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, 654 insertions, 0 deletions

diff --git a/drivers/base/class.c b/drivers/base/class.c
new file mode 100644
index 000000000..ffab0a9c8
--- /dev/null
+++ b/drivers/base/class.c
@@ -0,0 +1,654 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * class.c - basic device class management
+ *
+ * Copyright (c) 2002-3 Patrick Mochel
+ * Copyright (c) 2002-3 Open Source Development Labs
+ * Copyright (c) 2003-2004 Greg Kroah-Hartman
+ * Copyright (c) 2003-2004 IBM Corp.
+ */
+
+#include <linux/device/class.h>
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/string.h>
+#include <linux/kdev_t.h>
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/blkdev.h>
+#include <linux/mutex.h>
+#include "base.h"
+
+/* /sys/class */
+static struct kset *class_kset;
+
+#define to_class_attr(_attr) container_of(_attr, struct class_attribute, attr)
+
+/**
+ * class_to_subsys - Turn a struct class into a struct subsys_private
+ *
+ * @class: pointer to the struct bus_type to look up
+ *
+ * The driver core internals need to work on the subsys_private structure, not
+ * the external struct class pointer.  This function walks the list of
+ * registered classes in the system and finds the matching one and returns the
+ * internal struct subsys_private that relates to that class.
+ *
+ * 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 *class_to_subsys(const struct class *class)
+{
+	struct subsys_private *sp = NULL;
+	struct kobject *kobj;
+
+	if (!class || !class_kset)
+		return NULL;
+
+	spin_lock(&class_kset->list_lock);
+
+	if (list_empty(&class_kset->list))
+		goto done;
+
+	list_for_each_entry(kobj, &class_kset->list, entry) {
+		struct kset *kset = container_of(kobj, struct kset, kobj);
+
+		sp = container_of_const(kset, struct subsys_private, subsys);
+		if (sp->class == class)
+			goto done;
+	}
+	sp = NULL;
+done:
+	sp = subsys_get(sp);
+	spin_unlock(&class_kset->list_lock);
+	return sp;
+}
+
+static ssize_t class_attr_show(struct kobject *kobj, struct attribute *attr,
+			       char *buf)
+{
+	struct class_attribute *class_attr = to_class_attr(attr);
+	struct subsys_private *cp = to_subsys_private(kobj);
+	ssize_t ret = -EIO;
+
+	if (class_attr->show)
+		ret = class_attr->show(cp->class, class_attr, buf);
+	return ret;
+}
+
+static ssize_t class_attr_store(struct kobject *kobj, struct attribute *attr,
+				const char *buf, size_t count)
+{
+	struct class_attribute *class_attr = to_class_attr(attr);
+	struct subsys_private *cp = to_subsys_private(kobj);
+	ssize_t ret = -EIO;
+
+	if (class_attr->store)
+		ret = class_attr->store(cp->class, class_attr, buf, count);
+	return ret;
+}
+
+static void class_release(struct kobject *kobj)
+{
+	struct subsys_private *cp = to_subsys_private(kobj);
+	const struct class *class = cp->class;
+
+	pr_debug("class '%s': release.\n", class->name);
+
+	if (class->class_release)
+		class->class_release(class);
+	else
+		pr_debug("class '%s' does not have a release() function, "
+			 "be careful\n", class->name);
+
+	lockdep_unregister_key(&cp->lock_key);
+	kfree(cp);
+}
+
+static const struct kobj_ns_type_operations *class_child_ns_type(const struct kobject *kobj)
+{
+	const struct subsys_private *cp = to_subsys_private(kobj);
+	const struct class *class = cp->class;
+
+	return class->ns_type;
