_entry(link, &dev->links.consumers, s_node) {
		if (link->flags & DL_FLAG_STATELESS)
			continue;

		WARN_ON(link->flags & DL_FLAG_AUTOREMOVE);
		WARN_ON(link->status != DL_STATE_SUPPLIER_UNBIND);
		WRITE_ONCE(link->status, DL_STATE_DORMANT);
	}

	__device_links_no_driver(dev);

	device_links_write_unlock();
}

/**
 * device_links_busy - Check if there are any busy links to consumers.
 * @dev: Device to check.
 *
 * Check each consumer of the device and return 'true' if its link's status
 * is one of "consumer probe" or "active" (meaning that the given consumer is
 * probing right now or its driver is present).  Otherwise, change the link
 * state to "supplier unbind" to prevent the consumer from being probed
 * successfully going forward.
 *
 * Return 'false' if there are no probing or active consumers.
 *
 * Links with the DL_FLAG_STATELESS flag set are ignored.
 */
bool device_links_busy(struct device *dev)
{
	struct device_link *link;
	bool ret = false;

	device_links_write_lock();

	list_for_each_entry(link, &dev->links.consumers, s_node) {
		if (link->flags & DL_FLAG_STATELESS)
			continue;

		if (link->status == DL_STATE_CONSUMER_PROBE
		    || link->status == DL_STATE_ACTIVE) {
			ret = true;
			break;
		}
		WRITE_ONCE(link->status, DL_STATE_SUPPLIER_UNBIND);
	}

	dev->links.status = DL_DEV_UNBINDING;

	device_links_write_unlock();
	return ret;
}

/**
 * device_links_unbind_consumers - Force unbind consumers of the given device.
 * @dev: Device to unbind the consumers of.
 *
 * Walk the list of links to consumers for @dev and if any of them is in the
 * "consumer probe" state, wait for all device probes in progress to complete
 * and start over.
 *
 * If that's not the case, change the status of the link to "supplier unbind"
 * and check if the link was in the "active" state.  If so, force the consumer
 * driver to unbind and start over (the consumer will not re-probe as we have
 * changed the state of the link already).
 *
 * Links with the DL_FLAG_STATELESS flag set are ignored.
 */
void device_links_unbind_consumers(struct device *dev)
{
	struct device_link *link;

 start:
	device_links_write_lock();

	list_for_each_entry(link, &dev->links.consumers, s_node) {
		enum device_link_state status;

		if (link->flags & DL_FLAG_STATELESS)
			continue;

		status = link->status;
		if (status == DL_STATE_CONSUMER_PROBE) {
			device_links_write_unlock();

			wait_for_device_probe();
			goto start;
		}
		WRITE_ONCE(link->status, DL_STATE_SUPPLIER_UNBIND);
		if (status == DL_STATE_ACTIVE) {
			struct device *consumer = link->consumer;

			get_device(consumer);

			device_links_write_unlock();

			device_release_driver_internal(consumer, NULL,
						       consumer->parent);
			put_device(consumer);
			goto start;
		}
	}

	device_links_write_unlock();
}

/**
 * device_links_purge - Delete existing links to other devices.
 * @dev: Target device.
 */
static void device_links_purge(struct device *dev)
{
	struct device_link *link, *ln;

	/*
	 * Delete all of the remaining links from this device to any other
	 * devices (either consumers or suppliers).
	 */
	device_links_write_lock();

	list_for_each_entry_safe_reverse(link, ln, &dev->links.suppliers, c_node) {
		WARN_ON(link->status == DL_STATE_ACTIVE);
		__device_link_del(link);
	}

	list_for_each_entry_safe_reverse(link, ln, &dev->links.consumers, s_node) {
		WARN_ON(link->status != DL_STATE_DORMANT &&
			link->status != DL_STATE_NONE);
		__device_link_del(link);
	}

	device_links_write_unlock();
}

/* Device links support end. */

int (*platform_notify)(struct device *dev) = NULL;
int (*platform_notify_remove)(struct device *dev) = NULL;
static struct kobject *dev_kobj;
struct kobject *sysfs_dev_char_kobj;
struct kobject *sysfs_dev_block_kobj;

static DEFINE_MUTEX(device_hotplug_lock);

void lock_device_hotplug(void)
{
	mutex_lock(&device_hotplug_lock);
}

void unlock_device_hotplug(void)
{
	mutex_unlock(&device_hotplug_lock);
}

int lock_device_hotplug_sysfs(void)
{
	if (mutex_trylock(&device_hotplug_lock))
		return 0;

	/* Avoid busy looping (5 ms of sleep should do). */
	msleep(5);
	return restart_syscall();
}

#ifdef CONFIG_BLOCK
static inline int device_is_not_partition(struct device *dev)
{
	return !(dev->type == &part_type);
}
#else
static inline int device_is_not_partition(struct device *dev)
{
	return 1;
}
#endif

/**
 * dev_driver_string - Return a device's driver name, if at all possible
 * @dev: struct device to get the name of
 *
 * Will return the device's driver's name if it is bound to a device.  If
 * the device is not bound to a driver, it will return the name of the bus
 * it is attached to.  If it is not attached to a bus either, an empty
 * string will be returned.
 */
const char *dev_driver_string(const struct device *dev)
{
	struct device_driver *drv;

	/* dev->driver can change to NULL underneath us because of unbinding,
	 * so be careful about accessing it.  dev->bus and dev->class should
	 * never change once they are set, so they don't need special care.
	 */
	drv = ACCESS_ONCE(dev->driver);
	return drv ? drv->name :
			(dev->bus ? dev->bus->name :
			(dev->class ? dev->class->name : ""));
}
EXPORT_SYMBOL(dev_driver_string);

#define to_dev_attr(_attr) container_of(_attr, struct device_attribute, attr)

static ssize_t dev_attr_show(struct kobject *kobj, struct attribute *attr,
			     char *buf)
{
	struct device_attribute *dev_attr = to_dev_attr(attr);
	struct device *dev = kobj_to_dev(kobj);
	ssize_t ret = -EIO;

	if (dev_attr->show)
		ret = dev_attr->show(dev, dev_attr, buf);
	if (ret >= (ssize_t)PAGE_SIZE) {
		print_symbol("dev_attr_show: %s returned bad count\n",
				(unsigned long)dev_attr->show);
	}
	return ret;
}

static ssize_t dev_attr_store(struct kobject *kobj, struct attribute *attr,
			      const char *buf, size_t count)
{
	struct device_attribute *dev_attr = to_dev_attr(attr);
	struct device *dev = kobj_to_dev(kobj);
	ssize_t ret = -EIO;

	if (dev_attr->store)
		ret = dev_attr->store(dev, dev_attr, buf, count);
	return ret;
}

static const struct sysfs_ops dev_sysfs_ops = {
	.show	= dev_attr_show,
	.store	= dev_attr_store,
};

#define to_ext_attr(x) container_of(x, struct dev_ext_attribute, attr)

ssize_t device_store_ulong(struct device *dev,
			   struct device_attribute *attr,
			   const char *buf, size_t size)
{
	struct dev_ext_attribute *ea = to_ext_attr(attr);
	char *end;
	unsigned long new = simple_strtoul(buf, &end, 0);
	if (end == buf)
		return -EINVAL;
	*(unsigned long *)(ea->var) = new;
	/* Always return full write size even if we didn't consume all */
	return size;
}
EXPORT_SYMBOL_GPL(device_store_ulong);

ssize_t device_show_ulong(struct device *dev,
			  struct device_attribute *attr,
			  char *buf)
{
	struct dev_ext_attribute *ea = to_ext_attr(attr);
	return snprintf(buf, PAGE_SIZE, "%lx\n", *(unsigned long *)(ea->var));
}
EXPORT_SYMBOL_GPL(device_show_ulong);

ssize_t device_store_int(struct device *dev,
			 struct device_attribute *attr,
			 const char *buf, size_t size)
{
	struct dev_ext_attribute *ea = to_ext_attr(attr);
	char *end;
	long new = simple_strtol(buf, &end, 0);
	if (end == buf || new > INT_MAX || new < INT_MIN)
		return -EINVAL;
	*(int *)(ea->var) = new;
	/* Always return full write size even if we didn't consume all */
	return size;
}
EXPORT_SYMBOL_GPL(device_store_int);

ssize_t device_show_int(struct device *dev,
			struct device_attribute *attr,
			char *buf)
{
	struct dev_ext_attribute *ea = to_ext_attr(attr);

	return snprintf(buf, PAGE_SIZE, "%d\n", *(int *)(ea->var));
}
EXPORT_SYMBOL_GPL(device_show_int);

ssize_t device_store_bool(struct device *dev, struct device_attribute *attr,
			  const char *buf, size_t size)
{
	struct dev_ext_attribute *ea = to_ext_attr(attr);

	if (strtobool(buf, ea->var) < 0)
		return -EINVAL;

	return size;
}
EXPORT_SYMBOL_GPL(device_store_bool);

ssize_t device_show_bool(struct device *dev, struct device_attribute *attr,
			 char *buf)
{
	struct dev_ext_attribute *ea = to_ext_attr(attr);

	return snprintf(buf, PAGE_SIZE, "%d\n", *(bool *)(ea->var));
}
EXPORT_SYMBOL_GPL(device_show_bool);

