filesystem client mapping of uid_t/gid_t field in lookup

[Steve French <smfrench@austin.rr.com>]

RFC 1813 states:
   Using user
   ids and group ids implies that the client and server either
   share the same ID list or do local user and group ID mapping.
   Servers and clients must agree on the mapping from user to uid
   and from group to gid, for those sites that do not implement a
   consistent user ID and group ID space. In practice, such mapping
   is typically performed on the server, following a static mapping
   scheme or a mapping established by the user from a client at
   mount time.

which implies that other network filesystem clients passed in a table of 
uid mappings
at mount time. This would be extremely useful, but seems unwieldy to pass
in via mount.  Without adding an ioctl to set the uids for a particular 
mount (actually in my case it would
probably be for all mounts on the client to the same sharename (export) 
and/or a particular
server), would this be better to pass in via proc (which also seems 
awkward due
to size of proc writes presumably getting bigger than 4K if there were a 
lot of mappings).