nixpkgs/nixos/modules/tasks/filesystems/ext.nix

{ config, lib, pkgs, ... }:

let

  inInitrd = lib.any (fs: fs == "ext2" || fs == "ext3" || fs == "ext4") config.boot.initrd.supportedFilesystems;

in

{
  config = {

    system.fsPackages = lib.mkIf (config.boot.initrd.systemd.enable -> inInitrd) [ pkgs.e2fsprogs ];

    # As of kernel 4.3, there is no separate ext3 driver (they're also handled by ext4.ko)
    boot.initrd.availableKernelModules = lib.mkIf (config.boot.initrd.systemd.enable -> inInitrd) [ "ext2" "ext4" ];

    boot.initrd.extraUtilsCommands = lib.mkIf (!config.boot.initrd.systemd.enable)
      ''
        # Copy e2fsck and friends.
        copy_bin_and_libs ${pkgs.e2fsprogs}/sbin/e2fsck
        copy_bin_and_libs ${pkgs.e2fsprogs}/sbin/tune2fs
        ln -sv e2fsck $out/bin/fsck.ext2
        ln -sv e2fsck $out/bin/fsck.ext3
        ln -sv e2fsck $out/bin/fsck.ext4
      '';

  };
}