1 files changed, 95 insertions, 0 deletions

diff --git a/custom/lvm-snapshots.nix b/custom/lvm-snapshots.nix
new file mode 100644
index 00000000..67ee2cbd
--- /dev/null
+++ b/custom/lvm-snapshots.nix
@@ -0,0 +1,95 @@
+{ config, lib, pkgs, ... }:
+
+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}";
+
+  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";
+      };
+    };
+  };
+
+  
+  config = mkIf (cfg != {}) {
+
+    system.activationScripts = mapAttrs' (name: scfg: nameValuePair (lvm-mountpoint + name) ''
+      mkdir -p ${snapshotMount name}
+    '') cfg.snapshots;
+
+    systemd.services = mapAttrs' (name: scfg: nameValuePair ("lvm-snapshot@" + name) {
+      enable = true;
+
+      unitConfig = {
+        StopWhenUnneeded = true;
+      };
+
+      serviceConfig = with pkgs; {
+        Type = "oneshot";
+        ExecStart = "${devicemapper}/bin/lvcreate -s ${cfg.cowSize} --name ${name} ${scfg.VG}/${scfg.LV}";
+        ExecStop = "${devicemapper}/bin/lvremove ${scfg.VG}/${name}";
+        RemainAfterExit = true;
+      };
+    }) cfg.snapshots;
+
+    systemd.mounts = mapAttrsToList (name: scfg: {
+      enable = true;
+
+      unitConfig = {
+        AssertPathIsDirectory = snapshotMount name;
+        StopWhenUnneeded = !scfg.persist;
+      };
+
+      bindsTo = "lvm-snapshot@" + name;
+
+      options = mkIf scfg.readOnly "ro";
+
+      where = snapshotMount name;
+      what = "/dev/" + scfg.VG + "/" + name;
+    }) cfg.snapshots;
+  };
+}