While I'm sure you're right, this VFS implementation doesn't use any of that stuff. They just handwave concurrent writes away by saying the application has to e

While I'm sure you're right, this VFS implementation doesn't use any of that stuff. They just handwave concurrent writes away by saying the application has to ensure a single writer on its own. An S3 implementation appears to be planned; it's mentioned in the comments in the bcvmodule.c file.