lightdm & xserver service: add ability to spawn more than one X server

- if xserver.tty and/or display are set to null, then don't specify
  them, or the -logfile argument in the xserverArgs
- For lightdm, we set default tty and display to null and we determine
  those at runtime based on arguments passed. This is necessary because
  we run multiple X servers so they can't all be on the same display

1 files changed, 6 insertions, 5 deletions

diff --git a/nixos/modules/services/x11/xserver.nix b/nixos/modules/services/x11/xserver.nix
index 3348e8d0582c..8fcca70bc796 100644
--- a/nixos/modules/services/x11/xserver.nix
+++ b/nixos/modules/services/x11/xserver.nix
@@ -381,13 +381,13 @@ in
       };
 
       tty = mkOption {
-        type = types.int;
+        type = types.nullOr types.int;
         default = 7;
         description = "Virtual console for the X server.";
       };
 
       display = mkOption {
-        type = types.int;
+        type = types.nullOr types.int;
         default = 0;
         description = "Display number for the X server.";
       };
@@ -517,11 +517,12 @@ in
     services.xserver.displayManager.xserverArgs =
       [ "-ac"
         "-terminate"
-        "-logfile" "/var/log/X.${toString cfg.display}.log"
         "-config ${configFile}"
-        ":${toString cfg.display}" "vt${toString cfg.tty}"
         "-xkbdir" "${pkgs.xkeyboard_config}/etc/X11/xkb"
-      ] ++ optional (!cfg.enableTCP) "-nolisten tcp";
+      ] ++ optional (cfg.display != null) ":${tostring cfg.display}"
+        ++ optional (cfg.tty     != null) "vt${toString cfg.tty}"
+        ++ optional (cfg.display != null) [ "-logfile" "/var/log/X.${toString cfg.display}.log" ]
+        ++ optional (!cfg.enableTCP) "-nolisten tcp";
 
     services.xserver.modules =
       concatLists (catAttrs "modules" cfg.drivers) ++