/**
 * device_release - free device structure.
 * @kobj: device's kobject.
 *
 * This is called once the reference count for the object
 * reaches 0. We forward the call to the device's release
 * method, which should handle actually freeing the structure.
 */
static void device_release(struct kobject *kobj)
{
	struct device *dev = kobj_to_dev(kobj);
	struct device_private *p = dev->p;

	/*
	 * Some platform devices are driven without driver attached
	 * and managed resources may have been acquired.  Make sure
	 * all resources are released.
	 *
	 * Drivers still can add resources into device after device
	 * is deleted but alive, so release devres here to avoid
	 * possible memory leak.
	 */
	devres_release_all(dev);

	if (dev->release)
		dev->release(dev);
	else if (dev->type && dev->type->release)
		dev->type->release(dev);
	else if (dev->class && dev->class->dev_release)
		dev->class->dev_release(dev);
	else
		WARN(1, KERN_ERR "Device '%s' does not have a release() "
			"function, it is broken and must be fixed.\n",
			dev_name(dev));
	kfree(p);
}

static const void *device_namespace(struct kobject *kobj)
{
	struct device *dev = kobj_to_dev(kobj);
	const void *ns = NULL;

	if (dev->class && dev->class->ns_type)
		ns = dev->class->namespace(dev);

	return ns;
}

static struct kobj_type device_ktype = {
	.release	= device_release,
	.sysfs_ops	= &dev_sysfs_ops,
	.namespace	= device_namespace,
};


static int dev_uevent_filter(struct kset *kset, struct kobject *kobj)
{
	struct kobj_type *ktype = get_ktype(kobj);

	if (ktype == &device_ktype) {
		struct device *dev = kobj_to_dev(kobj);
		if (dev->bus)
			return 1;
		if (dev->class)
			return 1;
	}
	return 0;
}

static const char *dev_uevent_name(struct kset *kset, struct kobject *kobj)
{
	struct device *dev = kobj_to_dev(kobj);

	if (dev->bus)
		return dev->bus->name;
	if (dev->class)
		return dev->class->name;
	return NULL;
}

static int dev_uevent(struct kset *kset, struct kobject *kobj,
		      struct kobj_uevent_env *env)
{
	struct device *dev = kobj_to_dev(kobj);
	int retval = 0;

	/* add device node properties if present */
	if (MAJOR(dev->devt)) {
		const char *tmp;
		const char *name;
		umode_t mode = 0;
		kuid_t uid = GLOBAL_ROOT_UID;
		kgid_t gid = GLOBAL_ROOT_GID;

		add_uevent_var(env, "MAJOR=%u", MAJOR(dev->devt));
		add_uevent_var(env, "MINOR=%u", MINOR(dev->devt));
		name = device_get_devnode(dev, &mode, &uid, &gid, &tmp);
		if (name) {
			add_uevent_var(env, "DEVNAME=%s", name);
			if (mode)
				add_uevent_var(env, "DEVMODE=%#o", mode & 0777);
			if (!uid_eq(uid, GLOBAL_ROOT_UID))
				add_uevent_var(env, "DEVUID=%u", from_kuid(&init_user_ns, uid));
			if (!gid_eq(gid, GLOBAL_ROOT_GID))
				add_uevent_var(env, "DEVGID=%u", from_kgid(&init_user_ns, gid));
			kfree(tmp);
		}
	}

	if (dev->type && dev->type->name)
		add_uevent_var(env, "DEVTYPE=%s", dev->type->name);

	if (dev->driver)
		add_uevent_var(env, "DRIVER=%s", dev->driver->name);

	/* Add common DT information about the device */
	of_device_uevent(dev, env);

	/* have the bus specific function add its stuff */
	if (dev->bus && dev->bus->uevent) {
		retval = dev->bus->uevent(dev, env);
		if (retval)
			pr_debug("device: '%s': %s: bus uevent() returned %d\n",
				 dev_name(dev), __func__, retval);
	}

	/* have the class specific function add its stuff */
	if (dev->class && dev->class->dev_uevent) {
		retval = dev->class->dev_uevent(dev, env);
		if (retval)
			pr_debug("device: '%s': %s: class uevent() "
				 "returned %d\n", dev_name(dev),
				 __func__, retval);
	}

	/* have the device type specific function add its stuff */
	if (dev->type && dev->type->uevent) {
		retval = dev->type->uevent(dev, env);
		if (retval)
			pr_debug("device: '%s': %s: dev_type uevent() "
				 "returned %d\n", dev_name(dev),
				 __func__, retval);
	}

	return retval;
}

static const struct kset_uevent_ops device_uevent_ops = {
	.filter =	dev_uevent_filter,
	.name =		dev_uevent_name,
	.uevent =	dev_uevent,
};

static ssize_t uevent_show(struct device *dev, struct device_attribute *attr,
			   char *buf)
{
	struct kobject *top_kobj;
	struct kset *kset;
	struct kobj_uevent_env *env = NULL;
	int i;
	size_t count = 0;
	int retval;

	/* search the kset, the device belongs to */
	top_kobj = &dev->kobj;
	while (!top_kobj->kset && top_kobj->parent)
		top_kobj = top_kobj->parent;
	if (!top_kobj->kset)
		goto out;

	kset = top_kobj->kset;
	if (!kset->uevent_ops || !kset->uevent_ops->uevent)
		goto out;

	/* respect filter */
	if (kset->uevent_ops && kset->uevent_ops->filter)
		if (!kset->uevent_ops->filter(kset, &dev->kobj))
			goto out;

	env = kzalloc(sizeof(struct kobj_uevent_env), GFP_KERNEL);
	if (!env)
		return -ENOMEM;

	/* let the kset specific function add its keys */
	retval = kset->uevent_ops->uevent(kset, &dev->kobj, env);
	if (retval)
		goto out;

	/* copy keys to file */
	for (i = 0; i < env->envp_idx; i++)
		count += sprintf(&buf[count], "%s\n", env->envp[i]);
out:
	kfree(env);
	return count;
}

static ssize_t uevent_store(struct device *dev, struct device_attribute *attr,
			    const char *buf, size_t count)
{
	if (kobject_synth_uevent(&dev->kobj, buf, count))
		dev_err(dev, "uevent: failed to send synthetic uevent\n");

	return count;
}
static DEVICE_ATTR_RW(uevent);

static ssize_t online_show(struct device *dev, struct device_attribute *attr,
			   char *buf)
{
	bool val;

	device_lock(dev);
	val = !dev->offline;
	device_unlock(dev);
	return sprintf(buf, "%u\n", val);
}

static ssize_t online_store(struct device *dev, struct device_attribute *attr,
			    const char *buf, size_t count)
{
	bool val;
	int ret;

	ret = strtobool(buf, &val);
	if (ret < 0)
		return ret;

	ret = lock_device_hotplug_sysfs();
	if (ret)
		return ret;

	ret = val ? device_online(dev) : device_offline(dev);
	unlock_device_hotplug();
	return ret < 0 ? ret : count;
}
static DEVICE_ATTR_RW(online);

int device_add_groups(struct device *dev, const struct attribute_group **groups)
{
	return sysfs_create_groups(&dev->kobj, groups);
}
EXPORT_SYMBOL_GPL(device_add_groups);

void device_remove_groups(struct device *dev,
			  const struct attribute_group **groups)
{
	sysfs_remove_groups(&dev->kobj, groups);
}
EXPORT_SYMBOL_GPL(device_remove_groups);

union device_attr_group_devres {
	const struct attribute_group *group;
	const struct attribute_group **groups;
};

static int devm_attr_group_match(struct device *dev, void *res, void *data)
{
	return ((union device_attr_group_devres *)res)->group == data;
}

static void devm_attr_group_remove(struct device *dev, void *res)
{
	union device_attr_group_devres *devres = res;
	const struct attribute_group *group = devres->group;

	dev_dbg(dev, "%s: removing group %p\n", __func__, group);
	sysfs_remove_group(&dev->kobj, group);
}

static void devm_attr_groups_remove(struct device *dev, void *res)
{
	union device_attr_group_devres *devres = res;
	const struct attribute_group **groups = devres->groups;

	dev_dbg(dev, "%s: removing groups %p\n", __func__, groups);
	sysfs_remove_groups(&dev->kobj, groups);
}

/**
 * devm_device_add_group - given a device, create a managed attribute group
 * @dev:	The device to create the group for
 * @grp:	The attribute group to create
 *
 * This function creates a group for the first time.  It will explicitly
 * warn and error if any of the attribute files being created already exist.
 *
 * Returns 0 on success or error code on failure.
 */
int devm_device_add_group(struct device *dev, const struct attribute_group *grp)
{
	union device_attr_group_devres *devres;
	int error;

	devres = devres_alloc(devm_attr_group_remove,
			      sizeof(*devres), GFP_KERNEL);
	if (!devres)
		return -ENOMEM;

	error = sysfs_create_group(&dev->kobj, grp);
	if (error) {
		devres_free(devres);
		return error;
	}

	devres->group = grp;
	devres_add(dev, devres);
	return 0;
}
EXPORT_SYMBOL_GPL(devm_device_add_group);

