treewide: Fix typo in Documentation/DocBook

[mirror_ubuntu-artful-kernel.git] / drivers / base / bus.c

/*
 * bus.c - bus driver management
 *
 * Copyright (c) 2002-3 Patrick Mochel
 * Copyright (c) 2002-3 Open Source Development Labs
 * Copyright (c) 2007 Greg Kroah-Hartman <gregkh@suse.de>
 * Copyright (c) 2007 Novell Inc.
 *
 * This file is released under the GPLv2
 *
 */

#include <linux/device.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/mutex.h>
#include <linux/sysfs.h>
#include "base.h"
#include "power/power.h"

/* /sys/devices/system */
static struct kset *system_kset;

#define to_bus_attr(_attr) container_of(_attr, struct bus_attribute, attr)

/*
 * sysfs bindings for drivers
 */

#define to_drv_attr(_attr) container_of(_attr, struct driver_attribute, attr)


static int __must_check bus_rescan_devices_helper(struct device *dev,
                                                void *data);

static struct bus_type *bus_get(struct bus_type *bus)
{
        if (bus) {
                kset_get(&bus->p->subsys);
                return bus;
        }
        return NULL;
}

static void bus_put(struct bus_type *bus)
{
        if (bus)
                kset_put(&bus->p->subsys);
}

static ssize_t drv_attr_show(struct kobject *kobj, struct attribute *attr,
                             char *buf)
{
        struct driver_attribute *drv_attr = to_drv_attr(attr);
        struct driver_private *drv_priv = to_driver(kobj);
        ssize_t ret = -EIO;

        if (drv_attr->show)
                ret = drv_attr->show(drv_priv->driver, buf);
        return ret;
}

static ssize_t drv_attr_store(struct kobject *kobj, struct attribute *attr,
                              const char *buf, size_t count)
{
        struct driver_attribute *drv_attr = to_drv_attr(attr);
        struct driver_private *drv_priv = to_driver(kobj);
        ssize_t ret = -EIO;

        if (drv_attr->store)
                ret = drv_attr->store(drv_priv->driver, buf, count);
        return ret;
}

static const struct sysfs_ops driver_sysfs_ops = {
        .show   = drv_attr_show,
        .store  = drv_attr_store,
};

static void driver_release(struct kobject *kobj)
{
        struct driver_private *drv_priv = to_driver(kobj);

        pr_debug("driver: '%s': %s\n", kobject_name(kobj), __func__);
        kfree(drv_priv);
}

static struct kobj_type driver_ktype = {
        .sysfs_ops      = &driver_sysfs_ops,
        .release        = driver_release,
};

/*
 * sysfs bindings for buses
 */
static ssize_t bus_attr_show(struct kobject *kobj, struct attribute *attr,
                             char *buf)
{
        struct bus_attribute *bus_attr = to_bus_attr(attr);
        struct subsys_private *subsys_priv = to_subsys_private(kobj);
        ssize_t ret = 0;

        if (bus_attr->show)
                ret = bus_attr->show(subsys_priv->bus, buf);
        return ret;
}

static ssize_t bus_attr_store(struct kobject *kobj, struct attribute *attr,
                              const char *buf, size_t count)
{
        struct bus_attribute *bus_attr = to_bus_attr(attr);
        struct subsys_private *subsys_priv = to_subsys_private(kobj);
        ssize_t ret = 0;

        if (bus_attr->store)
                ret = bus_attr->store(subsys_priv->bus, buf, count);
        return ret;
}

static const struct sysfs_ops bus_sysfs_ops = {
        .show   = bus_attr_show,
        .store  = bus_attr_store,
};

int bus_create_file(struct bus_type *bus, struct bus_attribute *attr)
{
        int error;
        if (bus_get(bus)) {
                error = sysfs_create_file(&bus->p->subsys.kobj, &attr->attr);
                bus_put(bus);
        } else
                error = -EINVAL;
        return error;
}
EXPORT_SYMBOL_GPL(bus_create_file);

void bus_remove_file(struct bus_type *bus, struct bus_attribute *attr)
{
        if (bus_get(bus)) {
                sysfs_remove_file(&bus->p->subsys.kobj, &attr->attr);
                bus_put(bus);
        }
}
EXPORT_SYMBOL_GPL(bus_remove_file);

static struct kobj_type bus_ktype = {
        .sysfs_ops      = &bus_sysfs_ops,
};

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

        if (ktype == &bus_ktype)
                return 1;
        return 0;
}

static const struct kset_uevent_ops bus_uevent_ops = {
        .filter = bus_uevent_filter,
};

static struct kset *bus_kset;

