Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Don't destroy user event fields when removal fails

   User event fields are destroyed before the event is removed from
   visibility. But that can fail leaving the still visible event with no
   fields. Move the destroying of the fields to after the event is
   successfully removed from visibility.

 - Initialize function graph state is fork before calling
   copy_exec_state()

   For non-CLONE_VM forks, copy_exec_state() allocates a new
   task_exec_state. If that allocation fails, ftrace_graph_exit_task()
   will free the tasks ret_stack pointer. Since that pointer is still
   using the parent's ret_stack, it mistakenly frees the parent's
   pointer too.

   Call ftrace_graph_init() on the task first which will NULL out the
   new tasks's ret_stack and if the copy fails, it will not free
   anything.

 - Remove FGRAPH_MAX_INDEX

   The macro FGRAPH_MAX_INDEX was added but never used. Remove it.

 - Save ent_size in function graph printing of nested functions

   The function graph tracer needs to look at the next event to see if
   the next event is the return of the current function entry. If it is,
   it prints a single line:

	ktime_get();

   Otherwise it prints it like a nested function:

	tick_nohz_irq_exit() {
	    ktime_get();
	    kcpustat_irq_exit();
	}

   In order to look at the next event, it must save the current event so
   that it has the information to print from it. It saves the event in
   the iterator descriptor called "ent". What it doesn't save is the
   ent_size of the event which is now used to know if the function graph
   arguments are to be printed. The peek doesn't save the size so the
   size used happens to be that of the size of the last event that was
   seen.

   Save the entry event size in the iterator descriptor so that the
   correct size is used.

 - Fix several errors with freeing data in the histogram code

   The histogram code had a lot of leaked or or incorrect accounting
   when failures happen. Correct them.

 - Fix histogram regression of .percent and .graph modifiers

   Up until 6.3 histogram values could have "percent" or "graph"
   modifiers that changed how they were printed. But a change that added
   restricting histograms values from being strings, stack traces and
   other modifiers inadvertently prevented them from using the percent
   and graph modifiers, which were legal use cases for values.

   Put back the percent and graph modifiers.

 - Fix various typos in the comments

 - Set the trace_clock before initializing a histogram with clock
   argument

   The histogram API allows the user to specific which trace clock to
   use via a "clock=" string. The histogram is set up first before the
   clock is checked. If the passed in clock is not valid, it exits
   without fully fixing up the histogram leaving it on the list and a
   use-after-free can trigger.

   Update the clock argument first and if it fails then exit gracefully
   before the histogram trigger is placed on any lists.

 - Restore :mod: trailer after parsing in ftrace_set_clr_event

   The function ftrace_set_clr_event() modifies the parse string and
   needs to put it back to what was passed in. It searches for ":mod:"
   via a strsep() but fails to put back the first ':' in the string.

   Add back the ':' in the passed in string.

 - Take trace_array reference when opening a tracer options file

   The options files are dynamically created and some tracers add their
   own options. When a tracer adds their own list of options, the
   trace_array holding them has an array to hold the list of options for
   each tracer. This array increases in size via a krealloc(), and the
   new entry gets a newly allocated array to hold the options of the new
   tracer being added.

   The element in each entry of the tracer's option array holds a
   pointer back to the trace_array, a pointer to the tracer it is
   associated to, a pointer to the flags of the option.

   The issue is that these arrays are freed when the trace_array is
   freed when its instance it represents is removed from the instances
   directory. There's a race that an open of one of these options files
   can happen when the instance is being removed.

   Add a new helper function to be called by the open function of the
   options file to iterate all existing trace_arrays under a lock and
   find the one that has the given option element in one of it's tracer
   arrays. If found, then update the associated trace_array's reference
   counter to keep it from being freed. If not found, have the open call
   return -ENODEV.

 - Disable interrupts when acquiring the lock in rb_wake_up_waiters()

   The function rb_wake_up_waiters() assumes it will be called in
   interrupt context and does not disable irqs when taking
   cpu_buffer->reader_lock, which can be called in hard interrupt
   context. The issue is in PREEMPT_RT, this function is called in
   thread context leaving this lock open to a deadlock.

   Take the lock with interrupts disabled.