/**
 * devm_device_remove_group: remove a managed group from a device
 * @dev:	device to remove the group from
 * @grp:	group to remove
 *
 * This function removes a group of attributes from a device. The attributes
 * previously have to have been created for this group, otherwise it will fail.
 */
void devm_device_remove_group(struct device *dev,
			      const struct attribute_group *grp)
{
	WARN_ON(devres_release(dev, devm_attr_group_remove,
			       devm_attr_group_match,
			       /* cast away const */ (void *)grp));
}
EXPORT_SYMBOL_GPL(devm_device_remove_group);

/**
 * devm_device_add_groups - create a bunch of managed attribute groups
 * @dev:	The device to create the group for
 * @groups:	The attribute groups to create, NULL terminated
 *
 * This function creates a bunch of managed attribute groups.  If an error
 * occurs when creating a group, all previously created groups will be
 * removed, unwinding everything back to the original state when this
 * function was called.  It will explicitly warn and error if any of the
 * attribute files being created already exist.
 *
 * Returns 0 on success or error code from sysfs_create_group on failure.
 */
int devm_device_add_groups(struct device *dev,
			   const struct attribute_group **groups)
{
	union device_attr_group_devres *devres;
	int error;

	devres = devres_alloc(devm_attr_groups_remove,
			      sizeof(*devres), GFP_KERNEL);
	if (!devres)
		return -ENOMEM;

	error = sysfs_create_groups(&dev->kobj, groups);
	if (error) {
		devres_free(devres);
		return error;
	}

	devres->groups = groups;
	devres_add(dev, devres);
	return 0;
}
EXPORT_SYMBOL_GPL(devm_device_add_groups);

/**
 * devm_device_remove_groups - remove a list of managed groups
 *
 * @dev:	The device for the groups to be removed from
 * @groups:	NULL terminated list of groups to be removed
 *
 * If groups is not NULL, remove the specified groups from the device.
 */
void devm_device_remove_groups(struct device *dev,
			       const struct attribute_group **groups)
{
	WARN_ON(devres_release(dev, devm_attr_groups_remove,
			       devm_attr_group_match,
			       /* cast away const */ (void *)groups));
}
EXPORT_SYMBOL_GPL(devm_device_remove_groups);

static int device_add_attrs(struct device *dev)
{
	struct class *class = dev->class;
	const struct device_type *type = dev->type;
	int error;

	if (class) {
		error = device_add_groups(dev, class->dev_groups);
		if (error)
			return error;
	}

	if (type) {
		error = device_add_groups(dev, type->groups);
		if (error)
			goto err_remove_class_groups;
	}

	error = device_add_groups(dev, dev->groups);
	if (error)
		goto err_remove_type_groups;

	if (device_supports_offline(dev) && !dev->offline_disabled) {
		error = device_create_file(dev, &dev_attr_online);
		if (error)
			goto err_remove_dev_groups;
	}

	return 0;

 err_remove_dev_groups:
	device_remove_groups(dev, dev->groups);
 err_remove_type_groups:
	if (type)
		device_remove_groups(dev, type->groups);
 err_remove_class_groups:
	if (class)
		device_remove_groups(dev, class->dev_groups);

	return error;
}

static void device_remove_attrs(struct device *dev)
{
	struct class *class = dev->class;
	const struct device_type *type = dev->type;

	device_remove_file(dev, &dev_attr_online);
	device_remove_groups(dev, dev->groups);

	if (type)
		device_remove_groups(dev, type->groups);

	if (class)
		device_remove_groups(dev, class->dev_groups);
}

static ssize_t dev_show(struct device *dev, struct device_attribute *attr,
			char *buf)
{
	return print_dev_t(buf, dev->devt);
}
static DEVICE_ATTR_RO(dev);

/* /sys/devices/ */
struct kset *devices_kset;

/**
 * devices_kset_move_before - Move device in the devices_kset's list.
 * @deva: Device to move.
 * @devb: Device @deva should come before.
 */
static void devices_kset_move_before(struct device *deva, struct device *devb)
{
	if (!devices_kset)
		return;
	pr_debug("devices_kset: Moving %s before %s\n",
		 dev_name(deva), dev_name(devb));
	spin_lock(&devices_kset->list_lock);
	list_move_tail(&deva->kobj.entry, &devb->kobj.entry);
	spin_unlock(&devices_kset->list_lock);
}

/**
 * devices_kset_move_after - Move device in the devices_kset's list.
 * @deva: Device to move
 * @devb: Device @deva should come after.
 */
static void devices_kset_move_after(struct device *deva, struct device *devb)
{
	if (!devices_kset)
		return;
	pr_debug("devices_kset: Moving %s after %s\n",
		 dev_name(deva), dev_name(devb));
	spin_lock(&devices_kset->list_lock);
	list_move(&deva->kobj.entry, &devb->kobj.entry);
	spin_unlock(&devices_kset->list_lock);
}

/**
 * devices_kset_move_last - move the device to the end of devices_kset's list.
 * @dev: device to move
 */
void devices_kset_move_last(struct device *dev)
{
	if (!devices_kset)
		return;
	pr_debug("devices_kset: Moving %s to end of list\n", dev_name(dev));
	spin_lock(&devices_kset->list_lock);
	list_move_tail(&dev->kobj.entry, &devices_kset->list);
	spin_unlock(&devices_kset->list_lock);
}

/**
 * device_create_file - create sysfs attribute file for device.
 * @dev: device.
 * @attr: device attribute descriptor.
 */
int device_create_file(struct device *dev,
		       const struct device_attribute *attr)
{
	int error = 0;

	if (dev) {
		WARN(((attr->attr.mode & S_IWUGO) && !attr->store),
			"Attribute %s: write permission without 'store'\n",
			attr->attr.name);
		WARN(((attr->attr.mode & S_IRUGO) && !attr->show),
			"Attribute %s: read permission without 'show'\n",
			attr->attr.name);
		error = sysfs_create_file(&dev->kobj, &attr->attr);
	}

	return error;
}
EXPORT_SYMBOL_GPL(device_create_file);

/**
 * device_remove_file - remove sysfs attribute file.
 * @dev: device.
 * @attr: device attribute descriptor.
 */
void device_remove_file(struct device *dev,
			const struct device_attribute *attr)
{
	if (dev)
		sysfs_remove_file(&dev->kobj, &attr->attr);
}
EXPORT_SYMBOL_GPL(device_remove_file);

/**
 * device_remove_file_self - remove sysfs attribute file from its own method.
 * @dev: device.
 * @attr: device attribute descriptor.
 *
 * See kernfs_remove_self() for details.
 */
bool device_remove_file_self(struct device *dev,
			     const struct device_attribute *attr)
{
	if (dev)
		return sysfs_remove_file_self(&dev->kobj, &attr->attr);
	else
		return false;
}
EXPORT_SYMBOL_GPL(device_remove_file_self);

/**
 * device_create_bin_file - create sysfs binary attribute file for device.
 * @dev: device.
 * @attr: device binary attribute descriptor.
 */
int device_create_bin_file(struct device *dev,
			   const struct bin_attribute *attr)
{
	int error = -EINVAL;
	if (dev)
		error = sysfs_create_bin_file(&dev->kobj, attr);
	return error;
}
EXPORT_SYMBOL_GPL(device_create_bin_file);

/**
 * device_remove_bin_file - remove sysfs binary attribute file
 * @dev: device.
 * @attr: device binary attribute descriptor.
 */
void device_remove_bin_file(struct device *dev,
			    const struct bin_attribute *attr)
{
	if (dev)
		sysfs_remove_bin_file(&dev->kobj, attr);
}
EXPORT_SYMBOL_GPL(device_remove_bin_file);

static void klist_children_get(struct klist_node *n)
{
	struct device_private *p = to_device_private_parent(n);
	struct device *dev = p->device;

	get_device(dev);
}

static void klist_children_put(struct klist_node *n)
{
	struct device_private *p = to_device_private_parent(n);
	struct device *dev = p->device;

	put_device(dev);
}

/**
 * device_initialize - init device structure.
 * @dev: device.
 *
 * This prepares the device for use by other layers by initializing
 * its fields.
 * It is the first half of device_register(), if called by
 * that function, though it can also be called separately, so one
 * may use @dev's fields. In particular, get_device()/put_device()
 * may be used for reference counting of @dev after calling this
 * function.
 *
 * All fields in @dev must be initialized by the caller to 0, except
 * for those explicitly set to some other value.  The simplest
 * approach is to use kzalloc() to allocate the structure containing
 * @dev.
 *
 * NOTE: Use put_device() to give up your reference instead of freeing
 * @dev directly once you have called this function.
 */
void device_initialize(struct device *dev)
{
	dev->kobj.kset = devices_kset;
	kobject_init(&dev->kobj, &device_ktype);
	INIT_LIST_HEAD(&dev->dma_pools);
	mutex_init(&dev->mutex);
	lockdep_set_novalidate_class(&dev->mutex);
	spin_lock_init(&dev->devres_lock);
	INIT_LIST_HEAD(&dev->devres_head);
	device_pm_init(dev);
	set_dev_node(dev, -1);
#ifdef CONFIG_GENERIC_MSI_IRQ
	INIT_LIST_HEAD(&dev->msi_list);
#endif
	INIT_LIST_HEAD(&dev->links.consumers);
	INIT_LIST_HEAD(&dev->links.suppliers);
	dev->links.status = DL_DEV_NO_DRIVER;
}
EXPORT_SYMBOL_GPL(device_initialize);

struct kobject *virtual_device_parent(struct device *dev)
{
	static struct kobject *virtual_dir = NULL;

	if (!virtual_dir)
		virtual_dir = kobject_create_and_add("virtual",
						     &devices_kset->kobj);

	return virtual_dir;
}

struct class_dir {
	struct kobject kobj;
	struct class *class;
};

