anchor.diff:      virtualisation.pathsInNixDB = [ config.system.build.toplevel ];
   
       virtualisation.sharedDirectories = {
  -      nix-store = { source = "/nix/store"; target = "/nix/store"; };
  -      xchg      = { source = ''"$TMPDIR"/xchg''; target = "/tmp/xchg"; };
  -      shared    = { source = ''"''${SHARED_DIR:-$TMPDIR/xchg}"''; target = "/tmp/shared"; };
  +      nix-store = mkIf (!cfg.useNixStoreImage) {
  +        source = builtins.storeDir;
  +        target = "/nix/store";
  +      };
  +      xchg = {
  +        source = ''"$TMPDIR"/xchg'';
  +        target = "/tmp/xchg";
  +      };
  +      shared = {
  +        source = ''"''${SHARED_DIR:-$TMPDIR/xchg}"'';
  +        target = "/tmp/shared";
  +      };
       };
   
       virtualisation.qemu.networkingOptions =
  
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:         };
      };
  
      virtualisation.useNixStoreImage =
        mkOption {
          type = types.bool;
          default = false;
          description = ''
            Build and use a disk image for the Nix store, instead of
            accessing the host's one through 9p.
  
            For applications which do a lot of reads from the store,
            this can drastically improve performance, but at the cost of
            disk space and image build time.
          '';
        };
  
      virtualisation.useBootLoader =
        mkOption {
          type = types.bool;
  