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

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Message-ID: <Z7dct_AbaSO7uZ2h@kbusch-mbp>
Date: Thu, 20 Feb 2025 09:47:51 -0700
From: Keith Busch <kbusch@...nel.org>
To: Sagi Grimberg <sagi@...mberg.me>
Cc: Nilay Shroff <nilay@...ux.ibm.com>,
	John Meneghini <jmeneghi@...hat.com>, hch@....de,
	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, Feb 20, 2025 at 01:05:04PM +0200, Sagi Grimberg wrote:
> This discussion is not specific to RHEL, if there is a real use-case
> that we are interested in supporting, we can change our minds and keep
> it (and simply remove the log msg), but I haven't heard any real life
> use-cases thus far.

One use case: ublk.

Other use cases are manufacturing and debugging. Linux has been a great
environment for both, which don't want anything hidden behind virtual
devices.

The module parameter makes it possible to do this with your distro's
stock kernel that came with the CONFIG option enabled.

The device mapper multipath needed some layering violations out of the
driver to make failover work correctly/better. That's one reason it's
not supported here, and that's an appropriate place to draw the line on
what kinds of patches should be accepted.