Merge pull request #23974 from hopkings2008/devmapper_log

Add detail error logs when 'Unknown Device' error happens if devicema…
Upstream-commit: d2da1e3997c0d199c08c652c1285025415517f8d
Component: engine

components/engine/daemon/graphdriver/devmapper/deviceset.go

@@ -901,10 +901,12 @@ func (devices *DeviceSet) loadMetadata(hash string) *devInfo {
 
 	jsonData, err := ioutil.ReadFile(devices.metadataFile(info))
 	if err != nil {
+		logrus.Debugf("devmapper: Failed to read %s with err: %v", devices.metadataFile(info), err)
 		return nil
 	}
 
 	if err := json.Unmarshal(jsonData, &info); err != nil {
+		logrus.Debugf("devmapper: Failed to unmarshal devInfo from %s with err: %v", devices.metadataFile(info), err)
 		return nil
 	}