Revert "Add ssh backdoor to VM tests infrastructure."

This reverts commit d6e3db44cf.

See #53935 for explanations. In short, it may be causing issues with
tests on the build infrastructure.

nixos/doc/manual/development/debugging-nixos-tests.xml

@@ -1,37 +0,0 @@
-<section xmlns="http://docbook.org/ns/docbook"
-        xmlns:xlink="http://www.w3.org/1999/xlink"
-        xmlns:xi="http://www.w3.org/2001/XInclude"
-        version="5.0"
-        xml:id="sec-debugging-nixos-tests">
- <title>Debugging NixOS tests</title>
-
- <para>
-  Tests may fail and infrastructure offers access to inspect machine state.
- </para>
-
- <para>
-  To prevent test from stopping and cleaning up, insert a sleep command:
- </para>
-
-<programlisting>
-$machine->succeed("sleep 84000");
-</programlisting>
-
- <para>
-  As soon as machine starts run as root:
- </para>
-
-<programlisting>
-nix-shell -p socat --run "socat STDIO,raw,echo=0,escape=0x11 UNIX:/tmp/nix-build-vm-test-run-*.drv-0/vm-state-machine/backdoor"
-</programlisting>
-
- <para>
-  You may need to find the correct path, replacing <literal>/tmp</literal>,
-  <literal>*</literal> or <literal>machine</literal>.
- </para>
-
- <para>
-  Press "enter" to open up console and login as "root". After you're done,
-  press "ctrl-q" to exit the console.
- </para>
-</section>

nixos/doc/manual/development/nixos-tests.xml

@@ -16,5 +16,4 @@ xlink:href="https://github.com/NixOS/nixpkgs/tree/master/nixos/tests">nixos/test
  <xi:include href="writing-nixos-tests.xml" />
  <xi:include href="running-nixos-tests.xml" />
  <xi:include href="running-nixos-tests-interactively.xml" />
- <xi:include href="debugging-nixos-tests.xml" />
 </chapter>

nixos/lib/test-driver/Machine.pm

@@ -156,10 +156,8 @@ sub start {
         $ENV{USE_TMPDIR} = 1;
         $ENV{QEMU_OPTS} =
             ($self->{allowReboot} ? "" : "-no-reboot ") .
-            "-monitor unix:./monitor " .
-            "-chardev socket,id=shell,path=./shell -device virtio-serial -device virtconsole,chardev=shell " .
-            # socket backdoor, see "Debugging NixOS tests" section in NixOS manual
-            "-chardev socket,id=backdoor,path=./backdoor,server,nowait -device virtio-serial -device virtconsole,chardev=backdoor " .
+            "-monitor unix:./monitor -chardev socket,id=shell,path=./shell " .
+            "-device virtio-serial -device virtconsole,chardev=shell " .
             "-device virtio-rng-pci " .
             ($showGraphics ? "-serial stdio" : "-nographic") . " " . ($ENV{QEMU_OPTS} || "");
         chdir $self->{stateDir} or die;

nixos/modules/testing/test-instrumentation.nix

@@ -55,8 +55,7 @@ with import ../../lib/qemu-flags.nix { inherit pkgs; };
     systemd.services."serial-getty@hvc0".enable = false;
 
     # Only use a serial console, no TTY.
-    # hvc1: socket backdoor, see "Debugging NixOS tests" section in NixOS manual
-    virtualisation.qemu.consoles = [ "hvc1" qemuSerialDevice ];
+    virtualisation.qemu.consoles = [ qemuSerialDevice ];
 
     boot.initrd.preDeviceCommands =
       ''