selftest: add selftest for anycast notifications

This commit adds a new kernel selftest to verify RTNLGRP_IPV6_ACADDR
notifications. The test works by adding/removing a dummy interface,
enabling packet forwarding, and then confirming that user space can
correctly receive anycast notifications.

The test relies on the iproute2 version to be 6.13+.

Tested by the following command:
$ vng -v --user root --cpus 16 -- \
make -C tools/testing/selftests TARGETS=net
TEST_PROGS=rtnetlink_notification.sh \
TEST_GEN_PROGS="" run_tests

Cc: Maciej Żenczykowski <[e-mail]>
Cc: Lorenzo Colitti <[e-mail]>
Signed-off-by: Yuyang Huang <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

tools/testing/selftests/net/rtnetlink_notification.sh

···
 
 ALL_TESTS="
 	kci_test_mcast_addr_notification
+	kci_test_anycast_addr_notification
 "
 
 source lib.sh
+test_dev="test-dummy1"
 
 kci_test_mcast_addr_notification()
 {
···
 	local tmpfile
 	local monitor_pid
 	local match_result
-	local test_dev="test-dummy1"
 
 	tmpfile=$(mktemp)
 	defer rm "$tmpfile"
···
 	fi
 	log_test "mcast addr notification: Expected 4 matches, got $match_result"
 	return $RET
+}
+
+kci_test_anycast_addr_notification()
+{
+	RET=0
+	local tmpfile
+	local monitor_pid
+	local match_result
+
+	tmpfile=$(mktemp)
+	defer rm "$tmpfile"
+
+	ip monitor acaddress > "$tmpfile" &
+	monitor_pid=$!
+	defer kill_process "$monitor_pid"
+	sleep 1
+
+	if [ ! -e "/proc/$monitor_pid" ]; then
+		RET=$ksft_skip
+		log_test "anycast addr notification: iproute2 too old"
+		return "$RET"
+	fi
+
+	ip link add name "$test_dev" type dummy
+	check_err $? "failed to add dummy interface"
+	ip link set "$test_dev" up
+	check_err $? "failed to set dummy interface up"
+	sysctl -qw net.ipv6.conf."$test_dev".forwarding=1
+	ip link del dev "$test_dev"
+	check_err $? "Failed to delete dummy interface"
+	sleep 1
+
+	# There should be 2 line matches as follows.
+	# 9: dummy2    inet6 any fe80:: scope global
+	# Deleted 9: dummy2    inet6 any fe80:: scope global
+	match_result=$(grep -cE "$test_dev.*(fe80::)" "$tmpfile")
+	if [ "$match_result" -ne 2 ]; then
+		RET=$ksft_fail
+	fi
+	log_test "anycast addr notification: Expected 2 matches, got $match_result"
+	return "$RET"
 }
 
 #check for needed privileges