linux-kernel - Re: [PATCH v2 1/3] nvme: add capability to connect to an admin controller

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Message-ID: <22f8ec86-2d50-4237-9313-79bfc93c8e3d@kernel.org>
Date: Wed, 2 Jul 2025 11:11:35 +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 v2 1/3] nvme: add capability to connect to an admin
 controller

On 7/2/25 09:58, 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 in nvme_ctrl
> 
> Reference: NVMe Base rev 2.2, sec 3.1.3.4, fig 28.
> 
> Signed-off-by: Kamaljit Singh <kamaljit.singh1@....com>
> ---
>  drivers/nvme/host/core.c | 21 +++++++++++++++++++++
>  drivers/nvme/host/nvme.h |  1 +
>  drivers/nvme/host/rdma.c |  2 ++
>  drivers/nvme/host/tcp.c  |  2 ++
>  4 files changed, 26 insertions(+)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index e533d791955d..a1155fb8d5be 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -3149,6 +3149,22 @@ 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);

No need for the parenthesis.

> +}
> +
> +/*
> + * An admin controller has one admin queue, but no I/O queues.
> + * Override queue_count so it only creates an admin queue.
> + */
> +void nvme_override_prohibited_io_queues(struct nvme_ctrl *ctrl)
> +{
> +	if (nvme_admin_ctrl(ctrl))
> +		ctrl->queue_count = 1;
> +}
> +EXPORT_SYMBOL_GPL(nvme_override_prohibited_io_queues);

Why not have this done in nvme_init_subsystem() ? That would avoid needing to
call this in all fabrics drivers.

> +
>  static bool nvme_validate_cntlid(struct nvme_subsystem *subsys,
>  		struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
>  {
> @@ -3215,6 +3231,11 @@ static int nvme_init_subsystem(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
>  		kfree(subsys);
>  		return -EINVAL;
>  	}
> +	if (nvme_admin_ctrl(ctrl))
> +		dev_info(ctrl->device,
> +			"Subsystem %s is an administrative controller",
> +			subsys->subnqn);

We do not print an equivalent message for other subsystem controller types. So
drop this.

> +
>  	nvme_mpath_default_iopolicy(subsys);
>  
>  	subsys->dev.class = &nvme_subsys_class;


-- 
Damien Le Moal
Western Digital Research