I've stated looking a bit at the code, and the architectural model confuses me more than a bit. A first thing that would be very helpful is an actual problem statement. The only mention of a concrete use case is about containers, implying that this about a client in one container/namespace with the server or the servers in another containers/namespace. Is that the main use case, are there others? I kinda deduct from that that the client and server probably do not have the same view and access permissions to the underlying file systems? As this would defeat the use of NFS I suspect that is the case, but it should probably be stated clearly somewhere. Going from there I don't understand why we need multiple layers of server bypass. The normal way to do this in NFSv4 is to use pNFS layout. I.e. you add a pnfs localio layout that just does local reads and writes for the I/O path. We'd still need a way to find a good in-kernel way to get the file structure, but compared to the two separate layers of bypasses in the current code it should be significantly simpler.