#define to_class_dir(obj) container_of(obj, struct class_dir, kobj)

static void class_dir_release(struct kobject *kobj)
{
	struct class_dir *dir = to_class_dir(kobj);
	kfree(dir);
}

static const
struct kobj_ns_type_operations *class_dir_child_ns_type(struct kobject *kobj)
{
	struct class_dir *dir = to_class_dir(kobj);
	return dir->class->ns_type;
}

static struct kobj_type class_dir_ktype = {
	.release	= class_dir_release,
	.sysfs_ops	= &kobj_sysfs_ops,
	.child_ns_type	= class_dir_child_ns_type
};

static struct kobject *
class_dir_create_and_add(struct class *class, struct kobject *parent_kobj)
{
	struct class_dir *dir;
	int retval;

	dir = kzalloc(sizeof(*dir), GFP_KERNEL);
	if (!dir)
		return NULL;

	dir->class = class;
	kobject_init(&dir->kobj, &class_dir_ktype);

	dir->kobj.kset = &class->p->glue_dirs;

	retval = kobject_add(&dir->kobj, parent_kobj, "%s", class->name);
	if (retval < 0) {
		kobject_put(&dir->kobj);
		return NULL;
	}
	return &dir->kobj;
}

static DEFINE_MUTEX(gdp_mutex);

static struct kobject *get_device_parent(struct device *dev,
					 struct device *parent)
{
	if (dev->class) {
		struct kobject *kobj = NULL;
		struct kobject *parent_kobj;
		struct kobject *k;

#ifdef CONFIG_BLOCK
		/* block disks show up in /sys/block */
		if (sysfs_deprecated && dev->class == &block_class) {
			if (parent && parent->class == &block_class)
				return &parent->kobj;
			return &block_class.p->subsys.kobj;
		}
#endif

		/*
		 * 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);
		else if (parent->class && !dev->class->ns_type)
			return &parent->kobj;
		else
			parent_kobj = &parent->kobj;

		mutex_lock(&gdp_mutex);

		/* find our class-directory at the parent and reference it */
		spin_lock(&dev->class->p->glue_dirs.list_lock);
		list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
			if (k->parent == parent_kobj) {
				kobj = kobject_get(k);
				break;
			}
		spin_unlock(&dev->class->p->glue_dirs.list_lock);
		if (kobj) {
			mutex_unlock(&gdp_mutex);
			return kobj;
		}

		/* or create a new class-directory at the parent device */
		k = class_dir_create_and_add(dev->class, parent_kobj);
		/* do not emit an uevent for this simple "glue" directory */
		mutex_unlock(&gdp_mutex);
		return k;
	}

	/* subsystems can specify a default root directory for their devices */
	if (!parent && dev->bus && dev->bus->dev_root)
		return &dev->bus->dev_root->kobj;

	if (parent)
		return &parent->kobj;
	return NULL;
}

static inline bool live_in_glue_dir(struct kobject *kobj,
				    struct device *dev)
{
	if (!kobj || !dev->class ||
	    kobj->kset != &dev->class->p->glue_dirs)
		return false;
	return true;
}

static inline struct kobject *get_glue_dir(struct device *dev)
{
	return dev->kobj.parent;
}

/*
 * make sure cleaning up dir as the last step, we need to make
 * sure .release handler of kobject is run with holding the
 * global lock
 */
static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir)
{
	/* see if we live in a "glue" directory */
	if (!live_in_glue_dir(glue_dir, dev))
		return;

	mutex_lock(&gdp_mutex);
	kobject_put(glue_dir);
	mutex_unlock(&gdp_mutex);
}

static int device_add_class_symlinks(struct device *dev)
{
	struct device_node *of_node = dev_of_node(dev);
	int error;

	if (of_node) {
		error = sysfs_create_link(&dev->kobj, &of_node->kobj,"of_node");
		if (error)
			dev_warn(dev, "Error %d creating of_node link\n",error);
		/* An error here doesn't warrant bringing down the device */
	}

	if (!dev->class)
		return 0;

	error = sysfs_create_link(&dev->kobj,
				  &dev->class->p->subsys.kobj,
				  "subsystem");
	if (error)
		goto out_devnode;

	if (dev->parent && device_is_not_partition(dev)) {
		error = sysfs_create_link(&dev->kobj, &dev->parent->kobj,
					  "device");
		if (error)
			goto out_subsys;
	}

#ifdef CONFIG_BLOCK
	/* /sys/block has directories and does not need symlinks */
	if (sysfs_deprecated && dev->class == &block_class)
		return 0;
#endif

	/* link in the class directory pointing to the device */
	error = sysfs_create_link(&dev->class->p->subsys.kobj,
				  &dev->kobj, dev_name(dev));
	if (error)
		goto out_device;

	return 0;

out_device:
	sysfs_remove_link(&dev->kobj, "device");

out_subsys:
	sysfs_remove_link(&dev->kobj, "subsystem");
out_devnode:
	sysfs_remove_link(&dev->kobj, "of_node");
	return error;
}

static void device_remove_class_symlinks(struct device *dev)
{
	if (dev_of_node(dev))
		sysfs_remove_link(&dev->kobj, "of_node");

	if (!dev->class)
		return;

	if (dev->parent && device_is_not_partition(dev))
		sysfs_remove_link(&dev->kobj, "device");
	sysfs_remove_link(&dev->kobj, "subsystem");
#ifdef CONFIG_BLOCK
	if (sysfs_deprecated && dev->class == &block_class)
		return;
#endif
	sysfs_delete_link(&dev->class->p->subsys.kobj, &dev->kobj, dev_name(dev));
}

/**
 * dev_set_name - set a device name
 * @dev: device
 * @fmt: format string for the device's name
 */
int dev_set_name(struct device *dev, const char *fmt, ...)
{
	va_list vargs;
	int err;

	va_start(vargs, fmt);
	err = kobject_set_name_vargs(&dev->kobj, fmt, vargs);
	va_end(vargs);
	return err;
}
EXPORT_SYMBOL_GPL(dev_set_name);

/**
 * device_to_dev_kobj - select a /sys/dev/ directory for the device
 * @dev: device
 *
 * By default we select char/ for new entries.  Setting class->dev_obj
 * to NULL prevents an entry from being created.  class->dev_kobj must
 * be set (or cleared) before any devices are registered to the class
 * otherwise device_create_sys_dev_entry() and
 * device_remove_sys_dev_entry() will disagree about the presence of
 * the link.
 */
static struct kobject *device_to_dev_kobj(struct device *dev)
{
	struct kobject *kobj;

	if (dev->class)
		kobj = dev->class->dev_kobj;
	else
		kobj = sysfs_dev_char_kobj;

	return kobj;
}

static int device_create_sys_dev_entry(struct device *dev)
{
	struct kobject *kobj = device_to_dev_kobj(dev);
	int error = 0;
	char devt_str[15];

	if (kobj) {
		format_dev_t(devt_str, dev->devt);
		error = sysfs_create_link(kobj, &dev->kobj, devt_str);
	}

	return error;
}

static void device_remove_sys_dev_entry(struct device *dev)
{
	struct kobject *kobj = device_to_dev_kobj(dev);
	char devt_str[15];

	if (kobj) {
		format_dev_t(devt_str, dev->devt);
		sysfs_remove_link(kobj, devt_str);
	}
}

int device_private_init(struct device *dev)
{
	dev->p = kzalloc(sizeof(*dev->p), GFP_KERNEL);
	if (!dev->p)
		return -ENOMEM;
	dev->p->device = dev;
	klist_init(&dev->p->klist_children, klist_children_get,
		   klist_children_put);
	INIT_LIST_HEAD(&dev->p->deferred_probe);
	return 0;
}

/**
 * device_add - add device to device hierarchy.
 * @dev: device.
 *
 * This is part 2 of device_register(), though may be called
 * separately _iff_ device_initialize() has been called separately.
 *
 * This adds @dev to the kobject hierarchy via kobject_add(), adds it
 * to the global and sibling lists for the device, then
 * adds it to the other relevant subsystems of the driver model.
 *
 * Do not call this routine or device_register() more than once for
 * any device structure.  The driver model core is not designed to work
 * with devices that get unregistered and then spring back to life.
 * (Among other things, it's very hard to guarantee that all references
 * to the previous incarnation of @dev have been dropped.)  Allocate
 * and register a fresh new struct device instead.
 *
 * NOTE: _Never_ directly free @dev after calling this function, even
 * if it returned an error! Always use put_device() to give up your
 * reference instead.
 */
int device_add(struct device *dev)
{
	struct device *parent;
	struct kobject *kobj;
	struct class_interface *class_intf;
	int error = -EINVAL;
	struct kobject *glue_dir = NULL;

	dev = get_device(dev);
	if (!dev)
		goto done;

	if (!dev->p) {
		error = device_private_init(dev);
		if (error)
			goto done;
	}

	/*
	 * for statically allocated devices, which should all be converted
	 * some day, we need to initialize the name. We prevent reading back
	 * the name, and force the use of dev_name()
	 */
	if (dev->init_name) {
		dev_set_name(dev, "%s", dev->init_name);
		dev->init_name = NULL;
	}

