Re: NFSv4 referrals - custom (non-2049) port numbers in fs_locations?

[Martin Wege <martin.l.wege@gmail.com>]

On Tue, Nov 14, 2023 at 3:07 AM Chuck Lever III <chuck.lever@oracle.com> wrote:
>
>
> > On Nov 13, 2023, at 5:57 PM, Cedric Blancher <cedric.blancher@gmail.com> wrote:
> >
> > On Mon, 13 Nov 2023 at 17:19, Chuck Lever III <chuck.lever@oracle.com> wrote:
> >>
> >>
> >>> On Nov 10, 2023, at 2:54 AM, Martin Wege <martin.l.wege@gmail.com> wrote:
> >>>
> >>> On Wed, Nov 1, 2023 at 3:42 PM Benjamin Coddington <bcodding@redhat.com> wrote:
> >>>>
> >>>> On 1 Nov 2023, at 5:06, Martin Wege wrote:
> >>>>
> >>>>> Good morning!
> >>>>>
> >>>>> We have questions about NFSv4 referrals:
> >>>>> 1. Is there a way to test them in Debian Linux?
> >>>>>
> >>>>> 2. How does a fs_locations attribute look like when a nonstandard port
> >>>>> like 6666 is used?
> >>>>> RFC5661 says this:
> >>>>>
> >>>>> * http://tools.ietf.org/html/rfc5661#section-11.9
> >>>>> * 11.9. The Attribute fs_locations
> >>>>> * An entry in the server array is a UTF-8 string and represents one of a
> >>>>> * traditional DNS host name, IPv4 address, IPv6 address, or a zero-length
> >>>>> * string.  An IPv4 or IPv6 address is represented as a universal address
> >>>>> * (see Section 3.3.9 and [15]), minus the netid, and either with or without
> >>>>> * the trailing ".p1.p2" suffix that represents the port number.  If the
> >>>>> * suffix is omitted, then the default port, 2049, SHOULD be assumed.  A
> >>>>> * zero-length string SHOULD be used to indicate the current address being
> >>>>> * used for the RPC call.
> >>>>>
> >>>>> Does anyone have an example of how the content of fs_locations should
> >>>>> look like with a custom port number?
> >>>>
> >>>> If you keep following the references, you end up with the example in
> >>>> rfc5665, which gives an example for IPv4:
> >>>>
> >>>> https://datatracker.ietf.org/doc/html/rfc5665#section-5.2.3.3
> >>>
> >>> So just <address>.<upper-byte-of-port-number>.<lower-byte-of-port-number>?
> >>
> >>> How can I test that with the refer= option in /etc/exports? nfsref
> >>> does not seem to have a ports option...
> >>
> >> Neither refer= nor nfsref support alternate ports for exactly the
> >> same reason: The mountd upcall/downcall, which is how the kernel
> >> learns of referral target locations, needs to be fixed first. Then
> >> support for alternate ports can be implemented in both refer= and
> >> nfsref.
> >
> > Just turn "hostname" into "hostport", i.e. the "hostname" string in
> > the mountd protocol gets the port number encoded into it. Problem
> > done. This is seriously a non-brainer,
>
> It's not as simple as you think.
>
> As far as I can tell, the mountd upcall/downcall already uses the "@"
> character in the refer= value for another purpose. It has the same
> problem as using ":" -- it would overload the meaning of the character
> and make the refer= value ambiguous and unparsable.
>
> NFSD supports IPv4 addresses, IPv6 addresses, and DNS labels as the
> hostname part of each fs_locations entry. DNS label support is one
> reason we might have some difficulty using a universal address in
> this interface -- the dot notation for the port number bytes looks
> no different than the dot notation for subdomains, and we want to
> enable alternate ports for both raw IP addresses and DNS labels.

Which syntax does a DNS label have?

Thanks,
Martin