add serial module to vms

This is useful for debugging in the cli.

nixosModules/clanCore/serial.nix

@@ -0,0 +1,32 @@
+{ pkgs, ... }:
+let
+  # Based on https://unix.stackexchange.com/questions/16578/resizable-serial-console-window
+  resize = pkgs.writeShellScriptBin "resize" ''
+    export PATH=${pkgs.coreutils}/bin
+    if [ ! -t 0 ]; then
+      # not a interactive...
+      exit 0
+    fi
+    TTY="$(tty)"
+    if [[ "$TTY" != /dev/ttyS* ]] && [[ "$TTY" != /dev/ttyAMA* ]] && [[ "$TTY" != /dev/ttySIF* ]]; then
+      # probably not a known serial console, we could make this check more
+      # precise by using `setserial` but this would require some additional
+      # dependency
+      exit 0
+    fi
+    old=$(stty -g)
+    stty raw -echo min 0 time 5
+
+    printf '\0337\033[r\033[999;999H\033[6n\0338' > /dev/tty
+    IFS='[;R' read -r _ rows cols _ < /dev/tty
+
+    stty "$old"
+    stty cols "$cols" rows "$rows"
+  '';
+in
+{
+  environment.loginShellInit = "${resize}/bin/resize";
+
+  # default is something like vt220... however we want to get alt least some colors...
+  systemd.services."serial-getty@".environment.TERM = "xterm-256color";
+}

nixosModules/clanCore/vm.nix

@@ -3,6 +3,7 @@ let
   vmConfig = extendModules {
     modules = [
       (modulesPath + "/virtualisation/qemu-vm.nix")
+      ./serial.nix
       {
         virtualisation.fileSystems.${config.clanCore.secretsUploadDirectory} = lib.mkForce {
           device = "secrets";