+}
+
+static const struct sysfs_ops class_sysfs_ops = {
+	.show	   = class_attr_show,
+	.store	   = class_attr_store,
+};
+
+static const struct kobj_type class_ktype = {
+	.sysfs_ops	= &class_sysfs_ops,
+	.release	= class_release,
+	.child_ns_type	= class_child_ns_type,
+};
+
+int class_create_file_ns(const struct class *cls, const struct class_attribute *attr,
+			 const struct ns_common *ns)
+{
+	struct subsys_private *sp = class_to_subsys(cls);
+	int error;
+
+	if (!sp)
+		return -EINVAL;
+
+	error = sysfs_create_file_ns(&sp->subsys.kobj, &attr->attr, ns);
+	subsys_put(sp);
+
+	return error;
+}
+EXPORT_SYMBOL_GPL(class_create_file_ns);
+
+void class_remove_file_ns(const struct class *cls, const struct class_attribute *attr,
+			  const struct ns_common *ns)
+{
+	struct subsys_private *sp = class_to_subsys(cls);
+
+	if (!sp)
+		return;
+
+	sysfs_remove_file_ns(&sp->subsys.kobj, &attr->attr, ns);
+	subsys_put(sp);
+}
+EXPORT_SYMBOL_GPL(class_remove_file_ns);
+
+static struct device *klist_class_to_dev(struct klist_node *n)
+{
+	struct device_private *p = to_device_private_class(n);
+	return p->device;
+}
+
+static void klist_class_dev_get(struct klist_node *n)
+{
+	struct device *dev = klist_class_to_dev(n);
+
+	get_device(dev);
+}
+
+static void klist_class_dev_put(struct klist_node *n)
+{
+	struct device *dev = klist_class_to_dev(n);
+
+	put_device(dev);
+}
+
+int class_register(const struct class *cls)
+{
+	struct subsys_private *cp;
+	struct lock_class_key *key;
+	int error;
+
+	pr_debug("device class '%s': registering\n", cls->name);
+
+	if (cls->ns_type && !cls->namespace) {
+		pr_err("%s: class '%s' does not have namespace\n",
+		       __func__, cls->name);
+		return -EINVAL;
+	}
+	if (!cls->ns_type && cls->namespace) {
+		pr_err("%s: class '%s' does not have ns_type\n",
+		       __func__, cls->name);
+		return -EINVAL;
+	}
+
+	cp = kzalloc_obj(*cp);
+	if (!cp)
+		return -ENOMEM;
+	klist_init(&cp->klist_devices, klist_class_dev_get, klist_class_dev_put);
+	INIT_LIST_HEAD(&cp->interfaces);
+	kset_init(&cp->glue_dirs);
+	key = &cp->lock_key;
+	lockdep_register_key(key);
+	__mutex_init(&cp->mutex, "subsys mutex", key);
+	error = kobject_set_name(&cp->subsys.kobj, "%s", cls->name);
+	if (error)
+		goto err_out;
+
+	cp->subsys.kobj.kset = class_kset;
+	cp->subsys.kobj.ktype = &class_ktype;
+	cp->class = cls;
+
+	error = kset_register(&cp->subsys);
+	if (error)
+		goto err_out;
+
+	error = sysfs_create_groups(&cp->subsys.kobj, cls->class_groups);
+	if (error) {
+		kobject_del(&cp->subsys.kobj);
+		kfree_const(cp->subsys.kobj.name);
+		goto err_out;
+	}
+	return 0;
+
+err_out:
+	lockdep_unregister_key(key);
+	kfree(cp);
+	return error;
+}
+EXPORT_SYMBOL_GPL(class_register);
+
+void class_unregister(const struct class *cls)
+{
+	struct subsys_private *sp = class_to_subsys(cls);
+
+	if (!sp)
+		return;
+
+	pr_debug("device class '%s': unregistering\n", cls->name);
+
+	sysfs_remove_groups(&sp->subsys.kobj, cls->class_groups);
+	kset_unregister(&sp->subsys);
+	subsys_put(sp);
+}
+EXPORT_SYMBOL_GPL(class_unregister);
+
+static void class_create_release(const struct class *cls)
+{
+	pr_debug("%s called for %s\n", __func__, cls->name);
+	kfree(cls);
+}
+
+/**
+ * class_create - create a struct class structure
+ * @name: pointer to a string for the name of this class.
