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-rw-r--r--include/linux/klist.h1
-rw-r--r--lib/klist.c41
2 files changed, 42 insertions, 0 deletions
diff --git a/include/linux/klist.h b/include/linux/klist.h
index 61e5b723ae73..953f283f8451 100644
--- a/include/linux/klist.h
+++ b/include/linux/klist.h
@@ -63,6 +63,7 @@ extern void klist_iter_init(struct klist *k, struct klist_iter *i);
extern void klist_iter_init_node(struct klist *k, struct klist_iter *i,
struct klist_node *n);
extern void klist_iter_exit(struct klist_iter *i);
+extern struct klist_node *klist_prev(struct klist_iter *i);
extern struct klist_node *klist_next(struct klist_iter *i);
#endif
diff --git a/lib/klist.c b/lib/klist.c
index 89b485a2a58d..d74cf7a29afd 100644
--- a/lib/klist.c
+++ b/lib/klist.c
@@ -324,6 +324,47 @@ static struct klist_node *to_klist_node(struct list_head *n)
}
/**
+ * klist_prev - Ante up prev node in list.
+ * @i: Iterator structure.
+ *
+ * First grab list lock. Decrement the reference count of the previous
+ * node, if there was one. Grab the prev node, increment its reference
+ * count, drop the lock, and return that prev node.
+ */
+struct klist_node *klist_prev(struct klist_iter *i)
+{
+ void (*put)(struct klist_node *) = i->i_klist->put;
+ struct klist_node *last = i->i_cur;
+ struct klist_node *prev;
+
+ spin_lock(&i->i_klist->k_lock);
+
+ if (last) {
+ prev = to_klist_node(last->n_node.prev);
+ if (!klist_dec_and_del(last))
+ put = NULL;
+ } else
+ prev = to_klist_node(i->i_klist->k_list.prev);
+
+ i->i_cur = NULL;
+ while (prev != to_klist_node(&i->i_klist->k_list)) {
+ if (likely(!knode_dead(prev))) {
+ kref_get(&prev->n_ref);
+ i->i_cur = prev;
+ break;
+ }
+ prev = to_klist_node(prev->n_node.prev);
+ }
+
+ spin_unlock(&i->i_klist->k_lock);
+
+ if (put && last)
+ put(last);
+ return i->i_cur;
+}
+EXPORT_SYMBOL_GPL(klist_prev);
+
+/**
* klist_next - Ante up next node in list.
* @i: Iterator structure.
*