nixos/backup/tsm: init module

Based on the programs/tsm-client module,
this commit introduces a systemd service that uses the
tsm-client to create regular backups of the machine.

nixos/modules/module-list.nix

@@ -210,6 +210,7 @@
   ./services/backup/restic-rest-server.nix
   ./services/backup/rsnapshot.nix
   ./services/backup/tarsnap.nix
+  ./services/backup/tsm.nix
   ./services/backup/znapzend.nix
   ./services/cluster/hadoop/default.nix
   ./services/cluster/kubernetes/addons/dns.nix

nixos/modules/services/backup/tsm.nix

@@ -0,0 +1,106 @@
+{ config, lib, ... }:
+
+let
+
+  inherit (lib.attrsets) hasAttr;
+  inherit (lib.modules) mkDefault mkIf;
+  inherit (lib.options) mkEnableOption mkOption;
+  inherit (lib.types) nullOr strMatching;
+
+  options.services.tsmBackup = {
+    enable = mkEnableOption ''
+      automatic backups with the
+      IBM Spectrum Protect (Tivoli Storage Manager, TSM) client.
+      This also enables
+      <option>programs.tsmClient.enable</option>
+    '';
+    command = mkOption {
+      type = strMatching ".+";
+      default = "backup";
+      example = "incr";
+      description = ''
+        The actual command passed to the
+        <literal>dsmc</literal> executable to start the backup.
+      '';
+    };
+    servername = mkOption {
+      type = strMatching ".+";
+      example = "mainTsmServer";
+      description = ''
+        Create a systemd system service
+        <literal>tsm-backup.service</literal> that starts
+        a backup based on the given servername's stanza.
+        Note that this server's
+        <option>passwdDir</option> will default to
+        <filename>/var/lib/tsm-backup/password</filename>
+        (but may be overridden);
+        also, the service will use
+        <filename>/var/lib/tsm-backup</filename> as
+        <literal>HOME</literal> when calling
+        <literal>dsmc</literal>.
+      '';
+    };
+    autoTime = mkOption {
+      type = nullOr (strMatching ".+");
+      default = null;
+      example = "12:00";
+      description = ''
+        The backup service will be invoked
+        automatically at the given date/time,
+        which must be in the format described in
+        <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+        The default <literal>null</literal>
+        disables automatic backups.
+      '';
+    };
+  };
+
+  cfg = config.services.tsmBackup;
+  cfgPrg = config.programs.tsmClient;
+
+  assertions = [
+    {
+      assertion = hasAttr cfg.servername cfgPrg.servers;
+      message = "TSM service servername not found in list of servers";
+    }
+    {
+      assertion = cfgPrg.servers.${cfg.servername}.genPasswd;
+      message = "TSM service requires automatic password generation";
+    }
+  ];
+
+in
+
+{
+
+  inherit options;
+
+  config = mkIf cfg.enable {
+    inherit assertions;
+    programs.tsmClient.enable = true;
+    programs.tsmClient.servers."${cfg.servername}".passwdDir =
+      mkDefault "/var/lib/tsm-backup/password";
+    systemd.services.tsm-backup = {
+      description = "IBM Spectrum Protect (Tivoli Storage Manager) Backup";
+      # DSM_LOG needs a trailing slash to have it treated as a directory.
+      # `/var/log` would be littered with TSM log files otherwise.
+      environment.DSM_LOG = "/var/log/tsm-backup/";
+      # TSM needs a HOME dir to store certificates.
+      environment.HOME = "/var/lib/tsm-backup";
+      # for exit status description see
+      # https://www.ibm.com/support/knowledgecenter/en/SSEQVQ_8.1.8/client/c_sched_rtncode.html
+      serviceConfig.SuccessExitStatus = "4 8";
+      # The `-se` option must come after the command.
+      # The `-optfile` option suppresses a `dsm.opt`-not-found warning.
+      serviceConfig.ExecStart =
+        "${cfgPrg.wrappedPackage}/bin/dsmc ${cfg.command} -se='${cfg.servername}' -optfile=/dev/null";
+      serviceConfig.LogsDirectory = "tsm-backup";
+      serviceConfig.StateDirectory = "tsm-backup";
+      serviceConfig.StateDirectoryMode = "0750";
+      startAt = mkIf (cfg.autoTime!=null) cfg.autoTime;
+    };
+  };
+
+  meta.maintainers = [ lib.maintainers.yarny ];
+
+}