/* Manually detach a device from its associated driver. */
static ssize_t unbind_store(struct device_driver *drv, const char *buf,
                            size_t count)
{
        struct bus_type *bus = bus_get(drv->bus);
        struct device *dev;
        int err = -ENODEV;

        dev = bus_find_device_by_name(bus, NULL, buf);
        if (dev && dev->driver == drv) {
                if (dev->parent)        /* Needed for USB */
                        device_lock(dev->parent);
                device_release_driver(dev);
                if (dev->parent)
                        device_unlock(dev->parent);
                err = count;
        }
        put_device(dev);
        bus_put(bus);
        return err;
}
static DRIVER_ATTR_WO(unbind);

/*
 * Manually attach a device to a driver.
 * Note: the driver must want to bind to the device,
 * it is not possible to override the driver's id table.
 */
static ssize_t bind_store(struct device_driver *drv, const char *buf,
                          size_t count)
{
        struct bus_type *bus = bus_get(drv->bus);
        struct device *dev;
        int err = -ENODEV;

        dev = bus_find_device_by_name(bus, NULL, buf);
        if (dev && dev->driver == NULL && driver_match_device(drv, dev)) {
                if (dev->parent)        /* Needed for USB */
                        device_lock(dev->parent);
                device_lock(dev);
                err = driver_probe_device(drv, dev);
                device_unlock(dev);
                if (dev->parent)
                        device_unlock(dev->parent);

                if (err > 0) {
                        /* success */
                        err = count;
                } else if (err == 0) {
                        /* driver didn't accept device */
                        err = -ENODEV;
                }
        }
        put_device(dev);
        bus_put(bus);
        return err;
}
static DRIVER_ATTR_WO(bind);

static ssize_t show_drivers_autoprobe(struct bus_type *bus, char *buf)
{
        return sprintf(buf, "%d\n", bus->p->drivers_autoprobe);
}

static ssize_t store_drivers_autoprobe(struct bus_type *bus,
                                       const char *buf, size_t count)
{
        if (buf[0] == '0')
                bus->p->drivers_autoprobe = 0;
        else
                bus->p->drivers_autoprobe = 1;
        return count;
}

static ssize_t store_drivers_probe(struct bus_type *bus,
                                   const char *buf, size_t count)
{
        struct device *dev;

        dev = bus_find_device_by_name(bus, NULL, buf);
        if (!dev)
                return -ENODEV;
        if (bus_rescan_devices_helper(dev, NULL) != 0)
                return -EINVAL;
        return count;
}

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

        if (n) {
                dev_prv = to_device_private_bus(n);
                dev = dev_prv->device;
        }
        return dev;
}

/**
 * bus_for_each_dev - device iterator.
 * @bus: bus type.
 * @start: device to start iterating from.
 * @data: data for the callback.
 * @fn: function to be called for each device.
 *
 * Iterate over @bus's list of devices, and call @fn for each,
 * passing it @data. If @start is not NULL, we use that device to
 * begin iterating from.
 *
 * We check the return of @fn each time. If it returns anything
 * other than 0, we break out and return that value.
 *
 * NOTE: The device that returns a non-zero value is not retained
 * in any way, nor is its refcount incremented. If the caller needs
 * to retain this data, it should do so, and increment the reference
 * count in the supplied callback.
 */
int bus_for_each_dev(struct bus_type *bus, struct device *start,
                     void *data, int (*fn)(struct device *, void *))
{
        struct klist_iter i;
        struct device *dev;
        int error = 0;

        if (!bus || !bus->p)
                return -EINVAL;

        klist_iter_init_node(&bus->p->klist_devices, &i,
                             (start ? &start->p->knode_bus : NULL));
        while ((dev = next_device(&i)) && !error)
                error = fn(dev, data);
        klist_iter_exit(&i);
        return error;
}
EXPORT_SYMBOL_GPL(bus_for_each_dev);

/**
 * bus_find_device - device iterator for locating a particular device.
 * @bus: bus type
 * @start: Device to begin with
 * @data: Data to pass to match function
 * @match: Callback function to check device
 *
 * This is similar to the bus_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.
 */
struct device *bus_find_device(struct bus_type *bus,
                               struct device *start, void *data,
                               int (*match)(struct device *dev, void *data))
{
        struct klist_iter i;
        struct device *dev;

        if (!bus || !bus->p)
                return NULL;

        klist_iter_init_node(&bus->p->klist_devices, &i,
                             (start ? &start->p->knode_bus : NULL));
        while ((dev = next_device(&i)))
                if (match(dev, data) && get_device(dev))
                        break;
        klist_iter_exit(&i);
        return dev;
}
EXPORT_SYMBOL_GPL(bus_find_device);

