diff --git a/src/common/remoteio.h b/src/common/remoteio.h
--- a/src/common/remoteio.h
+++ b/src/common/remoteio.h
@@ -129,4 +129,10 @@ int remoteio_write(struct remoteio *rem,
 */
 int remoteio_close(struct remoteio *rem);
 
+/**
+ * Returns the number of unfulfilled remoteio_write() calls pending on
+ * a remoteio handle.
+ */
+size_t remoteio_sendq_len(const struct remoteio *rem);
+
 #endif