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

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Message-ID: <b99e0ae6-f273-4c2d-bdc3-dd8b301f2f0b@kernel.org>
Date: Fri, 18 Jul 2025 13:14:51 +0900
From: Damien Le Moal <dlemoal@...nel.org>
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
Subject: Re: [PATCH v3 1/2] nvme: add capability to connect to an
 administrative controller

On 2025/07/18 9:14, 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);

I do not think that this inline function is useful. Simply open-code it inside
the if above:

	if (nvme_admin_ctrl(ctrl)) {
		/*
		 * An admin controller has one admin queue, but no I/O queues.
		 * Override queue_count so it only creates an admin queue.
		 */
		dev_dbg(ctrl->device,
			"Subsystem %s is an administrative controller",
			ctrl->subsys->subnqn);
		ctrl->queue_count = 1;
	}

With this, feel free to add:

Reviewed-by: Damien Le Moal <dlemoal@...nel.org>

-- 
Damien Le Moal
Western Digital Research