Re: [net-next 3/3] selftests/net: Test PACKET_AUXDATA

Willem de Bruijn
2026-04-03T15:37:12Z

Joe Damato wrote:
> Extend the packet socket selftest, adding a recvmsg path, to test
> PACKET_AUXDATA. Check basic attributes of tpacket_auxdata.
>
> Signed-off-by: Joe Damato <joe@dama.to>
> ---
> tools/testing/selftests/net/psock_snd.c | 57 ++++++++++++++++++++++--
> tools/testing/selftests/net/psock_snd.sh | 5 +++
> 2 files changed, 59 insertions(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/net/psock_snd.c b/tools/testing/selftests/net/psock_snd.c
> index 7bbce274b9f0..682e0afe364d 100644
> --- a/tools/testing/selftests/net/psock_snd.c
> +++ b/tools/testing/selftests/net/psock_snd.c
> @@ -40,6 +40,7 @@ static bool cfg_use_qdisc_bypass;
> static bool cfg_use_vlan;
> static bool cfg_use_vnet;
> static bool cfg_drop;
> +static bool cfg_aux_data;
>
> static char *cfg_ifname = "lo";
> static int cfg_mtu = 1500;
> @@ -281,9 +282,26 @@ static int setup_rx(void)
>
> static void do_rx(int fd, int expected_len, char *expected)
> {
> + char cmsg_buf[1024] = {};
> + struct msghdr msg = {};
> + struct iovec iov[1];
> int ret;
>
> - ret = recv(fd, rbuf, sizeof(rbuf), 0);
> + if (cfg_aux_data) {
> + iov[0].iov_base = rbuf;
> + iov[0].iov_len = sizeof(rbuf);
> +
> + msg.msg_iov = iov;
> + msg.msg_iovlen = 1;
> +
> + msg.msg_control = cmsg_buf;
> + msg.msg_controllen = sizeof(cmsg_buf);
> +
> + ret = recvmsg(fd, &msg, 0);
> + } else {
> + ret = recv(fd, rbuf, sizeof(rbuf), 0);
> + }
> +
> if (ret == -1)
> error(1, errno, "recv");
> if (ret != expected_len)
> @@ -292,6 +310,31 @@ static void do_rx(int fd, int expected_len, char *expected)
> if (memcmp(rbuf, expected, ret))
> error(1, 0, "recv: data mismatch");
>
> + if (cfg_aux_data) {
> + struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
> + struct tpacket_auxdata *adata;
> +
> + if (!cmsg)
> + error(1, 0, "auxdata null");
> +
> + if (cmsg->cmsg_level != SOL_PACKET)
> + error(1, 0, "cmsg_level != SOL_PACKET");
> +
> + if (cmsg->cmsg_type != PACKET_AUXDATA)
> + error(1, 0, "cmsg_type != PACKET_AUXDATA");
> +
> + adata = (struct tpacket_auxdata *)CMSG_DATA(cmsg);
> +
> + if (adata->tp_net != ETH_HLEN)
> + error(1, 0, "cmsg tp_net != ETH_HLEN");
> +
> + if (adata->tp_len != expected_len)
> + error(1, 0, "cmsg tp_len != %u", expected_len);
> +
> + if (adata->tp_snaplen != expected_len)
> + error(1, 0, "cmsg tp_snaplen != %u", expected_len);
> + }
> +
> fprintf(stderr, "rx: %u\n", ret);
> }
>
> @@ -312,6 +355,10 @@ static int setup_sniffer(void)
> if (setsockopt(fd, SOL_SOCKET, SO_RCVBUF, &one, sizeof(one)))
> error(1, errno, "setsockopt SO_RCVBUF");
>
> + if (cfg_aux_data)
> + if (setsockopt(fd, SOL_PACKET, PACKET_AUXDATA, &one, sizeof(one)))
> + error(1, errno, "setsockopt PACKET_AUXDATA");
> +
> pair_udp_setfilter(fd);
> do_bind(fd);
>
> @@ -322,8 +369,11 @@ static void parse_opts(int argc, char **argv)
> {
> int c;
>
> - while ((c = getopt(argc, argv, "bcCdDgl:qt:vV")) != -1) {
> + while ((c = getopt(argc, argv, "abcCdDgl:qt:vV")) != -1) {
> switch (c) {
> + case 'a':
> + cfg_aux_data = true;
> + break;
> case 'b':
> cfg_use_bind = true;
> break;
> @@ -436,7 +486,8 @@ static void run_test(void)
> check_packet_stats(fds);
> }
>
> - do_rx(fdr, cfg_payload_len, tbuf + total_len - cfg_payload_len);
> + if (!cfg_aux_data)
> + do_rx(fdr, cfg_payload_len, tbuf + total_len - cfg_payload_len);

Slight preference to instead detect that this is a read not from a packet
socket and skip the cmsg processing inside do_rx as a result.

A roundabout way would be using getsockname. Simpler may be just to pass a new
boolean to do_rx is_psock or os.