linux-kernel - Re: [PATCH v3 1/2] nvme: add capability to connect to an administrative controller

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Message-ID: <845e9caa-093c-466b-9a9b-905359517568@suse.de>
Date: Tue, 22 Jul 2025 09:06:07 +0200
From: Hannes Reinecke <hare@...e.de>
To: Kamaljit Singh <kamaljit.singh1@....com>, kbusch@...nel.org,
 axboe@...nel.dk, hch@....de, sagi@...mberg.me,
 linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc: cassel@...nel.org, dlemoal@...nel.org
Subject: Re: [PATCH v3 1/2] nvme: add capability to connect to an
 administrative controller

On 7/18/25 02:14, Kamaljit Singh wrote:
> Suggested-by: Niklas Cassel <cassel@...nel.org>
> 
> Add capability to connect to an administrative controller by
> preventing ioq creation for admin-controllers.
> 
> * Add helper nvme_admin_ctrl() to check for an administrative controller
> * Add helper nvme_override_prohibited_io_queues() to override queue_count
> * Call nvme_override_prohibited_io_queues() from nvme_init_ctrl_finish()
>    so it applies to nvme/tcp and nvme/rdma
> 
> Signed-off-by: Kamaljit Singh <kamaljit.singh1@....com>
> ---
>   drivers/nvme/host/core.c | 21 +++++++++++++++++++++
>   1 file changed, 21 insertions(+)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index e533d791955d..105127638c31 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -3149,6 +3149,21 @@ static inline bool nvme_discovery_ctrl(struct nvme_ctrl *ctrl)
>   	return ctrl->opts && ctrl->opts->discovery_nqn;
>   }
>   
> +static inline bool nvme_admin_ctrl(struct nvme_ctrl *ctrl)
> +{
> +	return ctrl->cntrltype == NVME_CTRL_ADMIN;
> +}
> +
> +/*
> + * An admin controller has one admin queue, but no I/O queues.
> + * Override queue_count so it only creates an admin queue.
> + */
> +static inline void nvme_override_prohibited_io_queues(struct nvme_ctrl *ctrl)
> +{
> +	if (nvme_admin_ctrl(ctrl))
> +		ctrl->queue_count = 1;
> +}
> +
>   static bool nvme_validate_cntlid(struct nvme_subsystem *subsys,
>   		struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
>   {
> @@ -3670,6 +3685,12 @@ int nvme_init_ctrl_finish(struct nvme_ctrl *ctrl, bool was_suspended)
>   	if (ret)
>   		return ret;
>   
> +	if (nvme_admin_ctrl(ctrl))
> +		dev_dbg(ctrl->device,
> +			"Subsystem %s is an administrative controller",
> +			ctrl->subsys->subnqn);
> +	nvme_override_prohibited_io_queues(ctrl);
> +
>   	ret = nvme_configure_apst(ctrl);
>   	if (ret < 0)
>   		return ret;

One wonders why this is done for admin controllers only; surely 
discovery controllers also don't support I/O queues, and should
therefore have the same setting?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich