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[tomato.git] / release / src-rt-6.x / linux / linux-2.6 / drivers / base / 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 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 ktype_driver = {
        .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 (get_bus(bus)) {
                error = sysfs_create_file(&bus->subsys.kobj, &attr->attr);
                put_bus(bus);
        } else
                error = -EINVAL;
        return error;
}

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

static struct kobj_type ktype_bus = {
        .sysfs_ops      = &bus_sysfs_ops,

};

static decl_subsys(bus, &ktype_bus, NULL);


#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 = get_bus(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);
        put_bus(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 = get_bus(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);
        put_bus(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 = get_bus(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:
        put_bus(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);
                put_bus(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 int add_probe_files(struct bus_type *bus)
{
        int retval;

        bus->drivers_probe_attr.attr.name = "drivers_probe";
        bus->drivers_probe_attr.attr.mode = S_IWUSR;
        bus->drivers_probe_attr.attr.owner = bus->owner;
        bus->drivers_probe_attr.store = store_drivers_probe;
        retval = bus_create_file(bus, &bus->drivers_probe_attr);
        if (retval)
                goto out;

        bus->drivers_autoprobe_attr.attr.name = "drivers_autoprobe";
        bus->drivers_autoprobe_attr.attr.mode = S_IWUSR | S_IRUGO;
        bus->drivers_autoprobe_attr.attr.owner = bus->owner;
        bus->drivers_autoprobe_attr.show = show_drivers_autoprobe;
        bus->drivers_autoprobe_attr.store = store_drivers_autoprobe;
        retval = bus_create_file(bus, &bus->drivers_autoprobe_attr);
        if (retval)
                bus_remove_file(bus, &bus->drivers_probe_attr);
out:
        return retval;
}

static void remove_probe_files(struct bus_type *bus)
{
        bus_remove_file(bus, &bus->drivers_autoprobe_attr);
        bus_remove_file(bus, &bus->drivers_probe_attr);
}
#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

/**
 *      bus_add_driver - Add a driver to the bus.
 *      @drv:   driver.
 *
 */
int bus_add_driver(struct device_driver *drv)
{
        struct bus_type * bus = get_bus(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;
        if ((error = kobject_register(&drv->kobj)))
                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_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:
        put_bus(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);
        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);
        put_bus(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);

struct bus_type *get_bus(struct bus_type *bus)
{
        return bus ? container_of(subsys_get(&bus->subsys),
                                struct bus_type, subsys) : NULL;
}

void put_bus(struct bus_type * bus)
{
        subsys_put(&bus->subsys);
}


/**
 *      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++) {
                        if ((error = bus_create_file(bus,&bus->bus_attrs[i])))
                                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);
}

/**
 *      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;

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

        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 = &ktype_driver;
        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:
        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 put_bus() 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);
        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);