Re: [PATCH net-next v2 2/2] selftests/bpf: verify syncookie statistics in tcp_custom_syncookie

[Kuniyuki Iwashima]

On Fri, Apr 10, 2026 at 6:32 PM Jiayuan Chen <jiayuan.chen@xxxxxxxxx> wrote:
>
> Add read_tcpext_snmp() helper to network_helpers which reads a
> TcpExt SNMP counter via nstat, and use it in the tcp_custom_syncookie
> test to verify that LINUX_MIB_SYNCOOKIESRECV is incremented and
> LINUX_MIB_SYNCOOKIESFAILED stays unchanged across a successful
> BPF custom syncookie validation.
>
> The delta is captured between start_server() and accept(), which
> covers the full SYN/ACK/cookie-check path for one connection.
>
> Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>
> ---
>  tools/testing/selftests/bpf/network_helpers.c | 22 +++++++++++++++++++
>  tools/testing/selftests/bpf/network_helpers.h |  1 +
>  .../bpf/prog_tests/tcp_custom_syncookie.c     | 20 +++++++++++++++++

As you touch bpf selftest helper files, please rebase on bpf-next
to avoid possible conflicts and tag bpf-next in the Subject.

Change itself looks good.

Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>

one nit below.


>  3 files changed, 43 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/network_helpers.c b/tools/testing/selftests/bpf/network_helpers.c
> index b82f572641b7..3388dd5112b6 100644
> --- a/tools/testing/selftests/bpf/network_helpers.c
> +++ b/tools/testing/selftests/bpf/network_helpers.c
> @@ -621,6 +621,28 @@ int get_socket_local_port(int sock_fd)
>         return -1;
>  }
>
> +int read_tcpext_snmp(const char *name, unsigned long *val)
> +{
> +       char cmd[128], buf[128];
> +       int ret = 0;
> +       FILE *f;
> +
> +       snprintf(cmd, sizeof(cmd),
> +                "nstat -az TcpExt%s | awk '/TcpExt/ {print $2}'", name);
> +       f = popen(cmd, "r");
> +       if (!f)
> +               return -errno;
> +
> +       if (!fgets(buf, sizeof(buf), f)) {
> +               ret = ferror(f) ? -errno : -ENODATA;
> +               goto out;
> +       }
> +       *val = strtoul(buf, NULL, 10);
> +out:
> +       pclose(f);
> +       return ret;
> +}
> +
>  int get_hw_ring_size(char *ifname, struct ethtool_ringparam *ring_param)
>  {
>         struct ifreq ifr = {0};
> diff --git a/tools/testing/selftests/bpf/network_helpers.h b/tools/testing/selftests/bpf/network_helpers.h
> index 79a010c88e11..c53cd781df6e 100644
> --- a/tools/testing/selftests/bpf/network_helpers.h
> +++ b/tools/testing/selftests/bpf/network_helpers.h
> @@ -84,6 +84,7 @@ int make_sockaddr(int family, const char *addr_str, __u16 port,
>                   struct sockaddr_storage *addr, socklen_t *len);
>  char *ping_command(int family);
>  int get_socket_local_port(int sock_fd);
> +int read_tcpext_snmp(const char *name, unsigned long *val);
>  int get_hw_ring_size(char *ifname, struct ethtool_ringparam *ring_param);
>  int set_hw_ring_size(char *ifname, struct ethtool_ringparam *ring_param);
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c b/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c
> index eaf441dc7e79..6adfb4b892f8 100644
> --- a/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c
> +++ b/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c
> @@ -91,12 +91,21 @@ static void transfer_message(int sender, int receiver)
>
>  static void create_connection(struct test_tcp_custom_syncookie_case *test_case)
>  {
> +       unsigned long recv_before, recv_after;
> +       unsigned long failed_before, failed_after;

While at it, please keep reverse xmas tree order


>         int server, client, child;
>
>         server = start_server(test_case->family, test_case->type, test_case->addr, 0, 0);
>         if (!ASSERT_NEQ(server, -1, "start_server"))
>                 return;
>
> +       if (!ASSERT_OK(read_tcpext_snmp("SyncookiesRecv", &recv_before),
> +                      "read SyncookiesRecv before"))
> +               goto close_server;
> +       if (!ASSERT_OK(read_tcpext_snmp("SyncookiesFailed", &failed_before),
> +                      "read SyncookiesFailed before"))
> +               goto close_server;
> +
>         client = connect_to_fd(server, 0);
>         if (!ASSERT_NEQ(client, -1, "connect_to_fd"))
>                 goto close_server;
> @@ -105,9 +114,20 @@ static void create_connection(struct test_tcp_custom_syncookie_case *test_case)
>         if (!ASSERT_NEQ(child, -1, "accept"))
>                 goto close_client;
>
> +       if (!ASSERT_OK(read_tcpext_snmp("SyncookiesRecv", &recv_after),
> +                      "read SyncookiesRecv after"))
> +               goto close_child;
> +       if (!ASSERT_OK(read_tcpext_snmp("SyncookiesFailed", &failed_after),
> +                      "read SyncookiesFailed after"))
> +               goto close_child;
> +
> +       ASSERT_EQ(recv_after - recv_before, 1, "SyncookiesRecv delta");
> +       ASSERT_EQ(failed_after - failed_before, 0, "SyncookiesFailed delta");
> +
>         transfer_message(client, child);
>         transfer_message(child, client);
>
> +close_child:
>         close(child);
>  close_client:
>         close(client);
> --
> 2.43.0
>