 - Use rcu_assign_pointer() for tmp_ops filter hash

   The tmp_ops used in update_ftrace_direct_mod() assigns its
   filter_hash field directly, but that field is annotated as __rcu and
   sparse complains. Assign it with rcu_assign_pointer()

 - Fix use-after-free in enable_trigger_private_data_free()

   The trace_event_call is accessed through the event_trigger_data's
   trace_event_file pointer to put the trace_event_call on freeing. The
   issue is that the trace_event_file data may have been freed already
   causing a use-after-free. Add a field to the event_trigger_data that
   points directly to the trace_event_call so that it can decrement its
   reference directly without needing to go through the
   trace_event_file.

 - Fix accounting of buffer data remote headers

   trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
   the number of pages is needed for the asked for size as it doesn't
   take into account the meta data on each page. Add a helper function
   to do the calculation properly and use that in these functions.

 - Catch nr_page_va overflow in ring_buffer_desc sizing

   The number of pages per remote ring buffer is capped by
   ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
   overflow that field would silently allocate a descriptor smaller than
   what was asked for.

 - Do not resize the subbuf order if any per_cpu buffer is disabled

   The mmapping of ring buffers disables resizing the subbuffers, but it
   is done per-cpu whereas the subbuf size change is done for all the
   per_cpu buffers under the buffer->mutex. It could change the size of
   some while the mapping is happening on others. Have the resize of the
   subbuf order check all the per_cpu buffers under the lock to see if
   any of them is disabled before starting and causing an inconsistency
   between buffers that are being mapped.

* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
  ring-buffer: Check resize_disabled before publishing the new subbuf order
  tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
  tracing/remotes: Account for ring buffer page header in size calculation
  tracing: Don't dereference trace_event_file in deferred trigger free
  ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
  ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
  tracing: Take trace_array reference when opening a tracer options file
  tracing: Fix ring_buffer_read_page_size() kernel-doc
  tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
  tracing: Fix memory corruption from a "STACKTRACE" histogram key
  tracing: Fix memory corruption from the histogram stacktrace modifier
  tracing: Undo the registration when enabling the histogram trigger fails
  tracing: Take the reference before publishing the named histogram trigger
  tracing: Set the trace clock before registering the histogram trigger
  tracing: Fix typo "preceeded" in comment
  tracing: Fix typo "availabe" in comment
  tracing: Let histogram values keep the percent and graph modifiers
  tracing: Keep the entry count when the histogram stats allocation fails
  tracing: Free histogram the field rejected for a bad modifier
  tracing: Free histogram the var ref when its initialization fails
  ...

