[PATCH 2/3] rhashtable: Add rhashtable_walk_curr

[Andreas Gruenbacher <agruenba@redhat.com>]

When iterating through an rhashtable is stopped with
rhashtable_walk_stop and then resumed with rhashtable_walk_start, there
currently is no way to get back to the current object and thus revisit
the object rhashtable_walk_next has previously returned.

This functionality is useful when dumping an rhashtable via the seq file
interface: seq_read will convert one object after the other.  When an
object doesn't fit in the remaining buffer space anymore, user-space
will be returned all objects that have been fully converted so far.
Upon the next read from user-space, the object that didn't fit
previously will be revisited.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
---
 include/linux/rhashtable.h |  1 +
 lib/rhashtable.c           | 17 +++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 361c08e35dbc..1a1608bc5405 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);
 int rhashtable_walk_start(struct rhashtable_iter *iter) __acquires(RCU);
 void *rhashtable_walk_next(struct rhashtable_iter *iter);
+void *rhashtable_walk_curr(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 ddd7dde87c3c..1d45a4274b7a 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -842,6 +842,23 @@ void *rhashtable_walk_next(struct rhashtable_iter *iter)
 }
 EXPORT_SYMBOL_GPL(rhashtable_walk_next);
 
+/**
+ * rhashtable_walk_next - Return the current object
+ * @iter:	Hash table iterator
+ *
+ * Returns the object previously returned by rhashtable_walk_next.
+ *
+ * Returns -ENOENT if rhashtable_walk_next hasn't been called previously.
+ */
+void *rhashtable_walk_curr(struct rhashtable_iter *iter)
+{
+	if (!iter->skip)
+		return ERR_PTR(-ENOENT);
+	iter->skip--;
+	return rhashtable_walk_next(iter);
+}
+EXPORT_SYMBOL_GPL(rhashtable_walk_curr);
+
 /**
  * rhashtable_walk_stop - Finish a hash table walk
  * @iter:	Hash table iterator
-- 
2.14.3