anchor.diff:        echo "testing patched programs..."
         $out/bin/ash -c 'echo hello world' | grep "hello world"
         export LD_LIBRARY_PATH=$out/lib
  -      $out/bin/mount --help 2>&1 | grep -q "BusyBox"
  +      ${if zfsRequiresMountHelper then ''
  +        $out/bin/mount -V 1>&1 | grep -q "mount from util-linux"
  +        $out/bin/mount.zfs -h 2>&1 | grep -q "Usage: mount.zfs"
  +      '' else ''
  +        $out/bin/mount --help 2>&1 | grep -q "BusyBox"
  +      ''}
         $out/bin/blkid -V 2>&1 | grep -q 'libblkid'
         $out/bin/udevadm --version
         $out/bin/dmsetup --version 2>&1 | tee -a log | grep -q "version:"
  
positive.code:   # booting (such as the FS containing `/nix/store`, or an FS needed for
    # mounting `/`, like `/` on a loopback).
    fileSystems = filter utils.fsNeededForBoot config.system.build.fileSystems;
  
    # A utility for enumerating the shared-library dependencies of a program
    findLibs = pkgs.buildPackages.writeShellScriptBin "find-libs" ''
  
negative.code:       for BIN in ${pkgs.busybox}/{s,}bin/*; do
          copy_bin_and_libs $BIN
        done
  
        ${optionalString zfsRequiresMountHelper ''
          # Filesystems using the "zfsutil" option are mounted regardless of the
          # mount.zfs(8) helper, but it is required to ensure that ZFS properties
          # are used as mount options.
          #
          # BusyBox does not use the ZFS helper in the first place.
          # util-linux searches /sbin/ as last path for helpers (stage-1-init.sh
          # must symlink it to the store PATH).
          # Without helper program, both `mount`s silently fails back to internal
          # code, using default options and effectively ignore security relevant
          # ZFS properties such as `setuid=off` and `exec=off` (unless manually
          # duplicated in `fileSystems.*.options`, defeating "zfsutil"'s purpose).
          copy_bin_and_libs ${pkgs.util-linux}/bin/mount
          copy_bin_and_libs ${pkgs.zfs}/bin/mount.zfs
        ''}
  
        # Copy some util-linux stuff.
        copy_bin_and_libs ${pkgs.util-linux}/sbin/blkid
  