Today, sunrpc lives in net/sunrpc. As far as I can tell, the primary
production consumer of it is NFS. The RPC clients have the concept of
being tied back to a network namespace. On the other hand, NFS has its
own superblock with its own user namespace.

When sunrpc convert kuids to UIDs to send over the wire, should it use
the user namespace of the network namespace that the RPC client is
associated with? This is required for auth_unix (UID based).
Alternatively, should the sunrpc RPC client use the user namespace
associated with the NFS superblock?