1 files changed, 1489 insertions, 0 deletions

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
new file mode 100644
index 000000000..d17bd9149
--- /dev/null
+++ b/drivers/base/bus.c
@@ -0,0 +1,1489 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * 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.
+ * Copyright (c) 2023 Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+ */
+
+#include <linux/async.h>
+#include <linux/device/bus.h>
+#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;
+
+/* /sys/bus */
+static struct kset *bus_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)
+
+#define DRIVER_ATTR_IGNORE_LOCKDEP(_name, _mode, _show, _store) \
+	struct driver_attribute driver_attr_##_name =		\
+		__ATTR_IGNORE_LOCKDEP(_name, _mode, _show, _store)
+
+static int __must_check bus_rescan_devices_helper(struct device *dev,
+						void *data);
+
+/**
+ * bus_to_subsys - Turn a struct bus_type into a struct subsys_private
+ *
+ * @bus: pointer to the struct bus_type to look up
+ *
+ * The driver core internals needs to work on the subsys_private structure, not
+ * the external struct bus_type pointer.  This function walks the list of
+ * registered busses in the system and finds the matching one and returns the
+ * internal struct subsys_private that relates to that bus.
+ *
+ * Note, the reference count of the return value is INCREMENTED if it is not
+ * NULL.  A call to subsys_put() must be done when finished with the pointer in
+ * order for it to be properly freed.
+ */
+struct subsys_private *bus_to_subsys(const struct bus_type *bus)
+{
+	struct subsys_private *sp = NULL;
+	struct kobject *kobj;
+
+	if (!bus || !bus_kset)
+		return NULL;
+
+	spin_lock(&bus_kset->list_lock);
+
+	if (list_empty(&bus_kset->list))
+		goto done;
+
+	list_for_each_entry(kobj, &bus_kset->list, entry) {
+		struct kset *kset = container_of(kobj, struct kset, kobj);
+
+		sp = container_of_const(kset, struct subsys_private, subsys);
+		if (sp->bus == bus)
+			goto done;
+	}
+	sp = NULL;
+done:
+	sp = subsys_get(sp);
+	spin_unlock(&bus_kset->list_lock);
+	return sp;
+}
+
+static const struct bus_type *bus_get(const struct bus_type *bus)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+
+	if (sp)
+		return bus;
+	return NULL;
+}
+
+static void bus_put(const struct bus_type *bus)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+
+	/* two puts are required as the call to bus_to_subsys incremented it again */
+	subsys_put(sp);
+	subsys_put(sp);
+}
+
+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 const 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);
+	/* return -EIO for reading a bus attribute without show() */
+	ssize_t ret = -EIO;
+
+	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);
+	/* return -EIO for writing a bus attribute without store() */
+	ssize_t ret = -EIO;
+
+	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(const struct bus_type *bus, struct bus_attribute *attr)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+	int error;
+
+	if (!sp)
+		return -EINVAL;
+
+	error = sysfs_create_file(&sp->subsys.kobj, &attr->attr);
+
+	subsys_put(sp);
+	return error;
+}
+EXPORT_SYMBOL_GPL(bus_create_file);
+
+void bus_remove_file(const struct bus_type *bus, struct bus_attribute *attr)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+
+	if (!sp)
+		return;
+
+	sysfs_remove_file(&sp->subsys.kobj, &attr->attr);
+	subsys_put(sp);
+}
+EXPORT_SYMBOL_GPL(bus_remove_file);
+
+static void bus_release(struct kobject *kobj)
+{
+	struct subsys_private *priv = to_subsys_private(kobj);
+
+	lockdep_unregister_key(&priv->lock_key);
+	kfree(priv);
+}
+
+static const struct kobj_type bus_ktype = {
+	.sysfs_ops	= &bus_sysfs_ops,
+	.release	= bus_release,
+};
+
+static int bus_uevent_filter(const struct kobject *kobj)
+{
+	const 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,
+};
+
+/* Manually detach a device from its associated driver. */
+static ssize_t unbind_store(struct device_driver *drv, const char *buf,
+			    size_t count)
+{
+	const 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) {
