driver-core: use klist for class device list and implement iterator

Iterating over entries using callback usually isn't too fun especially
when the entry being iterated over can't be manipulated freely. This
patch converts class->p->class_devices to klist and implements class
device iterator so that the users can freely build their own control
structure. The users are also free to call back into class code
without worrying about locking.

class_for_each_device() and class_find_device() are converted to use
the new iterators, so their users don't have to worry about locking
anymore either.

Note: This depends on klist-dont-iterate-over-deleted-entries patch
because class_intf->add/remove_dev() depends on proper synchronization
with device removal.

Signed-off-by: Tejun Heo <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/base/base.h

···
  */
 struct class_private {
 	struct kset class_subsys;
-	struct list_head class_devices;
+	struct klist class_devices;
 	struct list_head class_interfaces;
 	struct kset class_dirs;
 	struct mutex class_mutex;

drivers/base/class.c

···
 	}
 }
 
+static void klist_class_dev_get(struct klist_node *n)
+{
+	struct device *dev = container_of(n, struct device, knode_class);
+
+	get_device(dev);
+}
+
+static void klist_class_dev_put(struct klist_node *n)
+{
+	struct device *dev = container_of(n, struct device, knode_class);
+
+	put_device(dev);
+}
+
 int __class_register(struct class *cls, struct lock_class_key *key)
 {
 	struct class_private *cp;
···
 	cp = kzalloc(sizeof(*cp), GFP_KERNEL);
 	if (!cp)
 		return -ENOMEM;
-	INIT_LIST_HEAD(&cp->class_devices);
+	klist_init(&cp->class_devices, klist_class_dev_get, klist_class_dev_put);
 	INIT_LIST_HEAD(&cp->class_interfaces);
 	kset_init(&cp->class_dirs);
 	__mutex_init(&cp->class_mutex, "struct class mutex", key);
···
 #endif
 
 /**
+ * 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, struct class *class,
+			 struct device *start, const struct device_type *type)
+{
+	struct klist_node *start_knode = NULL;
+
+	if (start)
+		start_knode = &start->knode_class;
+	klist_iter_init_node(&class->p->class_devices, &iter->ki, start_knode);
+	iter->type = type;
+}
+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;
+
+	while (1) {
+		knode = klist_next(&iter->ki);
+		if (!knode)
+			return NULL;
+		dev = container_of(knode, struct device, knode_class);
+		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);
+}
+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.
···
  * We check the return of @fn each time. If it returns anything
  * other than 0, we break out and return that value.
  *
- * Note, we hold class->class_mutex in this function, so it can not be
- * re-acquired in @fn, otherwise it will self-deadlocking. For
- * example, calls to add or remove class members would be verboten.
+ * @fn is allowed to do anything including calling back into class
+ * code.  There's no locking restriction.
  */
 int class_for_each_device(struct class *class, struct device *start,
 			  void *data, int (*fn)(struct device *, void *))
 {
+	struct class_dev_iter iter;
 	struct device *dev;
 	int error = 0;
 
···
 		return -EINVAL;
 	}
 
-	mutex_lock(&class->p->class_mutex);
-	list_for_each_entry(dev, &class->p->class_devices, node) {
-		if (start) {
-			if (start == dev)
-				start = NULL;
-			continue;
-		}
-		dev = get_device(dev);
+	class_dev_iter_init(&iter, class, start, NULL);
+	while ((dev = class_dev_iter_next(&iter))) {
 		error = fn(dev, data);
-		put_device(dev);
 		if (error)
 			break;
 	}
-	mutex_unlock(&class->p->class_mutex);
+	class_dev_iter_exit(&iter);
 
 	return error;
 }
···
  *
  * Note, you will need to drop the reference with put_device() after use.
  *
- * We hold class->class_mutex in this function, so it can not be
- * re-acquired in @match, otherwise it will self-deadlocking. For
- * example, calls to add or remove class members would be verboten.
+ * @fn is allowed to do anything including calling back into class
+ * code.  There's no locking restriction.
  */
 struct device *class_find_device(struct class *class, struct device *start,
 				 void *data,
 				 int (*match)(struct device *, void *))
 {
+	struct class_dev_iter iter;
 	struct device *dev;
-	int found = 0;
 
 	if (!class)
 		return NULL;
···
 		return NULL;
 	}
 
-	mutex_lock(&class->p->class_mutex);
-	list_for_each_entry(dev, &class->p->class_devices, node) {
-		if (start) {
-			if (start == dev)
-				start = NULL;
-			continue;
-		}
-		dev = get_device(dev);
+	class_dev_iter_init(&iter, class, start, NULL);
+	while ((dev = class_dev_iter_next(&iter))) {
 		if (match(dev, data)) {
-			found = 1;
+			get_device(dev);
 			break;
-		} else
-			put_device(dev);
+		}
 	}
-	mutex_unlock(&class->p->class_mutex);
+	class_dev_iter_exit(&iter);
 