static int match_name(struct device *dev, void *data)
{
        const char *name = data;

        return sysfs_streq(name, dev_name(dev));
}

/**
 * bus_find_device_by_name - device iterator for locating a particular device of a specific name
 * @bus: bus type
 * @start: Device to begin with
 * @name: name of the device to match
 *
 * This is similar to the bus_find_device() function above, but it handles
 * searching by a name automatically, no need to write another strcmp matching
 * function.
 */
struct device *bus_find_device_by_name(struct bus_type *bus,
                                       struct device *start, const char *name)
{
        return bus_find_device(bus, start, (void *)name, match_name);
}
EXPORT_SYMBOL_GPL(bus_find_device_by_name);

/**
 * subsys_find_device_by_id - find a device with a specific enumeration number
 * @subsys: subsystem
 * @id: index 'id' in struct device
 * @hint: device to check first
 *
 * Check the hint's next object and if it is a match return it directly,
 * otherwise, fall back to a full list search. Either way a reference for
 * the returned object is taken.
 */
struct device *subsys_find_device_by_id(struct bus_type *subsys, unsigned int id,
                                        struct device *hint)
{
        struct klist_iter i;
        struct device *dev;

        if (!subsys)
                return NULL;

        if (hint) {
                klist_iter_init_node(&subsys->p->klist_devices, &i, &hint->p->knode_bus);
                dev = next_device(&i);
                if (dev && dev->id == id && get_device(dev)) {
                        klist_iter_exit(&i);
                        return dev;
                }
                klist_iter_exit(&i);
        }

        klist_iter_init_node(&subsys->p->klist_devices, &i, NULL);
        while ((dev = next_device(&i))) {
                if (dev->id == id && get_device(dev)) {
                        klist_iter_exit(&i);
                        return dev;
                }
        }
        klist_iter_exit(&i);
        return NULL;
}
EXPORT_SYMBOL_GPL(subsys_find_device_by_id);

static struct device_driver *next_driver(struct klist_iter *i)
{
        struct klist_node *n = klist_next(i);
        struct driver_private *drv_priv;

        if (n) {
                drv_priv = container_of(n, struct driver_private, knode_bus);
                return drv_priv->driver;
        }
        return NULL;
}

/**
 * bus_for_each_drv - driver iterator
 * @bus: bus we're dealing with.
 * @start: driver to start iterating on.
 * @data: data to pass to the callback.
 * @fn: function to call for each driver.
 *
 * This is nearly identical to the device iterator above.
 * We iterate over each driver that belongs to @bus, and call
 * @fn for each. If @fn returns anything but 0, we break out
 * and return it. If @start is not NULL, we use it as the head
 * of the list.
 *
 * NOTE: we don't return the driver that returns a non-zero
 * value, nor do we leave the reference count incremented for that
 * driver. If the caller needs to know that info, it must set it
 * in the callback. It must also be sure to increment the refcount
 * so it doesn't disappear before returning to the caller.
 */
int bus_for_each_drv(struct bus_type *bus, struct device_driver *start,
                     void *data, int (*fn)(struct device_driver *, void *))
{
        struct klist_iter i;
        struct device_driver *drv;
        int error = 0;

        if (!bus)
                return -EINVAL;

        klist_iter_init_node(&bus->p->klist_drivers, &i,
                             start ? &start->p->knode_bus : NULL);
        while ((drv = next_driver(&i)) && !error)
                error = fn(drv, data);
        klist_iter_exit(&i);
        return error;
}
EXPORT_SYMBOL_GPL(bus_for_each_drv);

static int device_add_attrs(struct bus_type *bus, struct device *dev)
{
        int error = 0;
        int i;

        if (!bus->dev_attrs)
                return 0;

        for (i = 0; bus->dev_attrs[i].attr.name; i++) {
                error = device_create_file(dev, &bus->dev_attrs[i]);
                if (error) {
                        while (--i >= 0)
                                device_remove_file(dev, &bus->dev_attrs[i]);
                        break;
                }
        }
        return error;
}

static void device_remove_attrs(struct bus_type *bus, struct device *dev)
{
        int i;

        if (bus->dev_attrs) {
                for (i = 0; bus->dev_attrs[i].attr.name; i++)
                        device_remove_file(dev, &bus->dev_attrs[i]);
        }
}

