Treat discs with empty first 64k as blank, and as full otherwise.

src/isofs_wrap.c

@@ -240,8 +240,19 @@ int isoburn_start_emulation(struct isoburn *o, int flag)
    isoburn_set_start_byte(o, (off_t) 0, 0);
    o->fabricated_disc_status= BURN_DISC_BLANK;
  } else {
-   // TODO for now I treat this as a full disc
-   o->fabricated_disc_status= BURN_DISC_FULL;
+   int i;
+
+   /* check first 64K. If 0's, the disc is treated as a blank disc, and thus
+      overwritten without extra check. If not, the disc is treated as full,
+      and user needs to isoburn_disc_erase() it before burn it again */
+   i = sizeof(o->target_iso_head);
+   while (i && !o->target_iso_head[i-1]) 
+     --i;
+
+   if (i) 
+     o->fabricated_disc_status= BURN_DISC_FULL;
+   else
+     o->fabricated_disc_status= BURN_DISC_BLANK;
  }
  return 1;
 }