wal: fsync directory after wal file rename

Fixes etcd-io#6368

wal/wal.go

@@ -69,7 +69,11 @@ var (
 // A just opened WAL is in read mode, and ready for reading records.
 // The WAL will be ready for appending after reading out all the previous records.
 type WAL struct {
-	dir      string           // the living directory of the underlay files
+	dir string // the living directory of the underlay files
+
+	// dirFile is a fd for the wal directory for syncing on Rename
+	dirFile *os.File
+
 	metadata []byte           // metadata recorded at the head of each WAL
 	state    raftpb.HardState // hardstate recorded at the head of WAL
 
@@ -373,6 +377,10 @@ func (w *WAL) cut() error {
 	if err = os.Rename(newTail.Name(), fpath); err != nil {
 		return err
 	}
+	if err = fileutil.Fsync(w.dirFile); err != nil {
+		return err
+	}
+
 	newTail.Close()
 
 	if newTail, err = fileutil.LockFile(fpath, os.O_WRONLY, fileutil.PrivateFileMode); err != nil {
@@ -467,6 +475,7 @@ func (w *WAL) Close() error {
 			return err
 		}
 	}
+
 	for _, l := range w.locks {
 		if l == nil {
 			continue
@@ -475,7 +484,8 @@ func (w *WAL) Close() error {
 			plog.Errorf("failed to unlock during closing wal: %s", err)
 		}
 	}
-	return nil
+
+	return w.dirFile.Close()
 }
 
 func (w *WAL) saveEntry(e *raftpb.Entry) error {

wal/wal_unix.go

@@ -34,5 +34,12 @@ func (w *WAL) renameWal(tmpdirpath string) (*WAL, error) {
 	}
 
 	w.fp = newFilePipeline(w.dir, SegmentSizeBytes)
+
+	df, derr := os.Open(w.dir)
+	if derr != nil {
+		return nil, derr
+	}
+	w.dirFile = df
+
 	return w, nil
 }

wal/wal_windows.go

@@ -37,5 +37,13 @@ func (w *WAL) renameWal(tmpdirpath string) (*WAL, error) {
 		newWAL.Close()
 		return nil, err
 	}
+
+	// windows expects a writeable file for fsync
+	df, derr := os.OpenFile(w.dir, os.O_WRONLY, fileutil.PrivateFileMode)
+	if derr != nil {
+		return nil, derr
+	}
+	w.dirFile = df
+
 	return newWAL, nil
 }