selftests/net: Add test coverage for UDP GSO software fallback

Extend the existing test to exercise UDP GSO egress through devices with
various offload capabilities, including lack of checksum offload, which is
the default case for TUN/TAP devices.

Test against a dummy device because it is simpler to set up then TUN/TAP.
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20240626-linux-udpgso-v2-2-422dfcbd6b48@cloudflare.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/udpgso.c

@@ -53,6 +53,7 @@ static bool		cfg_do_ipv6;
 static bool		cfg_do_connected;
 static bool		cfg_do_connectionless;
 static bool		cfg_do_msgmore;
+static bool		cfg_do_recv = true;
 static bool		cfg_do_setsockopt;
 static int		cfg_specific_test_id = -1;
 
@@ -414,6 +415,9 @@ static void run_one(struct testcase *test, int fdt, int fdr,
 	if (!sent)
 		return;
 
+	if (!cfg_do_recv)
+		return;
+
 	if (test->gso_len)
 		mss = test->gso_len;
 	else
@@ -464,8 +468,10 @@ static void run_test(struct sockaddr *addr, socklen_t alen)
 	if (fdr == -1)
 		error(1, errno, "socket r");
 
-	if (bind(fdr, addr, alen))
-		error(1, errno, "bind");
+	if (cfg_do_recv) {
+		if (bind(fdr, addr, alen))
+			error(1, errno, "bind");
+	}
 
 	/* Have tests fail quickly instead of hang */
 	if (setsockopt(fdr, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv)))
@@ -524,7 +530,7 @@ static void parse_opts(int argc, char **argv)
 {
 	int c;
 
-	while ((c = getopt(argc, argv, "46cCmst:")) != -1) {
+	while ((c = getopt(argc, argv, "46cCmRst:")) != -1) {
 		switch (c) {
 		case '4':
 			cfg_do_ipv4 = true;
@@ -541,6 +547,9 @@ static void parse_opts(int argc, char **argv)
 		case 'm':
 			cfg_do_msgmore = true;
 			break;
+		case 'R':
+			cfg_do_recv = false;
+			break;
 		case 's':
 			cfg_do_setsockopt = true;
 			break;

tools/testing/selftests/net/udpgso.sh

@@ -27,6 +27,31 @@ test_route_mtu() {
 	ip route add local fd00::1/128 table local dev lo mtu 1500
 }
 
+setup_dummy_sink() {
+	ip link add name sink mtu 1500 type dummy
+	ip addr add dev sink 10.0.0.0/24
+	ip addr add dev sink fd00::2/64 nodad
+	ip link set dev sink up
+}
+
+test_hw_gso_hw_csum() {
+	setup_dummy_sink
+	ethtool -K sink tx-checksum-ip-generic on >/dev/null
+	ethtool -K sink tx-udp-segmentation on >/dev/null
+}
+
+test_sw_gso_hw_csum() {
+	setup_dummy_sink
+	ethtool -K sink tx-checksum-ip-generic on >/dev/null
+	ethtool -K sink tx-udp-segmentation off >/dev/null
+}
+
+test_sw_gso_sw_csum() {
+	setup_dummy_sink
+	ethtool -K sink tx-checksum-ip-generic off >/dev/null
+	ethtool -K sink tx-udp-segmentation off >/dev/null
+}
+
 if [ "$#" -gt 0 ]; then
 	"$1"
 	shift 2 # pop "test_*" arg and "--" delimiter
@@ -56,3 +81,21 @@ echo "ipv4 msg_more"
 
 echo "ipv6 msg_more"
 ./in_netns.sh "$0" test_dev_mtu -- ./udpgso -6 -C -m
+
+echo "ipv4 hw-gso hw-csum"
+./in_netns.sh "$0" test_hw_gso_hw_csum -- ./udpgso -4 -C -R
+
+echo "ipv6 hw-gso hw-csum"
+./in_netns.sh "$0" test_hw_gso_hw_csum -- ./udpgso -6 -C -R
+
+echo "ipv4 sw-gso hw-csum"
+./in_netns.sh "$0" test_sw_gso_hw_csum -- ./udpgso -4 -C -R
+
+echo "ipv6 sw-gso hw-csum"
+./in_netns.sh "$0" test_sw_gso_hw_csum -- ./udpgso -6 -C -R
+
+echo "ipv4 sw-gso sw-csum"
+./in_netns.sh "$0" test_sw_gso_sw_csum -- ./udpgso -4 -C -R
+
+echo "ipv6 sw-gso sw-csum"
+./in_netns.sh "$0" test_sw_gso_sw_csum -- ./udpgso -6 -C -R