xeon08: Add lttng module and tools

xeon08/kernel/kernel.nix

@@ -46,5 +46,8 @@ let
   latest = pkgs.linuxPackages_latest;
 
 in {
+  imports = [
+    ./lttng.nix
+  ];
   boot.kernelPackages = lib.mkForce kernel;
 }

xeon08/kernel/lttng.nix

@@ -0,0 +1,36 @@
+{ config, pkgs, lib, ... }:
+
+let
+
+  # the lttng btrfs probe crashes at compile time because of an undefined
+  # function. This disables the btrfs tracepoints to avoid the issue.
+  lttng-modules-fixed = config.boot.kernelPackages.lttng-modules.overrideAttrs (finalAttrs: previousAttrs: {
+    patchPhase = (lib.optionalString (previousAttrs ? patchPhase) previousAttrs.patchPhase) + ''
+      substituteInPlace src/probes/Kbuild \
+        --replace "  obj-\$(CONFIG_LTTNG) += lttng-probe-btrfs.o" "  #obj-\$(CONFIG_LTTNG) += lttng-probe-btrfs.o"
+    '';
+  });
+in {
+
+  # add the lttng tools and modules to the system environment
+  boot.extraModulePackages = [ lttng-modules-fixed ];
+  environment.systemPackages = with pkgs; [
+    lttng-tools lttng-ust babeltrace
+  ];
+
+  # start the lttng root daemon to manage kernel events
+  systemd.services.lttng-sessiond = {
+    wantedBy = [ "multi-user.target" ];
+    description = "LTTng session daemon for the root user";
+    serviceConfig = {
+      User = "root";
+      ExecStart = ''
+        ${pkgs.lttng-tools}/bin/lttng-sessiond
+      '';
+    };
+  };
+
+  # members of the tracing group can use the lttng-provided kernel events
+  # without root permissions
+  users.groups.tracing.members = [ "arocanon" ];
+}