How to call statvfs on a filesystem mounted using Arduino_UnifiedStorage?

[Vidbuf]

I'd like to get the size of the unused storage on a USB drive mounted using Arduino_UnifiedStorage. However it seems the mounted filesystem is held as a private member of the Arduino_POSIXStorage library, and thus I can't get a call to statvfs to return sane values.

Is there a recommended approach to getting the file system statistics (especially free space) using Arduino_UnifiedStorage?

Am I missing something or should this be considered for a feature request?