internal static bool ShouldPreallocate(long preallocationSize, FileAccess access, FileMode mode, SafeFileHandle fileHandle) => preallocationSize > 0 && (access & FileAccess.Write) != 0 && mode != FileMode.Open && mode != FileMode.Append && (mode != FileMode.OpenOrCreate || (fileHandle.CanSeek && RandomAccess.GetFileLength(fileHandle) == 0)); // allow to extend only new files
