anchor.diff:    createEmptyImage = {size, fullName}: ''
       mkdir $out
       diskImage=$out/disk-image.qcow2
  -    qemu-img create -f qcow2 $diskImage "${toString size}M"
  +    ${kvm}/bin/qemu-img create -f qcow2 $diskImage "${toString size}M"
   
       mkdir $out/nix-support
       echo "${fullName}" > $out/nix-support/full-name
  
positive.code:       diskImage=$(pwd)/disk-image.qcow2
        origImage=${attrs.diskImage}
        if test -d "$origImage"; then origImage="$origImage/disk-image.qcow2"; fi
        qemu-img create -b "$origImage" -f qcow2 $diskImage
      '';
  
      /* Inside the VM, run the stdenv setup script normally, but at the
  
negative.code:     fi
      diskImage="$1"
      if ! test -e "$diskImage"; then
        ${kvm}/bin/qemu-img create -b ${image}/disk-image.qcow2 -f qcow2 "$diskImage"
      fi
      export TMPDIR=$(mktemp -d)
      export out=/dummy
  