	/* subsystems can specify simple device enumeration */
	if (!dev_name(dev) && dev->bus && dev->bus->dev_name)
		dev_set_name(dev, "%s%u", dev->bus->dev_name, dev->id);

	if (!dev_name(dev)) {
		error = -EINVAL;
		goto name_error;
	}

	pr_debug("device: '%s': %s\n", dev_name(dev), __func__);

	parent = get_device(dev->parent);
	kobj = get_device_parent(dev, parent);
	if (kobj)
		dev->kobj.parent = kobj;

	/* use parent numa_node */
	if (parent && (dev_to_node(dev) == NUMA_NO_NODE))
		set_dev_node(dev, dev_to_node(parent));

	/* first, register with generic layer. */
	/* we require the name to be set before, and pass NULL */
	error = kobject_add(&dev->kobj, dev->kobj.parent, NULL);
	if (error) {
		glue_dir = get_glue_dir(dev);
		goto Error;
	}

	/* notify platform of device entry */
	if (platform_notify)
		platform_notify(dev);

	error = device_create_file(dev, &dev_attr_uevent);
	if (error)
		goto attrError;

	error = device_add_class_symlinks(dev);
	if (error)
		goto SymlinkError;
	error = device_add_attrs(dev);
	if (error)
		goto AttrsError;
	error = bus_add_device(dev);
	if (error)
		goto BusError;
	error = dpm_sysfs_add(dev);
	if (error)
		goto DPMError;
	device_pm_add(dev);

	if (MAJOR(dev->devt)) {
		error = device_create_file(dev, &dev_attr_dev);
		if (error)
			goto DevAttrError;

		error = device_create_sys_dev_entry(dev);
		if (error)
			goto SysEntryError;

		devtmpfs_create_node(dev);
	}

	/* Notify clients of device addition.  This call must come
	 * after dpm_sysfs_add() and before kobject_uevent().
	 */
	if (dev->bus)
		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
					     BUS_NOTIFY_ADD_DEVICE, dev);

	kobject_uevent(&dev->kobj, KOBJ_ADD);
	bus_probe_device(dev);
	if (parent)
		klist_add_tail(&dev->p->knode_parent,
			       &parent->p->klist_children);

	if (dev->class) {
		mutex_lock(&dev->class->p->mutex);
		/* tie the class to the device */
		klist_add_tail(&dev->knode_class,
			       &dev->class->p->klist_devices);

		/* notify any interfaces that the device is here */
		list_for_each_entry(class_intf,
				    &dev->class->p->interfaces, node)
			if (class_intf->add_dev)
				class_intf->add_dev(dev, class_intf);
		mutex_unlock(&dev->class->p->mutex);
	}
done:
	put_device(dev);
	return error;
 SysEntryError:
	if (MAJOR(dev->devt))
		device_remove_file(dev, &dev_attr_dev);
 DevAttrError:
	device_pm_remove(dev);
	dpm_sysfs_remove(dev);
 DPMError:
	bus_remove_device(dev);
 BusError:
	device_remove_attrs(dev);
 AttrsError:
	device_remove_class_symlinks(dev);
 SymlinkError:
	device_remove_file(dev, &dev_attr_uevent);
 attrError:
	kobject_uevent(&dev->kobj, KOBJ_REMOVE);
	glue_dir = get_glue_dir(dev);
	kobject_del(&dev->kobj);
 Error:
	cleanup_glue_dir(dev, glue_dir);
	put_device(parent);
name_error:
	kfree(dev->p);
	dev->p = NULL;
	goto done;
}
EXPORT_SYMBOL_GPL(device_add);

/**
 * device_register - register a device with the system.
 * @dev: pointer to the device structure
 *
 * This happens in two clean steps - initialize the device
 * and add it to the system. The two steps can be called
 * separately, but this is the easiest and most common.
 * I.e. you should only call the two helpers separately if
 * have a clearly defined need to use and refcount the device
 * before it is added to the hierarchy.
 *
 * For more information, see the kerneldoc for device_initialize()
 * and device_add().
 *
 * NOTE: _Never_ directly free @dev after calling this function, even
 * if it returned an error! Always use put_device() to give up the
 * reference initialized in this function instead.
 */
int device_register(struct device *dev)
{
	device_initialize(dev);
	return device_add(dev);
}
EXPORT_SYMBOL_GPL(device_register);

/**
 * get_device - increment reference count for device.
 * @dev: device.
 *
 * This simply forwards the call to kobject_get(), though
 * we do take care to provide for the case that we get a NULL
 * pointer passed in.
 */
struct device *get_device(struct device *dev)
{
	return dev ? kobj_to_dev(kobject_get(&dev->kobj)) : NULL;
}
EXPORT_SYMBOL_GPL(get_device);

/**
 * put_device - decrement reference count.
 * @dev: device in question.
 */
void put_device(struct device *dev)
{
	/* might_sleep(); */
	if (dev)
		kobject_put(&dev->kobj);
}
EXPORT_SYMBOL_GPL(put_device);

/**
 * device_del - delete device from system.
 * @dev: device.
 *
 * This is the first part of the device unregistration
 * sequence. This removes the device from the lists we control
 * from here, has it removed from the other driver model
 * subsystems it was added to in device_add(), and removes it
 * from the kobject hierarchy.
 *
 * NOTE: this should be called manually _iff_ device_add() was
 * also called manually.
 */
void device_del(struct device *dev)
{
	struct device *parent = dev->parent;
	struct kobject *glue_dir = NULL;
	struct class_interface *class_intf;

	/* Notify clients of device removal.  This call must come
	 * before dpm_sysfs_remove().
	 */
	if (dev->bus)
		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
					     BUS_NOTIFY_DEL_DEVICE, dev);

	device_links_purge(dev);
	dpm_sysfs_remove(dev);
	if (parent)
		klist_del(&dev->p->knode_parent);
	if (MAJOR(dev->devt)) {
		devtmpfs_delete_node(dev);
		device_remove_sys_dev_entry(dev);
		device_remove_file(dev, &dev_attr_dev);
	}
	if (dev->class) {
		device_remove_class_symlinks(dev);

		mutex_lock(&dev->class->p->mutex);
		/* notify any interfaces that the device is now gone */
		list_for_each_entry(class_intf,
				    &dev->class->p->interfaces, node)
			if (class_intf->remove_dev)
				class_intf->remove_dev(dev, class_intf);
		/* remove the device from the class list */
		klist_del(&dev->knode_class);
		mutex_unlock(&dev->class->p->mutex);
	}
	device_remove_file(dev, &dev_attr_uevent);
	device_remove_attrs(dev);
	bus_remove_device(dev);
	device_pm_remove(dev);
	driver_deferred_probe_del(dev);
	device_remove_properties(dev);

	/* Notify the platform of the removal, in case they
	 * need to do anything...
	 */
	if (platform_notify_remove)
		platform_notify_remove(dev);
	if (dev->bus)
		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
					     BUS_NOTIFY_REMOVED_DEVICE, dev);
	kobject_uevent(&dev->kobj, KOBJ_REMOVE);
	glue_dir = get_glue_dir(dev);
	kobject_del(&dev->kobj);
	cleanup_glue_dir(dev, glue_dir);
	put_device(parent);
}
EXPORT_SYMBOL_GPL(device_del);

/**
 * device_unregister - unregister device from system.
 * @dev: device going away.
 *
 * We do this in two parts, like we do device_register(). First,
 * we remove it from all the subsystems with device_del(), then
 * we decrement the reference count via put_device(). If that
 * is the final reference count, the device will be cleaned up
 * via device_release() above. Otherwise, the structure will
 * stick around until the final reference to the device is dropped.
 */
void device_unregister(struct device *dev)
{
	pr_debug("device: '%s': %s\n", dev_name(dev), __func__);
	device_del(dev);
	put_device(dev);
}
EXPORT_SYMBOL_GPL(device_unregister);

static struct device *prev_device(struct klist_iter *i)
{
	struct klist_node *n = klist_prev(i);
	struct device *dev = NULL;
	struct device_private *p;

	if (n) {
		p = to_device_private_parent(n);
		dev = p->device;
	}
	return dev;
}

static struct device *next_device(struct klist_iter *i)
{
	struct klist_node *n = klist_next(i);
	struct device *dev = NULL;
	struct device_private *p;

	if (n) {
		p = to_device_private_parent(n);
		dev = p->device;
	}
	return dev;
}

/**
 * device_get_devnode - path of device node file
 * @dev: device
 * @mode: returned file access mode
 * @uid: returned file owner
 * @gid: returned file group
 * @tmp: possibly allocated string
 *
 * Return the relative path of a possible device node.
 * Non-default names may need to allocate a memory to compose
 * a name. This memory is returned in tmp and needs to be
 * freed by the caller.
 */
const char *device_get_devnode(struct device *dev,
			       umode_t *mode, kuid_t *uid, kgid_t *gid,
			       const char **tmp)
{
	char *s;

	*tmp = NULL;

