nvme: allow ANA support to be independent of native multipathing

[loberman@redhat.com (Laurence Oberman)]

On Fri, 2018-11-16@14:28 -0500, Mike Snitzer wrote:
> On Fri, Nov 16 2018 at??5:17am -0500,
> Christoph Hellwig <hch@lst.de> wrote:
> 
> > On Fri, Nov 16, 2018@11:06:32AM +0100, Hannes Reinecke wrote:
> > > Ok, so would you be happy with making ANA support configurable?
> > 
> > I've looked a bit over the whole situation, and what I think we
> > need
> > to do is:
> > 
> > ?a) warn if we see a ANA capable device without multipath support
> > ????so people know it is not going to work properly.
> 
> I disagree with your cynicism but v2 of this patch now emits a
> warning
> accordingly.
> 
> > ?b) deprecate the multipath module option.??It was only intended as
> > ????a migration for any pre-existing PCIe multipath user if there
> > ????were any, not to support any new functionality.??So for 4.20
> > ????put in a patch that prints a clear warning when it is used,
> > ????including a link to the nvme list, and then for 4.25 or so
> > ????remove it entirely unless something unexpected come up.
> 
> You rejected the idea of allowing fine-grained control over whether
> native NVMe multipathing is enabled or not on a per-namespace basis.
> All we have is the coarse-grained nvme_core.multipath=N knob.??Now
> you're forecasting removing even that.??Please don't do that.
> 
> > This whole drama of optional multipath use has wasted way too much
> > of everyones time already.
> 
> It has wasted _way_ too much time.
> 
> But the drama is born out of you rejecting that we need to preserve
> multipath-tools and dm-multipath's ability to work across any
> transport.??You don't need to do that work: Hannes, myself and others
> have always been willing and able -- if you'd let us.
> 
> IIRC it was at 2016's LSF in Boston where Ewan Milne and I had a
> face-to-face conversation with you in the hallway track where you
> agreed
> that ANA support would be activated if the capability was advertised
> by
> the target.??The model we discussed is that it would be comparable to
> how ALUA gets enabled during SCSI LUN discovery.
> 
> I hope you can see your way forward to be more accommodating now.
> Especially given the proposed changes are backed by NVMe standards.
> 
> Please, PLEASE take v2 of this patch.. please? ;)
> 
> Thanks,
> Mike

I am begging you take it too please 
Thanks
Laurence