1 files changed, 91 insertions, 0 deletions
diff --git a/nixos/modules/testing/test-instrumentation.nix b/nixos/modules/testing/test-instrumentation.nix
new file mode 100644
index 00000000000..28494e1c7b2
--- /dev/null
+++ b/nixos/modules/testing/test-instrumentation.nix
@@ -0,0 +1,91 @@
+# This module allows the test driver to connect to the virtual machine
+# via a root shell attached to port 514.
+
+{ config, pkgs, ... }:
+
+with pkgs.lib;
+
+let kernel = config.boot.kernelPackages.kernel; in
+
+{
+
+  config = {
+
+    systemd.services.backdoor =
+      { wantedBy = [ "multi-user.target" ];
+        requires = [ "dev-hvc0.device" "dev-ttyS0.device" ];
+        after = [ "dev-hvc0.device" "dev-ttyS0.device" ];
+        script =
+          ''
+            export USER=root
+            export HOME=/root
+            export DISPLAY=:0.0
+            source /etc/profile
+            cd /tmp
+            exec < /dev/hvc0 > /dev/hvc0
+            while ! exec 2> /dev/ttyS0; do sleep 0.1; done
+            echo "connecting to host..." >&2
+            stty -F /dev/hvc0 raw -echo # prevent nl -> cr/nl conversion
+            echo
+            PS1= exec /bin/sh
+          '';
+        serviceConfig.KillSignal = "SIGHUP";
+      };
+
+    # Prevent agetty from being instantiated on ttyS0, since it
+    # interferes with the backdoor (writes to ttyS0 will randomly fail
+    # with EIO).  Likewise for hvc0.
+    systemd.services."serial-getty@ttyS0".enable = false;
+    systemd.services."serial-getty@hvc0".enable = false;
+
+    boot.initrd.postDeviceCommands =
+      ''
+        # 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).
+        echo acpi_pm > /sys/devices/system/clocksource/clocksource0/current_clocksource
+      '';
+
+    boot.postBootCommands =
+      ''
+        # 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.
+        echo 2 > /proc/sys/vm/panic_on_oom
+
+        # Coverage data is written into /tmp/coverage-data.
+        mkdir -p /tmp/xchg/coverage-data
+      '';
+
+    # If the kernel has been built with coverage instrumentation, make
+    # it available under /proc/gcov.
+    boot.kernelModules = [ "gcov-proc" ];
+
+    # Panic if an error occurs in stage 1 (rather than waiting for
+    # user intervention).
+    boot.kernelParams =
+      [ "console=tty1" "console=ttyS0" "panic=1" "boot.panic_on_fail" ];
+
+    # `xwininfo' is used by the test driver to query open windows.
+    environment.systemPackages = [ pkgs.xorg.xwininfo ];
+
+    # Log everything to the serial console.
+    services.journald.console = "/dev/console";
+
+    # Prevent tests from accessing the Internet.
+    networking.defaultGateway = mkOverride 150 "";
+    networking.nameservers = mkOverride 150 [ ];
+
+    systemd.globalEnvironment.GCOV_PREFIX = "/tmp/xchg/coverage-data";
+
+    system.requiredKernelConfig = with config.lib.kernelConfig; [
+      (isYes "SERIAL_8250_CONSOLE")
+      (isYes "SERIAL_8250")
+      (isEnabled "VIRTIO_CONSOLE")
+    ];
+
+  };
+
+}