nixos/qemu-vm: Use different serial port on ARM/AArch64

nixos/modules/testing/test-instrumentation.nix

@@ -5,7 +5,13 @@
 
 with lib;
 
-let kernel = config.boot.kernelPackages.kernel; in
+let
+  kernel = config.boot.kernelPackages.kernel;
+  # FIXME: figure out a common place for this instead of copy pasting
+  serialDevice = if pkgs.stdenv.isi686 || pkgs.stdenv.isx86_64 then "ttyS0"
+        else if pkgs.stdenv.isArm || pkgs.stdenv.isAarch64 then "ttyAMA0"
+        else throw "Unknown QEMU serial device for system '${pkgs.stdenv.system}'";
+in
 
 {
 
@@ -22,8 +28,8 @@ let kernel = config.boot.kernelPackages.kernel; in
 
     systemd.services.backdoor =
       { wantedBy = [ "multi-user.target" ];
-        requires = [ "dev-hvc0.device" "dev-ttyS0.device" ];
-        after = [ "dev-hvc0.device" "dev-ttyS0.device" ];
+        requires = [ "dev-hvc0.device" "dev-${serialDevice}.device" ];
+        after = [ "dev-hvc0.device" "dev-${serialDevice}.device" ];
         script =
           ''
             export USER=root
@@ -40,7 +46,7 @@ let kernel = config.boot.kernelPackages.kernel; in
 
             cd /tmp
             exec < /dev/hvc0 > /dev/hvc0
-            while ! exec 2> /dev/ttyS0; do sleep 0.1; done
+            while ! exec 2> /dev/${serialDevice}; do sleep 0.1; done
             echo "connecting to host..." >&2
             stty -F /dev/hvc0 raw -echo # prevent nl -> cr/nl conversion
             echo
@@ -49,10 +55,10 @@ let kernel = config.boot.kernelPackages.kernel; in
         serviceConfig.KillSignal = "SIGHUP";
       };
 
-    # Prevent agetty from being instantiated on ttyS0, since it
-    # interferes with the backdoor (writes to ttyS0 will randomly fail
+    # Prevent agetty from being instantiated on ${serialDevice}, since it
+    # interferes with the backdoor (writes to ${serialDevice} will randomly fail
     # with EIO).  Likewise for hvc0.
-    systemd.services."serial-getty@ttyS0".enable = false;
+    systemd.services."serial-getty@${serialDevice}".enable = false;
     systemd.services."serial-getty@hvc0".enable = false;
 
     boot.initrd.preDeviceCommands =
@@ -88,7 +94,7 @@ let kernel = config.boot.kernelPackages.kernel; in
     # Panic if an error occurs in stage 1 (rather than waiting for
     # user intervention).
     boot.kernelParams =
-      [ "console=ttyS0" "panic=1" "boot.panic_on_fail" ];
+      [ "console=${serialDevice}" "panic=1" "boot.panic_on_fail" ];
 
     # `xwininfo' is used by the test driver to query open windows.
     environment.systemPackages = [ pkgs.xorg.xwininfo ];

nixos/modules/virtualisation/qemu-vm.nix

@@ -21,6 +21,11 @@ let
     "aarch64-linux" = "${qemu}/bin/qemu-system-aarch64 -enable-kvm -machine virt -cpu host";
   }.${pkgs.stdenv.system};
 
+  # FIXME: figure out a common place for this instead of copy pasting
+  serialDevice = if pkgs.stdenv.isi686 || pkgs.stdenv.isx86_64 then "ttyS0"
+        else if pkgs.stdenv.isArm || pkgs.stdenv.isAarch64 then "ttyAMA0"
+        else throw "Unknown QEMU serial device for system '${pkgs.stdenv.system}'";
+
   vmName =
     if config.networking.hostName == ""
     then "noname"
@@ -29,7 +34,7 @@ let
   cfg = config.virtualisation;
 
   qemuGraphics = if cfg.graphics then "" else "-nographic";
-  kernelConsole = if cfg.graphics then "" else "console=ttyS0";
+  kernelConsole = if cfg.graphics then "" else "console=${serialDevice}";
   ttys = [ "tty1" "tty2" "tty3" "tty4" "tty5" "tty6" ];
 
   # Shell script to start the VM.