kobject: Add kset_get_next_obj() to allow a kset to be walked

To expose iommu_groups via the resctrl filesystem, the resctrl driver
needs to be able to walk the list of iommu_groups. These are exposed
via sysfs as a kset.

Add kset_get_next_obj() to allow resctrl to walk the kobjects in the
kset.

Signed-off-by: James Morse <james.morse@arm.com>

include/linux/kobject.h

@@ -205,6 +205,8 @@ static inline const struct kobj_type *get_ktype(const struct kobject *kobj)
 
 extern struct kobject *kset_find_obj(struct kset *, const char *);
 
+struct kobject *kset_get_next_obj(struct kset *kset, struct kobject *prev);
+
 /* The global /sys/kernel/ kobject for people to chain off of */
 extern struct kobject *kernel_kobj;
 /* The global /sys/kernel/mm/ kobject for people to chain off of */

lib/kobject.c

@@ -907,6 +907,27 @@ struct kobject *kset_find_obj(struct kset *kset, const char *name)
 }
 EXPORT_SYMBOL_GPL(kset_find_obj);
 
+struct kobject *kset_get_next_obj(struct kset *kset, struct kobject *prev)
+{
+	struct kobject *k;
+
+	spin_lock(&kset->list_lock);
+
+	if (!prev)
+		k = list_first_entry_or_null(&kset->list, typeof(*k), entry);
+	else
+		k = list_next_entry(prev, entry);
+
+	if (list_entry_is_head(k, &kset->list, entry))
+		k = NULL;
+
+	kobject_get(k);
+	spin_unlock(&kset->list_lock);
+	kobject_put(prev);
+
+	return k;
+}
+
 static void kset_release(struct kobject *kobj)
 {
 	struct kset *kset = container_of(kobj, struct kset, kobj);