defaults to inotify to detect changes in file datasource to avoid too many call to stat() (#2181)

pkg/acquisition/modules/file/file.go

@@ -39,6 +39,7 @@ type FileConfiguration struct {
 	Filename                          string
 	ForceInotify                      bool `yaml:"force_inotify"`
 	MaxBufferSize                     int  `yaml:"max_buffer_size"`
+	PollWithoutInotify                bool `yaml:"poll_without_inotify"`
 	configuration.DataSourceCommonCfg `yaml:",inline"`
 }
 
@@ -328,7 +329,7 @@ func (f *FileSource) StreamingAcquisition(out chan types.Event, t *tomb.Tomb) er
 			continue
 		}
 
-		tail, err := tail.TailFile(file, tail.Config{ReOpen: true, Follow: true, Poll: true, Location: &tail.SeekInfo{Offset: 0, Whence: io.SeekEnd}, Logger: log.NewEntry(log.StandardLogger())})
+		tail, err := tail.TailFile(file, tail.Config{ReOpen: true, Follow: true, Poll: f.config.PollWithoutInotify, Location: &tail.SeekInfo{Offset: 0, Whence: io.SeekEnd}, Logger: log.NewEntry(log.StandardLogger())})
 		if err != nil {
 			f.logger.Errorf("Could not start tailing file %s : %s", file, err)
 			continue
@@ -411,7 +412,7 @@ func (f *FileSource) monitorNewFiles(out chan types.Event, t *tomb.Tomb) error {
 					continue
 				}
 				//Slightly different parameters for Location, as we want to read the first lines of the newly created file
-				tail, err := tail.TailFile(event.Name, tail.Config{ReOpen: true, Follow: true, Poll: true, Location: &tail.SeekInfo{Offset: 0, Whence: io.SeekStart}})
+				tail, err := tail.TailFile(event.Name, tail.Config{ReOpen: true, Follow: true, Poll: f.config.PollWithoutInotify, Location: &tail.SeekInfo{Offset: 0, Whence: io.SeekStart}})
 				if err != nil {
 					logger.Errorf("Could not start tailing file %s : %s", event.Name, err)
 					break