{ config, lib, pkgs, utils, ... }: with lib; let inInitrd = any (fs: fs == "btrfs") config.boot.initrd.supportedFilesystems; inSystem = any (fs: fs == "btrfs") config.boot.supportedFilesystems; cfgScrub = config.services.btrfs.autoScrub; enableAutoScrub = cfgScrub.enable; enableBtrfs = inInitrd || inSystem || enableAutoScrub; in { options = { # One could also do regular btrfs balances, but that shouldn't be necessary # during normal usage and as long as the filesystems aren't filled near capacity services.btrfs.autoScrub = { enable = mkEnableOption "regular btrfs scrub"; fileSystems = mkOption { type = types.listOf types.path; example = [ "/" ]; description = lib.mdDoc '' List of paths to btrfs filesystems to regularily call {command}`btrfs scrub` on. Defaults to all mount points with btrfs filesystems. If you mount a filesystem multiple times or additionally mount subvolumes, you need to manually specify this list to avoid scrubbing multiple times. ''; }; interval = mkOption { default = "monthly"; type = types.str; example = "weekly"; description = '' Systemd calendar expression for when to scrub btrfs filesystems. The recommended period is a month but could be less (btrfs-scrub 8). See systemd.time 7 for more information on the syntax. ''; }; }; }; config = mkMerge [ (mkIf enableBtrfs { system.fsPackages = [ pkgs.btrfs-progs ]; boot.initrd.kernelModules = mkIf inInitrd [ "btrfs" ]; boot.initrd.availableKernelModules = mkIf inInitrd ( [ "crc32c" ] ++ optionals (config.boot.kernelPackages.kernel.kernelAtLeast "5.5") [ # Needed for mounting filesystems with new checksums "xxhash_generic" "blake2b_generic" "sha256_generic" # Should be baked into our kernel, just to be sure ] ); boot.initrd.extraUtilsCommands = mkIf (inInitrd && !config.boot.initrd.systemd.enable) '' copy_bin_and_libs ${pkgs.btrfs-progs}/bin/btrfs ln -sv btrfs $out/bin/btrfsck ln -sv btrfsck $out/bin/fsck.btrfs ''; boot.initrd.extraUtilsCommandsTest = mkIf (inInitrd && !config.boot.initrd.systemd.enable) '' $out/bin/btrfs --version ''; boot.initrd.postDeviceCommands = mkIf (inInitrd && !config.boot.initrd.systemd.enable) '' btrfs device scan ''; }) (mkIf enableAutoScrub { assertions = [ { assertion = cfgScrub.enable -> (cfgScrub.fileSystems != []); message = '' If 'services.btrfs.autoScrub' is enabled, you need to have at least one btrfs file system mounted via 'fileSystems' or specify a list manually in 'services.btrfs.autoScrub.fileSystems'. ''; } ]; # This will yield duplicated units if the user mounts a filesystem multiple times # or additionally mounts subvolumes, but going the other way around via devices would # yield duplicated units when a filesystem spans multiple devices. # This way around seems like the more sensible default. services.btrfs.autoScrub.fileSystems = mkDefault (mapAttrsToList (name: fs: fs.mountPoint) (filterAttrs (name: fs: fs.fsType == "btrfs") config.fileSystems)); # TODO: Did not manage to do it via the usual btrfs-scrub@.timer/.service # template units due to problems enabling the parameterized units, # so settled with many units and templating via nix for now. # https://github.com/NixOS/nixpkgs/pull/32496#discussion_r156527544 systemd.timers = let scrubTimer = fs: let fs' = utils.escapeSystemdPath fs; in nameValuePair "btrfs-scrub-${fs'}" { description = "regular btrfs scrub timer on ${fs}"; wantedBy = [ "timers.target" ]; timerConfig = { OnCalendar = cfgScrub.interval; AccuracySec = "1d"; Persistent = true; }; }; in listToAttrs (map scrubTimer cfgScrub.fileSystems); systemd.services = let scrubService = fs: let fs' = utils.escapeSystemdPath fs; in nameValuePair "btrfs-scrub-${fs'}" { description = "btrfs scrub on ${fs}"; # scrub prevents suspend2ram or proper shutdown conflicts = [ "shutdown.target" "sleep.target" ]; before = [ "shutdown.target" "sleep.target" ]; serviceConfig = { # simple and not oneshot, otherwise ExecStop is not used Type = "simple"; Nice = 19; IOSchedulingClass = "idle"; ExecStart = "${pkgs.btrfs-progs}/bin/btrfs scrub start -B ${fs}"; # if the service is stopped before scrub end, cancel it ExecStop = pkgs.writeShellScript "btrfs-scrub-maybe-cancel" '' (${pkgs.btrfs-progs}/bin/btrfs scrub status ${fs} | ${pkgs.gnugrep}/bin/grep finished) || ${pkgs.btrfs-progs}/bin/btrfs scrub cancel ${fs} ''; }; }; in listToAttrs (map scrubService cfgScrub.fileSystems); }) ]; }