Re: filesystem client mapping of uid_t/gid_t field in lookup

[Spencer Shepler <spencer.shepler@sun.com>]

On Mon, Bryan Henderson wrote:
> >> 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.
> >
> >Woah...All it says is that the NFSv3 client and server must have
> >matching uid/gid mappings. It says nothing about implementation details.
> 
> Then what do you make of the sentence that starts, "In practice, such 
> mapping is typically performed..."?  That's nothing if not a statement 
> about implementation details.  And I agree that this sentence implies what 
> Steve says.
> 
> It's somewhat of a surprise, however, because I always thought the mapping 
> was _typically_ done, if at all, by a table installed on the server 
> without client involvement.  A table that says, "whenever client A mounts, 
> consider his uid 8 to be our uid 13."  I base this on a vague memory, 
> though.  Correct me if I'm wrong.
> 
> The only uid-mapping NFS server I've ever used myself does neither.  The 
> client establishes the mapping via a login protocol which is independent 
> of mount.  Come to think of it, the login protocol
> in this system doesn't have to be initiated by the client.  A third party 
> can tell the server, "consider uid 8 from Client A to be uid 13."

At the time that RFC was crafted, the login protocol most commonly
used was the PCNFS protocol that most DOS/Windows NFS implementations 
to map the username to a uid to be used over the wire.  All of that 
mapping was done at user level at the server.

The rest of the mapping reference is the classic uid/gid mapping done
via /etc/passwd or NIS, etc.

That was the intent at least.

Spencer