nixpkgs/modules/testing/test-instrumentation.nix

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# 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;
{
config = {
jobs.backdoor =
{ startOn = "started network-interfaces";
preStart =
''
echo "guest running" > /dev/ttyS0
echo "===UP===" > dev/ttyS0
'';
exec = "${pkgs.socat}/bin/socat tcp-listen:514,fork exec:/bin/sh 2> /dev/ttyS0";
};
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. Symlink
# it to the host filesystem so that we don't need to copy it
# on shutdown.
( eval $(cat /proc/cmdline)
mkdir /hostfs/$hostTmpDir/coverage-data
ln -s /hostfs/$hostTmpDir/coverage-data /tmp/coverage-data
)
# Mount debugfs to gain access to the kernel coverage data (if
# available).
mount -t debugfs none /sys/kernel/debug || true
'';
# 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 = [ "stage1panic" ];
};
}