使用mgodb-go-driver将上载的文件存储在MongoDB GridFS中，而不保存到内存

I am using below Go MongoDB plugin MongoDB-GO-Driver to store ymal file data.

I am using gridfs.NewBucket() method.

 func (s *FS) CreateFilewithBytes(data []byte, filename string) error {

    buf := bytes.NewBuffer(data)
    chunksize, _ := binary.ReadVarint(buf)
    _, err := gridfs.NewBucket(db,
        options.GridFSBucket().
            SetName(filename).
            SetChunkSizeBytes(int32(chunksize))

    if err != nil {
        return err
    } 
} 

Please help me out how to store file and read file data.