[net-next 2/3] selftests/net: Test PACKET_STATISTICS drops

Joe Damato
2026-04-02T23:22:44Z

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>
---
tools/testing/selftests/net/psock_snd.c | 52 ++++++++++++++++++++----
tools/testing/selftests/net/psock_snd.sh | 5 +++
2 files changed, 48 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/net/psock_snd.c b/tools/testing/selftests/net/psock_snd.c
index 5be481a3d2bd..7bbce274b9f0 100644
--- a/tools/testing/selftests/net/psock_snd.c
+++ b/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)
+static int do_tx(bool burst)
{
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 (burst)
+ 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));
@@ -394,7 +422,12 @@ static void run_test(void)
fdr = setup_rx();
fds = setup_sniffer();

- total_len = do_tx();
+ total_len = do_tx(cfg_drop);
+
+ 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) {
@@ -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))
diff --git a/tools/testing/selftests/net/psock_snd.sh b/tools/testing/selftests/net/psock_snd.sh
index 1cbfeb5052ec..b6ef12fad5d5 100755
--- a/tools/testing/selftests/net/psock_snd.sh
+++ b/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"
--
2.52.0