[PATCH net v2 12/15] selftests: mptcp: lib: get counters for the right test

["Matthieu Baerts (NGI0)" <matttbe@kernel.org>]

When the value for a MIB counter is required, mptcp_lib_get_counter is
called. It tries to use the cache, if available. If not it falls back to
calling 'nstat' directly by looking at the absolute counters.

That's an issue for tests that don't recreate the netns for each
subtest. In this case, 'nstat -a' will look at the counters for the
netns.

Instead, it should look at the increment for the current test, by using
the history recorded in /tmp/<ns>.nstat, if available, and not using
'-a' which was dumping the absolute values.

While at it, rename the previous 'hist' variable to 'cache' as it was
used to look at the cache, not the nstat history.

Fixes: 71388a9f331d ("selftests: mptcp: lib: get counters from nstat history")
Cc: stable@vger.kernel.org
Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Cc: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
---
 tools/testing/selftests/net/mptcp/mptcp_lib.sh | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_lib.sh b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
index da1da414c30f..b9d14647f401 100644
--- a/tools/testing/selftests/net/mptcp/mptcp_lib.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
@@ -416,19 +416,21 @@ mptcp_lib_nstat_get() {
 }
 
 # $1: ns, $2: MIB counter
-# Get the counter from the history (mptcp_lib_nstat_{init,get}()) if available.
-# If not, get the counter from nstat ignoring any history.
+# Get the counter from the cache (mptcp_lib_nstat_{init,get}()) if available.
+# If not, get the counter from nstat ignoring any cache, but using the history.
 mptcp_lib_get_counter() {
 	local ns="${1}"
 	local counter="${2}"
-	local hist="/tmp/${ns}.out"
+	local cache="/tmp/${ns}.out"
+	local hist="/tmp/${ns}.nstat"
 	local count
 
-	if [[ -s "${hist}" && "${counter}" == *"Tcp"* ]]; then
-		count=$(awk "/^${counter} / {print \$2; exit}" "${hist}")
+	if [[ -s "${cache}" && "${counter}" == *"Tcp"* ]]; then
+		count=$(awk "/^${counter} / {print \$2; exit}" "${cache}")
 	else
-		count=$(ip netns exec "${ns}" nstat -asz "${counter}" |
-			awk 'NR==1 {next} {print $2}')
+		count=$(NSTAT_HISTORY="${hist}" ip netns exec "${ns}" \
+			nstat -sz "${counter}" |
+				awk 'NR==1 {next} {print $2}')
 	fi
 	if [ -z "${count}" ]; then
 		mptcp_lib_fail_if_expected_feature "${counter} counter"

-- 
2.55.0