Recently, some mib counters about fallback has been added, this patch
provides a method to check the expected behavior of these mib counters
during the test execution.

Link: https://github.com/multipath-tcp/mptcp_net-next/issues/571
Signed-off-by: Gang Yan <yangang@kylinos.cn>

------
Changelog:
  v3:
    - Squash into a single patch.
    - Using 'fb_' as a prefix instead of the suffix for variables.
    - Adjust the order of mib counters to check, ensuring it matches the
      variable declaration.
    - The namespace('ns1'/'ns2') is included in the output of 
      'chk_fallback_nr', like:
      "ns2 infinite map tx fallback        [IGNO] (flaky) got 1 infinite map tx fallback[s] in ns2 expected 0"
    - Add a new helper named 'chk_fallback_nr_all', which prints only
      when an error occurs.
    - Fix some code style issues.
 
  v2:
    - add a helper which can check all the fallback mib counters.
    - put the 'chk_fallback_nr' in 'chk_join_nr' like chk_join_tx_nr.

Notes:

Hi Matt,

I wanted to apologize for splitting the changes into multiple commits,
my intention was to ease the review process, but it unfortunately
backfired.

Thanks for your valuable suggestions, I've made some improvements based
on your feedback.

Please take another look at the updated changes.

Best regards,
Gang

---
 .../testing/selftests/net/mptcp/mptcp_join.sh | 123 ++++++++++++++++++
 1 file changed, 123 insertions(+)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index b8af65373b3a..898779a9af58 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -74,6 +74,17 @@ unset join_create_err
 unset join_bind_err
 unset join_connect_err
 
+unset fb_ns1
+unset fb_ns2
+unset fb_infinite_map_tx
+unset fb_dss_corruption
+unset fb_simult_conn
+unset fb_mpc_passive
+unset fb_mpc_active
+unset fb_mpc_data
+unset fb_md5_sig
+unset fb_dss
+
 # generated using "nfbpf_compile '(ip && (ip[54] & 0xf0) == 0x30) ||
 #				  (ip6 && (ip6[74] & 0xf0) == 0x30)'"
 CBPF_MPTCP_SUBOPTION_ADD_ADDR="14,
@@ -1399,6 +1410,115 @@ chk_join_tx_nr()
 	print_results "join Tx" ${rc}
 }
 
