Extend veth.sh to check that changing channel counts preserves carrier
state. When only one end is up, the running end must not report LOWER_UP.

Cover up/up and both mixed up/down combinations. Resize RX and TX queues
in both directions on each endpoint, and check carrier after a rejected
out-of-range request as well. Create the pair with two queues explicitly
so the carrier cases also run on single-CPU systems.

Reuse the existing namespace setup and cleanup. Run each carrier case
in a subshell to keep its variables separate from the other tests, and
accumulate failures in the caller. Only check LOWER_UP on running
interfaces, where the flag exposes carrier state.

Tested-by: Hangbin Liu <liuhangbin@kylinos.cn>
Reviewed-by: Hangbin Liu <liuhangbin@kylinos.cn>
Assisted-by: LLM
Signed-off-by: Xia Yan <yana06070@163.com>
---
Changes in v5:
- Drop unnecessary quotes around literal up, as suggested by Hangbin.
- Clarify that the v4 quoting change concerned variable expansions.
- Add Hangbin's Tested-by and Reviewed-by tags.

v4: https://lore.kernel.org/netdev/20261024093007.12981-1-yana06070@163.com/

Changes in v4:
- Drop the extra GRO on/off runs, as discussed with Hangbin.
  Keep up/up and both mixed up/down states.
- Use subshells for the new helpers and accumulate failures in the
  caller. Quote variable expansions and wrap long lines.
- Driver code is unchanged.

v3: https://lore.kernel.org/netdev/20261022085842.2527-1-yana06070@163.com/

Runtime testing of v4 on 513444cc62e2, x86_64 QEMU/KVM with three vCPUs:
- Complete default veth.sh:
  before: 56 checks pass, two mixed up/down carrier checks fail;
  after: all 58 checks pass. The 55 existing checks pass on both.
- Script exit status: 1 before, 0 after. No checks were skipped.
- Both guests powered down normally.
- The runtime results above are from v4. The only v5 script change
  removes quotes around a literal argument.

The repeated-word warning on chk_channels_carrier is for the two
endpoint state arguments.

 tools/testing/selftests/net/veth.sh | 81 ++++++++++++++++++++++++++++-
 1 file changed, 80 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/net/veth.sh b/tools/testing/selftests/net/veth.sh
index 8b867e0675a7c1eea300468c26f2a9528ddc1194..5fb4b8c199b906785ab09cae35cf1e70a042bbce 100755
--- a/tools/testing/selftests/net/veth.sh
+++ b/tools/testing/selftests/net/veth.sh
@@ -41,13 +41,16 @@ create_ns() {
 		ip -n $ns link set dev lo up
 	done
 
-	ip link add name veth$SRC type veth peer name veth$DST
+	ip link add name "veth$SRC" "$@" type veth \
+		peer name "veth$DST" "$@" || return 1
 
 	for ns in $SRC $DST; do
 		ip link set dev veth$ns netns $BASE$ns up
 		ip -n $BASE$ns addr add dev veth$ns $BM_NET_V4$ns/24
 		ip -n $BASE$ns addr add dev veth$ns $BM_NET_V6$ns/64 nodad
 	done
+
+	return 0
 }
 
 __chk_flag() {
@@ -130,6 +133,78 @@ chk_channels() {
 	fi
 }
 
+chk_carrier() (
+	target=$1
+	state=$2
+	expected=$3
+	carrier=0
+
+	# IFF_LOWER_UP is reported only for running interfaces.
+	[ "$state" = up ] || return 0
+
+	if ! link=$(ip -n "$BASE$target" -o link show dev "veth$target"); then
+		echo " fail - cannot read veth$target link state"
+		return 1
+	fi
+	case "$link" in
+		*LOWER_UP*) carrier=1 ;;
+	esac
+	if [ "$carrier" -ne "$expected" ]; then
+		printf ' fail - veth%s carrier is %s, expected %s\n' \
+			"$target" "$carrier" "$expected"
+		return 1
+	fi
+)
+
+# Keep per-case variables separate from the other tests.
+chk_channels_carrier() (
+	src_state=$1
+	dst_state=$2
+	expected=0
+	err=0
+	msg="carrier after channel change ($src_state/$dst_state)"
+
+	if ! create_ns numtxqueues 2 numrxqueues 2; then
+		printf "%-60s" "$msg"
+		echo " skip - cannot create veth pair"
+		cleanup
+		return 0
+	fi
+
+	ip -n "$NS_SRC" link set dev "veth$SRC" "$src_state" || err=1
+	ip -n "$NS_DST" link set dev "veth$DST" "$dst_state" || err=1
+	[ "$src_state" = up ] && [ "$dst_state" = up ] && expected=1
+	chk_carrier "$SRC" "$src_state" "$expected" || err=1
+	chk_carrier "$DST" "$dst_state" "$expected" || err=1
+
+	for target in "$SRC" "$DST"; do
+		for count in 1 2; do
+			ip netns exec "$BASE$target" ethtool -L "veth$target" \
+				rx "$count" tx "$count" || err=1
+			chk_carrier "$SRC" "$src_state" "$expected" || err=1
+			chk_carrier "$DST" "$dst_state" "$expected" || err=1
+		done
+
+		if ip netns exec "$BASE$target" ethtool -L "veth$target" \
+			rx 3 tx 3 \
+			>/dev/null 2>&1; then
+			echo " fail - out-of-range channel counts were accepted"
+			err=1
+		fi
+		chk_carrier "$SRC" "$src_state" "$expected" || err=1
+		chk_carrier "$DST" "$dst_state" "$expected" || err=1
+	done
+
+	cleanup
+	printf "%-60s" "$msg"
+	if [ "$err" -eq 0 ]; then
+		echo " ok "
+	else
+		echo " fail "
+	fi
+	return "$err"
+)
+
 chk_gro() {
 	local msg="$1"
 	local expected=$2
@@ -257,6 +332,10 @@ fi
 [ $STRESS -gt 0 -a $CPUS -lt 3 ] && echo " stress test will be skipped, too"
 [ ! -f "$YNL" ] && echo "ynl cli not found, ndo-xmit tests will be skipped"
 
+chk_channels_carrier up up || ret=1
+chk_channels_carrier up down || ret=1
+chk_channels_carrier down up || ret=1
+
 create_ns
 chk_gro_flag "default - gro flag" $SRC off
 chk_gro_flag "        - peer gro flag" $DST off

-- 
2.39.0.windows.2