-	return found ? dev : NULL;
+	return dev;
 }
 EXPORT_SYMBOL_GPL(class_find_device);
 
 int class_interface_register(struct class_interface *class_intf)
 {
 	struct class *parent;
+	struct class_dev_iter iter;
 	struct device *dev;
 
 	if (!class_intf || !class_intf->class)
···
 	mutex_lock(&parent->p->class_mutex);
 	list_add_tail(&class_intf->node, &parent->p->class_interfaces);
 	if (class_intf->add_dev) {
-		list_for_each_entry(dev, &parent->p->class_devices, node)
+		class_dev_iter_init(&iter, parent, NULL, NULL);
+		while ((dev = class_dev_iter_next(&iter)))
 			class_intf->add_dev(dev, class_intf);
+		class_dev_iter_exit(&iter);
 	}
 	mutex_unlock(&parent->p->class_mutex);
 
···
 void class_interface_unregister(struct class_interface *class_intf)
 {
 	struct class *parent = class_intf->class;
+	struct class_dev_iter iter;
 	struct device *dev;
 
 	if (!parent)
···
 	mutex_lock(&parent->p->class_mutex);
 	list_del_init(&class_intf->node);
 	if (class_intf->remove_dev) {
-		list_for_each_entry(dev, &parent->p->class_devices, node)
+		class_dev_iter_init(&iter, parent, NULL, NULL);
+		while ((dev = class_dev_iter_next(&iter)))
 			class_intf->remove_dev(dev, class_intf);
+		class_dev_iter_exit(&iter);
 	}
 	mutex_unlock(&parent->p->class_mutex);
 

drivers/base/core.c

···
 	klist_init(&dev->klist_children, klist_children_get,
 		   klist_children_put);
 	INIT_LIST_HEAD(&dev->dma_pools);
-	INIT_LIST_HEAD(&dev->node);
 	init_MUTEX(&dev->sem);
 	spin_lock_init(&dev->devres_lock);
 	INIT_LIST_HEAD(&dev->devres_head);
···
 	if (dev->class) {
 		mutex_lock(&dev->class->p->class_mutex);
 		/* tie the class to the device */
-		list_add_tail(&dev->node, &dev->class->p->class_devices);
+		klist_add_tail(&dev->knode_class,
+			       &dev->class->p->class_devices);
 
 		/* notify any interfaces that the device is here */
 		list_for_each_entry(class_intf,
···
 			if (class_intf->remove_dev)
 				class_intf->remove_dev(dev, class_intf);
 		/* remove the device from the class list */
-		list_del_init(&dev->node);
+		klist_del(&dev->knode_class);
 		mutex_unlock(&dev->class->p->class_mutex);
 	}
 	device_remove_file(dev, &uevent_attr);

include/linux/device.h

···
 	struct class_private *p;
 };
 
+struct class_dev_iter {
+	struct klist_iter		ki;
+	const struct device_type	*type;
+};
+
 extern struct kobject *sysfs_dev_block_kobj;
 extern struct kobject *sysfs_dev_char_kobj;
 extern int __must_check __class_register(struct class *class,
···
 	static struct lock_class_key __key;	\
 	__class_register(class, &__key);	\
 })
+
+extern void class_dev_iter_init(struct class_dev_iter *iter,
+				struct class *class,
+				struct device *start,
+				const struct device_type *type);
+extern struct device *class_dev_iter_next(struct class_dev_iter *iter);
+extern void class_dev_iter_exit(struct class_dev_iter *iter);
 
 extern int class_for_each_device(struct class *class, struct device *start,
 				 void *data,
···
 	spinlock_t		devres_lock;
 	struct list_head	devres_head;
 
-	struct list_head	node;
+	struct klist_node	knode_class;
 	struct class		*class;
 	dev_t			devt;	/* dev_t, creates the sysfs "dev" */
 	struct attribute_group	**groups;	/* optional groups */