+chk_fallback_nr()
+{
+	local infinite_map_tx=${fb_infinite_map_tx:-0}
+	local dss_corruption=${fb_dss_corruption:-0}
+	local simult_conn=${fb_simult_conn:-0}
+	local mpc_passive=${fb_mpc_passive:-0}
+	local mpc_active=${fb_mpc_active:-0}
+	local mpc_data=${fb_mpc_data:-0}
+	local md5_sig=${fb_md5_sig:-0}
+	local dss=${fb_dss:-0}
+	local rc=${KSFT_PASS}
+	local ns=$1
+	local count
+
+	count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtInfiniteMapTx")
+	if [ -z "$count" ]; then
+		rc=${KSFT_SKIP}
+	elif [ "$count" != "$infinite_map_tx" ]; then
+		rc=${KSFT_FAIL}
+		print_check "$ns infinite map tx fallback"
+		fail_test "got $count infinite map tx fallback[s] in $ns expected $infinite_map_tx"
+	fi
+
+	count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtDSSCorruptionFallback")
+	if [ -z "$count" ]; then
+		rc=${KSFT_SKIP}
+	elif [ "$count" != "$dss_corruption" ]; then
+		rc=${KSFT_FAIL}
+		print_check "$ns dss corruption fallback"
+		fail_test "got $count dss corruption fallback[s] in $ns expected $dss_corruption"
+	fi
+
+	count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtSimultConnectFallback")
+	if [ -z "$count" ]; then
+		rc=${KSFT_SKIP}
+	elif [ "$count" != "$simult_conn" ]; then
+		rc=${KSFT_FAIL}
+		print_check "$ns simult conn fallback"
+		fail_test "got $count simult conn fallback[s] in $ns expected $simult_conn"
+	fi
+
+	count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtMPCapableFallbackACK")
+	if [ -z "$count" ]; then
+		rc=${KSFT_SKIP}
+	elif [ "$count" != "$mpc_passive" ]; then
+		rc=${KSFT_FAIL}
+		print_check "$ns mpc passive fallback"
+		fail_test "got $count mpc passive fallback[s] in $ns expected $mpc_passive"
+	fi
+
+	count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtMPCapableFallbackSYNACK")
+	if [ -z "$count" ]; then
+		rc=${KSFT_SKIP}
+	elif [ "$count" != "$mpc_active" ]; then
+		rc=${KSFT_FAIL}
+		print_check "$ns mpc active fallback"
+		fail_test "got $count mpc active fallback[s] in $ns expected $mpc_active"
+	fi
+
+	count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtMPCapableDataFallback")
+	if [ -z "$count" ]; then
+		rc=${KSFT_SKIP}
+	elif [ "$count" != "$mpc_data" ]; then
+		rc=${KSFT_FAIL}
+		print_check "$ns mpc data fallback"
+		fail_test "got $count mpc data fallback[s] in $ns expected $mpc_data"
+	fi
+
+	count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtMD5SigFallback")
+	if [ -z "$count" ]; then
+		rc=${KSFT_SKIP}
+	elif [ "$count" != "$md5_sig" ]; then
+		rc=${KSFT_FAIL}
+		print_check "$ns MD5 Sig fallback"
+		fail_test "got $count MD5 Sig fallback[s] in $ns expected $MD5_Sig"
+	fi
+
+	count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtDssFallback")
+	if [ -z "$count" ]; then
+		rc=${KSFT_SKIP}
+	elif [ "$count" != "$dss" ]; then
+		rc=${KSFT_FAIL}
+		print_check "$ns dss fallback"
+		fail_test "got $count dss fallback[s] in $ns expected $dss"
+	fi
+
+	return $rc
+}
+
+chk_fallback_nr_all()
+{
+	local netns=("ns1" "ns2")
+	local fb_ns=("fb_ns1" "fb_ns2")
+	local rc=${KSFT_PASS}
+
+	for i in 0 1; do
+		if [ -n "${!fb_ns[i]}" ]; then
+			eval "${!fb_ns[i]}" \
+				chk_fallback_nr ${netns[i]} || rc={?}
+		else
+			chk_fallback_nr ${netns[i]} || rc={?}
+		fi
+	done
+
+	if [ "$rc" != "${KSFT_PASS}" ]; then
+		print_results "fallback" $rc
+	fi
+}
+
 chk_join_nr()
 {
 	local syn_nr=$1
@@ -1484,6 +1604,8 @@ chk_join_nr()
 	join_syn_tx="${join_syn_tx:-${syn_nr}}" \
 		chk_join_tx_nr
 
+	chk_fallback_nr_all
+
 	if $validate_checksum; then
 		chk_csum_nr $csum_ns1 $csum_ns2
 		chk_fail_nr $fail_nr $fail_nr
@@ -3337,6 +3459,7 @@ fail_tests()
 		join_csum_ns1=+1 join_csum_ns2=+0 \
 			join_fail_nr=1 join_rst_nr=0 join_infi_nr=1 \
 			join_corrupted_pkts="$(pedit_action_pkts)" \
+			fb_ns1="fb_dss=1" fb_ns2="fb_infinite_map_tx=1" \
 			chk_join_nr 0 0 0
 		chk_fail_nr 1 -1 invert
 	fi
-- 
2.43.0

Hi Gang,

Thank you for your modifications, that's great!

Our CI did some validations and here is its report:

- KVM Validation: normal: Success! ✅
- KVM Validation: debug: Success! ✅
- KVM Validation: btf-normal (only bpftest_all): Success! ✅
- KVM Validation: btf-debug (only bpftest_all): Success! ✅
- Task: https://github.com/multipath-tcp/mptcp_net-next/actions/runs/16985622382

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/9bc01d13d25b
Patchwork: https://patchwork.kernel.org/project/mptcp/list/?series=991819


If there are some issues, you can reproduce them using the same environment as
the one used by the CI thanks to a docker image, e.g.:

    $ cd [kernel source code]
    $ docker run -v "${PWD}:${PWD}:rw" -w "${PWD}" --privileged --rm -it \
        --pull always mptcp/mptcp-upstream-virtme-docker:latest \
        auto-normal

For more details:

    https://github.com/multipath-tcp/mptcp-upstream-virtme-docker


Please note that despite all the efforts that have been already done to have a
stable tests suite when executed on a public CI like here, it is possible some
reported issues are not due to your modifications. Still, do not hesitate to
help us improve that ;-)

