Subject: Re: [PATCH net-next v2 2/2] selftests: openvswitch: add pop_vlan test

From: Aaron Conole <[email-masked]>
Date: Mon, 04 May 2026 11:51:18 -0400

Hi Minxi,

Thanks for the test (and the support infra in 1/2).  Questions below.

Minxi Hou <[email-masked]> writes:

> Add a test for the OVS datapath POP_VLAN action.  The test uses
> the VLAN sub-interface of a veth pair to generate 802.1Q tagged
> frames and verifies that pop_vlan correctly strips the VLAN tag
> before delivery via pcap frame capture.
>
> The test has two verifications:
> - Negative: forward tagged frames without pop_vlan, verify the
>   VLAN tag is still present on the egress interface.
> - Positive: apply pop_vlan, verify the tag is removed and an
>   untagged ICMP echo request arrives at the egress interface.
>
> Static ARP entries avoid the complexity of VLAN-tagged ARP
> resolution (the egress side has no VLAN sub-interface and cannot
> process tagged ARP).
>
> Signed-off-by: Minxi Hou <[email-masked]>
> ---
> v1 -> v2: rebase to latest net-next/main, drop --base=auto
>
>  .../selftests/net/openvswitch/openvswitch.sh  | 132 ++++++++++++++++++
>  1 file changed, 132 insertions(+)
>
> diff --git a/tools/testing/selftests/net/openvswitch/openvswitch.sh b/tools/testing/selftests/net/openvswitch/openvswitch.sh
> index b327d3061ed5..cd614ff7b740 100755
> --- a/tools/testing/selftests/net/openvswitch/openvswitch.sh
> +++ b/tools/testing/selftests/net/openvswitch/openvswitch.sh
> @@ -27,6 +27,7 @@ tests="
>  	upcall_interfaces			ovs: test the upcall interfaces
>  	tunnel_metadata				ovs: test extraction of tunnel metadata
>  	drop_reason				drop: test drop reasons are emitted
> +	pop_vlan					vlan-pop: POP_VLAN action strips 802.1Q tag

nit: The whitespace alignment above is slightly off.

>  	psample					psample: Sampling packets with psample"
>  
>  info() {
> @@ -830,6 +831,137 @@ test_tunnel_metadata() {
>  	return 0
>  }
>  
> +test_pop_vlan() {
> +	modprobe -q openvswitch 2>/dev/null || true
> +	[ -d /sys/module/openvswitch ] || return $ksft_skip
> +	ip netns add __test_pop_vlan_netns__ 2>/dev/null || \
> +		{ info "CONFIG_NET_NS missing"; return $ksft_skip; }
> +	ip netns del __test_pop_vlan_netns__ 2>/dev/null

Weird that this is here.  All other tests would also not work if there
were no netns or OVS module.  Why were these added?

> +	modprobe -q 8021q 2>/dev/null || true
> +	[ -d /sys/module/8021q ] || { info "CONFIG_VLAN_8021Q missing"; return $ksft_skip; }
> +
> +	local sbx="test_pop_vlan"
> +	sbx_add "$sbx" || return $ksft_skip
> +	ovs_add_dp "$sbx" vlandp || return 1
> +
> +	# --- baseline: untagged forwarding ---
> +	ovs_add_netns_and_veths "$sbx" vlandp ns1 veth1 ns1veth 192.0.2.1/24 || return 1
> +	ovs_add_netns_and_veths "$sbx" vlandp ns2 veth2 ns2veth 192.0.2.2/24 || return 1
> +
> +	# ARP + IPv4 bidirectional (all untagged)
> +	ovs_add_flow "$sbx" vlandp \
> +		'in_port(1),eth(),eth_type(0x0806),arp()' '2' || return 1
> +	ovs_add_flow "$sbx" vlandp \
> +		'in_port(2),eth(),eth_type(0x0806),arp()' '1' || return 1
> +	ovs_add_flow "$sbx" vlandp \
> +		'in_port(1),eth(),eth_type(0x0800),ipv4()' '2' || return 1
> +	ovs_add_flow "$sbx" vlandp \
> +		'in_port(2),eth(),eth_type(0x0800),ipv4()' '1' || return 1
> +	ip netns exec ns1 ping -c 3 -W 2 192.0.2.2 || return 1
> +
> +	# --- POP_VLAN test ---
> +	# Register cleanup before creating resources (safe on failure paths)
> +	on_exit "ip -n ns1 link del ns1veth.10 2>/dev/null || true
> +		 ip -n ns2 addr del 198.51.100.2/24 dev ns2veth 2>/dev/null || true"
> +
> +	# ns1: VLAN sub-interface generates tagged frames
> +	ip -n ns1 link add link ns1veth name ns1veth.10 type vlan id 10
> +	ip -n ns1 addr add 198.51.100.1/24 dev ns1veth.10
> +	ip -n ns1 link set ns1veth.10 up
> +
> +	# ns2: no VLAN sub-interface. POP delivers untagged frames to ns2veth
> +	ip -n ns2 addr add 198.51.100.2/24 dev ns2veth
> +
> +	# veth disable VLAN offload + GRO (ensure kernel software tag processing)
> +	if command -v ethtool >/dev/null 2>&1; then
> +		ip netns exec ns1 ethtool -k ns1veth 2>/dev/null | grep -q vlan-offload && \
> +			ip netns exec ns1 ethtool -K ns1veth rx-vlan-offload off \
> +				tx-vlan-offload off gro off 2>/dev/null || true
> +		ip netns exec ns2 ethtool -k ns2veth 2>/dev/null | grep -q vlan-offload && \
> +			ip netns exec ns2 ethtool -K ns2veth rx-vlan-offload off \
> +				tx-vlan-offload off gro off 2>/dev/null || true
> +	fi
> +
> +	ovs_del_flows "$sbx" vlandp
> +
> +	# Static ARP avoids VLAN-tagged ARP complexity (ns2 has no VLAN
> +	# sub-interface, so tagged ARP would be invisible to ns2).
> +	local ns1veth10mac ns2mac
> +	ns1veth10mac=$(ip -n ns1 link show ns1veth.10 | \
> +		awk '/link\/ether/ {print $2}')
> +	ns2mac=$(ip -n ns2 link show ns2veth | \
> +		awk '/link\/ether/ {print $2}')
> +	[ -n "$ns1veth10mac" ] && echo "$ns1veth10mac" | \
> +		grep -qE "^([0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2}$" || return 1
> +	[ -n "$ns2mac" ] && echo "$ns2mac" | \
> +		grep -qE "^([0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2}$" || return 1
> +	ip -n ns1 neigh replace 198.51.100.2 lladdr "$ns2mac" \
> +		dev ns1veth.10 nud permanent || return 1
> +	ip -n ns2 neigh replace 198.51.100.1 lladdr "$ns1veth10mac" \
> +		dev ns2veth nud permanent || return 1
> +
> +	# --- Negative check: fwd without pop_vlan, VLAN tag stays ---
> +	ovs_add_flow "$sbx" vlandp \
> +		'in_port(1),eth(),eth_type(0x8100),vlan(vid=10),encap(eth_type(0x0800),ipv4(src=198.51.100.1,proto=1),icmp())' \
> +		'2' || return 1
> +
> +	local pcap_no_pop
> +	pcap_no_pop=$(mktemp --suffix=.pcap)
> +	on_exit "rm -f $pcap_no_pop"
> +	ip netns exec ns2 tcpdump -nei ns2veth -w "$pcap_no_pop" -U &
> +	local tpid_no_pop=$!
> +	on_exit "kill $tpid_no_pop 2>/dev/null || true"
> +	sleep $((WAIT_TIMEOUT / 5 < 2 ? 2 : WAIT_TIMEOUT / 5))
> +

