anchor.diff:  
     qemuCommandLinux = ''
       ${qemuProg} \
  -      -enable-kvm \
         ${lib.optionalString (pkgs.stdenv.system == "x86_64-linux") "-cpu kvm64"} \
         -nographic -no-reboot \
         -virtfs local,path=/nix/store,security_model=none,mount_tag=store \
  
positive.code:       diskImage=$(pwd)/disk-image.qcow2
        origImage=${attrs.diskImage}
        if test -d "$origImage"; then origImage="$origImage/disk-image.qcow2"; fi
        ${kvm}/bin/qemu-img create -b "$origImage" -f qcow2 $diskImage
      '';
  
      /* Inside the VM, run the stdenv setup script normally, but at the
  
negative.code: 
  rec {
  
    qemu = pkgs.qemu_kvm;
  
    qemuProg = "${qemu}/bin/qemu-kvm";
  
  
    modulesClosure = makeModulesClosure {
  