linux-kernel - [PATCH net-next v2 2/2] selftests: net: add test for dst hint mechanism with directed broadcast addresses

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Message-Id: <20250814140309.3742-3-oscmaes92@gmail.com>
Date: Thu, 14 Aug 2025 16:03:09 +0200
From: Oscar Maes <oscmaes92@...il.com>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net,
	dsahern@...nel.org,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	horms@...nel.org,
	shuah@...nel.org,
	linux-kernel@...r.kernel.org,
	Oscar Maes <oscmaes92@...il.com>
Subject: [PATCH net-next v2 2/2] selftests: net: add test for dst hint mechanism with directed broadcast addresses

Add a test for ensuring that the dst hint mechanism is used for
directed broadcast addresses.

This test relies on mausezahn for sending directed broadcast packets.
Additionally, a high GRO flush timeout is set to ensure that packets
will be received as lists.

The test determines if the hint mechanism was used by checking
the in_brd statistic using lnstat.

Signed-off-by: Oscar Maes <oscmaes92@...il.com>
---
 tools/testing/selftests/net/route_hint.sh | 58 +++++++++++++++++++++++
 1 file changed, 58 insertions(+)
 create mode 100755 tools/testing/selftests/net/route_hint.sh

diff --git a/tools/testing/selftests/net/route_hint.sh b/tools/testing/selftests/net/route_hint.sh
new file mode 100755
index 000000000000..fab08d8b742d
--- /dev/null
+++ b/tools/testing/selftests/net/route_hint.sh
@@ -0,0 +1,58 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# This test ensures directed broadcast routes use dst hint mechanism
+
+CLIENT_NS=$(mktemp -u client-XXXXXXXX)
+CLIENT_IP4="192.168.0.1"
+
+SERVER_NS=$(mktemp -u server-XXXXXXXX)
+SERVER_IP4="192.168.0.2"
+
+BROADCAST_ADDRESS="192.168.0.255"
+
+setup() {
+	ip netns add "${CLIENT_NS}"
+	ip netns add "${SERVER_NS}"
+
+	ip -net "${SERVER_NS}" link add link1 type veth peer name link0 netns "${CLIENT_NS}"
+
+	ip -net "${CLIENT_NS}" link set link0 up
+	ip -net "${CLIENT_NS}" addr add "${CLIENT_IP4}/24" dev link0
+
+	ip -net "${SERVER_NS}" link set link1 up
+	ip -net "${SERVER_NS}" addr add "${SERVER_IP4}/24" dev link1
+
+	ip netns exec "${CLIENT_NS}" ethtool -K link0 tcp-segmentation-offload off
+	ip netns exec "${SERVER_NS}" sh -c "echo 500000000 > /sys/class/net/link1/gro_flush_timeout"
+	ip netns exec "${SERVER_NS}" sh -c "echo 1 > /sys/class/net/link1/napi_defer_hard_irqs"
+	ip netns exec "${SERVER_NS}" ethtool -K link1 generic-receive-offload on
+}
+
+cleanup() {
+	ip -net "${SERVER_NS}" link del link1
+	ip netns del "${CLIENT_NS}"
+	ip netns del "${SERVER_NS}"
+}
+
+directed_bcast_hint_test()
+{
+	echo "Testing for directed broadcast route hint"
+
+	orig_in_brd=$(ip netns exec "${SERVER_NS}" lnstat -k in_brd -s0 -i1 -c1 | tr -d ' |')
+	ip netns exec "${CLIENT_NS}" mausezahn link0 -a own -b bcast -A "${CLIENT_IP4}" \
+		-B "${BROADCAST_ADDRESS}" -c1 -t tcp "sp=1-100,dp=1234,s=1,a=0" -p 5 -q
+	sleep 1
+	new_in_brd=$(ip netns exec "${SERVER_NS}" lnstat -k in_brd -s0 -i1 -c1 | tr -d ' |')
+
+	res=$(echo "${new_in_brd} - ${orig_in_brd}" | bc)
+
+	[ "${res}" -lt 100 ]
+}
+
+trap cleanup EXIT
+
+setup
+
+directed_bcast_hint_test
+exit $?
-- 
2.39.5