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

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Message-ID: <20250718001415.3774178-2-kamaljit.singh1@wdc.com>
Date: Thu, 17 Jul 2025 17:14:14 -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 v3 1/2] nvme: add capability to connect to an administrative controller

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;
-- 
2.43.0