+		device_driver_detach(dev);
+		err = count;
+	}
+	put_device(dev);
+	bus_put(bus);
+	return err;
+}
+static DRIVER_ATTR_IGNORE_LOCKDEP(unbind, 0200, NULL, unbind_store);
+
+/*
+ * 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)
+{
+	const 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 && driver_match_device(drv, dev)) {
+		err = device_driver_attach(drv, dev);
+		if (!err) {
+			/* success */
+			err = count;
+		}
+	}
+	put_device(dev);
+	bus_put(bus);
+	return err;
+}
+static DRIVER_ATTR_IGNORE_LOCKDEP(bind, 0200, NULL, bind_store);
+
+static ssize_t drivers_autoprobe_show(const struct bus_type *bus, char *buf)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+	int ret;
+
+	if (!sp)
+		return -EINVAL;
+
+	ret = sysfs_emit(buf, "%d\n", sp->drivers_autoprobe);
+	subsys_put(sp);
+	return ret;
+}
+
+static ssize_t drivers_autoprobe_store(const struct bus_type *bus,
+				       const char *buf, size_t count)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+
+	if (!sp)
+		return -EINVAL;
+
+	if (buf[0] == '0')
+		sp->drivers_autoprobe = 0;
+	else
+		sp->drivers_autoprobe = 1;
+
+	subsys_put(sp);
+	return count;
+}
+
+static ssize_t drivers_probe_store(const struct bus_type *bus,
+				   const char *buf, size_t count)
+{
+	struct device *dev;
+	int err = -EINVAL;
+
+	dev = bus_find_device_by_name(bus, NULL, buf);
+	if (!dev)
+		return -ENODEV;
+	if (bus_rescan_devices_helper(dev, NULL) == 0)
+		err = count;
+	put_device(dev);
+	return err;
+}
+
+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;
+}
+
+static struct device *prev_device(struct klist_iter *i)
+{
+	struct klist_node *n = klist_prev(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(const struct bus_type *bus, struct device *start,
+		     void *data, device_iter_t fn)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+	struct klist_iter i;
+	struct device *dev;
+	int error = 0;
+
+	if (!sp)
+		return -EINVAL;
+
+	klist_iter_init_node(&sp->klist_devices, &i,
+			     (start ? &start->p->knode_bus : NULL));
+	while (!error && (dev = next_device(&i)))
+		error = fn(dev, data);
+	klist_iter_exit(&i);
+	subsys_put(sp);
+	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(const struct bus_type *bus,
+			       struct device *start, const void *data,
+			       device_match_t match)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+	struct klist_iter i;
+	struct device *dev;
+
+	if (!sp)
+		return NULL;
+
+	klist_iter_init_node(&sp->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);
+	subsys_put(sp);
+	return dev;
+}
+EXPORT_SYMBOL_GPL(bus_find_device);
+
+struct device *bus_find_device_reverse(const struct bus_type *bus,
+				       struct device *start, const void *data,
+				       device_match_t match)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+	struct klist_iter i;
+	struct device *dev;
+
+	if (!sp)
+		return NULL;
+
+	klist_iter_init_node(&sp->klist_devices, &i,
+			     (start ? &start->p->knode_bus : NULL));
+	while ((dev = prev_device(&i))) {
+		if (match(dev, data)) {
+			get_device(dev);
+			break;
+		}
+	}
+	klist_iter_exit(&i);
+	subsys_put(sp);
+	return dev;
+}
+EXPORT_SYMBOL_GPL(bus_find_device_reverse);
+
+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(const struct bus_type *bus, struct device_driver *start,
+		     void *data, int (*fn)(struct device_driver *, void *))
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+	struct klist_iter i;
+	struct device_driver *drv;
+	int error = 0;
+
+	if (!sp)
+		return -EINVAL;
+
+	klist_iter_init_node(&sp->klist_drivers, &i,
+			     start ? &start->p->knode_bus : NULL);
+	while ((drv = next_driver(&i)) && !error)
+		error = fn(drv, data);
+	klist_iter_exit(&i);
+	subsys_put(sp);
+	return error;
+}
+EXPORT_SYMBOL_GPL(bus_for_each_drv);
+
+static ssize_t driver_override_store(struct device *dev,
+				     struct device_attribute *attr,
+				     const char *buf, size_t count)
+{
+	int ret;
+
+	ret = __device_set_driver_override(dev, buf, count);
+	if (ret)
+		return ret;
+
+	return count;
+}
+
+static ssize_t driver_override_show(struct device *dev,
