Re: nvme: allow ANA support to be independent of native multipathing

[Laurence Oberman]

On Fri, 2018-11-16 at 14:28 -0500, Mike Snitzer wrote:
> On Fri, Nov 16 2018 atÂÂ5:17am -0500,
> Christoph Hellwig <hch@xxxxxx> wrote:
> 
> > On Fri, Nov 16, 2018 at 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:
> > 
> > Âa) warn if we see a ANA capable device without multipath support
> > ÂÂÂÂso people know it is not going to work properly.
> 
> I disagree with your cynicism but v2 of this patch now emits a
> warning
> accordingly.
> 
> > Âb) deprecate the multipath module option.ÂÂIt was only intended as
> > ÂÂÂÂa migration for any pre-existing PCIe multipath user if there
> > ÂÂÂÂwere any, not to support any new functionality.ÂÂSo for 4.20
> > ÂÂÂÂput in a patch that prints a clear warning when it is used,
> > ÂÂÂÂincluding a link to the nvme list, and then for 4.25 or so
> > ÂÂÂÂremove 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.ÂÂNow
> you're forecasting removing even that.ÂÂPlease 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.ÂÂYou 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.ÂÂThe 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