linux-kernel - Re: [PATCH 2/4] nvme-multipath: add the NVME_MULTIPATH

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Message-ID: <cd731f6e-c0e0-4ea7-9012-5860b0be2920@redhat.com>
Date: Thu, 13 Mar 2025 17:46:25 -0400
From: John Meneghini <jmeneghi@...hat.com>
To: Christoph Hellwig <hch@....de>
Cc: kbusch@...nel.org, sagi@...mberg.me, loberman@...hat.com,
 linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
 emilne@...hat.com, bgurney@...hat.com
Subject: Re: [PATCH 2/4] nvme-multipath: add the NVME_MULTIPATH_PARAM config
 option

On 3/12/25 1:19 AM, Christoph Hellwig wrote:
> On Tue, Mar 11, 2025 at 10:35:40PM -0400, John Meneghini wrote:
>>> What's the point of adding yet another confusing option?
>>
>> If you'll read the kConfig description, hopefully it's not confusing.
> 
> It still is.

OK. I can fix that.

>> The whole point of this patch series is to remove the core.nvme_mulipath parameter.
> 
> Why would a compile time option be preferable over a runtime one?

Because distos like RHEL don't allow customers to recompile their kernel. And including this runtime
switch in the kernel let's users turn nvme-multipath off w/out recompiling the kernel.

Our RHEL customers do this all of the time to enable DMMP with their NVMe devices. This has caused tremendous
confusion and turmoil with our RHEL customers who keep on turning nvme-multipath off even when we ship
RHEL with nvme-multipath on and we tell them turning it off is not supported.

I finally decided that there is no good way to control this situation w/out removing the
core.nvme_multipath parameter while CONFIG_NVME_MULTIPATH is enabled.

This patch enables distros like RHEL simply config out the parameter w/out impacting all of the people out
there who currently want and use the run time switch when CONFIG_NVME_MULTIPATH is enabled.

Please let me know what I need to do to make these patches less confusing and get them accepted upstream.

/John