+/* check for OS and include appropriate headers */
+#if defined(__linux__)
+#include "linux.h"
+#elif defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
+#include "freebsd.h"
+#elif defined(__OpenBSD__)
+#include "openbsd.h"
+#endif
+
+/* OS specific prototypes to be implemented by linux.c & Co. */
+void update_entropy(void);
+