linux-kernel - Re: [PATCH v1 1/1] nvme: add admin controller support. prohibit ioq creation for admin & disco ctrlrs

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Message-ID:
 <BY5PR04MB6849D66446B2E05D92D80257BCAF2@BY5PR04MB6849.namprd04.prod.outlook.com>
Date: Wed, 2 Apr 2025 21:03:42 +0000
From: Kamaljit Singh <Kamaljit.Singh1@....com>
To: Niklas Cassel <cassel@...nel.org>
CC: Keith Busch <kbusch@...nel.org>, "axboe@...nel.dk" <axboe@...nel.dk>, hch
	<hch@....de>, "sagi@...mberg.me" <sagi@...mberg.me>,
	"linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Damien Le Moal
	<dlemoal@...nel.org>
Subject: Re: [PATCH v1 1/1] nvme: add admin controller support. prohibit ioq
 creation for admin & disco ctrlrs

Hi Niklas,

On Tue, Apr 01, 2025 at 11:37 PM, Niklas Cassel wrote:

>> > But to be honest, the code did previously
>> > allow an I/O controller with just the admin queue and no I/O queues.
>> Agree. Initially, I was able to use that hole by forcing nvme-cli to
>> allow zero IOQs. But based on your suggested driver change we don't
>> need to patch nvme-cli anymore. That's slick!
>>
>> However, from the nvme-cli's perspective it does feel awkward to be forced
>> by "nvme connect" to use -i <non-zero> for an admin-controller, even though
>> its now being overridden with this patch. We will have to come up with a
>> cleaner and standardized way to connect to an admin controller.  A standard
>> port number for an admin controller might be the way to go but it's not in
>> the spec yet.

>So, with this patch which overrides the user provided value,
>if the controller is an admin controller, you need to use:

>$ nvme connect -i <non-zero> ?

>Can't you simply omit the -i parameter?
That worked. But under the covers nvme-cli uses a default --nr-io-queues
based on the core count, which of course will be overridden by this patch to zero
in the kernel. I'm not sure if nvme-cli may hit any internal state/cache issues related 
to an inconsistency between requested vs actual nr-io-queues. This method works 
for now.

Thanks,
Kamaljit