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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Pradeep <pradeepthomas@gmail.com>
CC:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: NFSv4 referrals with FQDN.
Thread-Topic: NFSv4 referrals with FQDN.
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Date:   Wed, 24 Mar 2021 19:20:18 +0000
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> On Mar 23, 2021, at 5:56 PM, Pradeep <pradeepthomas@gmail.com> wrote:
>=20
> Hello,
>=20
> While testing NFSv4 referrals, I noticed that if the server name in FS
> locations does not have IPv4 mapping (server name has AAAA record for
> IPv6; but no A record in DNS), the referral mount fails.

IIRC, that is a known bug, but it has been rarely hit up to this point
(only case I'm aware of is during testing, which is how I know about
this issue).

The DNS upcall needs to be fixed to handle this case properly. As Bruce
likes to say, patches welcome!


> With debug enabled, I get something like this:
>=20
> nfs_follow_referral: referral at /nfs_export_1
> nfs4_path: path server-1.domain.com:/nfs_export_1 from nfs_path
> nfs4_path: path component /nfs_export_1
> nfs4_validate_fspath: comparing path /nfs_export_1 with fsroot /nfs_expor=
t_1
> =3D=3D> dns_query((null),server-2.domain.com,19,(null))
> call request_key(,server-2.domain.com,)
> <=3D=3D dns_query() =3D -126
> nfs_follow_referral: done
> nfs_do_refmount: done
> RPC:       shutting down nfs client for server-1.domain.com
> RPC:       rpc_release_client(ffff97fdf170c600)
> RPC:       destroying nfs client for server-1.domain.com
> <-- nfs_d_automount(): error -2
>=20
> It looks like NFS client does an upcall to "/sbin/key.dns_resolver".
> "/sbin/key.dns_resolver" works if callout info is set to 'ipv6'.
> Otherwise it fails too.
>=20
> Does this mean setups with only IPv6 records (AAAA records in DNS),
> NFSv4 referrals won't work if server returns FQDN in referral? If
> anyone has tried this and made it work, please let me know.
>=20
> Thanks,
> Pradeep

--
Chuck Lever