selftest: packetdrill: Require explicit setsockopt(TCP_FASTOPEN).

To enable TCP Fast Open on a server, net.ipv4.tcp_fastopen must
have 0x2 (TFO_SERVER_ENABLE), and we need to do either

  1. Call setsockopt(TCP_FASTOPEN) for the socket
  2. Set 0x400 (TFO_SERVER_WO_SOCKOPT1) additionally to net.ipv4.tcp_fastopen

The default.sh sets 0x70403 so that each test does not need setsockopt().
(0x1 is TFO_CLIENT_ENABLE, and 0x70000 is ...???)

However, some tests overwrite net.ipv4.tcp_fastopen without
TFO_SERVER_WO_SOCKOPT1 and forgot setsockopt(TCP_FASTOPEN).

For example, pure-syn-data.pkt [0] tests non-TFO servers unintentionally,
except in the first scenario.

To prevent such an accident, let's require explicit setsockopt().

TFO_CLIENT_ENABLE is necessary for
tcp_syscall_bad_arg_fastopen-invalid-buf-ptr.pkt.

Link: https://github.com/google/packetdrill/blob/bfc96251310f/gtests/net/tcp/fastopen/server/opt34/pure-syn-data.pkt
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250927213022.1850048-3-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/tools/testing/selftests/net/packetdrill/defaults.sh b/tools/testing/selftests/net/packetdrill/defaults.sh
index 1095a7b22f44d4e9a90b21d66094836852622320..34fcafefa344141cbfebae8d19f428c1a625cecc 100755 (executable)
--- a/tools/testing/selftests/net/packetdrill/defaults.sh
+++ b/tools/testing/selftests/net/packetdrill/defaults.sh
@@ -51,7 +51,7 @@ sysctl -q net.ipv4.tcp_pacing_ss_ratio=200
 sysctl -q net.ipv4.tcp_pacing_ca_ratio=120
 sysctl -q net.ipv4.tcp_notsent_lowat=4294967295 > /dev/null 2>&1
 
-sysctl -q net.ipv4.tcp_fastopen=0x70403
+sysctl -q net.ipv4.tcp_fastopen=0x3
 sysctl -q net.ipv4.tcp_fastopen_key=a1a1a1a1-b2b2b2b2-c3c3c3c3-d4d4d4d4
 
 sysctl -q net.ipv4.tcp_syncookies=1