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bus.c

/*
 * bus.c - bus driver management
 *
 * Copyright (c) 2002-3 Patrick Mochel
 * Copyright (c) 2002-3 Open Source Development Labs
 *
 * This file is released under the GPLv2
 *
 */

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

#define to_bus_attr(_attr) container_of(_attr, struct bus_attribute, attr)
#define to_bus(obj) container_of(obj, struct bus_type, subsys.kobj)

/*
 * sysfs bindings for drivers
 */

#define to_drv_attr(_attr) container_of(_attr, struct driver_attribute, attr)
#define to_driver(obj) container_of(obj, struct device_driver, kobj)


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

static struct bus_type *bus_get(struct bus_type *bus)
{
      return bus ? container_of(kset_get(&bus->subsys),
                        struct bus_type, subsys) : NULL;
}

static void bus_put(struct bus_type *bus)
{
      kset_put(&bus->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 device_driver * drv = to_driver(kobj);
      ssize_t ret = -EIO;

      if (drv_attr->show)
            ret = drv_attr->show(drv, 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 device_driver * drv = to_driver(kobj);
      ssize_t ret = -EIO;

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

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


static void driver_release(struct kobject * kobj)
{
      /*
       * Yes this is an empty release function, it is this way because struct
       * device is always a static object, not a dynamic one.  Yes, this is
       * not nice and bad, but remember, drivers are code, reference counted
       * by the module count, not a device, which is really data.  And yes,
       * in the future I do want to have all drivers be created dynamically,
       * and am working toward that goal, but it will take a bit longer...
       *
       * But do not let this example give _anyone_ the idea that they can
       * create a release function without any code in it at all, to do that
       * is almost always wrong.  If you have any questions about this,
       * please send an email to <greg@kroah.com>
       */
}

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 bus_type * bus = to_bus(kobj);
      ssize_t ret = 0;

      if (bus_attr->show)
            ret = bus_attr->show(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 bus_type * bus = to_bus(kobj);
      ssize_t ret = 0;

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

static 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->subsys.kobj, &attr->attr);
            bus_put(bus);
      } else
            error = -EINVAL;
      return error;
}

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

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

static decl_subsys(bus, &bus_ktype, &bus_uevent_ops);


#ifdef CONFIG_HOTPLUG
/* Manually detach a device from its associated driver. */
static int driver_helper(struct device *dev, void *data)
{
      const char *name = data;

      if (strcmp(name, dev->bus_id) == 0)
            return 1;
      return 0;
}

static ssize_t driver_unbind(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(bus, NULL, (void *)buf, driver_helper);
      if (dev && dev->driver == drv) {
            if (dev->parent)  /* Needed for USB */
                  down(&dev->parent->sem);
            device_release_driver(dev);
            if (dev->parent)
                  up(&dev->parent->sem);
            err = count;
      }
      put_device(dev);
      bus_put(bus);
      return err;
}
static DRIVER_ATTR(unbind, S_IWUSR, NULL, driver_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 driver_bind(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(bus, NULL, (void *)buf, driver_helper);
      if (dev && dev->driver == NULL) {
            if (dev->parent)  /* Needed for USB */
                  down(&dev->parent->sem);
            down(&dev->sem);
            err = driver_probe_device(drv, dev);
            up(&dev->sem);
            if (dev->parent)
                  up(&dev->parent->sem);

            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(bind, S_IWUSR, NULL, driver_bind);

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

static ssize_t store_drivers_autoprobe(struct bus_type *bus,
                               const char *buf, size_t count)
{
      if (buf[0] == '0')
            bus->drivers_autoprobe = 0;
      else
            bus->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(bus, NULL, (void *)buf, driver_helper);
      if (!dev)
            return -ENODEV;
      if (bus_rescan_devices_helper(dev, NULL) != 0)
            return -EINVAL;
      return count;
}
#endif

static struct device * next_device(struct klist_iter * i)
{
      struct klist_node * n = klist_next(i);
      return n ? container_of(n, struct device, knode_bus) : NULL;
}

/**
 *    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, 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)
            return -EINVAL;

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

/**
 * 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 *, void *))
{
      struct klist_iter i;
      struct device *dev;

      if (!bus)
            return NULL;

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


static struct device_driver * next_driver(struct klist_iter * i)
{
      struct klist_node * n = klist_next(i);
      return n ? container_of(n, struct device_driver, knode_bus) : 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->klist_drivers, &i,
                       start ? &start->knode_bus : NULL);
      while ((drv = next_driver(&i)) && !error)
            error = fn(drv, data);
      klist_iter_exit(&i);
      return error;
}

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; attr_name(bus->dev_attrs[i]); 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; attr_name(bus->dev_attrs[i]); i++)
                  device_remove_file(dev,&bus->dev_attrs[i]);
      }
}

#ifdef CONFIG_SYSFS_DEPRECATED
static int make_deprecated_bus_links(struct device *dev)
{
      return sysfs_create_link(&dev->kobj,
                         &dev->bus->subsys.kobj, "bus");
}

static void remove_deprecated_bus_links(struct device *dev)
{
      sysfs_remove_link(&dev->kobj, "bus");
}
#else
static inline int make_deprecated_bus_links(struct device *dev) { return 0; }
static inline void remove_deprecated_bus_links(struct device *dev) { }
#endif

