anchor.diff:        if [ -z "$TMPDIR" ] || [ -z "$USE_TMPDIR" ]; then
             TMPDIR=$(mktemp -d nix-vm.XXXXXXXXXX --tmpdir)
         fi
  +
  +      ${lib.optionalString cfg.useNixStoreImage
  +      ''
  +        # Create a writable copy/snapshot of the store image.
  +        ${qemu}/bin/qemu-img create -f qcow2 -F qcow2 -b ${storeImage}/nixos.qcow2 "$TMPDIR"/store.img
  +      ''}
   
         # Create a directory for exchanging data with the VM.
         mkdir -p "$TMPDIR/xchg"
  
positive.code:         driveExtraOpts.cache = "writeback";
          driveExtraOpts.werror = "report";
        }]
        (mkIf cfg.useBootLoader [
          # The order of this list determines the device names, see
          # note [Disk layout with `useBootLoader`].
  
negative.code:             options = [ "mode=1777" "strictatime" "nosuid" "nodev" "size=${toString config.boot.tmpOnTmpfsSize}" ];
            };
  
          "/nix/${if cfg.writableStore then ".ro-store" else "store"}" =
            mkIf cfg.useNixStoreImage
              { device = "${lookupDriveDeviceName "nix-store" cfg.qemu.drives}";
                neededForBoot = true;
                options = [ "ro" ];
              };
  
          "/nix/.rw-store" = mkIf (cfg.writableStore && cfg.writableStoreUseTmpfs)
            { fsType = "tmpfs";
              options = [ "mode=0755" ];
  