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

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

with lib;

let

  inInitrd = any (fs: fs == "btrfs") config.boot.initrd.supportedFilesystems;

in

{
  config = mkIf (any (fs: fs == "btrfs") config.boot.supportedFilesystems) {

    system.fsPackages = [ pkgs.btrfsProgs ];

    boot.initrd.kernelModules = mkIf inInitrd [ "btrfs" "crc32c" ];

    boot.initrd.extraUtilsCommands = mkIf inInitrd
      ''
        mkdir -p $out/bin
        cp -v ${pkgs.btrfsProgs}/bin/btrfs $out/bin
        ln -sv btrfs $out/bin/btrfsck
        ln -sv btrfsck $out/bin/fsck.btrfs
        # !!! Increases uncompressed initrd by 240k
        cp -pv ${pkgs.zlib}/lib/libz.so* $out/lib
        cp -pv ${pkgs.lzo}/lib/liblzo2.so* $out/lib
      '';

    boot.initrd.extraUtilsCommandsTest = mkIf inInitrd
      ''
        $out/bin/btrfs --version
      '';

    boot.initrd.postDeviceCommands = mkIf inInitrd
      ''
        btrfs device scan
      '';

    # !!! This is broken.  There should be a udev rule to do this when
    # new devices are discovered.
    jobs.udev.postStart =
      ''
        ${pkgs.btrfsProgs}/bin/btrfs device scan
      '';

  };
}