[PATCH blktests] nvme/075: test the per-queue io_cpu sysfs attribute

[Saravanan D]

nvme-tcp exposes /sys/class/nvme/nvmeX/queues/<qid>/io_cpu and managed,
so a control plane can choose the CPU that runs each I/O queue's socket
work [1]. Test that

  - io_cpu reads back a written CPU and rejects invalid values
  - managed is read only and turns 0 once io_cpu is written
  - an assignment survives a controller reset
  - the queue directories follow the queue count as attr_qid_max
    shrinks and grows it
  - removing the controller while io_cpu is written completes

The test skips when the kernel does not have the attribute.

[1] https://lore.kernel.org/linux-nvme/20261018010059.83120-1-saravanand@crusoe.ai/

Assisted-by: Claude:claude-opus-5-5 [Claude Code]
Signed-off-by: Saravanan D <saravanand at crusoe.ai>
---
This tests the kernel series in the parent thread, which is under
review on linux-nvme.

 tests/nvme/075     | 185 +++++++++++++++++++++++++++++++++++++++++++++
 tests/nvme/075.out |   2 +
 2 files changed, 187 insertions(+)
 create mode 100755 tests/nvme/075
 create mode 100644 tests/nvme/075.out

diff --git a/tests/nvme/075 b/tests/nvme/075
new file mode 100755
index 0000000..0b4bce5
--- /dev/null
+++ b/tests/nvme/075
@@ -0,0 +1,185 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-3.0+
+# Copyright (C) 2026 Saravanan D <saravanand at crusoe.ai>
+#
+# Test the per-queue io_cpu sysfs attribute of nvme-tcp
+
+. tests/nvme/rc
+
+DESCRIPTION="test the per-queue io_cpu sysfs attribute"
+
+requires() {
+	_nvme_requires
+	_have_loop
+	_require_nvme_trtype tcp
+	_require_min_cpus 2
+}
+
+set_conditions() {
+	_set_nvme_trtype "$@"
+}
+
+# last CPU in the online list, and the first CPU id past the possible ones
+last_online_cpu() {
+	awk -F'[-,]' '{ print $NF }' /sys/devices/system/cpu/online
+}
+
+first_impossible_cpu() {
+	echo $(( $(awk -F'[-,]' '{ print $NF }' /sys/devices/system/cpu/possible) + 1 ))
+}
+
+nr_queue_dirs() {
+	local nvmedev="$1"
+
+	find "/sys/class/nvme/${nvmedev}/queues" -mindepth 1 -maxdepth 1 \
+		-type d 2>/dev/null | wc -l
+}
+
+expect_attr() {
+	local file="$1"
+	local expected="$2"
+	local value
+
+	value=$(cat "${file}")
+	if [[ "${value}" != "${expected}" ]]; then
+		echo "${file}: read ${value}, expected ${expected}"
+		return 1
+	fi
+	return 0
+}
+
+test_read_write() {
+	local qdir="$1"
+	local cpu="$2"
+	local bad
+
+	expect_attr "${qdir}/1/managed" 1
+
+	echo "${cpu}" > "${qdir}/1/io_cpu"
+	expect_attr "${qdir}/1/io_cpu" "${cpu}"
+	expect_attr "${qdir}/1/managed" 0
+
+	for bad in "$(first_impossible_cpu)" -2 abc 0x1; do
+		if { echo "${bad}" > "${qdir}/1/io_cpu"; } 2>/dev/null; then
+			echo "io_cpu accepted ${bad}"
+		fi
+	done
+	expect_attr "${qdir}/1/io_cpu" "${cpu}"
+
+	if { echo 1 > "${qdir}/1/managed"; } 2>/dev/null; then
+		echo "managed is writable"
+	fi
+
+	echo unbound > "${qdir}/2/io_cpu"
