Re: [PATCH net-next v11 7/7] selftests: netconsole: validate target resume

[Matthieu Baerts <matttbe@kernel.org>]

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.

> diff --git a/tools/testing/selftests/drivers/net/netcons_resume.sh b/tools/testing/selftests/drivers/net/netcons_resume.sh
> new file mode 100755
> index 000000000000..fc5e5e3ad3d4
> --- /dev/null
> +++ b/tools/testing/selftests/drivers/net/netcons_resume.sh

(...)

> +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