How to make library generic?

ProgrammableLib/dll.h

@@ -0,0 +1,41 @@
+/*
+ * =====================================================================================
+ *
+ *       Filename:  dll.h
+ *
+ *    Description:  
+ *
+ *        Version:  1.0
+ *        Created:  05/02/24 12:08:34 AM IST
+ *       Revision:  none
+ *       Compiler:  gcc
+ *
+ *         Author:  YOUR NAME (), 
+ *   Organization:  
+ *
+ * =====================================================================================
+ */
+
+/*Header file for Doubly Linked List*/
+
+typedef struct dll_node_{
+
+    void *data;
+    struct dll_node_ *left;
+    struct dll_node_ *right;
+} dll_node_t;
+
+typedef struct dll_{
+    dll_node_t *head;
+} dll_t;
+
+
+/* Public Function declaration to create and return
+ * a new empty doubly linked list*/
+dll_t *
+get_new_dll();
+
+/*  Public Function declaration to add the appication
+ *  data to DLL*/
+int
+add_data_to_dll(dll_t *dll, void *appn_data);