+	expect_attr "${qdir}/2/io_cpu" -1
+	echo -1 > "${qdir}/2/io_cpu"
+	expect_attr "${qdir}/2/io_cpu" -1
+	expect_attr "${qdir}/2/managed" 0
+}
+
+test_reset() {
+	local nvmedev="$1"
+	local qdir="$2"
+	local cpu="$3"
+
+	echo 1 > "/sys/class/nvme/${nvmedev}/reset_controller"
+	_nvmf_wait_for_state "${def_subsysnqn}" "live" || return 1
+
+	expect_attr "${qdir}/1/io_cpu" "${cpu}"
+	expect_attr "${qdir}/1/managed" 0
+	expect_attr "${qdir}/2/io_cpu" -1
+	expect_attr "${qdir}/2/managed" 0
+}
+
+set_qid_max() {
+	local nvmedev="$1"
+	local qid_max="$2"
+	local queue_count_file="/sys/class/nvme-fabrics/ctl/${nvmedev}/queue_count"
+	local retries=10
+
+	echo "${qid_max}" > \
+		"${NVMET_CFS}/subsystems/${def_subsysnqn}/attr_qid_max"
+	while [[ "$(cat "${queue_count_file}")" -ne $((qid_max + 1)) ]]; do
+		if (( retries-- == 0 )); then
+			echo "queue count did not change to $((qid_max + 1))"
+			return 1
+		fi
+		sleep 1
+	done
+	_nvmf_wait_for_state "${def_subsysnqn}" "live" || return 1
+
+	if [[ "$(nr_queue_dirs "${nvmedev}")" -ne "${qid_max}" ]]; then
+		echo "$(nr_queue_dirs "${nvmedev}") queue directories," \
+			"expected ${qid_max}"
+		return 1
+	fi
+	return 0
+}
+
+io_cpu_writer() {
+	local qdir="$1"
+	local cpu="$2"
+	local file
+
+	while true; do
+		for file in "${qdir}"/*/io_cpu; do
+			{ echo "${cpu}" > "${file}"; } 2>/dev/null
+			{ echo unbound > "${file}"; } 2>/dev/null
+		done
+	done
+}
+
+test() {
+	echo "Running ${TEST_NAME}"
+
+	_setup_nvmet
+
+	local cfs_path="${NVMET_CFS}/subsystems/${def_subsysnqn}"
+	local skipped=false
+	local nvmedev qdir cpu writer
+
+	_nvmet_target_setup --blkdev file
+
+	_nvme_connect_subsys --keep-alive-tmo 1 --reconnect-delay 2
+	_nvmf_wait_for_state "${def_subsysnqn}" "live"
+	nvmedev=$(_find_nvme_dev "${def_subsysnqn}")
+	qdir="/sys/class/nvme/${nvmedev}/queues"
+	cpu=$(last_online_cpu)
+
+	if [[ ! -f "${qdir}/1/io_cpu" ]]; then
+		SKIP_REASONS+=("missing per-queue io_cpu attribute")
+		skipped=true
+	elif [[ "$(nr_queue_dirs "${nvmedev}")" -lt 2 ]]; then
+		SKIP_REASONS+=("controller has fewer than 2 I/O queues")
+		skipped=true
+	else
+		test_read_write "${qdir}" "${cpu}"
+		test_reset "${nvmedev}" "${qdir}" "${cpu}"
+
+		if [[ -f "${cfs_path}/attr_qid_max" ]]; then
+			set_qid_max "${nvmedev}" 1
+			expect_attr "${qdir}/1/io_cpu" "${cpu}"
+			set_qid_max "${nvmedev}" 2
+		fi
+
+		# remove the controller while its queue directories are written
+		io_cpu_writer "${qdir}" "${cpu}" &
+		writer=$!
+		sleep 1
+	fi
+
+	_nvme_disconnect_subsys
+
+	if [[ -n "${writer}" ]]; then
+		kill "${writer}"
+		wait "${writer}" 2>/dev/null
+	fi
+
+	_nvmet_target_cleanup
+
+	if [[ "${skipped}" = true ]] ; then
+		return 1
+	fi
+
+	echo "Test complete"
+}
diff --git a/tests/nvme/075.out b/tests/nvme/075.out
new file mode 100644
index 0000000..0613dfa
--- /dev/null
+++ b/tests/nvme/075.out
@@ -0,0 +1,2 @@
+Running nvme/075
+Test complete
-- 
2.55.0