Re: [PATCH v3] nfsd: disallow file locking and delegations for NFSv4 reexport

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

> On Oct 29, 2024, at 9:57 AM, Martin Wege <martin.l.wege@gmail.com> wrote:
> 
> On Wed, Oct 23, 2024 at 5:58 PM Mike Snitzer <snitzer@kernel.org> wrote:
>> 
>> We do not and cannot support file locking with NFS reexport over
>> NFSv4.x for the same reason we don't do it for NFSv3: NFS reexport
>> server reboot cannot allow clients to recover locks because the source
>> NFS server has not rebooted, and so it is not in grace.  Since the
>> source NFS server is not in grace, it cannot offer any guarantees that
>> the file won't have been changed between the locks getting lost and
>> any attempt to recover/reclaim them.  The same applies to delegations
>> and any associated locks, so disallow them too.
>> 
>> Add EXPORT_OP_NOLOCKSUPPORT and exportfs_lock_op_is_unsupported(), set
>> EXPORT_OP_NOLOCKSUPPORT in nfs_export_ops and check for it in
>> nfsd4_lock(), nfsd4_locku() and nfs4_set_delegation().  Clients are
>> not allowed to get file locks or delegations from a reexport server,
>> any attempts will fail with operation not supported.
> 
> Are you aware that this virtually castrates NFSv4 reexport to a point
> that it is no longer usable in real life?

"virtually castrates" is pretty nebulous. Please provide a
detailed (and less hostile) account of an existing application
that works today that no longer works when this patch is
applied. Only then can we count this as a regression report.


> If you really want this,
> then the only way forward is to disable and remove NFS reexport
> support completely.

"No locking" is already the way NFSv3 re-export works.

At the moment I cannot remember why we chose not to go with
the "only local locking for re-export" design instead.


--
Chuck Lever