Cheers,
MPTCP GH Action bot
Bot operated by Matthieu Baerts (NGI0 Core)

Hi Gang,

15 Aug 2025 09:32:11 Gang Yan <yangang@kylinos.cn>:

> Recently, some mib counters about fallback has been added, this patch
> provides a method to check the expected behavior of these mib counters
> during the test execution.
>
> Link: https://github.com/multipath-tcp/mptcp_net-next/issues/571
> Signed-off-by: Gang Yan <yangang@kylinos.cn>
>
> ------
> Changelog:
>   v3:
>     - Squash into a single patch.
>     - Using 'fb_' as a prefix instead of the suffix for variables.
>     - Adjust the order of mib counters to check, ensuring it matches the
>       variable declaration.
>     - The namespace('ns1'/'ns2') is included in the output of
>       'chk_fallback_nr', like:
>       "ns2 infinite map tx fallback        [IGNO] (flaky) got 1 infinite map tx fallback[s] in ns2 expected 0"
>     - Add a new helper named 'chk_fallback_nr_all', which prints only
>       when an error occurs.
>     - Fix some code style issues.

Thank you for the new version!

>   v2:
>     - add a helper which can check all the fallback mib counters.
>     - put the 'chk_fallback_nr' in 'chk_join_nr' like chk_join_tx_nr.
>
> Notes:
>
> Hi Matt,
>
> I wanted to apologize for splitting the changes into multiple commits,
> my intention was to ease the review process, but it unfortunately
> backfired.

That's OK, no need to apologize, I was just trying to explain when
splitting makes sense or not.

> Thanks for your valuable suggestions, I've made some improvements based
> on your feedback.
>
> Please take another look at the updated changes.
>
> Best regards,
> Gang
>
> ---
> .../testing/selftests/net/mptcp/mptcp_join.sh | 123 ++++++++++++++++++
> 1 file changed, 123 insertions(+)
>
> diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
> index b8af65373b3a..898779a9af58 100755
> --- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
> +++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
> @@ -74,6 +74,17 @@ unset join_create_err
> unset join_bind_err
> unset join_connect_err
>
> +unset fb_ns1
> +unset fb_ns2
> +unset fb_infinite_map_tx
> +unset fb_dss_corruption
> +unset fb_simult_conn
> +unset fb_mpc_passive
> +unset fb_mpc_active
> +unset fb_mpc_data
> +unset fb_md5_sig
> +unset fb_dss
> +
> # generated using "nfbpf_compile '(ip && (ip[54] & 0xf0) == 0x30) ||
> #                (ip6 && (ip6[74] & 0xf0) == 0x30)'"
> CBPF_MPTCP_SUBOPTION_ADD_ADDR="14,
> @@ -1399,6 +1410,115 @@ chk_join_tx_nr()
>     print_results "join Tx" ${rc}
> }
>
> +chk_fallback_nr()
> +{
> +   local infinite_map_tx=${fb_infinite_map_tx:-0}
> +   local dss_corruption=${fb_dss_corruption:-0}
> +   local simult_conn=${fb_simult_conn:-0}
> +   local mpc_passive=${fb_mpc_passive:-0}
> +   local mpc_active=${fb_mpc_active:-0}
> +   local mpc_data=${fb_mpc_data:-0}
> +   local md5_sig=${fb_md5_sig:-0}
> +   local dss=${fb_dss:-0}
> +   local rc=${KSFT_PASS}
> +   local ns=$1
> +   local count
> +
> +   count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtInfiniteMapTx")
> +   if [ -z "$count" ]; then
> +       rc=${KSFT_SKIP}
> +   elif [ "$count" != "$infinite_map_tx" ]; then
> +       rc=${KSFT_FAIL}
> +       print_check "$ns infinite map tx fallback"
> +       fail_test "got $count infinite map tx fallback[s] in $ns expected $infinite_map_tx"
> +   fi
> +
> +   count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtDSSCorruptionFallback")
> +   if [ -z "$count" ]; then
> +       rc=${KSFT_SKIP}
> +   elif [ "$count" != "$dss_corruption" ]; then
> +       rc=${KSFT_FAIL}
> +       print_check "$ns dss corruption fallback"
> +       fail_test "got $count dss corruption fallback[s] in $ns expected $dss_corruption"
> +   fi
> +
> +   count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtSimultConnectFallback")
> +   if [ -z "$count" ]; then
> +       rc=${KSFT_SKIP}
> +   elif [ "$count" != "$simult_conn" ]; then
> +       rc=${KSFT_FAIL}
> +       print_check "$ns simult conn fallback"
> +       fail_test "got $count simult conn fallback[s] in $ns expected $simult_conn"
> +   fi
> +
> +   count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtMPCapableFallbackACK")
> +   if [ -z "$count" ]; then
> +       rc=${KSFT_SKIP}
> +   elif [ "$count" != "$mpc_passive" ]; then
> +       rc=${KSFT_FAIL}
> +       print_check "$ns mpc passive fallback"
> +       fail_test "got $count mpc passive fallback[s] in $ns expected $mpc_passive"
> +   fi
> +
> +   count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtMPCapableFallbackSYNACK")
> +   if [ -z "$count" ]; then
> +       rc=${KSFT_SKIP}
> +   elif [ "$count" != "$mpc_active" ]; then
> +       rc=${KSFT_FAIL}
> +       print_check "$ns mpc active fallback"
> +       fail_test "got $count mpc active fallback[s] in $ns expected $mpc_active"
> +   fi
> +
> +   count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtMPCapableDataFallback")
> +   if [ -z "$count" ]; then
> +       rc=${KSFT_SKIP}
> +   elif [ "$count" != "$mpc_data" ]; then
> +       rc=${KSFT_FAIL}
> +       print_check "$ns mpc data fallback"
> +       fail_test "got $count mpc data fallback[s] in $ns expected $mpc_data"
> +   fi
> +
> +   count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtMD5SigFallback")
> +   if [ -z "$count" ]; then
> +       rc=${KSFT_SKIP}
> +   elif [ "$count" != "$md5_sig" ]; then
> +       rc=${KSFT_FAIL}
> +       print_check "$ns MD5 Sig fallback"
> +       fail_test "got $count MD5 Sig fallback[s] in $ns expected $MD5_Sig"

