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

From: Laurence Oberman <loberman@redhat.com>
To: Mike Snitzer <snitzer@redhat.com>, Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>,
	linux-nvme@lists.infradead.org,
	Keith Busch <keith.busch@intel.com>,
	Sagi Grimberg <sagi@grimberg.me>,
	axboe@kernel.dk, Martin Wilck <mwilck@suse.com>,
	lijie <lijie34@huawei.com>,
	xose.vazquez@gmail.com, chengjike.cheng@huawei.com,
	shenhong09@huawei.com, dm-devel@redhat.com,
	wangzhoumengjian@huawei.com, christophe.varoqui@opensvc.com,
	bmarzins@redhat.com, sschremm@netapp.com,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: nvme: allow ANA support to be independent of native multipathing
Date: Fri, 16 Nov 2018 14:34:26 -0500	[thread overview]
Message-ID: <1542396866.13202.0.camel@redhat.com> (raw)
In-Reply-To: <20181116192802.GA30057@redhat.com>

On Fri, 2018-11-16 at 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 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:
> > 
> >  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