Add mdb_cursor_txn() and mdb_cursor_dbi() for querying the cursor

libraries/libmdb/mdb.c

@@ -4700,6 +4700,20 @@ mdb_cursor_close(MDB_cursor *mc)
 	}
 }
 
+MDB_txn *
+mdb_cursor_txn(MDB_cursor *mc)
+{
+	if (!mc) return NULL;
+	return mc->mc_txn;
+}
+
+MDB_dbi
+mdb_cursor_dbi(MDB_cursor *mc)
+{
+	if (!mc) return 0;
+	return mc->mc_dbi;
+}
+
 /** Replace the key for a node with a new key.
  * @param[in] mp The page containing the node to operate on.
  * @param[in] indx The index of the node to operate on.

libraries/libmdb/mdb.h

@@ -846,6 +846,18 @@ int  mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
 	 */
 void mdb_cursor_close(MDB_cursor *cursor);
 
+	/** @brief Return the cursor's transaction handle.
+	 *
+	 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
+	 */
+MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
+
+	/** @brief Return the cursor's database handle.
+	 *
+	 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
+	 */
+MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor);
+
 	/** @brief Retrieve by cursor.
 	 *
 	 * This function retrieves key/data pairs from the database. The address and length