some cleanup/bug fixes

include/common.h

@@ -25,10 +25,13 @@
 #define RETVAL_INVALID_DIR          2
 #define RETVAL_UNRECOGNIZED_OPTION  3
 #define RETVAL_MISSING_OPTION       4
-#define RETVAL_INVALID_DEVICE      -5
+#define RETVAL_INVALID_DEVICE       5
 #define RETVAL_MEM_ERROR            6
+#define RETVAL_INTERNAL_ERROR       7
 #define RETVAL_SUCCESS              EXIT_SUCCESS
+extern int return_value;
 
+void mem_error(void);
 _Noreturn void usage(int exit_val);