Hi Andre, Breno,

On 18/01/2026 12:00, Andre Carvalho wrote:

Introduce a new netconsole selftest to validate that netconsole is able
to resume a deactivated target when the low level interface comes back.

The test setups the network using netdevsim, creates a netconsole target
and then remove/add netdevsim in order to bring the same interfaces
back. Afterwards, the test validates that the target works as expected.

Targets are created via cmdline parameters to the module to ensure that
we are able to resume targets that were bound by mac and interface name.

I'm sorry to react on this "old" patch, but I have some troubles running
this netcons_resume.sh test in a new environment with containers.

(...)

+function trigger_reactivation() {
+	# Add back low level module
+	modprobe netdevsim
+	# Recreate namespace and two interfaces
+	set_network
+	# Restore MACs
+	ip netns exec "${NAMESPACE}" ip link set "${DSTIF}" \
+		address "${SAVED_DSTMAC}"
+	if [ "${BINDMODE}" == "mac" ]; then
+		ip link set dev "${SRCIF}" down
+		ip link set dev "${SRCIF}" address "${SAVED_SRCMAC}"
+		# Rename device in order to trigger target resume, as initial
+		# when device was recreated it didn't have correct mac address.
+		ip link set dev "${SRCIF}" name "${TARGET}"

When I execute the test, the "ifname" bind mode works without issues,
but the "mac" one not. From what I see, the socat process doesn't get
any UDP packet when expected. I wonder if the problem might not come
from here: the interface is disabled before changing the MAC address and
renaming the interface, but not re-enabled at the end. Is it normal?

If I add 'up' at the end of this last line here, or if I remove the
whole if-statement block, the test passes.

In the console, I can see these messages, with or without re-enabling
the interface:

  netdevsim netdevsim642 eni642np1: renamed from eth0
  netdevsim netdevsim387 eni387np1: renamed from eth1
  netconsole: netconsole: local port 1514
  netconsole: netconsole: local IPv4 address 192.0.2.1
  netconsole: netconsole: interface name ''
  netconsole: netconsole: local ethernet address '1e:95:b7:ae:ab:dc'
  netconsole: netconsole: remote port 6666
  netconsole: netconsole: remote IPv4 address 192.0.2.2
  netconsole: netconsole: remote ethernet address e6:12:42:f8:4c:b2
  printk: console [netcon_ext0] enabled
  netconsole: network logging started
  netconsole: network logging stopped on interface eni387np1 as it
unregistered
  netdevsim netdevsim642 eni642np1: renamed from eth0
  netdevsim netdevsim387 eni387np1: renamed from eth1
  netconsole: Process resuming  (mac: 1e:95:b7:ae:ab:dc), s:2, r:-1
  netpoll: netconsole: device 1e:95:b7:ae:ab:dc not up yet, forcing it
  netconsole: network logging resumed on interface eni387np1
  netdevsim netdevsim387 netcons_LFLQP: renamed from eni387np1
  netconsole selftest: netcons_LFLQP

The "network logging resumed on interface" seems to suggest that the
previous patch of this series here, commit 220dbe3c76ed ("netconsole:
resume previously deactivated target"), managed to resume the previously
activated target, but not in my case.

What I don't understand is why is it working on the Netdev CI, and not
on my side. The main difference is that I might be missing some
userspace packages -- but I don't see what can be missing here, all
other netconsole tests pass -- a specific kernel config, or not applied
patch. Or something different on the host -- in a container on my side
-- but there shouldn't be any interactions with the host here,
everything is happening in the VM. Any ideas? :)

+	fi
+}
+
+function trigger_deactivation() {
+	# Start by storing mac addresses so we can be restored in reactivate
+	SAVED_DSTMAC=$(ip netns exec "${NAMESPACE}" \
+		cat /sys/class/net/"$DSTIF"/address)
+	SAVED_SRCMAC=$(mac_get "${SRCIF}")
+	# Remove low level module
+	rmmod netdevsim
+}
+
+trap cleanup EXIT
+
+# Run the test twice, with different cmdline parameters
+for BINDMODE in "ifname" "mac"
+do
+	echo "Running with bind mode: ${BINDMODE}" >&2
+	# Set current loglevel to KERN_INFO(6), and default to KERN_NOTICE(5)
+	echo "6 5" > /proc/sys/kernel/printk

Can we remove this? Without that, it is hard to understand what went
wrong in case of issues.

+
+	# Create one namespace and two interfaces
+	set_network
+
+	# Create the command line for netconsole, with the configuration from
+	# the function above
+	CMDLINE=$(create_cmdline_str "${BINDMODE}")
+
+	# The content of kmsg will be save to the following file
+	OUTPUT_FILE="/tmp/${TARGET}-${BINDMODE}"
+
+	# Load the module, with the cmdline set
+	modprobe netconsole "${CMDLINE}"
+	# Expose cmdline target in configfs
+	mkdir "${NETCONS_CONFIGFS}/cmdline0"
+
+	# Target should be enabled
+	wait_target_state "cmdline0" "enabled"
+
+	# Trigger deactivation by unloading netdevsim module. Target should be
+	# disabled.
+	trigger_deactivation
+	wait_target_state "cmdline0" "disabled"
+
+	# Trigger reactivation by loading netdevsim, recreating the network and
+	# restoring mac addresses. Target should be re-enabled.
+	trigger_reactivation
+	wait_target_state "cmdline0" "enabled"
+
+	# Listen for netconsole port inside the namespace and destination
+	# interface
+	listen_port_and_save_to "${OUTPUT_FILE}" &
+	# Wait for socat to start and listen to the port.
+	wait_local_port_listen "${NAMESPACE}" "${PORT}" udp
+	# Send the message
+	echo "${MSG}: ${TARGET}" > /dev/kmsg
+	# Wait until socat saves the file to disk
+	busywait "${BUSYWAIT_TIMEOUT}" test -s "${OUTPUT_FILE}"

In my case, the script was stopping here, without any message. I can
send a patch adding "|| true" to go to the next instruction, and display
"FAIL: File was not generated.".

+	# Make sure the message was received in the dst part
+	# and exit
+	validate_msg "${OUTPUT_FILE}"
+
+	# kill socat in case it is still running
+	pkill_socat
+	# Cleanup & unload the module
+	cleanup
+
+	echo "${BINDMODE} : Test passed" >&2
+done
+
+trap - EXIT
+exit "${EXIT_STATUS}"

Cheers,
Matt