int walk_directory (const char *dir, dirwalk_callback_f callback,
void *user_data, int hidden);
/* Returns the number of bytes read or negative on error. */
-int read_file_contents (const char *filename, char *buf, int bufsize);
+ssize_t read_file_contents (char const *filename, char *buf, size_t bufsize);
counter_t counter_diff (counter_t old_value, counter_t new_value);