linux-kernel - Re: [PATCH] nvme: remove multipath module parameter

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Message-ID: <Z8m4vzE36UHWjwep@kbusch-mbp>
Date: Thu, 6 Mar 2025 08:01:19 -0700
From: Keith Busch <kbusch@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: Hannes Reinecke <hare@...e.de>, Sagi Grimberg <sagi@...mberg.me>,
	Nilay Shroff <nilay@...ux.ibm.com>,
	John Meneghini <jmeneghi@...hat.com>, bmarzins@...hat.com,
	Bryan Gurney <bgurney@...hat.com>, linux-nvme@...ts.infradead.org,
	linux-kernel@...r.kernel.org, Marco Patalano <mpatalan@...hat.com>,
	axboe@...nel.dk
Subject: Re: [PATCH] nvme: remove multipath module parameter

On Thu, Mar 06, 2025 at 03:18:37PM +0100, Christoph Hellwig wrote:
> On Thu, Mar 06, 2025 at 08:12:03AM +0100, Hannes Reinecke wrote:
> > Single ported.
> > There is a range of Samsung NVMe where one is a normal, single ported,
> > NVMe, and one with a nearly identical model number reporting CMIC.
> >
> > Causing _quite_ a lot of confusion with the customer (and L3) when
> > used under MD, as for the first hotplug works, for the second ... not so 
> > much.
> 
> If the device is indeed entirely single ported and Samsung can confirm
> the setting is incorret and not easily fixable by a firmware update
> we can quirk it.

It's not one vendor or device. Making this a quirk is a good way to get
the mailing list spammed with requests to add yet another device to a
quirk table.

Or consider a true multiport PCIe where each port connects to a
different host. Each host sees a single port so they're not using
multipath capabilities, and the admin wants the MD behavior that removes
a disk on hot plug. Or even if one host sees both paths of a multiport
PCIe, they still might want that hot plug behavior. The module parameter
makes that possible, so some equivalent should be available before
removing it.