+				    struct device_attribute *attr, char *buf)
+{
+	guard(spinlock)(&dev->driver_override.lock);
+	return sysfs_emit(buf, "%s\n", dev->driver_override.name);
+}
+static DEVICE_ATTR_RW(driver_override);
+
+static struct attribute *driver_override_dev_attrs[] = {
+	&dev_attr_driver_override.attr,
+	NULL,
+};
+
+static const struct attribute_group driver_override_dev_group = {
+	.attrs = driver_override_dev_attrs,
+};
+
+/**
+ * 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 subsys_private *sp;
+	int error;
+
+	if (!dev->bus) {
+		/*
+		 * This is a normal operation for many devices that do not
+		 * have a bus assigned to them, just say that all went
+		 * well.
+		 */
+		return 0;
+	}
+
+	sp = bus_to_subsys(dev->bus);
+	if (!sp) {
+		pr_err("%s: cannot add device '%s' to unregistered bus '%s'\n",
+		       __func__, dev_name(dev), dev->bus->name);
+		return -EINVAL;
+	}
+
+	/*
+	 * Reference in sp is now incremented and will be dropped when
+	 * the device is removed from the bus
+	 */
+
+	pr_debug("bus: '%s': add device %s\n", sp->bus->name, dev_name(dev));
+
+	error = device_add_groups(dev, sp->bus->dev_groups);
+	if (error)
+		goto out_put;
+
+	if (dev->bus->driver_override) {
+		error = device_add_group(dev, &driver_override_dev_group);
+		if (error)
+			goto out_groups;
+	}
+
+	error = sysfs_create_link(&sp->devices_kset->kobj, &dev->kobj, dev_name(dev));
+	if (error)
+		goto out_override;
+
+	error = sysfs_create_link(&dev->kobj, &sp->subsys.kobj, "subsystem");
+	if (error)
+		goto out_subsys;
+
+	klist_add_tail(&dev->p->knode_bus, &sp->klist_devices);
+	return 0;
+
+out_subsys:
+	sysfs_remove_link(&sp->devices_kset->kobj, dev_name(dev));
+out_override:
+	if (dev->bus->driver_override)
+		device_remove_group(dev, &driver_override_dev_group);
+out_groups:
+	device_remove_groups(dev, sp->bus->dev_groups);
+out_put:
+	subsys_put(sp);
+	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 subsys_private *sp = bus_to_subsys(dev->bus);
+	struct subsys_interface *sif;
+
+	if (!sp)
+		return;
+
+	device_initial_probe(dev);
+
+	mutex_lock(&sp->mutex);
+	list_for_each_entry(sif, &sp->interfaces, node)
+		if (sif->add_dev)
+			sif->add_dev(dev, sif);
+	mutex_unlock(&sp->mutex);
+	subsys_put(sp);
+}
+
+/**
+ * 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 subsys_private *sp = bus_to_subsys(dev->bus);
+	struct subsys_interface *sif;
+
+	if (!sp)
+		return;
+
+	mutex_lock(&sp->mutex);
+	list_for_each_entry(sif, &sp->interfaces, node)
+		if (sif->remove_dev)
+			sif->remove_dev(dev, sif);
+	mutex_unlock(&sp->mutex);
+
+	sysfs_remove_link(&dev->kobj, "subsystem");
+	sysfs_remove_link(&sp->devices_kset->kobj, dev_name(dev));
+	if (dev->bus->driver_override)
+		device_remove_group(dev, &driver_override_dev_group);
+	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);
+
+	/*
+	 * Decrement the reference count twice, once for the bus_to_subsys()
+	 * call in the start of this function, and the second one from the
+	 * reference increment in bus_add_device()
+	 */
+	subsys_put(sp);
+	subsys_put(sp);
+}
+
+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_WO(drivers_probe);
+static BUS_ATTR_RW(drivers_autoprobe);
+
+static int add_probe_files(const 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(const 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)
+{
+	int rc;
+
+	rc = kobject_synth_uevent(&drv->p->kobj, buf, count);
+	return rc ? rc : 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 subsys_private *sp = bus_to_subsys(drv->bus);
+	struct driver_private *priv;
+	int error = 0;
+
+	if (!sp)
+		return -EINVAL;
+
+	/*
+	 * Reference in sp is now incremented and will be dropped when
+	 * the driver is removed from the bus
+	 */
+	pr_debug("bus: '%s': add driver %s\n", sp->bus->name, drv->name);
+
+	priv = kzalloc_obj(*priv);
+	if (!priv) {
+		error = -ENOMEM;
+		goto out_put_bus;
+	}
+	klist_init(&priv->klist_devices, NULL, NULL);
+	priv->driver = drv;
+	drv->p = priv;
+	priv->kobj.kset = sp->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, &sp->klist_drivers);
+	if (sp->drivers_autoprobe) {
+		error = driver_attach(drv);
