Possibility to physically reserve space without writing leaf blocks

@@ -304,10 +304,11 @@
         uint8_t                 zp_level;
         uint8_t                 zp_copies;
         boolean_t               zp_dedup;
         boolean_t               zp_dedup_verify;
         boolean_t               zp_nopwrite;
+        boolean_t               zp_zero_write;
 } zio_prop_t;
 
 typedef struct zio_cksum_report zio_cksum_report_t;
 
 typedef void zio_cksum_finish_f(zio_cksum_report_t *rep,