From c8a4cb3806071b651fc71c03a85e1ac15732d75d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan-Otto=20Kr=C3=B6pke?= <mail@jkroepke.de>
Date: Tue, 26 Aug 2025 20:52:09 +0200
Subject: [PATCH] mssql: expose correct patch level without restart (#2187)

---
 internal/collector/mssql/mssql_instance.go | 55 +++++++++++++++++-----
 internal/collector/mssql/types.go          |  5 +-
 2 files changed, 45 insertions(+), 15 deletions(-)

diff --git a/internal/collector/mssql/mssql_instance.go b/internal/collector/mssql/mssql_instance.go
index 10de2078..f524d921 100644
--- a/internal/collector/mssql/mssql_instance.go
+++ b/internal/collector/mssql/mssql_instance.go
@@ -18,34 +18,63 @@
 package mssql
 
 import (
+	"fmt"
+	"log/slog"
+
 	"github.com/prometheus-community/windows_exporter/internal/types"
 	"github.com/prometheus/client_golang/prometheus"
+	"golang.org/x/sys/windows/registry"
 )
 
 type collectorInstance struct {
-	instances *prometheus.GaugeVec
+	instances *prometheus.Desc
 }
 
 func (c *Collector) buildInstance() error {
-	c.instances = prometheus.NewGaugeVec(
-		prometheus.GaugeOpts{
-			Namespace: types.Namespace,
-			Subsystem: Name,
-			Name:      "instance_info",
-			Help:      "A metric with a constant '1' value labeled with mssql instance information",
-		},
+	c.instances = prometheus.NewDesc(
+		prometheus.BuildFQName(types.Namespace, Name, "instance_info"),
+		"A metric with a constant '1' value labeled with mssql instance information",
 		[]string{"edition", "mssql_instance", "patch", "version"},
+		nil,
 	)
 
-	for _, instance := range c.mssqlInstances {
-		c.instances.WithLabelValues(instance.edition, instance.name, instance.patchVersion, instance.majorVersion.String()).Set(1)
-	}
-
 	return nil
 }
 
 func (c *Collector) collectInstance(ch chan<- prometheus.Metric) error {
-	c.instances.Collect(ch)
+	for _, instance := range c.mssqlInstances {
+		regKeyName := fmt.Sprintf(`Software\Microsoft\Microsoft SQL Server\%s\Setup`, instance.instanceName)
+
+		regKey, err := registry.OpenKey(registry.LOCAL_MACHINE, regKeyName, registry.QUERY_VALUE)
+		if err != nil {
+			c.logger.Debug(fmt.Sprintf("couldn't open registry %s:", regKeyName),
+				slog.Any("err", err),
+			)
+
+			continue
+		}
+
+		patchVersion, _, err := regKey.GetStringValue("PatchLevel")
+		_ = regKey.Close()
+
+		if err != nil {
+			c.logger.Debug("couldn't get version from registry",
+				slog.Any("err", err),
+			)
+
+			continue
+		}
+
+		ch <- prometheus.MustNewConstMetric(
+			c.instances,
+			prometheus.GaugeValue,
+			1,
+			instance.edition,
+			instance.name,
+			patchVersion,
+			instance.majorVersion.String(),
+		)
+	}
 
 	return nil
 }
diff --git a/internal/collector/mssql/types.go b/internal/collector/mssql/types.go
index 316f7e09..5d3e9474 100644
--- a/internal/collector/mssql/types.go
+++ b/internal/collector/mssql/types.go
@@ -26,8 +26,8 @@ import (
 
 type mssqlInstance struct {
 	name            string
+	instanceName    string
 	majorVersion    mssqlServerMajorVersion
-	patchVersion    string
 	edition         string
 	isFirstInstance bool
 }
@@ -54,14 +54,15 @@ func newMssqlInstance(key, name string) (mssqlInstance, error) {
 		return mssqlInstance{}, fmt.Errorf("couldn't get version from registry: %w", err)
 	}
 
+	instanceName := name
 	_, name, _ = strings.Cut(name, ".")
 
 	return mssqlInstance{
 		edition:         edition,
 		name:            name,
 		majorVersion:    newMajorVersion(patchVersion),
-		patchVersion:    patchVersion,
 		isFirstInstance: key == "MSSQLSERVER",
+		instanceName:    instanceName,
 	}, nil
 }