Should be $md5_sig without capital letters. I wonder if shellcheck
will detect this.

If the CI is happy with this version, I can do the modification when
applying the patch.

Cheers,
Matt

> +   fi
> +
> +   count=$(mptcp_lib_get_counter ${!ns} "MPTcpExtDssFallback")
> +   if [ -z "$count" ]; then
> +       rc=${KSFT_SKIP}
> +   elif [ "$count" != "$dss" ]; then
> +       rc=${KSFT_FAIL}
> +       print_check "$ns dss fallback"
> +       fail_test "got $count dss fallback[s] in $ns expected $dss"
> +   fi
> +
> +   return $rc
> +}
> +
> +chk_fallback_nr_all()
> +{
> +   local netns=("ns1" "ns2")
> +   local fb_ns=("fb_ns1" "fb_ns2")
> +   local rc=${KSFT_PASS}
> +
> +   for i in 0 1; do
> +       if [ -n "${!fb_ns[i]}" ]; then
> +           eval "${!fb_ns[i]}" \
> +               chk_fallback_nr ${netns[i]} || rc={?}
> +       else
> +           chk_fallback_nr ${netns[i]} || rc={?}
> +       fi
> +   done
> +
> +   if [ "$rc" != "${KSFT_PASS}" ]; then
> +       print_results "fallback" $rc
> +   fi
> +}
> +
> chk_join_nr()
> {
>     local syn_nr=$1
> @@ -1484,6 +1604,8 @@ chk_join_nr()
>     join_syn_tx="${join_syn_tx:-${syn_nr}}" \
>         chk_join_tx_nr
>
> +   chk_fallback_nr_all
> +
>     if $validate_checksum; then
>         chk_csum_nr $csum_ns1 $csum_ns2
>         chk_fail_nr $fail_nr $fail_nr
> @@ -3337,6 +3459,7 @@ fail_tests()
>         join_csum_ns1=+1 join_csum_ns2=+0 \
>             join_fail_nr=1 join_rst_nr=0 join_infi_nr=1 \
>             join_corrupted_pkts="$(pedit_action_pkts)" \
> +           fb_ns1="fb_dss=1" fb_ns2="fb_infinite_map_tx=1" \
>             chk_join_nr 0 0 0
>         chk_fail_nr 1 -1 invert
>     fi
> --
> 2.43.0