+		if (error)
+			goto out_del_list;
+	}
+	error = module_add_driver(drv->owner, drv);
+	if (error) {
+		printk(KERN_ERR "%s: failed to create module links for %s\n",
+			__func__, drv->name);
+		goto out_detach;
+	}
+
+	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, sp->bus->drv_groups);
+	if (error) {
+		/* How the hell do we get out of this pickle? Give up */
+		printk(KERN_ERR "%s: driver_add_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_detach:
+	driver_detach(drv);
+out_del_list:
+	klist_del(&priv->knode_bus);
+out_unregister:
+	kobject_put(&priv->kobj);
+	/* drv->p is freed in driver_release()  */
+	drv->p = NULL;
+out_put_bus:
+	subsys_put(sp);
+	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)
+{
+	struct subsys_private *sp = bus_to_subsys(drv->bus);
+
+	if (!sp)
+		return;
+
+	pr_debug("bus: '%s': remove driver %s\n", sp->bus->name, drv->name);
+
+	if (!drv->suppress_bind_attrs)
+		remove_bind_files(drv);
+	driver_remove_groups(drv, sp->bus->drv_groups);
+	driver_remove_file(drv, &driver_attr_uevent);
+	klist_remove(&drv->p->knode_bus);
+	driver_detach(drv);
+	module_remove_driver(drv);
+	kobject_put(&drv->p->kobj);
+
+	/*
+	 * Decrement the reference count twice, once for the bus_to_subsys()
+	 * call in the start of this function, and the second one from the
+	 * reference increment in bus_add_driver()
+	 */
+	subsys_put(sp);
+	subsys_put(sp);
+}
+
+/* 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 && dev->bus->need_parent_lock)
+			device_lock(dev->parent);
+		ret = device_attach(dev);
+		if (dev->parent && dev->bus->need_parent_lock)
+			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(const 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)
+		device_driver_detach(dev);
+	return bus_rescan_devices_helper(dev, NULL);
+}
+EXPORT_SYMBOL_GPL(device_reprobe);
+
+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(const struct bus_type *bus,
+				const char *buf, size_t count)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+	int ret;
+
+	if (!sp)
+		return -EINVAL;
+
+	ret = kobject_synth_uevent(&sp->subsys.kobj, buf, count);
+	subsys_put(sp);
+
+	if (ret)
+		return ret;
+	return count;
+}
+/*
+ * "open code" the old BUS_ATTR() macro here.  We want to use BUS_ATTR_WO()
+ * here, but can not use it as earlier in the file we have
+ * DEVICE_ATTR_WO(uevent), which would cause a clash with the with the store
+ * function name.
+ */
+static struct bus_attribute bus_attr_uevent = __ATTR(uevent, 0200, 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(const struct bus_type *bus)
+{
+	int retval;
+	struct subsys_private *priv;
+	struct kobject *bus_kobj;
+	struct lock_class_key *key;
+
+	priv = kzalloc_obj(struct subsys_private);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->bus = bus;
+
+	BLOCKING_INIT_NOTIFIER_HEAD(&priv->bus_notifier);
+
+	bus_kobj = &priv->subsys.kobj;
+	retval = kobject_set_name(bus_kobj, "%s", bus->name);
+	if (retval)
+		goto out;
+
+	bus_kobj->kset = bus_kset;
+	bus_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, bus_kobj);
+	if (!priv->devices_kset) {
+		retval = -ENOMEM;
+		goto bus_devices_fail;
+	}
+
+	priv->drivers_kset = kset_create_and_add("drivers", NULL, bus_kobj);
+	if (!priv->drivers_kset) {
+		retval = -ENOMEM;
+		goto bus_drivers_fail;
+	}
+
+	INIT_LIST_HEAD(&priv->interfaces);
+	key = &priv->lock_key;
+	lockdep_register_key(key);
+	__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 = sysfs_create_groups(bus_kobj, 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(priv->drivers_kset);
+bus_drivers_fail:
+	kset_unregister(priv->devices_kset);
+bus_devices_fail:
+	bus_remove_file(bus, &bus_attr_uevent);
+bus_uevent_fail:
+	kset_unregister(&priv->subsys);
+	/* Above kset_unregister() will kfree @priv */
+	priv = NULL;
+out:
+	kfree(priv);
+	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(const struct bus_type *bus)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+	struct kobject *bus_kobj;
+
+	if (!sp)
+		return;
+
+	pr_debug("bus: '%s': unregistering\n", bus->name);
+	if (sp->dev_root)
+		device_unregister(sp->dev_root);