/**
 * bus_add_device - add device to bus
 * @dev: device being added
 *
 * - Add device's bus attributes.
 * - Create links to device's bus.
 * - Add the device to its bus's list of devices.
 */
int bus_add_device(struct device *dev)
{
        struct bus_type *bus = bus_get(dev->bus);
        int error = 0;

        if (bus) {
                pr_debug("bus: '%s': add device %s\n", bus->name, dev_name(dev));
                error = device_add_attrs(bus, dev);
                if (error)
                        goto out_put;
                error = device_add_groups(dev, bus->dev_groups);
                if (error)
                        goto out_groups;
                error = sysfs_create_link(&bus->p->devices_kset->kobj,
                                                &dev->kobj, dev_name(dev));
                if (error)
                        goto out_id;
                error = sysfs_create_link(&dev->kobj,
                                &dev->bus->p->subsys.kobj, "subsystem");
                if (error)
                        goto out_subsys;
                klist_add_tail(&dev->p->knode_bus, &bus->p->klist_devices);
        }
        return 0;

out_subsys:
        sysfs_remove_link(&bus->p->devices_kset->kobj, dev_name(dev));
out_groups:
        device_remove_groups(dev, bus->dev_groups);
out_id:
        device_remove_attrs(bus, dev);
out_put:
        bus_put(dev->bus);
        return error;
}

/**
 * bus_probe_device - probe drivers for a new device
 * @dev: device to probe
 *
 * - Automatically probe for a driver if the bus allows it.
 */
void bus_probe_device(struct device *dev)
{
        struct bus_type *bus = dev->bus;
        struct subsys_interface *sif;
        int ret;

        if (!bus)
                return;

        if (bus->p->drivers_autoprobe) {
                ret = device_attach(dev);
                WARN_ON(ret < 0);
        }

        mutex_lock(&bus->p->mutex);
        list_for_each_entry(sif, &bus->p->interfaces, node)
                if (sif->add_dev)
                        sif->add_dev(dev, sif);
        mutex_unlock(&bus->p->mutex);
}

/**
 * bus_remove_device - remove device from bus
 * @dev: device to be removed
 *
 * - Remove device from all interfaces.
 * - Remove symlink from bus' directory.
 * - Delete device from bus's list.
 * - Detach from its driver.
 * - Drop reference taken in bus_add_device().
 */
void bus_remove_device(struct device *dev)
{
        struct bus_type *bus = dev->bus;
        struct subsys_interface *sif;

        if (!bus)
                return;

        mutex_lock(&bus->p->mutex);
        list_for_each_entry(sif, &bus->p->interfaces, node)
                if (sif->remove_dev)
                        sif->remove_dev(dev, sif);
        mutex_unlock(&bus->p->mutex);

        sysfs_remove_link(&dev->kobj, "subsystem");
        sysfs_remove_link(&dev->bus->p->devices_kset->kobj,
                          dev_name(dev));
        device_remove_attrs(dev->bus, dev);
        device_remove_groups(dev, dev->bus->dev_groups);
        if (klist_node_attached(&dev->p->knode_bus))
                klist_del(&dev->p->knode_bus);

        pr_debug("bus: '%s': remove device %s\n",
                 dev->bus->name, dev_name(dev));
        device_release_driver(dev);
        bus_put(dev->bus);
}

static int __must_check add_bind_files(struct device_driver *drv)
{
        int ret;

        ret = driver_create_file(drv, &driver_attr_unbind);
        if (ret == 0) {
                ret = driver_create_file(drv, &driver_attr_bind);
                if (ret)
                        driver_remove_file(drv, &driver_attr_unbind);
        }
        return ret;
}

static void remove_bind_files(struct device_driver *drv)
{
        driver_remove_file(drv, &driver_attr_bind);
        driver_remove_file(drv, &driver_attr_unbind);
}

static BUS_ATTR(drivers_probe, S_IWUSR, NULL, store_drivers_probe);
static BUS_ATTR(drivers_autoprobe, S_IWUSR | S_IRUGO,
                show_drivers_autoprobe, store_drivers_autoprobe);

static int add_probe_files(struct bus_type *bus)
{
        int retval;

        retval = bus_create_file(bus, &bus_attr_drivers_probe);
        if (retval)
                goto out;

        retval = bus_create_file(bus, &bus_attr_drivers_autoprobe);
        if (retval)
                bus_remove_file(bus, &bus_attr_drivers_probe);
out:
        return retval;
}

static void remove_probe_files(struct bus_type *bus)
{
        bus_remove_file(bus, &bus_attr_drivers_autoprobe);
        bus_remove_file(bus, &bus_attr_drivers_probe);
}

static ssize_t uevent_store(struct device_driver *drv, const char *buf,
                            size_t count)
{
        enum kobject_action action;

        if (kobject_action_type(buf, count, &action) == 0)
                kobject_uevent(&drv->p->kobj, action);
        return count;
}
static DRIVER_ATTR_WO(uevent);

