Possibility to physically reserve space without writing leaf blocks

@@ -134,10 +134,11 @@
 
 /*
  * boot archive compression
  */
 #define _FIO_COMPRESSED         _IO('f', 99) /* mark file as compressed */
+#define _FIO_RESERVE_SPACE      _IO('f', 100) /* Reserve space */
 
 #ifdef  __cplusplus
 }
 #endif