Re: [nfs-utils PATCH] exports: Fix referrals when --enable-junction=no

[Steve Dickson <steved@redhat.com>]

Hey!

On 12/3/24 9:28 AM, Chuck Lever III wrote:
> 
> 
>> On Dec 2, 2024, at 10:19 PM, Steve Dickson <SteveD@redhat.com> wrote:
>>
>> Hey,
>>
>> On 12/2/24 3:30 PM, Scott Mayhew wrote:
>>> Commit 15dc0bea ("exportd: Moved cache upcalls routines into
>>> libexport.a") caused write_fsloc() to be elided when junction support is
>>> disabled.  Get rid of the bogus #ifdef HAVE_JUNCTION_SUPPORT blocks so
>>> that referrals work again (the only #ifdef HAVE_JUNCTION_SUPPORT should
>>> be around actual junction code).
>> Why not just take the enable_junction config variable
>> out of configure.ac as well?
> 
> It's not generally good practice, but I will break up your
> sentence below to reply to each bit. There is something to
> unpack in each part.
I agree not being a good practice... But sometimes
config switches out live their usefulness...
Basically that's what I was thinking

> 
> 
>> If we want junctions/referrals (which are the same)
>> IMHO...
> 
> Junctions and refer= are related, but they aren't
> the same. As Scott demonstrated, a junction is a file
> system object that stores NFSv4 referral information.
> The "refer=" export option stores that information in
> /etc/exports.
Is there a point to have both ways?
What is the advantage of one way over the other?

> 
> The common part of these two mechanisms resides in
> NFSD, which turns that information into the response
> to a GETATTR(fs_locations).
Right... both ways use the same protocol.

> 
> 
>> on all the time...
> 
> We want "refer=" on all the time, yes.
Fine.. Scott's patch will be in the coming releases.

> 
> Junction support has to be enabled manually. This is
> because it depends on libxml2, which not every distro
> wants to, or can, pull into its nfs-utils package.
Yeah... libxml2 seems to be an Fedora only thing.

> 
> That is in fact exactly how Salvatore is using this
> option. The stable version of Debian's nfs-utils
> package does not want libxml2, so junction support is
> disabled there. But they /do/ want "refer=" support.
Yeah... The bug has been around for a while
(pre-pandemic ;-) ) so it appears somebody is
starting to use referrals...

> 
> 
>> Lets not be able to turn them off at all?
> 
> That would be nice, but it's not yet practical for
> every distro to enable it.
Understood.

> 
> I am told that Debian unstable's nfs-utils will
> enable junction support, and has added the libxml2
> dependency successfully.
> 
> We will get there eventually.
Patches are welcome! :-)

steved.