+ *
+ * This is used to create a struct class pointer that can then be used
+ * in calls to device_create().
+ *
+ * Returns &struct class pointer on success, or ERR_PTR() on error.
+ *
+ * Note, the pointer created here is to be destroyed when finished by
+ * making a call to class_destroy().
+ */
+struct class *class_create(const char *name)
+{
+	struct class *cls;
+	int retval;
+
+	cls = kzalloc_obj(*cls);
+	if (!cls) {
+		retval = -ENOMEM;
+		goto error;
+	}
+
+	cls->name = name;
+	cls->class_release = class_create_release;
+
+	retval = class_register(cls);
+	if (retval)
+		goto error;
+
+	return cls;
+
+error:
+	kfree(cls);
+	return ERR_PTR(retval);
+}
+EXPORT_SYMBOL_GPL(class_create);
+
+/**
+ * class_destroy - destroys a struct class structure
+ * @cls: pointer to the struct class that is to be destroyed
+ *
+ * Note, the pointer to be destroyed must have been created with a call
+ * to class_create().
+ */
+void class_destroy(const struct class *cls)
+{
+	if (IS_ERR_OR_NULL(cls))
+		return;
+
+	class_unregister(cls);
+}
+EXPORT_SYMBOL_GPL(class_destroy);
+
+/**
+ * class_dev_iter_init - initialize class device iterator
+ * @iter: class iterator to initialize
+ * @class: the class 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 class iterator @iter such that it iterates over devices
+ * of @class.  If @start is set, the list iteration will start there,
+ * otherwise if it is NULL, the iteration starts at the beginning of
+ * the list.
+ */
+void class_dev_iter_init(struct class_dev_iter *iter, const struct class *class,
+			 const struct device *start, const struct device_type *type)
+{
+	struct subsys_private *sp = class_to_subsys(class);
+	struct klist_node *start_knode = NULL;
+
+	memset(iter, 0, sizeof(*iter));
+	if (!sp) {
+		pr_crit("%s: class %p was not registered yet\n",
+			__func__, class);
+		return;
+	}
+
+	if (start)
+		start_knode = &start->p->knode_class;
+	klist_iter_init_node(&sp->klist_devices, &iter->ki, start_knode);
+	iter->type = type;
+	iter->sp = sp;
+}
+EXPORT_SYMBOL_GPL(class_dev_iter_init);
+
+/**
+ * class_dev_iter_next - iterate to the next device
+ * @iter: class 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 class code.
+ */
+struct device *class_dev_iter_next(struct class_dev_iter *iter)
+{
+	struct klist_node *knode;
+	struct device *dev;
+
+	if (!iter->sp)
+		return NULL;
+
+	while (1) {
+		knode = klist_next(&iter->ki);
+		if (!knode)
+			return NULL;
+		dev = klist_class_to_dev(knode);
+		if (!iter->type || iter->type == dev->type)
+			return dev;
+	}
+}
+EXPORT_SYMBOL_GPL(class_dev_iter_next);
+
+/**
+ * class_dev_iter_exit - finish iteration
+ * @iter: class iterator to finish
+ *
+ * Finish an iteration.  Always call this function after iteration is
+ * complete whether the iteration ran till the end or not.
+ */
+void class_dev_iter_exit(struct class_dev_iter *iter)
+{
+	klist_iter_exit(&iter->ki);
+	subsys_put(iter->sp);
+}
+EXPORT_SYMBOL_GPL(class_dev_iter_exit);
+
+/**
+ * class_for_each_device - device iterator
+ * @class: the class we're iterating
+ * @start: the device to start with in the list, if any.
