collectors/mdadm_linux: support reshape status

Signed-off-by: Philipp Born <git@pborn.eu>

Author: tamcore

collector/fixtures/proc/mdstat

@@ -57,4 +57,9 @@ md120 : active linear sda1[1] sdb1[0]
 md101 : active (read-only) raid0 sdb[2] sdd[1] sdc[0]
       322560 blocks super 1.2 512k chunks
 
+md42 : active raid5 sda1[3](S) sdd1[0] sde1[1]
+      1953381440 blocks super 1.2 level 5, 64k chunk, algorithm 2 [3/2] [UU_]
+      [===========>.........]  reshape = 56.1% (1096879076/1953381440) finish=1868.1min speed=7640K/sec
+      bitmap: 4/15 pages [16KB], 65536KB chunk
+
 unused devices: <none>

collector/mdadm_linux.go

@@ -58,6 +58,12 @@ var (
 		[]string{"device"},
 		prometheus.Labels{"state": "recovering"},
 	)
+	reshapingDesc = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, "md", "state"),
+		"Indicates the state of md-device.",
+		[]string{"device"},
+		prometheus.Labels{"state": "reshaping"},
+	)
 	resyncDesc = prometheus.NewDesc(
 		prometheus.BuildFQName(namespace, "md", "state"),
 		"Indicates the state of md-device.",
@@ -166,6 +172,13 @@ func (c *mdadmCollector) Update(ch chan<- prometheus.Metric) error {
 			mdStat.Name,
 		)
 
+		ch <- prometheus.MustNewConstMetric(
+			reshapingDesc,
+			prometheus.GaugeValue,
+			stateVals["reshaping"],
+			mdStat.Name,
+		)
+
 		ch <- prometheus.MustNewConstMetric(
 			recoveringDesc,
 			prometheus.GaugeValue,