[PATCH] tools/testing/selftests/bpf/test_tc_tunnel.sh: Prevent client connect before server bind

["Alessandro Carminati (Red Hat)" <alessandro.carminati@gmail.com>]

In some systems, the netcat server can incur in delay to start listening.
When this happens, the test can randomly fail in various points.
This is an example error message:
   # ip gre none gso
   # encap 192.168.1.1 to 192.168.1.2, type gre, mac none len 2000
   # test basic connectivity
   # Ncat: Connection refused.

Signed-off-by: Alessandro Carminati (Red Hat) <alessandro.carminati@gmail.com>
---
 tools/testing/selftests/bpf/test_tc_tunnel.sh | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/test_tc_tunnel.sh b/tools/testing/selftests/bpf/test_tc_tunnel.sh
index 910044f08908..01c0f4b1a8c2 100755
--- a/tools/testing/selftests/bpf/test_tc_tunnel.sh
+++ b/tools/testing/selftests/bpf/test_tc_tunnel.sh
@@ -72,7 +72,6 @@ cleanup() {
 server_listen() {
 	ip netns exec "${ns2}" nc "${netcat_opt}" -l "${port}" > "${outfile}" &
 	server_pid=$!
-	sleep 0.2
 }
 
 client_connect() {
@@ -93,6 +92,22 @@ verify_data() {
 	fi
 }
 
+wait_for_port() {
+	local digits=8
+	local port2check=$(printf ":%04X" $1)
+	local prot=$([ "$2" == "-6" ] && echo 6 && digits=32)
+
+	for i in $(seq 20); do
+		if ip netns exec "${ns2}" cat /proc/net/tcp${prot} | \
+			sed -r 's/^[ \t]+[0-9]+: ([0-9A-F]{'${digits}'}:[0-9A-F]{4}) .*$/\1/' | \
+			grep -q "${port2check}"; then
+			return 0
+		fi
+		sleep 0.1
+	done
+	return 1
+}
+
 set -e
 
 # no arguments: automated test, run all
@@ -193,6 +208,7 @@ setup
 # basic communication works
 echo "test basic connectivity"
 server_listen
+wait_for_port ${port} ${netcat_opt}
 client_connect
 verify_data
 
@@ -204,6 +220,7 @@ ip netns exec "${ns1}" tc filter add dev veth1 egress \
 	section "encap_${tuntype}_${mac}"
 echo "test bpf encap without decap (expect failure)"
 server_listen
+wait_for_port ${port} ${netcat_opt}
 ! client_connect
 
 if [[ "$tuntype" =~ "udp" ]]; then
-- 
2.34.1