[PATCH net-next 2/5] rhashtable: Add rhastable_walk_peek

[Tom Herbert <tom@quantonium.net>]

This function is like rhashtable_walk_next except that it only returns
the current element in the inter and does not advance the iter.

This patch also creates __rhashtable_walk_find_next. It finds the next
element in the table when the entry cached in iter is NULL or at the end
of a slot. __rhashtable_walk_find_next is called from
rhashtable_walk_next and rhastable_walk_peek.

Signed-off-by: Tom Herbert <tom@quantonium.net>
---
 include/linux/rhashtable.h |   1 +
 lib/rhashtable.c           | 103 ++++++++++++++++++++++++++++++++++++++-------
 2 files changed, 88 insertions(+), 16 deletions(-)

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 4c976bf320a8..7f3e674e127a 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -380,6 +380,7 @@ void rhashtable_walk_enter(struct rhashtable *ht,
 void rhashtable_walk_exit(struct rhashtable_iter *iter);
 void rhashtable_walk_start(struct rhashtable_iter *iter) __acquires(RCU);
 void *rhashtable_walk_next(struct rhashtable_iter *iter);
+void *rhashtable_walk_peek(struct rhashtable_iter *iter);
 void rhashtable_walk_stop(struct rhashtable_iter *iter) __releases(RCU);
 
 void rhashtable_free_and_destroy(struct rhashtable *ht,
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index eeddfb3199cd..1d58231110af 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -753,18 +753,16 @@ void rhashtable_walk_start(struct rhashtable_iter *iter)
 EXPORT_SYMBOL_GPL(rhashtable_walk_start);
 
 /**
- * rhashtable_walk_next - Return the next object and advance the iterator
+ * __rhashtable_walk_find_next - Find the next element in a table (or the first
+ * one in case of a new walk).
+ *
  * @iter:	Hash table iterator
  *
- * Note that you must call rhashtable_walk_stop when you are finished
- * with the walk.
+ * Returns the found object or NULL when the end of the table is reached.
  *
- * Returns the next object or NULL when the end of the table is reached.
- *
- * Returns -EAGAIN if resize event occured.  Note that the iterator
- * will rewind back to the beginning and you may continue to use it.
+ * Returns -EAGAIN if resize event occurred.
  */
-void *rhashtable_walk_next(struct rhashtable_iter *iter)
+static void *__rhashtable_walk_find_next(struct rhashtable_iter *iter)
 {
 	struct bucket_table *tbl = iter->walker.tbl;
 	struct rhlist_head *list = iter->list;
@@ -772,14 +770,6 @@ void *rhashtable_walk_next(struct rhashtable_iter *iter)
 	struct rhash_head *p = iter->p;
 	bool rhlist = ht->rhlist;
 
-	if (p) {
-		if (!rhlist || !(list = rcu_dereference(list->next))) {
-			p = rcu_dereference(p->next);
-			list = container_of(p, struct rhlist_head, rhead);
-		}
-		goto next;
-	}
-
 	for (; iter->slot < tbl->size; iter->slot++) {
 		int skip = iter->skip;
 
@@ -826,9 +816,90 @@ void *rhashtable_walk_next(struct rhashtable_iter *iter)
 
 	return NULL;
 }
+
+/**
+ * rhashtable_walk_next - Return the next object and advance the iterator
+ * @iter:	Hash table iterator
+ *
+ * Note that you must call rhashtable_walk_stop when you are finished
+ * with the walk.
+ *
+ * Returns the next object or NULL when the end of the table is reached.
+ *
+ * Returns -EAGAIN if resize event occurred.  Note that the iterator
+ * will rewind back to the beginning and you may continue to use it.
+ */
+void *rhashtable_walk_next(struct rhashtable_iter *iter)
+{
+	struct rhlist_head *list = iter->list;
+	struct rhashtable *ht = iter->ht;
+	struct rhash_head *p = iter->p;
+	bool rhlist = ht->rhlist;
+
+	if (!iter->walker.tbl)
+		return NULL;
+
+	if (p) {
+		if (!rhlist || !(list = rcu_dereference(list->next))) {
+			p = rcu_dereference(p->next);
+			list = container_of(p, struct rhlist_head, rhead);
+		}
+		if (!rht_is_a_nulls(p)) {
+			iter->skip++;
+			iter->p = p;
+			iter->list = list;
+			return rht_obj(ht, rhlist ? &list->rhead : p);
+		}
+
+		/* At the end of this slot, switch to next one and then find
+		 * next entry from that point.
+		 */
+		iter->skip = 0;
+		iter->slot++;
+	}
+
+	return __rhashtable_walk_find_next(iter);
+}
 EXPORT_SYMBOL_GPL(rhashtable_walk_next);
 
 /**
+ * rhashtable_walk_peek - Return the next object but don't advance the iterator
+ * @iter:	Hash table iterator
+ *
+ * Returns the next object or NULL when the end of the table is reached.
+ *
+ * Returns -EAGAIN if resize event occurred.  Note that the iterator
+ * will rewind back to the beginning and you may continue to use it.
+ */
+void *rhashtable_walk_peek(struct rhashtable_iter *iter)
+{
+	struct rhlist_head *list = iter->list;
+	struct rhashtable *ht = iter->ht;
+	struct rhash_head *p = iter->p;
+
+	if (!iter->walker.tbl)
+		return NULL;
+
+	if (p)
+		return rht_obj(ht, ht->rhlist ? &list->rhead : p);
+
+	/* No object found in current iter, find next one in the table. */
+
+	if (iter->skip) {
+		/* A nonzero skip value points to the next entry in the table
+		 * beyond that last one that was found. Decrement skip so
+		 * we find the current value. __rhashtable_walk_find_next
+		 * will restore the original value of skip assuming that
+		 * the table hasn't changed.
+		 */
+		iter->skip--;
+	}
+
+	return __rhashtable_walk_find_next(iter);
+}
+EXPORT_SYMBOL_GPL(rhashtable_walk_peek);
+
+/**
  * rhashtable_walk_stop - Finish a hash table walk
  * @iter:	Hash table iterator
  *
-- 
2.11.0