Add counter for the number of devices configured or dynamically discovered

Signed-off-by: Niklas Schwarz <schwarz.niklas@hotmail.de>

main.go

@@ -56,6 +56,11 @@ func (i SMARTctlManagerCollector) Collect(ch chan<- prometheus.Metric) {
 			smart.Collect()
 		}
 	}
+	ch <- prometheus.MustNewConstMetric(
+		metricDeviceCount,
+		prometheus.GaugeValue,
+		float64(len(i.Devices)),
+	)
 	info.Collect()
 }
 
@@ -123,11 +128,7 @@ func main() {
 	} else {
 		level.Info(logger).Log("msg", "No devices specified, trying to load them automatically")
 		devices = scanDevices(logger)
-	}
+		level.Info(logger).Log("msg", "Number of devices found", "count", len(devices))
-
-	if len(devices) == 0 {
-		level.Error(logger).Log("msg", "No devices found")
-		os.Exit(1)
 	}
 
 	collector := SMARTctlManagerCollector{

metrics.go

@@ -47,6 +47,12 @@ var (
 		},
 		nil,
 	)
+	metricDeviceCount = prometheus.NewDesc(
+		"smartctl_device_count",
+		"Number of devices configured or dynamically discovered",
+		[]string{},
+		nil,
+	)
 	metricDeviceCapacityBlocks = prometheus.NewDesc(
 		"smartctl_device_capacity_blocks",
 		"Device capacity in blocks",