linux-kernel - [PATCH v4 1/2] nvme: add capability to connect to an administrative controller

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Message-ID: <20250721173700.4153098-2-kamaljit.singh1@wdc.com>
Date: Mon, 21 Jul 2025 10:36:59 -0700
From: Kamaljit Singh <kamaljit.singh1@....com>
To: 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,
	kamaljit.singh1@....com
Subject: [PATCH v4 1/2] nvme: add capability to connect to an administrative controller

Add capability to connect to an administrative controller by
preventing ioq creation for admin-controllers.

* Add helper nvme_admin_ctrl() to check if a controller's CNTRLTYPE
  indicates that it is an administrative controller.
* Override ctrl->queue_count to 1, so only one admin queue and no IO
  queues are allocated for an administrative controller.
* This override is done in nvme_init_ctrl_finish() after ctrl->cntrltype
  has been initialized in nvme_init_identify() so nvme_admin_ctrl() will
  work correctly.
* Doing this override in generic code (nvme_init_ctrl_finish) makes it
  transport agnostic and will work properly for nvme/tcp as well as for
  nvme/rdma.

Suggested-by: Niklas Cassel <cassel@...nel.org>
Reviewed-by: Damien Le Moal <dlemoal@...nel.org>
Reviewed-by: Niklas Cassel <cassel@...nel.org>
Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Kamaljit Singh <kamaljit.singh1@....com>
---
 drivers/nvme/host/core.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index e533d791955d..a6388ed3ddca 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3149,6 +3149,11 @@ 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;
+}
+
 static bool nvme_validate_cntlid(struct nvme_subsystem *subsys,
 		struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
 {
@@ -3670,6 +3675,17 @@ int nvme_init_ctrl_finish(struct nvme_ctrl *ctrl, bool was_suspended)
 	if (ret)
 		return ret;
 
+	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;
+	}
+
 	ret = nvme_configure_apst(ctrl);
 	if (ret < 0)
 		return ret;
-- 
2.43.0