[PATCH net 2/2] selftests: net: check veth carrier after changing channel counts

[Xia Yan <yana06070@163.com>]

Add a regression test for veth_set_channels() incorrectly enabling
carrier when the peer is administratively down.

Check all combinations of the two ends' administrative states with GRO
enabled and disabled. Resize the RX and TX channel counts in both
directions on each end and verify that carrier is on only when both ends
are up. Also verify that rejecting an out-of-range channel count leaves
carrier unchanged.

On an unpatched kernel the two mixed up/down cases fail with each GRO
setting. All eight cases pass with the carrier restoration fix.

Assisted-by: LLM

Signed-off-by: Xia Yan <yana06070@163.com>
---

Notes (validation):
    Tested with iproute2 and ethtool in an isolated network namespace under
    the unpatched and patched UML kernels. The mixed up/down states fail
    before the driver fix with both GRO settings; all eight cases pass after
    the fix. The script also passes bash -n.
    
    The new file is covered by the existing MAINTAINERS entry for
    tools/testing/selftests/; no MAINTAINERS update is needed.

 tools/testing/selftests/net/Makefile          |  1 +
 .../selftests/net/veth_channels_carrier.sh    | 89 +++++++++++++++++++
 2 files changed, 90 insertions(+)
 create mode 100755 tools/testing/selftests/net/veth_channels_carrier.sh

diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 590b33e..4004014 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -128,6 +128,7 @@ TEST_PROGS := \
 	udpgso_bench.sh \
 	unicast_extensions.sh \
 	veth.sh \
+	veth_channels_carrier.sh \
 	vlan_bridge_binding.sh \
 	vlan_hw_filter.sh \
 	vrf-xfrm-tests.sh \
diff --git a/tools/testing/selftests/net/veth_channels_carrier.sh b/tools/testing/selftests/net/veth_channels_carrier.sh
new file mode 100755
index 0000000..c72a03b
--- /dev/null
+++ b/tools/testing/selftests/net/veth_channels_carrier.sh
@@ -0,0 +1,89 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+source "$(dirname "${BASH_SOURCE[0]}")/lib.sh"
+
+require_command ip
+require_command ethtool
+
+if [ "$EUID" -ne 0 ]; then
+	echo "SKIP: root privileges are required"
+	exit "$ksft_skip"
+fi
+
+trap cleanup_all_ns EXIT
+setup_ns ns || exit $?
+
+check_carrier()
+{
+	local dev=$1
+	local expected=$2
+	local carrier=0
+	local link
+
+	link=$(ip -n "$ns" -o link show dev "$dev")
+	check_err $? "Failed to read $dev link state"
+	[[ $link == *LOWER_UP* ]] && carrier=1
+	[ "$carrier" -eq "$expected" ]
+	check_err $? "$dev carrier is $carrier, expected $expected"
+}
+
+check_state()
+{
+	local left=$1
+	local right=$2
+	local gro=$3
+	local expected=0
+	local count dev
+
+	RET=0
+	if ! ip -n "$ns" link add vca numtxqueues 2 numrxqueues 2 \
+		type veth peer name vcb numtxqueues 2 numrxqueues 2; then
+		RET=$ksft_skip
+		log_test "veth carrier: $left/$right, GRO $gro"
+		return
+	fi
+
+	ip -n "$ns" link set vca "$left"
+	check_err $? "Failed to configure vca"
+	ip -n "$ns" link set vcb "$right"
+	check_err $? "Failed to configure vcb"
+	ip netns exec "$ns" ethtool -K vca gro "$gro" >/dev/null
+	check_err $? "Failed to configure GRO"
+	ip netns exec "$ns" ethtool -K vcb gro "$gro" >/dev/null
+	check_err $? "Failed to configure peer GRO"
+
+	[ "$left" = up ] && [ "$right" = up ] && expected=1
+	check_carrier vca "$expected"
+	check_carrier vcb "$expected"
+
+	for dev in vca vcb; do
+		for count in 1 2; do
+			ip netns exec "$ns" ethtool -L "$dev" \
+				rx "$count" tx "$count"
+			check_err $? "Failed to resize $dev channels"
+			check_carrier vca "$expected"
+			check_carrier vcb "$expected"
+		done
+
+		ip netns exec "$ns" ethtool -L "$dev" rx 3 tx 3 \
+			>/dev/null 2>&1
+		check_fail $? "Out-of-range channel counts were accepted"
+		check_carrier vca "$expected"
+		check_carrier vcb "$expected"
+	done
+
+	ip -n "$ns" link del vca
+	check_err $? "Failed to delete the veth pair"
+	log_test "veth carrier: $left/$right, GRO $gro"
+}
+
+for gro in off on; do
+	for left in down up; do
+		for right in down up; do
+			check_state "$left" "$right" "$gro"
+		done
+	done
+done
+
+exit "$EXIT_STATUS"
-- 
2.33.0