anchor.diff:      export > saved-env
   
       PATH=${coreutils}/bin
  +    mkdir xchg
  +    mv saved-env xchg/
   
       diskImage=''${diskImage:-/dev/null}
   
  
positive.code:       -drive file=$diskImage,if=virtio,cache=writeback,werror=report \
        -kernel ${kernel}/${img} \
        -initrd ${initrd}/initrd \
        -append "console=ttyS0 panic=1 command=${stage2Init} tmpDir=$TMPDIR out=$out mountDisk=$mountDisk" \
        $QEMU_OPTS
    '';
  
  
negative.code:   
    stage2Init = writeScript "vm-run-stage2" ''
      #! ${bash}/bin/sh
      source /tmp/xchg/saved-env
      
      export NIX_STORE=/nix/store
      export NIX_BUILD_TOP=/tmp
      export TMPDIR=/tmp
      export PATH=/empty
      out="$1"
      cd "$NIX_BUILD_TOP"
  
      if ! test -e /bin/sh; then
  