Merge pull request #178 from yfyf/active-vte-shortcut

Change active VTE restriction implementation to a xmodmap script

application.nix

@@ -19,16 +19,14 @@ rec {
 
     overlays = [
       (import ./application/overlays version)
-      # Limit virtual terminals that can be switched to
-      # Virtual terminal 7 is the kiosk, 8 is the status screen
-      (import ./application/overlays/xorg { activeVirtualTerminals = [ 7 8 ]; })
     ];
 
     module = { config, lib, pkgs, ... }: {
 
       imports = [
         ./application/playos-status.nix
         ./application/power-management/default.nix
+        ./application/limit-vtes.nix
       ];
 
       # Kiosk runs as a non-privileged user
@@ -47,6 +45,10 @@ rec {
         group = "users";
       };
 
+      # Limit virtual terminals that can be switched to
+      # Virtual terminal 7 is the kiosk, 8 is the status screen
+      playos.xserver.activeVirtualTerminals = [ 7 8 ];
+
       # System-wide packages
       environment.systemPackages = with pkgs; [ breeze-contrast-cursor-theme ];
 

application/limit-vtes.nix

@@ -0,0 +1,53 @@
+{ pkgs, config, lib, ... }:
+let
+    inherit (lib.lists) range subtractLists;
+    allVTEs = range 1 12;
+    activeVTEs = config.playos.xserver.activeVirtualTerminals;
+    disabledVTEs = (subtractLists activeVTEs allVTEs);
+in
+{
+    options = {
+      playos.xserver.activeVirtualTerminals = with lib.types; lib.mkOption {
+        # prevent merging
+        type = types.uniq (types.listOf (types.ints.between 1 12));
+        default =  allVTEs;
+        defaultText = "Defaults to [1 2 ... 12], which implies all VTEs are active.";
+        example = [ 7 8 ];
+        description =
+          lib.mdDoc ''
+          Restrict the directly accessible virtual terminal shortcuts
+          (Ctrl-Alt-FN).
+
+          The goal is primarily to limit possible cause of confusion for users,
+          especially accidental activation of VT 12 instead of opening the
+          PlayOS controller (Ctrl-Shift-F12).
+
+          Note that this is only a usability measure, since once a non-Xserver
+          VT has been switched to, VT switching is handled by the Linux kernel
+          and thus no longer limited to our whitelist.
+          '';
+      };
+    };
+
+    config = lib.mkIf (disabledVTEs != []) {
+        environment.systemPackages = [ pkgs.xorg.xmodmap pkgs.gnugrep pkgs.gnused ];
+
+        # This works by finding the keycodes that map to F1...F12 and
+        # replacing any combinations in them that map to XF86Switch_VT_{N} to
+        # F{N} for all the disabled VTEs.
+        services.xserver.displayManager.sessionCommands = ''
+            MODS=$(mktemp --tmpdir xmodmap-XXXX)
+            for i in ${toString disabledVTEs}; do
+                xmodmap -pke |
+                    sed -E 's/[ ]+/ /g' | \
+                    grep -E "keycode [0-9]+ = F$i .*XF86Switch_VT_$i" | \
+                    sed "s/XF86Switch_VT_$i/F$i/g" \
+                    >> $MODS
+            done
+            # sanity check
+            test "$(wc -l < $MODS)" -eq "${toString (builtins.length disabledVTEs)}"
+            xmodmap $MODS
+            rm $MODS
+        '';
+    };
+}