anchor.diff:              options = [ "trans=virtio" "version=9p2000.L" ];
               neededForBoot = true;
             };
  -      } // optionalAttrs cfg.writableStore
  -      { "/nix/store" =
  -          { fsType = "unionfs-fuse";
  -            device = "unionfs";
  -            options = [ "allow_other" "cow" "nonempty" "chroot=/mnt-root" "max_files=32768" "hide_meta_files" "dirs=/nix/.rw-store=rw:/nix/.ro-store=ro" ];
  -          };
         } // optionalAttrs (cfg.writableStore && cfg.writableStoreUseTmpfs)
         { "/nix/.rw-store" =
             { fsType = "tmpfs";
  
positive.code:       '';
  
      boot.initrd.availableKernelModules =
        optional (cfg.qemu.diskInterface == "scsi") "sym53c8xx";
  
      virtualisation.bootDevice =
        mkDefault (if cfg.qemu.diskInterface == "scsi" then "/dev/sda" else "/dev/vda");
  
negative.code:         description =
            ''
              If enabled, the Nix store in the VM is made writable by
              layering an overlay filesystem on top of the host's Nix
              store.
            '';
        };
  