anchor.diff:  
     buildCommand =
       ''
  +      (
  +      mkdir -p ./files
  +      ${populateImageCommands}
  +      )
         # Add the closures of the top-level store objects.
         storePaths=$(cat ${sdClosureInfo}/store-paths)
   
         # Make a crude approximation of the size of the target image.
         # If the script starts failing, increase the fudge factors here.
  -      numInodes=$(find $storePaths | wc -l)
  -      numDataBlocks=$(du -c -B 4096 --apparent-size $storePaths | awk '$2 == "total" { print int($1 * 1.03) }')
  +      numInodes=$(find $storePaths ./files | wc -l)
  +      numDataBlocks=$(du -s -c -B 4096 --apparent-size $storePaths ./files | tail -1 | awk '{ print int($1 * 1.03) }')
         bytes=$((2 * 4096 * $numInodes + 4096 * $numDataBlocks))
         echo "Creating an EXT4 image of $bytes bytes (numInodes=$numInodes, numDataBlocks=$numDataBlocks)"
   
  
positive.code: 
        echo "copying store paths to image..."
        cptofs -t ext4 -i $out $storePaths /nix/store/
  
        # I have ended up with corrupted images sometimes, I suspect that happens when the build machine's disk gets full during the build.
        if ! fsck.ext4 -n -f $out; then
  
negative.code: # Builds an ext4 image containing a populated /nix/store with the closure
  # of store paths passed in the storePaths parameter, in addition to the
  # contents of a directory that can be populated with commands. The
  # generated image is sized to only fit its contents, with the expectation
  # that a script resizes the filesystem at boot time.
  { pkgs
  # List of derivations to be included
  , storePaths
  # Shell commands to populate the ./files directory.
  # All files in that directory are copied to the root of the FS.
  , populateImageCommands ? ""
  , volumeLabel
  , uuid ? "44444444-4444-4444-8888-888888888888"
  , e2fsprogs
  