/**
 * bus_add_driver - Add a driver to the bus.
 * @drv: driver.
 */
int bus_add_driver(struct device_driver *drv)
{
        struct bus_type *bus;
        struct driver_private *priv;
        int error = 0;

        bus = bus_get(drv->bus);
        if (!bus)
                return -EINVAL;

        pr_debug("bus: '%s': add driver %s\n", bus->name, drv->name);

        priv = kzalloc(sizeof(*priv), GFP_KERNEL);
        if (!priv) {
                error = -ENOMEM;
                goto out_put_bus;
        }
        klist_init(&priv->klist_devices, NULL, NULL);
        priv->driver = drv;
        drv->p = priv;
        priv->kobj.kset = bus->p->drivers_kset;
        error = kobject_init_and_add(&priv->kobj, &driver_ktype, NULL,
                                     "%s", drv->name);
        if (error)
                goto out_unregister;

        klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
        if (drv->bus->p->drivers_autoprobe) {
                error = driver_attach(drv);
                if (error)
                        goto out_unregister;
        }
        module_add_driver(drv->owner, drv);

        error = driver_create_file(drv, &driver_attr_uevent);
        if (error) {
                printk(KERN_ERR "%s: uevent attr (%s) failed\n",
                        __func__, drv->name);
        }
        error = driver_add_groups(drv, bus->drv_groups);
        if (error) {
                /* How the hell do we get out of this pickle? Give up */
                printk(KERN_ERR "%s: driver_create_groups(%s) failed\n",
                        __func__, drv->name);
        }

        if (!drv->suppress_bind_attrs) {
                error = add_bind_files(drv);
                if (error) {
                        /* Ditto */
                        printk(KERN_ERR "%s: add_bind_files(%s) failed\n",
                                __func__, drv->name);
                }
        }

        return 0;

out_unregister:
        kobject_put(&priv->kobj);
        kfree(drv->p);
        drv->p = NULL;
out_put_bus:
        bus_put(bus);
        return error;
}

/**
 * bus_remove_driver - delete driver from bus's knowledge.
 * @drv: driver.
 *
 * Detach the driver from the devices it controls, and remove
 * it from its bus's list of drivers. Finally, we drop the reference
 * to the bus we took in bus_add_driver().
 */
void bus_remove_driver(struct device_driver *drv)
{
        if (!drv->bus)
                return;

        if (!drv->suppress_bind_attrs)
                remove_bind_files(drv);
        driver_remove_groups(drv, drv->bus->drv_groups);
        driver_remove_file(drv, &driver_attr_uevent);
        klist_remove(&drv->p->knode_bus);
        pr_debug("bus: '%s': remove driver %s\n", drv->bus->name, drv->name);
        driver_detach(drv);
        module_remove_driver(drv);
        kobject_put(&drv->p->kobj);
        bus_put(drv->bus);
}

/* Helper for bus_rescan_devices's iter */
static int __must_check bus_rescan_devices_helper(struct device *dev,
                                                  void *data)
{
        int ret = 0;

        if (!dev->driver) {
                if (dev->parent)        /* Needed for USB */
                        device_lock(dev->parent);
                ret = device_attach(dev);
                if (dev->parent)
                        device_unlock(dev->parent);
        }
        return ret < 0 ? ret : 0;
}

/**
 * bus_rescan_devices - rescan devices on the bus for possible drivers
 * @bus: the bus to scan.
 *
 * This function will look for devices on the bus with no driver
 * attached and rescan it against existing drivers to see if it matches
 * any by calling device_attach() for the unbound devices.
 */
int bus_rescan_devices(struct bus_type *bus)
{
        return bus_for_each_dev(bus, NULL, NULL, bus_rescan_devices_helper);
}
EXPORT_SYMBOL_GPL(bus_rescan_devices);

/**
 * device_reprobe - remove driver for a device and probe for a new driver
 * @dev: the device to reprobe
 *
 * This function detaches the attached driver (if any) for the given
 * device and restarts the driver probing process.  It is intended
 * to use if probing criteria changed during a devices lifetime and
 * driver attachment should change accordingly.
 */
int device_reprobe(struct device *dev)
{
        if (dev->driver) {
                if (dev->parent)        /* Needed for USB */
                        device_lock(dev->parent);
                device_release_driver(dev);
                if (dev->parent)
                        device_unlock(dev->parent);
        }
        return bus_rescan_devices_helper(dev, NULL);
}
EXPORT_SYMBOL_GPL(device_reprobe);