+
+	bus_kobj = &sp->subsys.kobj;
+	sysfs_remove_groups(bus_kobj, bus->bus_groups);
+	remove_probe_files(bus);
+	bus_remove_file(bus, &bus_attr_uevent);
+
+	kset_unregister(sp->drivers_kset);
+	kset_unregister(sp->devices_kset);
+	kset_unregister(&sp->subsys);
+	subsys_put(sp);
+}
+EXPORT_SYMBOL_GPL(bus_unregister);
+
+int bus_register_notifier(const struct bus_type *bus, struct notifier_block *nb)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+	int retval;
+
+	if (!sp)
+		return -EINVAL;
+
+	retval = blocking_notifier_chain_register(&sp->bus_notifier, nb);
+	subsys_put(sp);
+	return retval;
+}
+EXPORT_SYMBOL_GPL(bus_register_notifier);
+
+int bus_unregister_notifier(const struct bus_type *bus, struct notifier_block *nb)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+	int retval;
+
+	if (!sp)
+		return -EINVAL;
+	retval = blocking_notifier_chain_unregister(&sp->bus_notifier, nb);
+	subsys_put(sp);
+	return retval;
+}
+EXPORT_SYMBOL_GPL(bus_unregister_notifier);
+
+void bus_notify(struct device *dev, enum bus_notifier_event value)
+{
+	struct subsys_private *sp = bus_to_subsys(dev->bus);
+
+	if (!sp)
+		return;
+
+	blocking_notifier_call_chain(&sp->bus_notifier, value, dev);
+	subsys_put(sp);
+}
+
+struct kset *bus_get_kset(const struct bus_type *bus)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+	struct kset *kset;
+
+	if (!sp)
+		return NULL;
+
+	kset = &sp->subsys;
+	subsys_put(sp);
+
+	return kset;
+}
+EXPORT_SYMBOL_GPL(bus_get_kset);
+
+/*
+ * 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 klist_node *n;
+	struct device_private *dev_prv;
+	struct device *b;
+
+	list_for_each_entry(n, list, 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(const struct bus_type *bus,
+			   int (*compare)(const struct device *a,
+					  const struct device *b))
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+	LIST_HEAD(sorted_devices);
+	struct klist_node *n, *tmp;
+	struct device_private *dev_prv;
+	struct device *dev;
+	struct klist *device_klist;
+
+	if (!sp)
+		return;
+	device_klist = &sp->klist_devices;
+
+	spin_lock(&device_klist->k_lock);
+	list_for_each_entry_safe(n, tmp, &device_klist->k_list, 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);
+	subsys_put(sp);
+}
+EXPORT_SYMBOL_GPL(bus_sort_breadthfirst);
+
+struct subsys_dev_iter {
+	struct klist_iter		ki;
+	const struct device_type	*type;
+};
+
+/**
+ * subsys_dev_iter_init - initialize subsys device iterator
+ * @iter: subsys iterator to initialize
+ * @sp: the subsys private (i.e. bus) 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.
+ */
+static void subsys_dev_iter_init(struct subsys_dev_iter *iter, struct subsys_private *sp,
+				 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(&sp->klist_devices, &iter->ki, start_knode);
+	iter->type = type;
+}
+
+/**
+ * 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.
+ */
+static 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 = to_device_private_bus(knode)->device;
+		if (!iter->type || iter->type == dev->type)
+			return dev;
+	}
+}
+
+/**
+ * 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.
+ */
+static void subsys_dev_iter_exit(struct subsys_dev_iter *iter)
+{
+	klist_iter_exit(&iter->ki);
+}
+
+int subsys_interface_register(struct subsys_interface *sif)
+{
+	struct subsys_private *sp;
+	struct subsys_dev_iter iter;
+	struct device *dev;
+
+	if (!sif || !sif->subsys)
+		return -ENODEV;
+
+	sp = bus_to_subsys(sif->subsys);
+	if (!sp)
+		return -EINVAL;
+
+	/*
+	 * Reference in sp is now incremented and will be dropped when
+	 * the interface is removed from the bus
+	 */
+
+	mutex_lock(&sp->mutex);
+	list_add_tail(&sif->node, &sp->interfaces);
+	if (sif->add_dev) {
+		subsys_dev_iter_init(&iter, sp, NULL, NULL);
+		while ((dev = subsys_dev_iter_next(&iter)))
+			sif->add_dev(dev, sif);
+		subsys_dev_iter_exit(&iter);
+	}
+	mutex_unlock(&sp->mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(subsys_interface_register);
+
+void subsys_interface_unregister(struct subsys_interface *sif)
+{
+	struct subsys_private *sp;
+	struct subsys_dev_iter iter;
