nixpkgs/nixos/modules/testing/test-instrumentation.nix

# This module allows the test driver to connect to the virtual machine
# via a root shell attached to port 514.

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

with lib;

let
  qemu-common = import ../../lib/qemu-common.nix { inherit lib pkgs; };
in

{

  config = {

    systemd.services.backdoor =
      { wantedBy = [ "multi-user.target" ];
        requires = [ "dev-hvc0.device" "dev-${qemu-common.qemuSerialDevice}.device" ];
        after = [ "dev-hvc0.device" "dev-${qemu-common.qemuSerialDevice}.device" ];
        script =
          ''
            export USER=root
            export HOME=/root
            export DISPLAY=:0.0

            source /etc/profile

            # Don't use a pager when executing backdoor
            # actions. Because we use a tty, commands like systemctl
            # or nix-store get confused into thinking they're running
            # interactively.
            export PAGER=

            cd /tmp
            exec < /dev/hvc0 > /dev/hvc0
            while ! exec 2> /dev/${qemu-common.qemuSerialDevice}; do sleep 0.1; done
            echo "connecting to host..." >&2
            stty -F /dev/hvc0 raw -echo # prevent nl -> cr/nl conversion
            # The following line is essential since it signals to
            # the test driver that the shell is ready.
            # See: the connect method in the Machine class.
            echo "Spawning backdoor root shell..."
            # Passing the terminal device makes bash run non-interactively.
            # Otherwise we get errors on the terminal because bash tries to
            # setup things like job control.
            # Note: calling bash explicitly here instead of sh makes sure that
            # we can also run non-NixOS guests during tests.
            PS1= exec /usr/bin/env bash --norc /dev/hvc0
          '';
        serviceConfig.KillSignal = "SIGHUP";
      };

    # Prevent agetty from being instantiated on the serial device, since it
    # interferes with the backdoor (writes to it will randomly fail
    # with EIO).  Likewise for hvc0.
    systemd.services."serial-getty@${qemu-common.qemuSerialDevice}".enable = false;
    systemd.services."serial-getty@hvc0".enable = false;

    # Only set these settings when the options exist. Some tests (e.g. those
    # that do not specify any nodes, or an empty attr set as nodes) will not
    # have the QEMU module loaded and thuse these options can't and should not
    # be set.
    virtualisation = lib.optionalAttrs (options ? virtualisation.qemu) {
      qemu = {
        # Only use a serial console, no TTY.
        # NOTE: optionalAttrs
        #       test-instrumentation.nix appears to be used without qemu-vm.nix, so
        #       we avoid defining consoles if not possible.
        # TODO: refactor such that test-instrumentation can import qemu-vm
        #       or declare virtualisation.qemu.console option in a module that's always imported
        consoles = [ qemu-common.qemuSerialDevice ];
        package  = lib.mkDefault pkgs.qemu_test;
      };
    };

    boot.kernel.sysctl = {
      "kernel.hung_task_timeout_secs" = 600;
      # Panic on out-of-memory conditions rather than letting the
      # OOM killer randomly get rid of processes, since this leads
      # to failures that are hard to diagnose.
      "vm.panic_on_oom" = lib.mkDefault 2;
    };

    boot.kernelParams = [
      "console=${qemu-common.qemuSerialDevice}"
      # Panic if an error occurs in stage 1 (rather than waiting for
      # user intervention).
      "panic=1" "boot.panic_on_fail"
      # Using acpi_pm as a clock source causes the guest clock to
      # slow down under high host load.  This is usually a bad
      # thing, but for VM tests it should provide a bit more
      # determinism (e.g. if the VM runs at lower speed, then
      # timeouts in the VM should also be delayed).
      "clock=acpi_pm"
    ];

    # `xwininfo' is used by the test driver to query open windows.
    environment.systemPackages = [ pkgs.xorg.xwininfo ];

    # Log everything to the serial console.
    services.journald.extraConfig =
      ''
        ForwardToConsole=yes
        MaxLevelConsole=debug
      '';

    boot.initrd.systemd.contents."/etc/systemd/journald.conf".text = ''
      [Journal]
      ForwardToConsole=yes
      MaxLevelConsole=debug
    '';

    systemd.extraConfig = ''
      # Don't clobber the console with duplicate systemd messages.
      ShowStatus=no
      # Allow very slow start
      DefaultTimeoutStartSec=300
      DefaultDeviceTimeoutSec=300
    '';
    systemd.user.extraConfig = ''
      # Allow very slow start
      DefaultTimeoutStartSec=300
      DefaultDeviceTimeoutSec=300
    '';

    boot.initrd.systemd.extraConfig = config.systemd.extraConfig;

    boot.consoleLogLevel = 7;

    # Prevent tests from accessing the Internet.
    networking.defaultGateway = mkOverride 150 "";
    networking.nameservers = mkOverride 150 [ ];

    system.requiredKernelConfig = with config.lib.kernelConfig; [
      (isYes "SERIAL_8250_CONSOLE")
      (isYes "SERIAL_8250")
      (isEnabled "VIRTIO_CONSOLE")
    ];

    networking.usePredictableInterfaceNames = false;

    # Make it easy to log in as root when running the test interactively.
    users.users.root.initialHashedPassword = mkOverride 150 "";

    services.xserver.displayManager.job.logToJournal = true;

    # Make sure we use the Guest Agent from the QEMU package for testing
    # to reduce the closure size required for the tests.
    services.qemuGuest.package = pkgs.qemu_test.ga;

    # Squelch warning about unset system.stateVersion
    system.stateVersion = lib.mkDefault lib.trivial.release;
  };

}