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

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Message-ID: <20250702005830.889217-2-kamaljit.singh1@wdc.com>
Date: Tue,  1 Jul 2025 17:58:27 -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 v2 1/3] nvme: add capability to connect to an admin 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 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);
+}
+
+/*
+ * 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);
+
 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);
+
 	nvme_mpath_default_iopolicy(subsys);
 
 	subsys->dev.class = &nvme_subsys_class;
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 7df2ea21851f..5e07ba634e97 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -1212,6 +1212,7 @@ struct nvme_ctrl *nvme_ctrl_from_file(struct file *file);
 struct nvme_ns *nvme_find_get_ns(struct nvme_ctrl *ctrl, unsigned nsid);
 bool nvme_get_ns(struct nvme_ns *ns);
 void nvme_put_ns(struct nvme_ns *ns);
+void nvme_override_prohibited_io_queues(struct nvme_ctrl *ctrl);
 
 static inline bool nvme_multi_css(struct nvme_ctrl *ctrl)
 {
diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
index 9bd3646568d0..7d50a2f31c3a 100644
--- a/drivers/nvme/host/rdma.c
+++ b/drivers/nvme/host/rdma.c
@@ -1026,6 +1026,8 @@ static int nvme_rdma_setup_ctrl(struct nvme_rdma_ctrl *ctrl, bool new)
 		goto destroy_admin;
 	}
 
+	nvme_override_prohibited_io_queues(&ctrl->ctrl);
+
 	if (ctrl->ctrl.opts->queue_size > ctrl->ctrl.sqsize + 1) {
 		dev_warn(ctrl->ctrl.device,
 			"queue_size %zu > ctrl sqsize %u, clamping down\n",
diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index d924008c3949..bfb52a487c45 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -2381,6 +2381,8 @@ static int nvme_tcp_setup_ctrl(struct nvme_ctrl *ctrl, bool new)
 		goto destroy_admin;
 	}
 
+	nvme_override_prohibited_io_queues(ctrl);
+
 	if (opts->queue_size > ctrl->sqsize + 1)
 		dev_warn(ctrl->device,
 			"queue_size %zu > ctrl sqsize %u, clamping down\n",
-- 
2.43.0