/**
 * find_bus - locate bus by name.
 * @name: name of bus.
 *
 * Call kset_find_obj() to iterate over list of buses to
 * find a bus by name. Return bus if found.
 *
 * Note that kset_find_obj increments bus' reference count.
 */
#if 0
struct bus_type *find_bus(char *name)
{
        struct kobject *k = kset_find_obj(bus_kset, name);
        return k ? to_bus(k) : NULL;
}
#endif  /*  0  */

static int bus_add_groups(struct bus_type *bus,
                          const struct attribute_group **groups)
{
        return sysfs_create_groups(&bus->p->subsys.kobj, groups);
}

static void bus_remove_groups(struct bus_type *bus,
                              const struct attribute_group **groups)
{
        sysfs_remove_groups(&bus->p->subsys.kobj, groups);
}

static void klist_devices_get(struct klist_node *n)
{
        struct device_private *dev_prv = to_device_private_bus(n);
        struct device *dev = dev_prv->device;

        get_device(dev);
}

static void klist_devices_put(struct klist_node *n)
{
        struct device_private *dev_prv = to_device_private_bus(n);
        struct device *dev = dev_prv->device;

        put_device(dev);
}

static ssize_t bus_uevent_store(struct bus_type *bus,
                                const char *buf, size_t count)
{
        enum kobject_action action;

        if (kobject_action_type(buf, count, &action) == 0)
                kobject_uevent(&bus->p->subsys.kobj, action);
        return count;
}
static BUS_ATTR(uevent, S_IWUSR, NULL, bus_uevent_store);

/**
 * bus_register - register a driver-core subsystem
 * @bus: bus to register
 *
 * Once we have that, we register the bus with the kobject
 * infrastructure, then register the children subsystems it has:
 * the devices and drivers that belong to the subsystem.
 */
int bus_register(struct bus_type *bus)
{
        int retval;
        struct subsys_private *priv;
        struct lock_class_key *key = &bus->lock_key;

        priv = kzalloc(sizeof(struct subsys_private), GFP_KERNEL);
        if (!priv)
                return -ENOMEM;

        priv->bus = bus;
        bus->p = priv;

        BLOCKING_INIT_NOTIFIER_HEAD(&priv->bus_notifier);

        retval = kobject_set_name(&priv->subsys.kobj, "%s", bus->name);
        if (retval)
                goto out;

        priv->subsys.kobj.kset = bus_kset;
        priv->subsys.kobj.ktype = &bus_ktype;
        priv->drivers_autoprobe = 1;

        retval = kset_register(&priv->subsys);
        if (retval)
                goto out;

        retval = bus_create_file(bus, &bus_attr_uevent);
        if (retval)
                goto bus_uevent_fail;

        priv->devices_kset = kset_create_and_add("devices", NULL,
                                                 &priv->subsys.kobj);
        if (!priv->devices_kset) {
                retval = -ENOMEM;
                goto bus_devices_fail;
        }

        priv->drivers_kset = kset_create_and_add("drivers", NULL,
                                                 &priv->subsys.kobj);
        if (!priv->drivers_kset) {
                retval = -ENOMEM;
                goto bus_drivers_fail;
        }

        INIT_LIST_HEAD(&priv->interfaces);
        __mutex_init(&priv->mutex, "subsys mutex", key);
        klist_init(&priv->klist_devices, klist_devices_get, klist_devices_put);
        klist_init(&priv->klist_drivers, NULL, NULL);

        retval = add_probe_files(bus);
        if (retval)
                goto bus_probe_files_fail;

        retval = bus_add_groups(bus, bus->bus_groups);
        if (retval)
                goto bus_groups_fail;

        pr_debug("bus: '%s': registered\n", bus->name);
        return 0;

bus_groups_fail:
        remove_probe_files(bus);
bus_probe_files_fail:
        kset_unregister(bus->p->drivers_kset);
bus_drivers_fail:
        kset_unregister(bus->p->devices_kset);
bus_devices_fail:
        bus_remove_file(bus, &bus_attr_uevent);
bus_uevent_fail:
        kset_unregister(&bus->p->subsys);
out:
        kfree(bus->p);
        bus->p = NULL;
        return retval;
}
EXPORT_SYMBOL_GPL(bus_register);

