kobject: Introduce kset_find_obj_hinted.

One call chain getting to kset_find_obj is:
  link_mem_sections()
    find_mem_section()
      kset_find_obj()

This is done during boot.  The memory sections were added in a linearly
increasing order and link_mem_sections tends to utilize them in that
same linear order.

Introduce a kset_find_obj_hinted which is passed the result of the
previous kset_find_obj which it uses for a quick "is the next object
our desired object" check before falling back to the old behavior.
Signed-off-by: NRobin Holt <holt@sgi.com>
To: Robert P. J. Day <rpjday@crashcourse.ca>
Reviewed-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

include/linux/kobject.h

@@ -191,6 +191,8 @@ static inline struct kobj_type *get_ktype(struct kobject *kobj)
 }
 
 extern struct kobject *kset_find_obj(struct kset *, const char *);
+extern struct kobject *kset_find_obj_hinted(struct kset *, const char *,
+						struct kobject *);
 
 /* The global /sys/kernel/ kobject for people to chain off of */
 extern struct kobject *kernel_kobj;

lib/kobject.c

@@ -745,18 +745,57 @@ void kset_unregister(struct kset *k)
  * take a reference and return the object.
  */
 struct kobject *kset_find_obj(struct kset *kset, const char *name)
+{
+	return kset_find_obj_hinted(kset, name, NULL);
+}
+
+/**
+ * kset_find_obj_hinted - search for object in kset given a predecessor hint.
+ * @kset: kset we're looking in.
+ * @name: object's name.
+ * @hint: hint to possible object's predecessor.
+ *
+ * Check the hint's next object and if it is a match return it directly,
+ * otherwise, fall back to the behavior of kset_find_obj().  Either way
+ * a reference for the returned object is held and the reference on the
+ * hinted object is released.
+ */
+struct kobject *kset_find_obj_hinted(struct kset *kset, const char *name,
+				     struct kobject *hint)
 {
 	struct kobject *k;
 	struct kobject *ret = NULL;
 
 	spin_lock(&kset->list_lock);
+
+	if (!hint)
+		goto slow_search;
+
+	/* end of list detection */
+	if (hint->entry.next == kset->list.next)
+		goto slow_search;
+
+	k = container_of(hint->entry.next, struct kobject, entry);
+	if (!kobject_name(k) || strcmp(kobject_name(k), name))
+		goto slow_search;
+
+	ret = kobject_get(k);
+	goto unlock_exit;
+
+slow_search:
 	list_for_each_entry(k, &kset->list, entry) {
 		if (kobject_name(k) && !strcmp(kobject_name(k), name)) {
 			ret = kobject_get(k);
 			break;
 		}
 	}
+
+unlock_exit:
 	spin_unlock(&kset->list_lock);
+
+	if (hint)
+		kobject_put(hint);
+
 	return ret;
 }