	/* the device type may provide a specific name */
	if (dev->type && dev->type->devnode)
		*tmp = dev->type->devnode(dev, mode, uid, gid);
	if (*tmp)
		return *tmp;

	/* the class may provide a specific name */
	if (dev->class && dev->class->devnode)
		*tmp = dev->class->devnode(dev, mode);
	if (*tmp)
		return *tmp;

	/* return name without allocation, tmp == NULL */
	if (strchr(dev_name(dev), '!') == NULL)
		return dev_name(dev);

	/* replace '!' in the name with '/' */
	s = kstrdup(dev_name(dev), GFP_KERNEL);
	if (!s)
		return NULL;
	strreplace(s, '!', '/');
	return *tmp = s;
}

/**
 * device_for_each_child - device child iterator.
 * @parent: parent struct device.
 * @fn: function to be called for each device.
 * @data: data for the callback.
 *
 * Iterate over @parent's child devices, and call @fn for each,
 * passing it @data.
 *
 * We check the return of @fn each time. If it returns anything
 * other than 0, we break out and return that value.
 */
int device_for_each_child(struct device *parent, void *data,
			  int (*fn)(struct device *dev, void *data))
{
	struct klist_iter i;
	struct device *child;
	int error = 0;

	if (!parent->p)
		return 0;

	klist_iter_init(&parent->p->klist_children, &i);
	while ((child = next_device(&i)) && !error)
		error = fn(child, data);
	klist_iter_exit(&i);
	return error;
}
EXPORT_SYMBOL_GPL(device_for_each_child);

/**
 * device_for_each_child_reverse - device child iterator in reversed order.
 * @parent: parent struct device.
 * @fn: function to be called for each device.
 * @data: data for the callback.
 *
 * Iterate over @parent's child devices, and call @fn for each,
 * passing it @data.
 *
 * We check the return of @fn each time. If it returns anything
 * other than 0, we break out and return that value.
 */
int device_for_each_child_reverse(struct device *parent, void *data,
				  int (*fn)(struct device *dev, void *data))
{
	struct klist_iter i;
	struct device *child;
	int error = 0;

	if (!parent->p)
		return 0;

	klist_iter_init(&parent->p->klist_children, &i);
	while ((child = prev_device(&i)) && !error)
		error = fn(child, data);
	klist_iter_exit(&i);
	return error;
}
EXPORT_SYMBOL_GPL(device_for_each_child_reverse);

/**
 * device_find_child - device iterator for locating a particular device.
 * @parent: parent struct device
 * @match: Callback function to check device
 * @data: Data to pass to match function
 *
 * This is similar to the device_for_each_child() 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 and a reference to the
 * current device can be obtained, 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.
 */
struct device *device_find_child(struct device *parent, void *data,
				 int (*match)(struct device *dev, void *data))
{
	struct klist_iter i;
	struct device *child;

	if (!parent)
		return NULL;

	klist_iter_init(&parent->p->klist_children, &i);
	while ((child = next_device(&i)))
		if (match(child, data) && get_device(child))
			break;
	klist_iter_exit(&i);
	return child;
}
EXPORT_SYMBOL_GPL(device_find_child);

int __init devices_init(void)
{
	devices_kset = kset_create_and_add("devices", &device_uevent_ops, NULL);
	if (!devices_kset)
		return -ENOMEM;
	dev_kobj = kobject_create_and_add("dev", NULL);
	if (!dev_kobj)
		goto dev_kobj_err;
	sysfs_dev_block_kobj = kobject_create_and_add("block", dev_kobj);
	if (!sysfs_dev_block_kobj)
		goto block_kobj_err;
	sysfs_dev_char_kobj = kobject_create_and_add("char", dev_kobj);
	if (!sysfs_dev_char_kobj)
		goto char_kobj_err;

	return 0;

 char_kobj_err:
	kobject_put(sysfs_dev_block_kobj);
 block_kobj_err:
	kobject_put(dev_kobj);
 dev_kobj_err:
	kset_unregister(devices_kset);
	return -ENOMEM;
}

static int device_check_offline(struct device *dev, void *not_used)
{
	int ret;

	ret = device_for_each_child(dev, NULL, device_check_offline);
	if (ret)
		return ret;

	return device_supports_offline(dev) && !dev->offline ? -EBUSY : 0;
}

/**
 * device_offline - Prepare the device for hot-removal.
 * @dev: Device to be put offline.
 *
 * Execute the device bus type's .offline() callback, if present, to prepare
 * the device for a subsequent hot-removal.  If that succeeds, the device must
 * not be used until either it is removed or its bus type's .online() callback
 * is executed.
 *
 * Call under device_hotplug_lock.
 */
int device_offline(struct device *dev)
{
	int ret;

	if (dev->offline_disabled)
		return -EPERM;

	ret = device_for_each_child(dev, NULL, device_check_offline);
	if (ret)
		return ret;

	device_lock(dev);
	if (device_supports_offline(dev)) {
		if (dev->offline) {
			ret = 1;
		} else {
			ret = dev->bus->offline(dev);
			if (!ret) {
				kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
				dev->offline = true;
			}
		}
	}
	device_unlock(dev);

	return ret;
}

/**
 * device_online - Put the device back online after successful device_offline().
 * @dev: Device to be put back online.
 *
 * If device_offline() has been successfully executed for @dev, but the device
 * has not been removed subsequently, execute its bus type's .online() callback
 * to indicate that the device can be used again.
 *
 * Call under device_hotplug_lock.
 */
int device_online(struct device *dev)
{
	int ret = 0;

	device_lock(dev);
	if (device_supports_offline(dev)) {
		if (dev->offline) {
			ret = dev->bus->online(dev);
			if (!ret) {
				kobject_uevent(&dev->kobj, KOBJ_ONLINE);
				dev->offline = false;
			}
		} else {
			ret = 1;
		}
	}
	device_unlock(dev);

	return ret;
}

struct root_device {
	struct device dev;
	struct module *owner;
};

static inline struct root_device *to_root_device(struct device *d)
{
	return container_of(d, struct root_device, dev);
}

static void root_device_release(struct device *dev)
{
	kfree(to_root_device(dev));
}

/**
 * __root_device_register - allocate and register a root device
 * @name: root device name
 * @owner: owner module of the root device, usually THIS_MODULE
 *
 * This function allocates a root device and registers it
 * using device_register(). In order to free the returned
 * device, use root_device_unregister().
 *
 * Root devices are dummy devices which allow other devices
 * to be grouped under /sys/devices. Use this function to
 * allocate a root device and then use it as the parent of
 * any device which should appear under /sys/devices/{name}
 *
 * The /sys/devices/{name} directory will also contain a
 * 'module' symlink which points to the @owner directory
 * in sysfs.
 *
 * Returns &struct device pointer on success, or ERR_PTR() on error.
 *
 * Note: You probably want to use root_device_register().
 */
struct device *__root_device_register(const char *name, struct module *owner)
{
	struct root_device *root;
	int err = -ENOMEM;

	root = kzalloc(sizeof(struct root_device), GFP_KERNEL);
	if (!root)
		return ERR_PTR(err);

	err = dev_set_name(&root->dev, "%s", name);
	if (err) {
		kfree(root);
		return ERR_PTR(err);
	}

	root->dev.release = root_device_release;

	err = device_register(&root->dev);
	if (err) {
		put_device(&root->dev);
		return ERR_PTR(err);
	}

#ifdef CONFIG_MODULES	/* gotta find a "cleaner" way to do this */
	if (owner) {
		struct module_kobject *mk = &owner->mkobj;

		err = sysfs_create_link(&root->dev.kobj, &mk->kobj, "module");
		if (err) {
			device_unregister(&root->dev);
			return ERR_PTR(err);
		}
		root->owner = owner;
	}
#endif

	return &root->dev;
}
EXPORT_SYMBOL_GPL(__root_device_register);

/**
 * root_device_unregister - unregister and free a root device
 * @dev: device going away
 *
 * This function unregisters and cleans up a device that was created by
 * root_device_register().
 */
void root_device_unregister(struct device *dev)
{
	struct root_device *root = to_root_device(dev);

	if (root->owner)
		sysfs_remove_link(&root->dev.kobj, "module");

	device_unregister(dev);
}
EXPORT_SYMBOL_GPL(root_device_unregister);


static void device_create_release(struct device *dev)
{
	pr_debug("device: '%s': %s\n", dev_name(dev), __func__);
	kfree(dev);
}

static struct device *
device_create_groups_vargs(struct class *class, struct device *parent,
			   dev_t devt, void *drvdata,
			   const struct attribute_group **groups,
			   const char *fmt, va_list args)
{
	struct device *dev = NULL;
	int retval = -ENODEV;

	if (class == NULL || IS_ERR(class))
		goto error;

