diff --git a/qemu/qapi/qobject-input-visitor.c b/qemu/qapi/qobject-input-visitor.c
index 672ecd9a..68dd3a4e 100644
--- a/qemu/qapi/qobject-input-visitor.c
+++ b/qemu/qapi/qobject-input-visitor.c
@@ -50,6 +50,17 @@ static QObjectInputVisitor *to_qiv(Visitor *v)
     return container_of(v, QObjectInputVisitor, visitor);
 }
 
+/*
+ * Find the full name of something @qiv is currently visiting.
+ * @qiv is visiting something named @name in the stack of containers
+ * @qiv->stack.
+ * If @n is zero, return its full name.
+ * If @n is positive, return the full name of the @n-th container
+ * counting from the top.  The stack of containers must have at least
+ * @n elements.
+ * The returned string is valid until the next full_name_nth(@v) or
+ * destruction of @v.
+ */
 static const char *full_name_nth(QObjectInputVisitor *qiv, const char *name,
                                  int n)
 {