nixos-config/modules/virtualisation/gaming.nix

{ config, lib, pkgs, ... }:

let
  cfg = config.ptw.virtualisation.gaming;
in {
  options.ptw.virtualisation.gaming = {
    enable = lib.mkEnableOption "Configure virtualisation for gaming purposes";
  };

  config = lib.mkIf cfg.enable {
    environment.etc = {
      "evdev-proxy/config.toml".source = pkgs.writeText "config.toml" ''
        log_level = "INFO"

        [[device]]
          [device.Simple]
            name = "EvdevProxyMouse"
            vendor = 0x1337
            model = 0x1337
            class = "Mouse"
            [[device.Simple.selector]]
              USBIDClass = {vendor=0x046d, model=0xc531, class="Mouse"}
            [[device.Simple.selector]]
              USBIDClass = {vendor=0x046d, model=0xc07c, class="Mouse"}
        [[device]]
          [device.Simple]
            name = "EvdevProxyTartarus"
            vendor = 0x1337
            model = 0x1338
            class = "Keyboard"
            # This is to give a deterministic /dev/input/by-id/ path to
            # the mapped version of the Tartarus evdev node.
            # (Useful for qemu)
            [[device.Simple.selector]]
              EVDEVClass = {phys="\"key-mapper\""}
      '';
      "libvirt/hooks/qemu".source = let
        vfio-isolate-state = "/tmp/vfio-isolate-state";
      in pkgs.writeScript "qemu" ''
        #!${pkgs.stdenv.shell}
        guest=$1
        action=$2
        phase=$3
        extra=$4

        if [[ "$guest" = "win10" ]]; then
            case "$action" in
                prepare)
                # Only do this while in preparation
                [[ ! "$phase" = "prepare" ]] && exit 0

                sudo -u alexander systemctl --user start evdev-proxy.service
                sudo -u alexander systemctl --user start scream.service
                sleep 2

                ${pkgs.vfio-isolate}/bin/vfio-isolate \
                  -u ${vfio-isolate-state} \
                 	cpu-governor performance "$GUEST_CORES" \
                  cpuset-create --cpus "$GUEST_CORES" /guest.slice \
                  cpuset-create --cpus C0,4 /host.slice \
                  move-tasks / /host.slice \
                  irq-affinity mask "$GUEST_CORES"
                ;;
                stopped)
                # Only run when the VM is fully stopped
                [[ ! "$phase" = "end" ]] && exit 0
                sudo -u alexander systemctl --user stop evdev-proxy.service
                sudo -u alexander systemctl --user stop scream.service

                ${pkgs.vfio-isolate}/bin/vfio-isolate \
                  restore ${vfio-isolate-state}
            esac
        fi
      '';
    };

    # NOTE: Workaround for libvirt's SYSCONFDIR being set to /var/lib
    # (See https://github.com/NixOS/nixpkgs/issues/51152#issuecomment-899374407)
    system.activationScripts.libvirt-hooks.text = ''
      ln -Tfs /etc/libvirt/hooks /var/lib/libvirt/hooks
    '';

    services.udev.packages = with pkgs; [ evdev-proxy ];
    
    systemd = {
      services = {
        libvirtd.path = with pkgs; [ vfio-isolate systemd bash ];
        virtiofsd = {
          description = "vhost-user virtio-fs device backend written in Rust";
          wantedBy = [ "default.target" "libvirtd.service" ];
          serviceConfig = {
            Type = "simple";
            ExecStart = "${pkgs.virtiofsd}/bin/virtiofsd --socket-path=/tmp/vfsd.sock --shared-dir /mnt/Storage/Games --announce-submounts --inode-file-handles=mandatory";
            Restart = "always";
          };
        };
      };

      user.services.evdev-proxy = {
        description = "Creates virtual device to proxy evdev devices events";
        wantedBy = [ "default.target" ];
        serviceConfig = {
          Type = "simple";
          ExecStart = "${pkgs.evdev-proxy}/bin/evdev-proxy";
          Restart = "always";
        };
      };
    };
  };
}