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

	device_initialize(dev);
	dev->devt = devt;
	dev->class = class;
	dev->parent = parent;
	dev->groups = groups;
	dev->release = device_create_release;
	dev_set_drvdata(dev, drvdata);

	retval = kobject_set_name_vargs(&dev->kobj, fmt, args);
	if (retval)
		goto error;

	retval = device_add(dev);
	if (retval)
		goto error;

	return dev;

error:
	put_device(dev);
	return ERR_PTR(retval);
}

/**
 * device_create_vargs - creates a device and registers it with sysfs
 * @class: pointer to the struct class that this device should be registered to
 * @parent: pointer to the parent struct device of this new device, if any
 * @devt: the dev_t for the char device to be added
 * @drvdata: the data to be added to the device for callbacks
 * @fmt: string for the device's name
 * @args: va_list for the device's name
 *
 * This function can be used by char device classes.  A struct device
 * will be created in sysfs, registered to the specified class.
 *
 * A "dev" file will be created, showing the dev_t for the device, if
 * the dev_t is not 0,0.
 * If a pointer to a parent struct device is passed in, the newly created
 * struct device will be a child of that device in sysfs.
 * The pointer to the struct device will be returned from the call.
 * Any further sysfs files that might be required can be created using this
 * pointer.
 *
 * Returns &struct device pointer on success, or ERR_PTR() on error.
 *
 * Note: the struct class passed to this function must have previously
 * been created with a call to class_create().
 */
struct device *device_create_vargs(struct class *class, struct device *parent,
				   dev_t devt, void *drvdata, const char *fmt,
				   va_list args)
{
	return device_create_groups_vargs(class, parent, devt, drvdata, NULL,
					  fmt, args);
}
EXPORT_SYMBOL_GPL(device_create_vargs);

/**
 * device_create - creates a device and registers it with sysfs
 * @class: pointer to the struct class that this device should be registered to
 * @parent: pointer to the parent struct device of this new device, if any
 * @devt: the dev_t for the char device to be added
 * @drvdata: the data to be added to the device for callbacks
 * @fmt: string for the device's name
 *
 * This function can be used by char device classes.  A struct device
 * will be created in sysfs, registered to the specified class.
 *
 * A "dev" file will be created, showing the dev_t for the device, if
 * the dev_t is not 0,0.
 * If a pointer to a parent struct device is passed in, the newly created
 * struct device will be a child of that device in sysfs.
 * The pointer to the struct device will be returned from the call.
 * Any further sysfs files that might be required can be created using this
 * pointer.
 *
 * Returns &struct device pointer on success, or ERR_PTR() on error.
 *
 * Note: the struct class passed to this function must have previously
 * been created with a call to class_create().
 */
struct device *device_create(struct class *class, struct device *parent,
			     dev_t devt, void *drvdata, const char *fmt, ...)
{
	va_list vargs;
	struct device *dev;

	va_start(vargs, fmt);
	dev = device_create_vargs(class, parent, devt, drvdata, fmt, vargs);
	va_end(vargs);
	return dev;
}
EXPORT_SYMBOL_GPL(device_create);

/**
 * device_create_with_groups - creates a device and registers it with sysfs
 * @class: pointer to the struct class that this device should be registered to
 * @parent: pointer to the parent struct device of this new device, if any
 * @devt: the dev_t for the char device to be added
 * @drvdata: the data to be added to the device for callbacks
 * @groups: NULL-terminated list of attribute groups to be created
 * @fmt: string for the device's name
 *
 * This function can be used by char device classes.  A struct device
 * will be created in sysfs, registered to the specified class.
 * Additional attributes specified in the groups parameter will also
 * be created automatically.
 *
 * A "dev" file will be created, showing the dev_t for the device, if
 * the dev_t is not 0,0.
 * If a pointer to a parent struct device is passed in, the newly created
 * struct device will be a child of that device in sysfs.
 * The pointer to the struct device will be returned from the call.
 * Any further sysfs files that might be required can be created using this
 * pointer.
 *
 * Returns &struct device pointer on success, or ERR_PTR() on error.
 *
 * Note: the struct class passed to this function must have previously
 * been created with a call to class_create().
 */
struct device *device_create_with_groups(struct class *class,
					 struct device *parent, dev_t devt,
					 void *drvdata,
					 const struct attribute_group **groups,
					 const char *fmt, ...)
{
	va_list vargs;
	struct device *dev;

	va_start(vargs, fmt);
	dev = device_create_groups_vargs(class, parent, devt, drvdata, groups,
					 fmt, vargs);
	va_end(vargs);
	return dev;
}
EXPORT_SYMBOL_GPL(device_create_with_groups);

static int __match_devt(struct device *dev, const void *data)
{
	const dev_t *devt = data;

	return dev->devt == *devt;
}

/**
 * device_destroy - removes a device that was created with device_create()
 * @class: pointer to the struct class that this device was registered with
 * @devt: the dev_t of the device that was previously registered
 *
 * This call unregisters and cleans up a device that was created with a
 * call to device_create().
 */
void device_destroy(struct class *class, dev_t devt)
{
	struct device *dev;

	dev = class_find_device(class, NULL, &devt, __match_devt);
	if (dev) {
		put_device(dev);
		device_unregister(dev);
	}
}
EXPORT_SYMBOL_GPL(device_destroy);

/**
 * device_rename - renames a device
 * @dev: the pointer to the struct device to be renamed
 * @new_name: the new name of the device
 *
 * It is the responsibility of the caller to provide mutual
 * exclusion between two different calls of device_rename
 * on the same device to ensure that new_name is valid and
 * won't conflict with other devices.
 *
 * Note: Don't call this function.  Currently, the networking layer calls this
 * function, but that will change.  The following text from Kay Sievers offers
 * some insight:
 *
 * Renaming devices is racy at many levels, symlinks and other stuff are not
 * replaced atomically, and you get a "move" uevent, but it's not easy to
 * connect the event to the old and new device. Device nodes are not renamed at
 * all, there isn't even support for that in the kernel now.
 *
 * In the meantime, during renaming, your target name might be taken by another
 * driver, creating conflicts. Or the old name is taken directly after you
 * renamed it -- then you get events for the same DEVPATH, before you even see
 * the "move" event. It's just a mess, and nothing new should ever rely on
 * kernel device renaming. Besides that, it's not even implemented now for
 * other things than (driver-core wise very simple) network devices.
 *
 * We are currently about to change network renaming in udev to completely
 * disallow renaming of devices in the same namespace as the kernel uses,
 * because we can't solve the problems properly, that arise with swapping names
 * of multiple interfaces without races. Means, renaming of eth[0-9]* will only
 * be allowed to some other name than eth[0-9]*, for the aforementioned
 * reasons.
 *
 * Make up a "real" name in the driver before you register anything, or add
 * some other attributes for userspace to find the device, or use udev to add
 * symlinks -- but never rename kernel devices later, it's a complete mess. We
 * don't even want to get into that and try to implement the missing pieces in
 * the core. We really have other pieces to fix in the driver core mess. :)
 */
int device_rename(struct device *dev, const char *new_name)
{
	struct kobject *kobj = &dev->kobj;
	char *old_device_name = NULL;
	int error;

	dev = get_device(dev);
	if (!dev)
		return -EINVAL;

	dev_dbg(dev, "renaming to %s\n", new_name);

	old_device_name = kstrdup(dev_name(dev), GFP_KERNEL);
	if (!old_device_name) {
		error = -ENOMEM;
		goto out;
	}

	if (dev->class) {
		error = sysfs_rename_link_ns(&dev->class->p->subsys.kobj,
					     kobj, old_device_name,
					     new_name, kobject_namespace(kobj));
		if (error)
			goto out;
	}

	error = kobject_rename(kobj, new_name);
	if (error)
		goto out;

out:
	put_device(dev);

	kfree(old_device_name);

	return error;
}
EXPORT_SYMBOL_GPL(device_rename);

static int device_move_class_links(struct device *dev,
				   struct device *old_parent,
				   struct device *new_parent)
{
	int error = 0;

	if (old_parent)
		sysfs_remove_link(&dev->kobj, "device");
	if (new_parent)
		error = sysfs_create_link(&dev->kobj, &new_parent->kobj,
					  "device");
	return error;
}

/**
 * device_move - moves a device to a new parent
 * @dev: the pointer to the struct device to be moved
 * @new_parent: the new parent of the device (can by NULL)
 * @dpm_order: how to reorder the dpm_list
 */
int device_move(struct device *dev, struct device *new_parent,
		enum dpm_order dpm_order)
{
	int error;
	struct device *old_parent;
	struct kobject *new_parent_kobj;

	dev = get_device(dev);
	if (!dev)
		return -EINVAL;

	device_pm_lock();
	new_parent = get_device(new_parent);
	new_parent_kobj = get_device_parent(dev, new_parent);

	pr_debug("device: '%s': %s: moving to '%s'\n", dev_name(dev),
		 __func__, new_parent ? dev_name(new_parent) : "<NULL>");
	error = kobject_move(&dev->kobj, new_parent_kobj);
	if (error) {
		cleanup_glue_dir(dev, new_parent_kobj);
		put_device(new_parent);
		goto out;
	}
	old_parent = dev->parent;
	dev->parent = new_parent;
	if (old_parent)
		klist_remove(&dev->p->knode_parent);
	if (new_parent) {
		klist_add_tail(&dev->p->knode_parent,
			       &new_parent->p->klist_children);
		set_dev_node(dev, dev_to_node(new_parent));
	}

	if (dev->class) {
		error = device_move_class_links(dev, old_parent, new_parent);
		if (error) {
			/* We ignore errors on cleanup since we're hosed anyway... */
			device_move_class_links(dev, new_parent, old_parent);
			if (!kobject_move(&dev->kobj, &old_parent->kobj)) {
				if (new_parent)
					klist_remove(&dev->p->knode_parent);
				dev->parent = old_parent;
				if (old_parent) {
					klist_add_tail(&dev->p->knode_parent,
						       &old_parent->p->klist_children);
					set_dev_node(dev, dev_to_node(old_parent));
				}
			}
			cleanup_glue_dir(dev, new_parent_kobj);
			put_device(new_parent);
			goto out;
		}
	}
	switch (dpm_order) {
	case DPM_ORDER_NONE:
		break;
	case DPM_ORDER_DEV_AFTER_PARENT:
		device_pm_move_after(dev, new_parent);
		devices_kset_move_after(dev, new_parent);
		break;
	case DPM_ORDER_PARENT_BEFORE_DEV:
		device_pm_move_before(new_parent, dev);
		devices_kset_move_before(new_parent, dev);
		break;
	case DPM_ORDER_DEV_LAST:
		device_pm_move_last(dev);
		devices_kset_move_last(dev);
		break;
	}

	put_device(old_parent);
out:
	device_pm_unlock();
	put_device(dev);
	return error;
}
EXPORT_SYMBOL_GPL(device_move);

