-struct hashtab *hashtab_create(u32 (*hash_value)(struct hashtab *h, void *key),
- int (*keycmp)(struct hashtab *h, void *key1, void *key2),
+struct hashtab *hashtab_create(u32 (*hash_value)(struct hashtab *h, const void *key),
+ int (*keycmp)(struct hashtab *h, const void *key1, const void *key2),