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

[Chuck Lever III <chuck.lever@oracle.com>]

> On Nov 10, 2023, at 8:49 AM, Benjamin Coddington <bcodding@redhat.com> wrote:
> 
> On 10 Nov 2023, at 2:54, Martin Wege 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...
> 
> Just test it!
> 
> I thought the nfsref program actually populates the "trusted.junction.nfs"
> xattr, which is part of the "fedfs" project's metadata to link filesystems
> together.  I don't think that's what you want here.

No, nfsref is what Martin wants.


> Chuck - am I right to say that the nfsref program does not populate
> nfsd4_fs_locations on knfsd?

nfsref is the proper tool to use.

nfsref turns a directory into a junction by doing two things:

1. It adds a trusted.junction.nfs xattr containing the information
   that the server returns when a client does a GETATTR(fs_locations)
   on that directory

2. It updates the directory's mode bits to mark it as a junction

It is mountd that takes either the refer=/replica= export option
or the junction xattr and feeds that to the kernel so it can
construct a GETATTR(fs_locations) response.


--
Chuck Lever