diff -r 3ee5a5c7823a -r 313fd460d264 src/cx/linked_list.h
--- a/src/cx/linked_list.h	Sun Nov 30 15:06:02 2025 +0100
+++ b/src/cx/linked_list.h	Sun Nov 30 15:41:15 2025 +0100
@@ -62,7 +62,14 @@
      */
     off_t loc_data;
     /**
+     * Location of extra data (optional).
+     * Negative when no extra data is requested.
+     * @see cx_linked_list_extra_data()
+     */
+    off_t loc_extra;
+    /**
      * Additional bytes to allocate @em behind the payload (e.g. for metadata).
+     * @see cx_linked_list_extra_data()
      */
     size_t extra_data_len;
     /**
@@ -112,6 +119,23 @@
         cxLinkedListCreate(NULL, NULL, elem_size)
 
 /**
+ * Instructs the linked list to reserve extra data in each node.
+ *
+ * The extra data will be aligned and placed behind the element data.
+ * The exact location in the node is stored in the @c loc_extra field
+ * of the linked list.
+ *
+ * You should usually not use this function except when you are creating an
+ * own linked-list implementation that is based on the UCX linked list and
+ * needs to store extra data in each node.
+ *
+ * @param list the list (must be a linked list)
+ * @param len the length of the extra data
+ */
+cx_attr_nonnull
+CX_EXPORT void cx_linked_list_extra_data(cx_linked_list *list, size_t len);
+
+/**
  * Finds the node at a certain index.
  *
  * This function can be used to start at an arbitrary position within the list.