/**
 * bus_unregister - remove a bus from the system
 * @bus: bus.
 *
 * Unregister the child subsystems and the bus itself.
 * Finally, we call bus_put() to release the refcount
 */
void bus_unregister(struct bus_type *bus)
{
        pr_debug("bus: '%s': unregistering\n", bus->name);
        if (bus->dev_root)
                device_unregister(bus->dev_root);
        bus_remove_groups(bus, bus->bus_groups);
        remove_probe_files(bus);
        kset_unregister(bus->p->drivers_kset);
        kset_unregister(bus->p->devices_kset);
        bus_remove_file(bus, &bus_attr_uevent);
        kset_unregister(&bus->p->subsys);
        kfree(bus->p);
        bus->p = NULL;
}
EXPORT_SYMBOL_GPL(bus_unregister);

int bus_register_notifier(struct bus_type *bus, struct notifier_block *nb)
{
        return blocking_notifier_chain_register(&bus->p->bus_notifier, nb);
}
EXPORT_SYMBOL_GPL(bus_register_notifier);

int bus_unregister_notifier(struct bus_type *bus, struct notifier_block *nb)
{
        return blocking_notifier_chain_unregister(&bus->p->bus_notifier, nb);
}
EXPORT_SYMBOL_GPL(bus_unregister_notifier);

struct kset *bus_get_kset(struct bus_type *bus)
{
        return &bus->p->subsys;
}
EXPORT_SYMBOL_GPL(bus_get_kset);

struct klist *bus_get_device_klist(struct bus_type *bus)
{
        return &bus->p->klist_devices;
}
EXPORT_SYMBOL_GPL(bus_get_device_klist);

/*
 * Yes, this forcibly breaks the klist abstraction temporarily.  It
 * just wants to sort the klist, not change reference counts and
 * take/drop locks rapidly in the process.  It does all this while
 * holding the lock for the list, so objects can't otherwise be
 * added/removed while we're swizzling.
 */
static void device_insertion_sort_klist(struct device *a, struct list_head *list,
                                        int (*compare)(const struct device *a,
                                                        const struct device *b))
{
        struct list_head *pos;
        struct klist_node *n;
        struct device_private *dev_prv;
        struct device *b;

        list_for_each(pos, list) {
                n = container_of(pos, struct klist_node, n_node);
                dev_prv = to_device_private_bus(n);
                b = dev_prv->device;
                if (compare(a, b) <= 0) {
                        list_move_tail(&a->p->knode_bus.n_node,
                                       &b->p->knode_bus.n_node);
                        return;
                }
        }
        list_move_tail(&a->p->knode_bus.n_node, list);
}

void bus_sort_breadthfirst(struct bus_type *bus,
                           int (*compare)(const struct device *a,
                                          const struct device *b))
{
        LIST_HEAD(sorted_devices);
        struct list_head *pos, *tmp;
        struct klist_node *n;
        struct device_private *dev_prv;
        struct device *dev;
        struct klist *device_klist;

        device_klist = bus_get_device_klist(bus);

        spin_lock(&device_klist->k_lock);
        list_for_each_safe(pos, tmp, &device_klist->k_list) {
                n = container_of(pos, struct klist_node, n_node);
                dev_prv = to_device_private_bus(n);
                dev = dev_prv->device;
                device_insertion_sort_klist(dev, &sorted_devices, compare);
        }
        list_splice(&sorted_devices, &device_klist->k_list);
        spin_unlock(&device_klist->k_lock);
}
EXPORT_SYMBOL_GPL(bus_sort_breadthfirst);

/**
 * subsys_dev_iter_init - initialize subsys device iterator
 * @iter: subsys iterator to initialize
 * @subsys: the subsys 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 subsys iterator @iter such that it iterates over devices
 * of @subsys.  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 subsys_dev_iter_init(struct subsys_dev_iter *iter, struct bus_type *subsys,
                          struct device *start, const struct device_type *type)
{
        struct klist_node *start_knode = NULL;

        if (start)
                start_knode = &start->p->knode_bus;
        klist_iter_init_node(&subsys->p->klist_devices, &iter->ki, start_knode);
        iter->type = type;
}
EXPORT_SYMBOL_GPL(subsys_dev_iter_init);

/**
 * subsys_dev_iter_next - iterate to the next device
 * @iter: subsys 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 subsys code.
 */
struct device *subsys_dev_iter_next(struct subsys_dev_iter *iter)
{
        struct klist_node *knode;
        struct device *dev;

        for (;;) {
                knode = klist_next(&iter->ki);
                if (!knode)
                        return NULL;
                dev = container_of(knode, struct device_private, knode_bus)->device;
                if (!iter->type || iter->type == dev->type)
                        return dev;
        }
}
EXPORT_SYMBOL_GPL(subsys_dev_iter_next);

