selftests: forwarding: add helpers for IP multicast group joins/leaves

Extend the forwarding library with calls to some small C programs which
join an IP multicast group and send some packets to it. Both IPv4 and
IPv6 groups are supported. Use cases range from testing IGMP/MLD
snooping, to RX filtering, to multicast routing.

Testing multicast traffic using msend/mreceive is intended to be done
using tcpdump.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: vladimiroltean

tools/testing/selftests/net/forwarding/lib.sh

@@ -27,6 +27,7 @@ INTERFACE_TIMEOUT=${INTERFACE_TIMEOUT:=600}
 LOW_AGEING_TIME=${LOW_AGEING_TIME:=1000}
 REQUIRE_JQ=${REQUIRE_JQ:=yes}
 REQUIRE_MZ=${REQUIRE_MZ:=yes}
+REQUIRE_MTOOLS=${REQUIRE_MTOOLS:=no}
 STABLE_MAC_ADDRS=${STABLE_MAC_ADDRS:=no}
 TCPDUMP_EXTRA_FLAGS=${TCPDUMP_EXTRA_FLAGS:=}
 
@@ -161,6 +162,12 @@ fi
 if [[ "$REQUIRE_MZ" = "yes" ]]; then
 	require_command $MZ
 fi
+if [[ "$REQUIRE_MTOOLS" = "yes" ]]; then
+	# https://github.com/vladimiroltean/mtools/
+	# patched for IPv6 support
+	require_command msend
+	require_command mreceive
+fi
 
 if [[ ! -v NUM_NETIFS ]]; then
 	echo "SKIP: importer does not define \"NUM_NETIFS\""
@@ -1548,6 +1555,37 @@ brmcast_check_sg_state()
 	done
 }
 
+mc_join()
+{
+	local if_name=$1
+	local group=$2
+	local vrf_name=$(master_name_get $if_name)
+
+	# We don't care about actual reception, just about joining the
+	# IP multicast group and adding the L2 address to the device's
+	# MAC filtering table
+	ip vrf exec $vrf_name \
+		mreceive -g $group -I $if_name > /dev/null 2>&1 &
+	mreceive_pid=$!
+
+	sleep 1
+}
+
+mc_leave()
+{
+	kill "$mreceive_pid" && wait "$mreceive_pid"
+}
+
+mc_send()
+{
+	local if_name=$1
+	local groups=$2
+	local vrf_name=$(master_name_get $if_name)
+
+	ip vrf exec $vrf_name \
+		msend -g $groups -I $if_name -c 1 > /dev/null 2>&1
+}
+
 start_ip_monitor()
 {
 	local mtype=$1; shift