mount: file fsync

fix https://github.com/chrislusf/seaweedfs/issues/2561

weed/filesys/wfs.go

@@ -179,6 +179,28 @@ func (wfs *WFS) AcquireHandle(file *File, uid, gid uint32) (fileHandle *FileHand
 	return
 }
 
+func (wfs *WFS) Fsync(file *File, header fuse.Header) error {
+
+	inodeId := file.Id()
+
+	wfs.handlesLock.Lock()
+	existingHandle, found := wfs.handles[inodeId]
+	wfs.handlesLock.Unlock()
+
+	if found && existingHandle != nil && existingHandle.f.isOpen > 0 {
+
+		existingHandle.Add(1)
+		defer existingHandle.Done()
+
+		existingHandle.Lock()
+		defer existingHandle.Unlock()
+
+		return existingHandle.doFlush(context.Background(), header)
+	}
+
+	return nil
+}
+
 func (wfs *WFS) ReleaseHandle(fullpath util.FullPath, handleId fuse.HandleID) {
 	wfs.handlesLock.Lock()
 	defer wfs.handlesLock.Unlock()