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

int subsys_interface_register(struct subsys_interface *sif)
{
        struct bus_type *subsys;
        struct subsys_dev_iter iter;
        struct device *dev;

        if (!sif || !sif->subsys)
                return -ENODEV;

        subsys = bus_get(sif->subsys);
        if (!subsys)
                return -EINVAL;

        mutex_lock(&subsys->p->mutex);
        list_add_tail(&sif->node, &subsys->p->interfaces);
        if (sif->add_dev) {
                subsys_dev_iter_init(&iter, subsys, NULL, NULL);
                while ((dev = subsys_dev_iter_next(&iter)))
                        sif->add_dev(dev, sif);
                subsys_dev_iter_exit(&iter);
        }
        mutex_unlock(&subsys->p->mutex);

        return 0;
}
EXPORT_SYMBOL_GPL(subsys_interface_register);

void subsys_interface_unregister(struct subsys_interface *sif)
{
        struct bus_type *subsys;
        struct subsys_dev_iter iter;
        struct device *dev;

        if (!sif || !sif->subsys)
                return;

        subsys = sif->subsys;

        mutex_lock(&subsys->p->mutex);
        list_del_init(&sif->node);
        if (sif->remove_dev) {
                subsys_dev_iter_init(&iter, subsys, NULL, NULL);
                while ((dev = subsys_dev_iter_next(&iter)))
                        sif->remove_dev(dev, sif);
                subsys_dev_iter_exit(&iter);
        }
        mutex_unlock(&subsys->p->mutex);

        bus_put(subsys);
}
EXPORT_SYMBOL_GPL(subsys_interface_unregister);

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

static int subsys_register(struct bus_type *subsys,
                           const struct attribute_group **groups,
                           struct kobject *parent_of_root)
{
        struct device *dev;
        int err;

        err = bus_register(subsys);
        if (err < 0)
                return err;

        dev = kzalloc(sizeof(struct device), GFP_KERNEL);
        if (!dev) {
                err = -ENOMEM;
                goto err_dev;
        }

        err = dev_set_name(dev, "%s", subsys->name);
        if (err < 0)
                goto err_name;

        dev->kobj.parent = parent_of_root;
        dev->groups = groups;
        dev->release = system_root_device_release;

        err = device_register(dev);
        if (err < 0)
                goto err_dev_reg;

        subsys->dev_root = dev;
        return 0;

err_dev_reg:
        put_device(dev);
        dev = NULL;
err_name:
        kfree(dev);
err_dev:
        bus_unregister(subsys);
        return err;
}

/**
 * subsys_system_register - register a subsystem at /sys/devices/system/
 * @subsys: system subsystem
 * @groups: default attributes for the root device
 *
 * All 'system' subsystems have a /sys/devices/system/<name> root device
 * with the name of the subsystem. The root device can carry subsystem-
 * wide attributes. All registered devices are below this single root
 * device and are named after the subsystem with a simple enumeration
 * number appended. The registered devices are not explicitly named;
 * only 'id' in the device needs to be set.
 *
 * Do not use this interface for anything new, it exists for compatibility
 * with bad ideas only. New subsystems should use plain subsystems; and
 * add the subsystem-wide attributes should be added to the subsystem
 * directory itself and not some create fake root-device placed in
 * /sys/devices/system/<name>.
 */
int subsys_system_register(struct bus_type *subsys,
                           const struct attribute_group **groups)
{
        return subsys_register(subsys, groups, &system_kset->kobj);
}
EXPORT_SYMBOL_GPL(subsys_system_register);

/**
 * subsys_virtual_register - register a subsystem at /sys/devices/virtual/
 * @subsys: virtual subsystem
 * @groups: default attributes for the root device
 *
 * All 'virtual' subsystems have a /sys/devices/system/<name> root device
 * with the name of the subystem.  The root device can carry subsystem-wide
 * attributes.  All registered devices are below this single root device.
 * There's no restriction on device naming.  This is for kernel software
 * constructs which need sysfs interface.
 */
int subsys_virtual_register(struct bus_type *subsys,
                            const struct attribute_group **groups)
{
        struct kobject *virtual_dir;

        virtual_dir = virtual_device_parent(NULL);
        if (!virtual_dir)
                return -ENOMEM;

        return subsys_register(subsys, groups, virtual_dir);
}
EXPORT_SYMBOL_GPL(subsys_virtual_register);

int __init buses_init(void)
{
        bus_kset = kset_create_and_add("bus", &bus_uevent_ops, NULL);
        if (!bus_kset)
                return -ENOMEM;

        system_kset = kset_create_and_add("system", NULL, &devices_kset->kobj);
        if (!system_kset)
                return -ENOMEM;

        return 0;
}