test/interactive: helper scripts for tracing

The vm state is discarded often, and it is quite cumbersome to set everything up again when the shell history is gone.

Signed-off-by: Ophestra <cat@gensokyo.uk>

flake.nix

@@ -195,6 +195,7 @@
                   ./test/interactive/configuration.nix
                   ./test/interactive/vm.nix
                   ./test/interactive/hakurei.nix
+                  ./test/interactive/trace.nix
 
                   self.nixosModules.hakurei
                   self.inputs.home-manager.nixosModules.home-manager

test/interactive/trace.nix

@@ -0,0 +1,28 @@
+{ lib, pkgs, ... }:
+let
+  tracing = name: "\"/sys/kernel/debug/tracing/${name}\"";
+in
+{
+  environment.systemPackages = [
+    (pkgs.writeShellScriptBin "hakurei-set-up-tracing" ''
+      set -e
+      echo "$1" > ${tracing "set_graph_function"}
+      echo function_graph > ${tracing "current_tracer"}
+      echo funcgraph-tail > ${tracing "trace_options"}
+      echo funcgraph-retval > ${tracing "trace_options"}
+      echo nofuncgraph-cpu > ${tracing "trace_options"}
+      echo nofuncgraph-overhead > ${tracing "trace_options"}
+      echo nofuncgraph-duration > ${tracing "trace_options"}
+    '')
+    (pkgs.writeShellScriptBin "hakurei-print-trace" "exec cat ${tracing "trace"}")
+    (pkgs.writeShellScriptBin "hakurei-consume-trace" "exec cat ${tracing "trace_pipe"}")
+  ];
+
+  boot.kernelPatches = [
+    {
+      name = "funcgraph-retval";
+      patch = null;
+      extraStructuredConfig.FUNCTION_GRAPH_RETVAL = lib.kernel.yes;
+    }
+  ];
+}