We know that Write::flush for on-disk file is actually a no-op.
And BufWriter::flush also wont send flush system call in Linux.
So, how to do?
Btw, I don't want to call mem::drop(file)
Because I want to write to mounted path with blobfuse. Blobfuse may be for the sake of perf, so the upload file is only available when close file. Refer: https://github.com/Azure/azure-storage-fuse/blob/master/blobfuse/fileapis.cpp#L346