We don't like to make extra files when not requested.  For example, this
is making some pcap file but do we need it?  We also have a specific
spawn function `ovs_netns_spawn_daemon` that should take care of
cleaning up at least the PID.

> +	ip netns exec ns1 ping -I ns1veth.10 -c 3 -W 1 198.51.100.2 \
> +		>/dev/null 2>&1 || true
> +	kill $tpid_no_pop 2>/dev/null || true; wait $tpid_no_pop 2>/dev/null || true
> +
> +	# assert: VLAN tag still present (no pop_vlan in action)
> +	tcpdump -nr "$pcap_no_pop" 'vlan' 2>/dev/null | grep -q . || {
> +		info "FAIL: negative check: no VLAN tag (expected tag present)"; return 1
> +	}
> +
> +	ovs_del_flows "$sbx" vlandp
> +
> +	# --- Positive: pop_vlan strips tag ---
> +	ovs_add_flow "$sbx" vlandp \
> +		'in_port(1),eth(),eth_type(0x8100),vlan(vid=10),encap(eth_type(0x0800),ipv4(src=198.51.100.1,proto=1),icmp())' \
> +		'pop_vlan,2' || return 1
> +	ovs_add_flow "$sbx" vlandp \
> +		'in_port(2),eth(),eth_type(0x0800),ipv4()' '1' || return 1
> +
> +	local pcap
> +	pcap=$(mktemp --suffix=.pcap)
> +	on_exit "rm -f $pcap"
> +	ip netns exec ns2 tcpdump -nei ns2veth -w "$pcap" -U &
> +	local tpid=$!
> +	on_exit "kill $tpid 2>/dev/null || true"
> +	sleep $((WAIT_TIMEOUT / 5 < 2 ? 2 : WAIT_TIMEOUT / 5))
> +
> +	# ping reply unreachable: ns1veth.10 only accepts tagged frames,
> +	# ns2 sends untagged reply -> dropped by ns1veth.10.
> +	local ping_rc=0
> +	ip netns exec ns1 ping -I ns1veth.10 -c 3 -W 1 198.51.100.2 \
> +		>/dev/null 2>&1 || ping_rc=$?
> +	kill $tpid 2>/dev/null || true; wait $tpid 2>/dev/null || true
> +
> +	# ping failure is expected (reply path asymmetric)
> +	[ "$ping_rc" -ne 0 ] || \
> +		info "NOTE: ping succeeded unexpectedly (reply reached ns1veth.10)"
> +
> +	# assert: no VLAN tag (POP succeeded), untagged ICMP echo request arrived
> +	tcpdump -nr "$pcap" 'vlan' 2>/dev/null | grep -q . && {
> +		info "FAIL: POP_VLAN: VLAN tag still present"; return 1
> +	}
> +	tcpdump -nr "$pcap" 'icmp and icmp[icmptype]=8' \
> +		2>/dev/null | grep -q . || {
> +		info "FAIL: POP_VLAN: no untagged ICMP echo request"; return 1
> +	}

Do we really need these tcpdump checks?  The ping commands above should
already capture when we are expecting tagged / untagged traffic.

> +	return 0
> +}
> +
>  run_test() {
>  	(
>  	tname="$1"