Merge pull request #1292 from timstclair/tail

Fixes for log tailing

utils/tail/tail.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"path/filepath"
 	"sync"
 	"time"
 
@@ -37,8 +38,10 @@ type Tail struct {
 	watcher    *inotify.Watcher
 }
 
-const retryOpenInterval = time.Second
-const maxOpenAttempts = 3
+const (
+	defaultRetryInterval = 100 * time.Millisecond
+	maxRetryInterval     = 30 * time.Second
+)
 
 // NewTail starts opens the given file and watches it for deletion/rotation
 func NewTail(filename string) (*Tail, error) {
@@ -72,31 +75,15 @@ func (t *Tail) Close() {
 	close(t.stop)
 }
 
-func isEvent(event *inotify.Event, flag uint32) bool {
-	return event.Mask&flag == flag
-}
-
-func (t *Tail) fileChanged() error {
-	for {
-		select {
-		case event := <-t.watcher.Event:
-			// We don't get IN_DELETE because we are holding the file open
-			if isEvent(event, inotify.IN_ATTRIB) || isEvent(event, inotify.IN_MOVE_SELF) {
-				return nil
-			}
-		case <-t.stop:
-			return fmt.Errorf("watch was cancelled")
-		}
-	}
-}
-
 func (t *Tail) attemptOpen() error {
 	t.readerLock.Lock()
 	defer t.readerLock.Unlock()
 	t.reader = nil
 	t.readerErr = nil
-	for attempt := 1; attempt <= maxOpenAttempts; attempt++ {
-		glog.V(4).Infof("Opening %s (attempt %d of %d)", t.filename, attempt, maxOpenAttempts)
+	attempt := 0
+	for interval := defaultRetryInterval; ; interval *= 2 {
+		attempt++
+		glog.V(4).Infof("Opening %s (attempt %d)", t.filename, attempt)
 		var err error
 		t.file, err = os.Open(t.filename)
 		if err == nil {
@@ -105,8 +92,11 @@ func (t *Tail) attemptOpen() error {
 			t.reader = bufio.NewReader(t.file)
 			return nil
 		}
+		if interval >= maxRetryInterval {
+			break
+		}
 		select {
-		case <-time.After(retryOpenInterval):
+		case <-time.After(interval):
 		case <-t.stop:
 			t.readerErr = io.EOF
 			return fmt.Errorf("watch was cancelled")
@@ -133,15 +123,24 @@ func (t *Tail) watchFile() error {
 		return err
 	}
 	defer t.file.Close()
-	err = t.watcher.Watch(t.filename)
+
+	watchDir := filepath.Dir(t.filename)
+	err = t.watcher.AddWatch(watchDir, inotify.IN_MOVED_FROM|inotify.IN_DELETE)
 	if err != nil {
-		return err
+		return fmt.Errorf("Failed to add watch to directory %s: %v", watchDir, err)
 	}
-	defer t.watcher.RemoveWatch(t.filename)
-	err = t.fileChanged()
-	if err != nil {
-		return err
+	defer t.watcher.RemoveWatch(watchDir)
+
+	for {
+		select {
+		case event := <-t.watcher.Event:
+			eventPath := filepath.Clean(event.Name) // Directory events have an extra '/'
+			if eventPath == t.filename {
+				glog.V(4).Infof("Log file %s moved/deleted", t.filename)
+				return nil
+			}
+		case <-t.stop:
+			return fmt.Errorf("watch was cancelled")
+		}
 	}
-	glog.V(4).Infof("Log file %s moved/deleted", t.filename)
-	return nil
 }