class_cooling_device: ignore EINVAL (etc) when reading files. (#783)

Fixes: #746, fixes prometheus/node_exporter#3420

Some cooling devices return errors when attempting to read state files.
When that happens, ignore the error, and skip to the next device rather
than failing to return any devices.

Signed-off-by: Malcolm Rowe <malcolmr@google.com>

Author: malcolmr

sysfs/class_cooling_device.go

@@ -40,17 +40,20 @@ func (fs FS) ClassCoolingDeviceStats() ([]ClassCoolingDeviceStats, error) {
 	}
 
 	var coolingDeviceStats = ClassCoolingDeviceStats{}
-	stats := make([]ClassCoolingDeviceStats, len(cds))
-	for i, cd := range cds {
+	stats := make([]ClassCoolingDeviceStats, 0, len(cds))
+	for _, cd := range cds {
 		cdName := strings.TrimPrefix(filepath.Base(cd), "cooling_device")
 
 		coolingDeviceStats, err = parseCoolingDeviceStats(cd)
 		if err != nil {
+			if canIgnoreError(err) {
+				continue
+			}
 			return []ClassCoolingDeviceStats{}, err
 		}
 
 		coolingDeviceStats.Name = cdName
-		stats[i] = coolingDeviceStats
+		stats = append(stats, coolingDeviceStats)
 	}
 	return stats, nil
 }

sysfs/class_cooling_device_test.go

@@ -40,7 +40,7 @@ func TestClassCoolingDeviceStats(t *testing.T) {
 			CurState: 0,
 		},
 		{
-			Name:     "1",
+			Name:     "2",
 			Type:     "intel_powerclamp",
 			MaxState: 27,
 			CurState: -1,

testdata/fixtures.ttar

@@ -7057,20 +7057,33 @@ Mode: 644
 Directory: fixtures/sys/class/thermal/cooling_device1
 Mode: 755
 # ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-Path: fixtures/sys/class/thermal/cooling_device1/cur_state
+Path: fixtures/sys/class/thermal/cooling_device1/max_state
 Lines: 1
--1
+50
 Mode: 644
 # ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-Path: fixtures/sys/class/thermal/cooling_device1/max_state
+Path: fixtures/sys/class/thermal/cooling_device1/type
 Lines: 1
-27
+TFN1
 Mode: 644
 # ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-Path: fixtures/sys/class/thermal/cooling_device1/type
+Directory: fixtures/sys/class/thermal/cooling_device2
+Mode: 750
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Path: fixtures/sys/class/thermal/cooling_device2/cur_state
+Lines: 1
+-1
+Mode: 640
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Path: fixtures/sys/class/thermal/cooling_device2/max_state
+Lines: 1
+27
+Mode: 640
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Path: fixtures/sys/class/thermal/cooling_device2/type
 Lines: 1
 intel_powerclamp
-Mode: 644
+Mode: 640
 # ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 Directory: fixtures/sys/class/thermal/thermal_zone0
 Mode: 755