[PATCH v2 3/4] selftests: net: udpgso_bench: Fix racing bug between the rx/tx programs

[Andrei Gherzan <andrei.gherzan@canonical.com>]

"udpgro_bench.sh" invokes udpgso_bench_rx/udpgso_bench_tx programs
subsequently and while doing so, there is a chance that the rx one is not
ready to accept socket connections. This racing bug could fail the test
with at least one of the following:

./udpgso_bench_tx: connect: Connection refused
./udpgso_bench_tx: sendmsg: Connection refused
./udpgso_bench_tx: write: Connection refused

This change addresses this by making udpgro_bench.sh wait for the rx
program to be ready before firing off the tx one - with an exponential back
off algorithm from 1s to 10s.

Signed-off-by: Andrei Gherzan <andrei.gherzan@canonical.com>
---
 tools/testing/selftests/net/udpgso_bench.sh | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/tools/testing/selftests/net/udpgso_bench.sh b/tools/testing/selftests/net/udpgso_bench.sh
index dc932fd65363..20b5db8fcbde 100755
--- a/tools/testing/selftests/net/udpgso_bench.sh
+++ b/tools/testing/selftests/net/udpgso_bench.sh
@@ -7,6 +7,7 @@ readonly GREEN='\033[0;92m'
 readonly YELLOW='\033[0;33m'
 readonly RED='\033[0;31m'
 readonly NC='\033[0m' # No Color
+readonly TESTPORT=8000 # Keep this in sync with udpgso_bench_rx/tx
 
 readonly KSFT_PASS=0
 readonly KSFT_FAIL=1
@@ -56,10 +57,27 @@ trap wake_children EXIT
 
 run_one() {
 	local -r args=$@
+	local -r init_delay_s=1
+	local -r max_delay_s=10
+	local delay_s=0
+	local nr_socks=0
 
 	./udpgso_bench_rx &
 	./udpgso_bench_rx -t &
 
+	# Wait for the above test program to get ready to receive connections.
+	delay_s="${init_delay_s}"
+	while [ "$delay_s" -lt "$max_delay_s" ]; do
+		nr_socks="$(ss -lnHi | grep -c "\*:${TESTPORT}")"
+		[ "$nr_socks" -eq 2 ] && break
+		sleep "$delay_s"
+		delay="$((delay*2))"
+	done
+	if [ "$nr_socks" -ne 2 ]; then
+		echo "timed out while waiting for udpgso_bench_rx"
+		exit 1
+	fi
+
 	./udpgso_bench_tx ${args}
 }
 
-- 
2.34.1