+ * @data: data for the callback
+ * @fn: function to be called for each device
+ *
+ * Iterate over @class's list of devices, and call @fn for each,
+ * passing it @data.  If @start is set, the list iteration will start
+ * there, otherwise if it is NULL, the iteration starts at the
+ * beginning of the list.
+ *
+ * We check the return of @fn each time. If it returns anything
+ * other than 0, we break out and return that value.
+ *
+ * @fn is allowed to do anything including calling back into class
+ * code.  There's no locking restriction.
+ */
+int class_for_each_device(const struct class *class, const struct device *start,
+			  void *data, device_iter_t fn)
+{
+	struct subsys_private *sp = class_to_subsys(class);
+	struct class_dev_iter iter;
+	struct device *dev;
+	int error = 0;
+
+	if (!class)
+		return -EINVAL;
+	if (!sp) {
+		WARN(1, "%s called for class '%s' before it was registered",
+		     __func__, class->name);
+		return -EINVAL;
+	}
+
+	class_dev_iter_init(&iter, class, start, NULL);
+	while ((dev = class_dev_iter_next(&iter))) {
+		error = fn(dev, data);
+		if (error)
+			break;
+	}
+	class_dev_iter_exit(&iter);
+	subsys_put(sp);
+
+	return error;
+}
+EXPORT_SYMBOL_GPL(class_for_each_device);
+
+/**
+ * class_find_device - device iterator for locating a particular device
+ * @class: the class we're iterating
+ * @start: Device to begin with
+ * @data: data for the match function
+ * @match: function to check device
+ *
+ * This is similar to the class_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.
+ *
+ * Note, you will need to drop the reference with put_device() after use.
+ *
+ * @match is allowed to do anything including calling back into class
+ * code.  There's no locking restriction.
+ */
+struct device *class_find_device(const struct class *class, const struct device *start,
+				 const void *data, device_match_t match)
+{
+	struct subsys_private *sp = class_to_subsys(class);
+	struct class_dev_iter iter;
+	struct device *dev;
+
+	if (!class)
+		return NULL;
+	if (!sp) {
+		WARN(1, "%s called for class '%s' before it was registered",
+		     __func__, class->name);
+		return NULL;
+	}
+
+	class_dev_iter_init(&iter, class, start, NULL);
+	while ((dev = class_dev_iter_next(&iter))) {
+		if (match(dev, data)) {
+			get_device(dev);
+			break;
+		}
+	}
+	class_dev_iter_exit(&iter);
+	subsys_put(sp);
+
+	return dev;
+}
+EXPORT_SYMBOL_GPL(class_find_device);
+
+int class_interface_register(struct class_interface *class_intf)
+{
+	struct subsys_private *sp;
+	const struct class *parent;
+	struct class_dev_iter iter;
+	struct device *dev;
+
+	if (!class_intf || !class_intf->class)
+		return -ENODEV;
+
+	parent = class_intf->class;
+	sp = class_to_subsys(parent);
+	if (!sp)
+		return -EINVAL;
+
+	/*
+	 * Reference in sp is now incremented and will be dropped when
+	 * the interface is removed in the call to class_interface_unregister()
+	 */
+
+	mutex_lock(&sp->mutex);
+	list_add_tail(&class_intf->node, &sp->interfaces);
+	if (class_intf->add_dev) {
+		class_dev_iter_init(&iter, parent, NULL, NULL);
+		while ((dev = class_dev_iter_next(&iter)))
+			class_intf->add_dev(dev);
+		class_dev_iter_exit(&iter);
+	}
+	mutex_unlock(&sp->mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(class_interface_register);
+
+void class_interface_unregister(struct class_interface *class_intf)
+{
+	struct subsys_private *sp;
+	const struct class *parent = class_intf->class;
+	struct class_dev_iter iter;
+	struct device *dev;
+
+	if (!parent)
