selftests/net: Test PACKET_STATISTICS drops

Extend psock_snd to test drops by setting a tiny receive buffer and
sending a large burst of packets.

Signed-off-by: Joe Damato <joe@dama.to>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20260720122714.759175-3-joe@dama.to
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/psock_snd.c

@@ -39,6 +39,7 @@ static bool	cfg_use_gso;
 static bool	cfg_use_qdisc_bypass;
 static bool	cfg_use_vlan;
 static bool	cfg_use_vnet;
+static bool	cfg_drop;
 
 static char	*cfg_ifname = "lo";
 static int	cfg_mtu	= 1500;
@@ -49,6 +50,8 @@ static uint16_t	cfg_port = 8000;
 /* test sending up to max mtu + 1 */
 #define TEST_SZ	(sizeof(struct virtio_net_hdr) + ETH_HLEN + ETH_MAX_MTU + 1)
 
+#define BURST_CNT (1000)
+
 static char tbuf[TEST_SZ], rbuf[TEST_SZ];
 
 static unsigned long add_csum_hword(const uint16_t *start, int num_u16)
@@ -212,13 +215,14 @@ static void do_send(int fd, char *buf, int len)
 	if (ret != len)
 		error(1, 0, "write: %u %u", ret, len);
 
-	fprintf(stderr, "tx: %u\n", ret);
+	if (!cfg_drop)
+		fprintf(stderr, "tx: %u\n", ret);
 }
 
 static int do_tx(void)
 {
 	const int one = 1;
-	int fd, len;
+	int i, fd, len;
 
 	fd = socket(PF_PACKET, cfg_use_dgram ? SOCK_DGRAM : SOCK_RAW, 0);
 	if (fd == -1)
@@ -242,6 +246,10 @@ static int do_tx(void)
 
 	do_send(fd, tbuf, len);
 
+	if (cfg_drop)
+		for (i = 0; i < BURST_CNT; i++)
+			do_send(fd, tbuf, len);
+
 	if (close(fd))
 		error(1, errno, "close t");
 
@@ -290,6 +298,7 @@ static void do_rx(int fd, int expected_len, char *expected)
 static int setup_sniffer(void)
 {
 	struct timeval tv = { .tv_usec = 100 * 1000 };
+	const int one = 1;
 	int fd;
 
 	fd = socket(PF_PACKET, SOCK_RAW, 0);
@@ -299,6 +308,10 @@ static int setup_sniffer(void)
 	if (setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv)))
 		error(1, errno, "setsockopt rcv timeout");
 
+	if (cfg_drop)
+		if (setsockopt(fd, SOL_SOCKET, SO_RCVBUF, &one, sizeof(one)))
+			error(1, errno, "setsockopt SO_RCVBUF");
+
 	pair_udp_setfilter(fd);
 	do_bind(fd);
 
@@ -309,7 +322,7 @@ static void parse_opts(int argc, char **argv)
 {
 	int c;
 
-	while ((c = getopt(argc, argv, "bcCdgl:qt:vV")) != -1) {
+	while ((c = getopt(argc, argv, "bcCdDgl:qt:vV")) != -1) {
 		switch (c) {
 		case 'b':
 			cfg_use_bind = true;
@@ -323,6 +336,9 @@ static void parse_opts(int argc, char **argv)
 		case 'd':
 			cfg_use_dgram = true;
 			break;
+		case 'D':
+			cfg_drop = true;
+			break;
 		case 'g':
 			cfg_use_gso = true;
 			break;
@@ -367,11 +383,23 @@ static void check_packet_stats(int fd)
 	if (getsockopt(fd, SOL_PACKET, PACKET_STATISTICS, &st, &len))
 		error(1, errno, "getsockopt packet statistics");
 
-	if (st.tp_packets != 1)
-		error(1, 0, "stats: tp_packets %u != 1", st.tp_packets);
+	if (cfg_drop) {
+		/* PACKET_STATISTICS reports all packets seen (including
+		 * drops) in tp_packets
+		 */
+		if (st.tp_packets < st.tp_drops)
+			error(1, 0, "stats: tp_packets %u < tp_drops %u",
+			      st.tp_packets, st.tp_drops);
 
-	if (st.tp_drops != 0)
-		error(1, 0, "stats: tp_drops %u != 0", st.tp_drops);
+		if (st.tp_drops == 0)
+			error(1, 0, "stats: expected drops but tp_drops == 0");
+	} else {
+		if (st.tp_packets != 1)
+			error(1, 0, "stats: tp_packets %u != 1", st.tp_packets);
+
+		if (st.tp_drops != 0)
+			error(1, 0, "stats: tp_drops %u != 0", st.tp_drops);
+	}
 
 	/* verify clear on read */
 	memset(&st, 0xff, sizeof(st));
@@ -396,6 +424,11 @@ static void run_test(void)
 
 	total_len = do_tx();
 
+	if (cfg_drop) {
+		check_packet_stats(fds);
+		goto out;
+	}
+
 	/* BPF filter accepts only this length, vlan changes MAC */
 	if (cfg_payload_len == DATA_LEN && !cfg_use_vlan) {
 		do_rx(fds, total_len - sizeof(struct virtio_net_hdr),
@@ -405,6 +438,7 @@ static void run_test(void)
 
 	do_rx(fdr, cfg_payload_len, tbuf + total_len - cfg_payload_len);
 
+out:
 	if (close(fds))
 		error(1, errno, "close s");
 	if (close(fdr))

tools/testing/selftests/net/psock_snd.sh

@@ -92,4 +92,9 @@ echo "raw gso max size"
 echo "raw gso max size + 1 (expected to fail)"
 (! ./in_netns.sh ./psock_snd -v -c -g -l "${max_mss_exceeds}")
 
+# test drops statistics
+
+echo "test drops statistics"
+./in_netns.sh ./psock_snd -D
+
 echo "OK. All tests passed"