+/**
+ * shachain_next_index - what's the next index I can add to the shachain?
+ * @chain: the chain
+ *
+ * This returns 0xFFFFFFFFFFFFFFFF (for a freshly
+ * initialized chain), or one less than the previously successfully
+ * added value.
+ */
+uint64_t shachain_next_index(const struct shachain *chain);
+