services: add GlusterFS service

This service is only limited in configuration options.
But it is sufficient to run glusterd and configure it using the gluster command

nixos/modules/module-list.nix

@@ -339,6 +339,7 @@
   ./services/monitoring/zabbix-server.nix
   ./services/network-filesystems/cachefilesd.nix
   ./services/network-filesystems/drbd.nix
+  ./services/network-filesystems/glusterfs.nix
   ./services/network-filesystems/ipfs.nix
   ./services/network-filesystems/netatalk.nix
   ./services/network-filesystems/nfsd.nix

nixos/modules/services/network-filesystems/glusterfs.nix

@@ -0,0 +1,84 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  inherit (pkgs) glusterfs;
+
+  cfg = config.services.glusterfs;
+
+in
+
+{
+
+  ###### interface
+
+  options = {
+
+    services.glusterfs = {
+
+      enable = mkEnableOption "GlusterFS Daemon";
+
+      logLevel = mkOption {
+        type = types.enum ["DEBUG" "INFO" "WARNING" "ERROR" "CRITICAL" "TRACE" "NONE"];
+        description = "Log level used by the GlusterFS daemon";
+        default = "INFO";
+      };
+
+      extraFlags = mkOption {
+        type = types.listOf types.str;
+        description = "Extra flags passed to the GlusterFS daemon";
+        default = [];
+      };
+    };
+  };
+
+  ###### implementation
+
+  config = mkIf cfg.enable {
+    environment.systemPackages = [ pkgs.glusterfs ];
+
+    services.rpcbind.enable = true;
+
+    systemd.services.glusterd = {
+
+      description = "GlusterFS, a clustered file-system server";
+
+      wantedBy = [ "multi-user.target" ];
+
+      requires = [ "rpcbind.service" ];
+      after = [ "rpcbind.service" "network.target" "local-fs.target" ];
+      before = [ "network-online.target" ];
+
+      preStart = ''
+        install -m 0755 -d /var/log/glusterfs
+      '';
+
+      serviceConfig = {
+        Type="forking";
+        PIDFile="/run/glusterd.pid";
+        LimitNOFILE=65536;
+        ExecStart="${glusterfs}/sbin/glusterd -p /run/glusterd.pid --log-level=${cfg.logLevel} ${toString cfg.extraFlags}";
+        KillMode="process";
+      };
+    };
+
+    systemd.services.glustereventsd = {
+
+      description = "Gluster Events Notifier";
+
+      wantedBy = [ "multi-user.target" ];
+
+      after = [ "syslog.target" "network.target" ];
+
+      serviceConfig = {
+        Type="simple";
+        Environment="PYTHONPATH=${glusterfs}/usr/lib/python2.7/site-packages";
+        PIDFile="/run/glustereventsd.pid";
+        ExecStart="${glusterfs}/sbin/glustereventsd --pid-file /run/glustereventsd.pid";
+        ExecReload="/bin/kill -SIGUSR2 $MAINPID";
+        KillMode="control-group";
+      };
+    };
+  };
+}