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.

Signed-off-by: Andre Carvalho <asantostc@gmail.com>
---
 tools/testing/selftests/drivers/net/Makefile       |  1 +
 .../selftests/drivers/net/lib/sh/lib_netcons.sh    | 23 ++++++++
 .../selftests/drivers/net/netcons_resume.sh        | 68 ++++++++++++++++++++++
 3 files changed, 92 insertions(+)

diff --git a/tools/testing/selftests/drivers/net/Makefile b/tools/testing/selftests/drivers/net/Makefile
index 984ece05f7f92e836592107ba4c692da6d8ce1b3..f47c4d57f7b4ce82b0b59bee4c87a9660819675e 100644
--- a/tools/testing/selftests/drivers/net/Makefile
+++ b/tools/testing/selftests/drivers/net/Makefile
@@ -17,6 +17,7 @@ TEST_PROGS := \
 	netcons_fragmented_msg.sh \
 	netcons_overflow.sh \
 	netcons_sysdata.sh \
+	netcons_resume.sh \
 	netpoll_basic.py \
 	ping.py \
 	queues.py \
diff --git a/tools/testing/selftests/drivers/net/lib/sh/lib_netcons.sh b/tools/testing/selftests/drivers/net/lib/sh/lib_netcons.sh
index 8e1085e896472d5c87ec8b236240878a5b2d00d2..ba7c865b1be3b60f53ea548aba269059ca74aee6 100644
--- a/tools/testing/selftests/drivers/net/lib/sh/lib_netcons.sh
+++ b/tools/testing/selftests/drivers/net/lib/sh/lib_netcons.sh
@@ -350,6 +350,29 @@ function check_netconsole_module() {
 	fi
 }
 
+function wait_target_state() {
+	local TARGET=${1}
+	local STATE=${2}
+	local FILENAME="${NETCONS_CONFIGFS}"/"${TARGET}"/"enabled"
+
+	if [ "${STATE}" == "enabled" ]
+	then
+		ENABLED=1
+	else
+		ENABLED=0
+	fi
+
+	if [ ! -f "$FILENAME" ]; then
+		echo "FAIL: Target does not exist." >&2
+		exit "${ksft_fail}"
+	fi
+
+	slowwait 2 sh -c 'test -n "$(grep '"'${ENABLED}'"' '"'${FILENAME}'"')"' || {
+		echo "FAIL: ${TARGET} is not ${STATE}." >&2
+		exit "${ksft_fail}"
+	}
+}
+
 # A wrapper to translate protocol version to udp version
 function wait_for_port() {
 	local NAMESPACE=${1}
diff --git a/tools/testing/selftests/drivers/net/netcons_resume.sh b/tools/testing/selftests/drivers/net/netcons_resume.sh
new file mode 100755
index 0000000000000000000000000000000000000000..7e8ea74821fffdac8be0c3db2f1aa7953b4d5bd5
--- /dev/null
+++ b/tools/testing/selftests/drivers/net/netcons_resume.sh
@@ -0,0 +1,68 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: GPL-2.0
+
+# This test validates that netconsole is able to resume a target that was
+# deactivated when its interface was removed.
+#
+# The test configures a netconsole dynamic target and then removes netdevsim
+# module to cause the interface to disappear. The test veries that the target
+# moved to disabled state before adding netdevsim and the interface back.
+#
+# Finally, the test verifies that the target is re-enabled automatically and
+# the message is received on the destination interface.
+#
+# Author: Andre Carvalho <asantostc@gmail.com>
+
+set -euo pipefail
+
+SCRIPTDIR=$(dirname "$(readlink -e "${BASH_SOURCE[0]}")")
+
+source "${SCRIPTDIR}"/lib/sh/lib_netcons.sh
+
+modprobe netdevsim 2> /dev/null || true
+modprobe netconsole 2> /dev/null || true
+
+# The content of kmsg will be save to the following file
+OUTPUT_FILE="/tmp/${TARGET}"
+
+# Check for basic system dependency and exit if not found
+check_for_dependencies
+
+# Set current loglevel to KERN_INFO(6), and default to KERN_NOTICE(5)
+echo "6 5" > /proc/sys/kernel/printk
+# Remove the namespace, interfaces and netconsole target on exit
+trap cleanup EXIT
+
+# Create one namespace and two interfaces
+set_network
+# Create a dynamic target for netconsole
+create_dynamic_target
+
+# Remove low level module
+rmmod netdevsim
+# Target should be disabled
+wait_target_state "${TARGET}" "disabled"
+
+# Add back low level module
+modprobe netdevsim
+# Recreate namespace and two interfaces
+set_network
+# Target should be enabled again
+wait_target_state "${TARGET}" "enabled"
+
+# Listed 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 "${OUTPUT_FILE}"
+# Make sure the message was received in the dst part
+# and exit
+validate_msg "${OUTPUT_FILE}"
+# kill socat in case it is still running
+pkill_socat
+
+exit "${ksft_pass}"

-- 
2.51.0