1 files changed, 133 insertions, 0 deletions

diff --git a/modules/borgbackup/lvm-snapshots.nix b/modules/borgbackup/lvm-snapshots.nix
new file mode 100644
index 00000000..9b2a6562
--- /dev/null
+++ b/modules/borgbackup/lvm-snapshots.nix
@@ -0,0 +1,133 @@
+{ config, lib, utils, pkgs, ... }:
+
+with utils;
+with lib;
+
+let
+  cfg = config.services.lvm-snapshots;
+
+  snapshotMount = name: "${cfg.mountPoint}/${if isNull cfg.snapshots."${name}".mountName then name else cfg.snapshots."${name}".mountName}";
+  snapshotName = name: "${name}-${cfg.mountSuffix}";
+
+  snapshotConfig = {
+    options = {
+      LV = mkOption {
+        type = types.str;
+      };
+
+      VG = mkOption {
+        type = types.str;
+      };
+
+      mountName = mkOption {
+        type = types.nullOr types.str;
+        default = null;
+      };
+      
+      cowSize = mkOption {
+        type = types.str;
+        default = "-l20%ORIGIN";
+      };
+
+      readOnly = mkOption {
+        type = types.bool;
+        default = true;
+      };
+
+      persist = mkOption {
+        type = types.bool;
+        default = false;
+      };
+    };
+  };
+in {
+  options = {
+
+    services.lvm-snapshots = {
+      snapshots = mkOption {
+        type = types.attrsOf (types.submodule snapshotConfig);
+        default = {};
+      };
+
+      mountPoint = mkOption {
+        type = types.path;
+        default = "/mnt";
+      };
+
+      mountSuffix = mkOption {
+        type = types.str;
+        default = "-snapshot";
+      };
+    };
+  };
+
+  
+  config = mkIf (cfg != {}) {
+
+    boot.kernelModules = [ "dm_snapshot" ];
+
+    # system.activationScripts = mapAttrs' (name: scfg: nameValuePair ("lvm-mountpoint" + name) ''
+    #   mkdir -p ${snapshotMount name}
+    # '') cfg.snapshots;
+
+    systemd.services = mapAttrs' (name: scfg: nameValuePair ("lvm-snapshot@" + escapeSystemdPath name) {
+      enable = true;
+
+      description = "LVM-snapshot of ${scfg.VG}/${scfg.LV}";
+
+      bindsTo = ["${escapeSystemdPath "/dev/${scfg.VG}/${scfg.LV}"}.device"];
+      after = ["${escapeSystemdPath "/dev/${scfg.VG}/${scfg.LV}"}.device"];
+
+      unitConfig = {
+        StopWhenUnneeded = !scfg.persist;
+        AssertPathIsDirectory = "/var/lock";
+      };
+
+      path = with pkgs; [ devicemapper utillinux ];
+      
+      script = ''
+        (
+          flock -xn -E 4 9
+          if [[ "$?" -ne 0 ]]; then
+            exit $?
+          fi
+          
+          lvcreate -s ${scfg.cowSize} --name ${snapshotName name} ${scfg.VG}/${scfg.LV}
+
+          sleep infinity &
+        ) 9>/var/lock/lvm-snapshot.${scfg.VG}
+      '';
+      
+      preStart = ''
+        lvremove -f ${scfg.VG}/${snapshotName name}
+      '';
+
+      preStop = ''
+        lvremove -f ${scfg.VG}/${snapshotName name}
+      '';
+
+      serviceConfig = with pkgs; {
+        Type = "forking";
+        RestartForceExitStatus = [ "4" ];
+        RestartSec = "5min";
+      };
+    }) cfg.snapshots;
+
+    systemd.mounts = mapAttrsToList (name: scfg: {
+      enable = true;
+
+      unitConfig = {
+        # AssertPathIsDirectory = snapshotMount name;
+        StopWhenUnneeded = !scfg.persist;
+      };
+
+      bindsTo = [ ("lvm-snapshot@" + escapeSystemdPath name + ".service") ];
+      after = [ ("lvm-snapshot@" + escapeSystemdPath name + ".service") ];
+
+      options = concatStringsSep "," ([ "noauto" ] ++ optional scfg.readOnly "ro");
+
+      where = snapshotMount name;
+      what = "/dev/" + scfg.VG + "/" + snapshotName name;
+    }) cfg.snapshots;
+  };
+}