/**
 * device_shutdown - call ->shutdown() on each device to shutdown.
 */
void device_shutdown(void)
{
	struct device *dev, *parent;

	spin_lock(&devices_kset->list_lock);
	/*
	 * Walk the devices list backward, shutting down each in turn.
	 * Beware that device unplug events may also start pulling
	 * devices offline, even as the system is shutting down.
	 */
	while (!list_empty(&devices_kset->list)) {
		dev = list_entry(devices_kset->list.prev, struct device,
				kobj.entry);

		/*
		 * hold reference count of device's parent to
		 * prevent it from being freed because parent's
		 * lock is to be held
		 */
		parent = get_device(dev->parent);
		get_device(dev);
		/*
		 * Make sure the device is off the kset list, in the
		 * event that dev->*->shutdown() doesn't remove it.
		 */
		list_del_init(&dev->kobj.entry);
		spin_unlock(&devices_kset->list_lock);

		/* hold lock to avoid race with probe/release */
		if (parent)
			device_lock(parent);
		device_lock(dev);

		/* Don't allow any more runtime suspends */
		pm_runtime_get_noresume(dev);
		pm_runtime_barrier(dev);

		if (dev->class && dev->class->shutdown_pre) {
			if (initcall_debug)
				dev_info(dev, "shutdown_pre\n");
			dev->class->shutdown_pre(dev);
		}
		if (dev->bus && dev->bus->shutdown) {
			if (initcall_debug)
				dev_info(dev, "shutdown\n");
			dev->bus->shutdown(dev);
		} else if (dev->driver && dev->driver->shutdown) {
			if (initcall_debug)
				dev_info(dev, "shutdown\n");
			dev->driver->shutdown(dev);
		}

		device_unlock(dev);
		if (parent)
			device_unlock(parent);

		put_device(dev);
		put_device(parent);

		spin_lock(&devices_kset->list_lock);
	}
	spin_unlock(&devices_kset->list_lock);
}

/*
 * Device logging functions
 */

#ifdef CONFIG_PRINTK
static int
create_syslog_header(const struct device *dev, char *hdr, size_t hdrlen)
{
	const char *subsys;
	size_t pos = 0;

	if (dev->class)
		subsys = dev->class->name;
	else if (dev->bus)
		subsys = dev->bus->name;
	else
		return 0;

	pos += snprintf(hdr + pos, hdrlen - pos, "SUBSYSTEM=%s", subsys);
	if (pos >= hdrlen)
		goto overflow;

	/*
	 * Add device identifier DEVICE=:
	 *   b12:8         block dev_t
	 *   c127:3        char dev_t
	 *   n8            netdev ifindex
	 *   +sound:card0  subsystem:devname
	 */
	if (MAJOR(dev->devt)) {
		char c;

		if (strcmp(subsys, "block") == 0)
			c = 'b';
		else
			c = 'c';
		pos++;
		pos += snprintf(hdr + pos, hdrlen - pos,
				"DEVICE=%c%u:%u",
				c, MAJOR(dev->devt), MINOR(dev->devt));
	} else if (strcmp(subsys, "net") == 0) {
		struct net_device *net = to_net_dev(dev);

		pos++;
		pos += snprintf(hdr + pos, hdrlen - pos,
				"DEVICE=n%u", net->ifindex);
	} else {
		pos++;
		pos += snprintf(hdr + pos, hdrlen - pos,
				"DEVICE=+%s:%s", subsys, dev_name(dev));
	}

	if (pos >= hdrlen)
		goto overflow;

	return pos;

overflow:
	dev_WARN(dev, "device/subsystem name too long");
	return 0;
}

int dev_vprintk_emit(int level, const struct device *dev,
		     const char *fmt, va_list args)
{
	char hdr[128];
	size_t hdrlen;

	hdrlen = create_syslog_header(dev, hdr, sizeof(hdr));

	return vprintk_emit(0, level, hdrlen ? hdr : NULL, hdrlen, fmt, args);
}
EXPORT_SYMBOL(dev_vprintk_emit);

int dev_printk_emit(int level, const struct device *dev, const char *fmt, ...)
{
	va_list args;
	int r;

	va_start(args, fmt);

	r = dev_vprintk_emit(level, dev, fmt, args);

	va_end(args);

	return r;
}
EXPORT_SYMBOL(dev_printk_emit);

static void __dev_printk(const char *level, const struct device *dev,
			struct va_format *vaf)
{
	if (dev)
		dev_printk_emit(level[1] - '0', dev, "%s %s: %pV",
				dev_driver_string(dev), dev_name(dev), vaf);
	else
		printk("%s(NULL device *): %pV", level, vaf);
}

void dev_printk(const char *level, const struct device *dev,
		const char *fmt, ...)
{
	struct va_format vaf;
	va_list args;

	va_start(args, fmt);

	vaf.fmt = fmt;
	vaf.va = &args;

	__dev_printk(level, dev, &vaf);

	va_end(args);
}
EXPORT_SYMBOL(dev_printk);

#define define_dev_printk_level(func, kern_level)		\
void func(const struct device *dev, const char *fmt, ...)	\
{								\
	struct va_format vaf;					\
	va_list args;						\
								\
	va_start(args, fmt);					\
								\
	vaf.fmt = fmt;						\
	vaf.va = &args;						\
								\
	__dev_printk(kern_level, dev, &vaf);			\
								\
	va_end(args);						\
}								\
EXPORT_SYMBOL(func);

define_dev_printk_level(dev_emerg, KERN_EMERG);
define_dev_printk_level(dev_alert, KERN_ALERT);
define_dev_printk_level(dev_crit, KERN_CRIT);
define_dev_printk_level(dev_err, KERN_ERR);
define_dev_printk_level(dev_warn, KERN_WARNING);
define_dev_printk_level(dev_notice, KERN_NOTICE);
define_dev_printk_level(_dev_info, KERN_INFO);

#endif

static inline bool fwnode_is_primary(struct fwnode_handle *fwnode)
{
	return fwnode && !IS_ERR(fwnode->secondary);
}

/**
 * set_primary_fwnode - Change the primary firmware node of a given device.
 * @dev: Device to handle.
 * @fwnode: New primary firmware node of the device.
 *
 * Set the device's firmware node pointer to @fwnode, but if a secondary
 * firmware node of the device is present, preserve it.
 */
void set_primary_fwnode(struct device *dev, struct fwnode_handle *fwnode)
{
	if (fwnode) {
		struct fwnode_handle *fn = dev->fwnode;

		if (fwnode_is_primary(fn))
			fn = fn->secondary;

		if (fn) {
			WARN_ON(fwnode->secondary);
			fwnode->secondary = fn;
		}
		dev->fwnode = fwnode;
	} else {
		dev->fwnode = fwnode_is_primary(dev->fwnode) ?
			dev->fwnode->secondary : NULL;
	}
}
EXPORT_SYMBOL_GPL(set_primary_fwnode);

/**
 * set_secondary_fwnode - Change the secondary firmware node of a given device.
 * @dev: Device to handle.
 * @fwnode: New secondary firmware node of the device.
 *
 * If a primary firmware node of the device is present, set its secondary
 * pointer to @fwnode.  Otherwise, set the device's firmware node pointer to
 * @fwnode.
 */
void set_secondary_fwnode(struct device *dev, struct fwnode_handle *fwnode)
{
	if (fwnode)
		fwnode->secondary = ERR_PTR(-ENODEV);

	if (fwnode_is_primary(dev->fwnode))
		dev->fwnode->secondary = fwnode;
	else
		dev->fwnode = fwnode;
}

/**
 * device_set_of_node_from_dev - reuse device-tree node of another device
 * @dev: device whose device-tree node is being set
 * @dev2: device whose device-tree node is being reused
 *
 * Takes another reference to the new device-tree node after first dropping
 * any reference held to the old node.
 */
void device_set_of_node_from_dev(struct device *dev, const struct device *dev2)
{
	of_node_put(dev->of_node);
	dev->of_node = of_node_get(dev2->of_node);
	dev->of_node_reused = true;
}
EXPORT_SYMBOL_GPL(device_set_of_node_from_dev);