From 4bfe837a586c8ecc1bc577207faf15c152dd1e22 Mon Sep 17 00:00:00 2001
From: Amanda Cameron <amanda@darkdna.net>
Date: Fri, 19 Nov 2021 13:09:56 -0500
Subject: [PATCH 1/2] nixos/prometheus/systemd: Implement the extraFlags config
 option.

---
 .../services/monitoring/prometheus/exporters/systemd.nix        | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/nixos/modules/services/monitoring/prometheus/exporters/systemd.nix b/nixos/modules/services/monitoring/prometheus/exporters/systemd.nix
index c0a50f07d717..2edd1de83e1b 100644
--- a/nixos/modules/services/monitoring/prometheus/exporters/systemd.nix
+++ b/nixos/modules/services/monitoring/prometheus/exporters/systemd.nix
@@ -11,7 +11,7 @@ in {
     serviceConfig = {
       ExecStart = ''
         ${pkgs.prometheus-systemd-exporter}/bin/systemd_exporter \
-          --web.listen-address ${cfg.listenAddress}:${toString cfg.port}
+          --web.listen-address ${cfg.listenAddress}:${toString cfg.port} ${concatStringsSep " " cfg.extraFlags}
       '';
       RestrictAddressFamilies = [
         # Need AF_UNIX to collect data

From f1bcb88bf6b075856570c433014ed123d53abdc0 Mon Sep 17 00:00:00 2001
From: Amanda Cameron <amanda@darkdna.net>
Date: Fri, 19 Nov 2021 13:52:49 -0500
Subject: [PATCH 2/2] nixos/tests/prometheus-exporters: Add a test to cover a
 regression.

---
 nixos/tests/prometheus-exporters.nix | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/nixos/tests/prometheus-exporters.nix b/nixos/tests/prometheus-exporters.nix
index 38b93c4087c0..55877b0e10d6 100644
--- a/nixos/tests/prometheus-exporters.nix
+++ b/nixos/tests/prometheus-exporters.nix
@@ -1123,6 +1123,10 @@ let
     systemd = {
       exporterConfig = {
         enable = true;
+
+        extraFlags = [
+          "--collector.enable-restart-count"
+        ];
       };
       metricProvider = { };
       exporterTest = ''
@@ -1133,6 +1137,11 @@ let
                 'systemd_unit_state{name="basic.target",state="active",type="target"} 1'
             )
         )
+        succeed(
+            "curl -sSf localhost:9558/metrics | grep '{}'".format(
+                'systemd_service_restart_total{state="prometheus-systemd-exporter.service"} 0'
+            )
+        )
       '';
     };