+	struct device *dev;
+
+	if (!sif || !sif->subsys)
+		return;
+
+	sp = bus_to_subsys(sif->subsys);
+	if (!sp)
+		return;
+
+	mutex_lock(&sp->mutex);
+	list_del_init(&sif->node);
+	if (sif->remove_dev) {
+		subsys_dev_iter_init(&iter, sp, NULL, NULL);
+		while ((dev = subsys_dev_iter_next(&iter)))
+			sif->remove_dev(dev, sif);
+		subsys_dev_iter_exit(&iter);
+	}
+	mutex_unlock(&sp->mutex);
+
+	/*
+	 * Decrement the reference count twice, once for the bus_to_subsys()
+	 * call in the start of this function, and the second one from the
+	 * reference increment in subsys_interface_register()
+	 */
+	subsys_put(sp);
+	subsys_put(sp);
+}
+EXPORT_SYMBOL_GPL(subsys_interface_unregister);
+
+static void system_root_device_release(struct device *dev)
+{
+	kfree(dev);
+}
+
+static int subsys_register(const struct bus_type *subsys,
+			   const struct attribute_group **groups,
+			   struct kobject *parent_of_root)
+{
+	struct subsys_private *sp;
+	struct device *dev;
+	int err;
+
+	err = bus_register(subsys);
+	if (err < 0)
+		return err;
+
+	sp = bus_to_subsys(subsys);
+	if (!sp) {
+		err = -EINVAL;
+		goto err_sp;
+	}
+
+	dev = kzalloc_obj(struct device);
+	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;
+
+	sp->dev_root = dev;
+	subsys_put(sp);
+	return 0;
+
+err_dev_reg:
+	put_device(dev);
+	dev = NULL;
+err_name:
+	kfree(dev);
+err_dev:
+	subsys_put(sp);
+err_sp:
+	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(const 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 subsystem.  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(const struct bus_type *subsys,
+			    const struct attribute_group **groups)
+{
+	struct kobject *virtual_dir;
+
+	virtual_dir = virtual_device_parent();
+	if (!virtual_dir)
+		return -ENOMEM;
+
+	return subsys_register(subsys, groups, virtual_dir);
+}
+EXPORT_SYMBOL_GPL(subsys_virtual_register);
+
+/**
+ * driver_find - locate driver on a bus by its name.
+ * @name: name of the driver.
+ * @bus: bus to scan for the driver.
+ *
+ * Call kset_find_obj() to iterate over list of drivers on
+ * a bus to find driver by name. Return driver if found.
+ *
+ * This routine provides no locking to prevent the driver it returns
+ * from being unregistered or unloaded while the caller is using it.
+ * The caller is responsible for preventing this.
+ */
+struct device_driver *driver_find(const char *name, const struct bus_type *bus)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+	struct kobject *k;
+	struct driver_private *priv;
+
+	if (!sp)
+		return NULL;
+
+	k = kset_find_obj(sp->drivers_kset, name);
+	subsys_put(sp);
+	if (!k)
+		return NULL;
+
+	priv = to_driver(k);
+
+	/* Drop reference added by kset_find_obj() */
+	kobject_put(k);
+	return priv->driver;
+}
+EXPORT_SYMBOL_GPL(driver_find);
+
+/*
+ * Warning, the value could go to "removed" instantly after calling this function, so be very
+ * careful when calling it...
+ */
+bool bus_is_registered(const struct bus_type *bus)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+	bool is_initialized = false;
+
+	if (sp) {
+		is_initialized = true;
+		subsys_put(sp);
+	}
+	return is_initialized;
+}
+
+/**
+ * bus_get_dev_root - return a pointer to the "device root" of a bus
+ * @bus: bus to return the device root of.
+ *
+ * If a bus has a "device root" structure, return it, WITH THE REFERENCE
+ * COUNT INCREMENTED.
+ *
+ * Note, when finished with the device, a call to put_device() is required.
+ *
+ * If the device root is not present (or bus is not a valid pointer), NULL
+ * will be returned.
+ */
+struct device *bus_get_dev_root(const struct bus_type *bus)
+{
+	struct subsys_private *sp = bus_to_subsys(bus);
+	struct device *dev_root;
+
+	if (!sp)
+		return NULL;
+
+	dev_root = get_device(sp->dev_root);
+	subsys_put(sp);
+	return dev_root;
+}
+EXPORT_SYMBOL_GPL(bus_get_dev_root);
+
+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) {
+		/* Do error handling here as devices_init() do */
+		kset_unregister(bus_kset);
+		bus_kset = NULL;
+		pr_err("%s: failed to create and add kset 'bus'\n", __func__);
+		return -ENOMEM;
+	}
+
+	return 0;
+}