/**
 *    bus_add_device - add device to bus
 *    @dev: device being added
 *
 *    - Add the device to its bus's list of devices.
 *    - Create link to device's bus.
 */
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->bus_id);
            error = device_add_attrs(bus, dev);
            if (error)
                  goto out_put;
            error = sysfs_create_link(&bus->devices.kobj,
                                    &dev->kobj, dev->bus_id);
            if (error)
                  goto out_id;
            error = sysfs_create_link(&dev->kobj,
                        &dev->bus->subsys.kobj, "subsystem");
            if (error)
                  goto out_subsys;
            error = make_deprecated_bus_links(dev);
            if (error)
                  goto out_deprecated;
      }
      return 0;

out_deprecated:
      sysfs_remove_link(&dev->kobj, "subsystem");
out_subsys:
      sysfs_remove_link(&bus->devices.kobj, dev->bus_id);
out_id:
      device_remove_attrs(bus, dev);
out_put:
      bus_put(dev->bus);
      return error;
}

/**
 *    bus_attach_device - add device to bus
 *    @dev: device tried to attach to a driver
 *
 *    - Add device to bus's list of devices.
 *    - Try to attach to driver.
 */
void bus_attach_device(struct device * dev)
{
      struct bus_type *bus = dev->bus;
      int ret = 0;

      if (bus) {
            dev->is_registered = 1;
            if (bus->drivers_autoprobe)
                  ret = device_attach(dev);
            WARN_ON(ret < 0);
            if (ret >= 0)
                  klist_add_tail(&dev->knode_bus, &bus->klist_devices);
            else
                  dev->is_registered = 0;
      }
}

/**
 *    bus_remove_device - remove device from bus
 *    @dev: device to be removed
 *
 *    - Remove symlink from bus's 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)
{
      if (dev->bus) {
            sysfs_remove_link(&dev->kobj, "subsystem");
            remove_deprecated_bus_links(dev);
            sysfs_remove_link(&dev->bus->devices.kobj, dev->bus_id);
            device_remove_attrs(dev->bus, dev);
            if (dev->is_registered) {
                  dev->is_registered = 0;
                  klist_del(&dev->knode_bus);
            }
            pr_debug("bus %s: remove device %s\n", dev->bus->name, dev->bus_id);
            device_release_driver(dev);
            bus_put(dev->bus);
      }
}

static int driver_add_attrs(struct bus_type * bus, struct device_driver * drv)
{
      int error = 0;
      int i;

      if (bus->drv_attrs) {
            for (i = 0; attr_name(bus->drv_attrs[i]); i++) {
                  error = driver_create_file(drv, &bus->drv_attrs[i]);
                  if (error)
                        goto Err;
            }
      }
 Done:
      return error;
 Err:
      while (--i >= 0)
            driver_remove_file(drv, &bus->drv_attrs[i]);
      goto Done;
}


static void driver_remove_attrs(struct bus_type * bus, struct device_driver * drv)
{
      int i;

      if (bus->drv_attrs) {
            for (i = 0; attr_name(bus->drv_attrs[i]); i++)
                  driver_remove_file(drv, &bus->drv_attrs[i]);
      }
}

#ifdef CONFIG_HOTPLUG
/*
 * Thanks to drivers making their tables __devinit, we can't allow manual
 * bind and unbind from userspace unless CONFIG_HOTPLUG is enabled.
 */
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);
}
#else
static inline int add_bind_files(struct device_driver *drv) { return 0; }
static inline void remove_bind_files(struct device_driver *drv) {}
static inline int add_probe_files(struct bus_type *bus) { return 0; }
static inline void remove_probe_files(struct bus_type *bus) {}
#endif

static ssize_t driver_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->kobj, action);
      return count;
}
static DRIVER_ATTR(uevent, S_IWUSR, NULL, driver_uevent_store);

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

      if (!bus)
            return -EINVAL;

      pr_debug("bus %s: add driver %s\n", bus->name, drv->name);
      error = kobject_set_name(&drv->kobj, "%s", drv->name);
      if (error)
            goto out_put_bus;
      drv->kobj.kset = &bus->drivers;
      error = kobject_register(&drv->kobj);
      if (error)
            goto out_put_bus;

      if (drv->bus->drivers_autoprobe) {
            error = driver_attach(drv);
            if (error)
                  goto out_unregister;
      }
      klist_add_tail(&drv->knode_bus, &bus->klist_drivers);
      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",
                  __FUNCTION__, drv->name);
      }
      error = driver_add_attrs(bus, drv);
      if (error) {
            /* How the hell do we get out of this pickle? Give up */
            printk(KERN_ERR "%s: driver_add_attrs(%s) failed\n",
                  __FUNCTION__, drv->name);
      }
      error = add_bind_files(drv);
      if (error) {
            /* Ditto */
            printk(KERN_ERR "%s: add_bind_files(%s) failed\n",
                  __FUNCTION__, drv->name);
      }

      return error;
out_unregister:
      kobject_unregister(&drv->kobj);
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;

      remove_bind_files(drv);
      driver_remove_attrs(drv->bus, drv);
      driver_remove_file(drv, &driver_attr_uevent);
      klist_remove(&drv->knode_bus);
      pr_debug("bus %s: remove driver %s\n", drv->bus->name, drv->name);
      driver_detach(drv);
      module_remove_driver(drv);
      kobject_unregister(&drv->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 */
                  down(&dev->parent->sem);
            ret = device_attach(dev);
            if (dev->parent)
                  up(&dev->parent->sem);
      }
      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);
}