+		return;
+
+	sp = class_to_subsys(parent);
+	if (!sp)
+		return;
+
+	mutex_lock(&sp->mutex);
+	list_del_init(&class_intf->node);
+	if (class_intf->remove_dev) {
+		class_dev_iter_init(&iter, parent, NULL, NULL);
+		while ((dev = class_dev_iter_next(&iter)))
+			class_intf->remove_dev(dev);
+		class_dev_iter_exit(&iter);
+	}
+	mutex_unlock(&sp->mutex);
+
+	/*
+	 * Decrement the reference count twice, once for the class_to_subsys()
+	 * call in the start of this function, and the second one from the
+	 * reference increment in class_interface_register()
+	 */
+	subsys_put(sp);
+	subsys_put(sp);
+}
+EXPORT_SYMBOL_GPL(class_interface_unregister);
+
+ssize_t show_class_attr_string(const struct class *class,
+			       const struct class_attribute *attr, char *buf)
+{
+	struct class_attribute_string *cs;
+
+	cs = container_of(attr, struct class_attribute_string, attr);
+	return sysfs_emit(buf, "%s\n", cs->str);
+}
+
+EXPORT_SYMBOL_GPL(show_class_attr_string);
+
+struct class_compat {
+	struct kobject *kobj;
+};
+
+/**
+ * class_compat_register - register a compatibility class
+ * @name: the name of the class
+ *
+ * Compatibility class are meant as a temporary user-space compatibility
+ * workaround when converting a family of class devices to a bus devices.
+ */
+struct class_compat *class_compat_register(const char *name)
+{
+	struct class_compat *cls;
+
+	cls = kmalloc_obj(struct class_compat);
+	if (!cls)
+		return NULL;
+	cls->kobj = kobject_create_and_add(name, &class_kset->kobj);
+	if (!cls->kobj) {
+		kfree(cls);
+		return NULL;
+	}
+	return cls;
+}
+EXPORT_SYMBOL_GPL(class_compat_register);
+
+/**
+ * class_compat_unregister - unregister a compatibility class
+ * @cls: the class to unregister
+ */
+void class_compat_unregister(struct class_compat *cls)
+{
+	kobject_put(cls->kobj);
+	kfree(cls);
+}
+EXPORT_SYMBOL_GPL(class_compat_unregister);
+
+/**
+ * class_compat_create_link - create a compatibility class device link to
+ *			      a bus device
+ * @cls: the compatibility class
+ * @dev: the target bus device
+ */
+int class_compat_create_link(struct class_compat *cls, struct device *dev)
+{
+	return sysfs_create_link(cls->kobj, &dev->kobj, dev_name(dev));
+}
+EXPORT_SYMBOL_GPL(class_compat_create_link);
+
+/**
+ * class_compat_remove_link - remove a compatibility class device link to
+ *			      a bus device
+ * @cls: the compatibility class
+ * @dev: the target bus device
+ */
+void class_compat_remove_link(struct class_compat *cls, struct device *dev)
+{
+	sysfs_remove_link(cls->kobj, dev_name(dev));
+}
+EXPORT_SYMBOL_GPL(class_compat_remove_link);
+
+/**
+ * class_is_registered - determine if at this moment in time, a class is
+ *			 registered in the driver core or not.
+ * @class: the class to check
+ *
+ * Returns a boolean to state if the class is registered in the driver core
+ * or not.  Note that the value could switch right after this call is made,
+ * so only use this in places where you "know" it is safe to do so (usually
+ * to determine if the specific class has been registered yet or not).
+ *
+ * Be careful in using this.
+ */
+bool class_is_registered(const struct class *class)
+{
+	struct subsys_private *sp = class_to_subsys(class);
+	bool is_initialized = false;
+
+	if (sp) {
+		is_initialized = true;
+		subsys_put(sp);
+	}
+	return is_initialized;
+}
+EXPORT_SYMBOL_GPL(class_is_registered);
+
+int __init classes_init(void)
+{
+	class_kset = kset_create_and_add("class", NULL, NULL);
+	if (!class_kset)
+		return -ENOMEM;
+	return 0;
+}