-struct cvg *get_mod_cov(PyObject *py_cov, char *module_name);
-void cvg_add(struct cvg *dst, struct cvg *src);
-struct cvg *cvg_new(void);
-gboolean find_missed_line(struct cvg *cvg, char *linespec);
+static struct cvg *get_mod_cov(PyObject *py_cov, const char *module_name);
+static void cvg_add(struct cvg *dst, const struct cvg *src);
+static struct cvg *cvg_new(void);
+static gboolean find_missed_line(struct cvg *cvg, const char *linespec);