/**
 * 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 */
                  down(&dev->parent->sem);
            device_release_driver(dev);
            if (dev->parent)
                  up(&dev->parent->sem);
      }
      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_subsys.kset, name);
      return k ? to_bus(k) : NULL;
}
#endif  /*  0  */


/**
 *    bus_add_attrs - Add default attributes for this bus.
 *    @bus: Bus that has just been registered.
 */

static int bus_add_attrs(struct bus_type * bus)
{
      int error = 0;
      int i;

      if (bus->bus_attrs) {
            for (i = 0; attr_name(bus->bus_attrs[i]); i++) {
                  error = bus_create_file(bus,&bus->bus_attrs[i]);
                  if (error)
                        goto Err;
            }
      }
 Done:
      return error;
 Err:
      while (--i >= 0)
            bus_remove_file(bus,&bus->bus_attrs[i]);
      goto Done;
}

static void bus_remove_attrs(struct bus_type * bus)
{
      int i;

      if (bus->bus_attrs) {
            for (i = 0; attr_name(bus->bus_attrs[i]); i++)
                  bus_remove_file(bus,&bus->bus_attrs[i]);
      }
}

static void klist_devices_get(struct klist_node *n)
{
      struct device *dev = container_of(n, struct device, knode_bus);

      get_device(dev);
}

static void klist_devices_put(struct klist_node *n)
{
      struct device *dev = container_of(n, struct device, knode_bus);

      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->subsys.kobj, action);
      return count;
}
static BUS_ATTR(uevent, S_IWUSR, NULL, bus_uevent_store);

/**
 *    bus_register - register a bus with the system.
 *    @bus: bus.
 *
 *    Once we have that, we registered the bus with the kobject
 *    infrastructure, then register the children subsystems it has:
 *    the devices and drivers that belong to the bus.
 */
int bus_register(struct bus_type * bus)
{
      int retval;

      BLOCKING_INIT_NOTIFIER_HEAD(&bus->bus_notifier);

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

      bus->subsys.kobj.kset = &bus_subsys;

      retval = subsystem_register(&bus->subsys);
      if (retval)
            goto out;

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

      kobject_set_name(&bus->devices.kobj, "devices");
      bus->devices.kobj.parent = &bus->subsys.kobj;
      retval = kset_register(&bus->devices);
      if (retval)
            goto bus_devices_fail;

      kobject_set_name(&bus->drivers.kobj, "drivers");
      bus->drivers.kobj.parent = &bus->subsys.kobj;
      bus->drivers.ktype = &driver_ktype;
      retval = kset_register(&bus->drivers);
      if (retval)
            goto bus_drivers_fail;

      klist_init(&bus->klist_devices, klist_devices_get, klist_devices_put);
      klist_init(&bus->klist_drivers, NULL, NULL);

      bus->drivers_autoprobe = 1;
      retval = add_probe_files(bus);
      if (retval)
            goto bus_probe_files_fail;

      retval = bus_add_attrs(bus);
      if (retval)
            goto bus_attrs_fail;

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

bus_attrs_fail:
      remove_probe_files(bus);
bus_probe_files_fail:
      kset_unregister(&bus->drivers);
bus_drivers_fail:
      kset_unregister(&bus->devices);
bus_devices_fail:
      bus_remove_file(bus, &bus_attr_uevent);
bus_uevent_fail:
      subsystem_unregister(&bus->subsys);
out:
      return retval;
}

/**
 *    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);
      bus_remove_attrs(bus);
      remove_probe_files(bus);
      kset_unregister(&bus->drivers);
      kset_unregister(&bus->devices);
      bus_remove_file(bus, &bus_attr_uevent);
      subsystem_unregister(&bus->subsys);
}

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

int __init buses_init(void)
{
      return subsystem_register(&bus_subsys);
}


EXPORT_SYMBOL_GPL(bus_for_each_dev);
EXPORT_SYMBOL_GPL(bus_find_device);
EXPORT_SYMBOL_GPL(bus_for_each_drv);

EXPORT_SYMBOL_GPL(bus_register);
EXPORT_SYMBOL_GPL(bus_unregister);
EXPORT_SYMBOL_GPL(bus_rescan_devices);

EXPORT_SYMBOL_GPL(bus_create_file);
EXPORT_SYMBOL_GPL(bus_remove_file);

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