selftests: mptcp: lib: add time per subtests in TAP output

It adds 'time=<N>ms' in the diagnostic data of the TAP output, e.g.

  ok 1 - pm_netlink: defaults addr list # time=9ms

This addition is useful to quickly identify which subtests are taking a
longer time than the others, or more than expected.

Note that there are no specific formats to follow to show this time
according to the TAP 13 [1], TAP 14 [2] and KTAP [3] specifications.
Let's then define this one here.

Link: https://testanything.org/tap-version-13-specification.html [1]
Link: https://testanything.org/tap-version-14-specification.html [2]
Link: https://docs.kernel.org/dev-tools/ktap.html [3]
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240906-net-next-mptcp-ksft-subtest-time-v2-1-31d5ee4f3bdf@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/mptcp/mptcp_lib.sh

@@ -29,6 +29,7 @@ declare -rx MPTCP_LIB_AF_INET6=10
 MPTCP_LIB_SUBTESTS=()
 MPTCP_LIB_SUBTESTS_DUPLICATED=0
 MPTCP_LIB_SUBTEST_FLAKY=0
+MPTCP_LIB_SUBTESTS_LAST_TS_MS=
 MPTCP_LIB_TEST_COUNTER=0
 MPTCP_LIB_TEST_FORMAT="%02u %-50s"
 MPTCP_LIB_IP_MPTCP=0
@@ -205,6 +206,11 @@ mptcp_lib_kversion_ge() {
 	mptcp_lib_fail_if_expected_feature "kernel version ${1} lower than ${v}"
 }
 
+mptcp_lib_subtests_last_ts_reset() {
+	MPTCP_LIB_SUBTESTS_LAST_TS_MS="$(date +%s%3N)"
+}
+mptcp_lib_subtests_last_ts_reset
+
 __mptcp_lib_result_check_duplicated() {
 	local subtest
 
@@ -219,13 +225,22 @@ __mptcp_lib_result_check_duplicated() {
 
 __mptcp_lib_result_add() {
 	local result="${1}"
+	local time="time="
+	local ts_prev_ms
 	shift
 
 	local id=$((${#MPTCP_LIB_SUBTESTS[@]} + 1))
 
 	__mptcp_lib_result_check_duplicated "${*}"
 
-	MPTCP_LIB_SUBTESTS+=("${result} ${id} - ${KSFT_TEST}: ${*}")
+	# not to add two '#'
+	[[ "${*}" != *"#"* ]] && time="# ${time}"
+
+	ts_prev_ms="${MPTCP_LIB_SUBTESTS_LAST_TS_MS}"
+	mptcp_lib_subtests_last_ts_reset
+	time+="$((MPTCP_LIB_SUBTESTS_LAST_TS_MS - ts_prev_ms))ms"
+
+	MPTCP_LIB_SUBTESTS+=("${result} ${id} - ${KSFT_TEST}: ${*} ${time}")
 }
 
 # $1: test name