Add test_pop_vlan() to verify OVS kernel datapath pop_vlan action
correctly strips 802.1Q VLAN tags from frames.

Test structure:
- Baseline: untagged forwarding validates basic connectivity.
- Negative: forward without pop_vlan, assert VLAN tag preserved.
- Positive: forward with pop_vlan, assert tag stripped and
  untagged ICMP echo request arrives.

Add start_capture/stop_capture helpers using ovs_wait for
deterministic tcpdump readiness instead of ad-hoc sleep.

Signed-off-by: Minxi Hou <[email protected]>
---
 .../selftests/net/openvswitch/openvswitch.sh  | 196 ++++++++++++++++++
 1 file changed, 196 insertions(+)

diff --git a/tools/testing/selftests/net/openvswitch/openvswitch.sh 
b/tools/testing/selftests/net/openvswitch/openvswitch.sh
index b327d3061ed5..95fb8f824b15 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_VLAN action strips tag
        psample                                 psample: Sampling packets with 
psample"
 
 info() {
@@ -830,6 +831,201 @@ test_tunnel_metadata() {
        return 0
 }
 
+# Start tcpdump capture with deterministic readiness wait.
+# Usage: start_capture <netns> <iface> <pcap_path> <out_pid_var> <out_log_var>
+# $4 and $5 are variable NAMES — start_capture writes the tcpdump PID
+# and log path into those caller variables via nameref (bash 4.3+).
+# Contract: caller MUST call stop_capture with the returned PID and log
+#           before returning from the function.
+start_capture() {
+       local ns="$1" iface="$2" pcap="$3"
+       local -n _out_pid="$4"
+       local -n _out_log="$5"
+       local log pid
+
+       command -v tcpdump >/dev/null 2>&1 || {
+               info "tcpdump missing"
+               return $ksft_skip
+       }
+
+       log=$(mktemp)
+       ip netns exec "$ns" tcpdump -nei "$iface" \
+               -w "$pcap" -U 2>"$log" &
+       pid=$!
+       ovs_wait grep -q "listening on" "$log" || {
+               kill $pid 2>/dev/null
+               wait $pid 2>/dev/null
+               rm -f "$log"
+               info "FAIL: tcpdump failed to start on $iface"
+               return 1
+       }
+       kill -0 $pid 2>/dev/null || {
+               wait $pid 2>/dev/null
+               rm -f "$log"
+               info "FAIL: tcpdump died after start on $iface"
+               return 1
+       }
+       # $pid/$log expand now (intentional — captures concrete values)
+       on_exit "kill $pid 2>/dev/null; rm -f $log"
+       _out_pid=$pid
+       _out_log=$log
+}
+
+# Stop capture and cleanup temp files.
+# Usage: stop_capture <pid> <log_path>
+stop_capture() {
+       kill "$1" 2>/dev/null
+       wait "$1" 2>/dev/null
+       rm -f "$2"
+}
+
+test_pop_vlan() {
+       modprobe -q openvswitch 2>/dev/null || true
+       [ -d /sys/module/openvswitch ] || return $ksft_skip
+       local ns_err
+       ns_err=$(mktemp)
+       if ! ip netns add __test_pop_vlan_netns__ 2>"$ns_err"; then
+               if grep -q "File exists" "$ns_err"; then
+                       ip netns del __test_pop_vlan_netns__ 2>/dev/null
+               else
+                       info "CONFIG_NET_NS missing or unavailable"
+                       rm -f "$ns_err"
+                       return $ksft_skip
+               fi
+       fi
+       ip netns del __test_pop_vlan_netns__ 2>/dev/null
+       rm -f "$ns_err"
+       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 $?
+       ovs_add_dp "$sbx" vlandp || return 1
+
+       # Validate basic connectivity before testing pop_vlan.
+       # --- 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 ---
+       # ns1: VLAN sub-interface generates tagged frames
+       ip -n ns1 link add link ns1veth name ns1veth.10 \
+               type vlan id 10 || return 1
+       on_exit "ip -n ns1 link del ns1veth.10 2>/dev/null || true"
+       ip -n ns1 addr add 198.51.100.1/24 dev ns1veth.10 || return 1
+       ip -n ns1 link set ns1veth.10 up || return 1
+
+       # ns2: no VLAN sub-interface. POP delivers untagged frames to ns2veth
+       ip -n ns2 addr add 198.51.100.2/24 dev ns2veth || return 1
+       on_exit "ip -n ns2 addr del 198.51.100.2/24 dev ns2veth 2>/dev/null"
+
+       # veth: disable VLAN offload + GRO (force 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 "$ns1veth10mac" \
+               dev ns2veth nud permanent || return 1
+
+       # --- Negative check: fwd without pop_vlan, VLAN tag stays ---
+       local vlan_match='in_port(1),eth(),eth_type(0x8100),'
+       vlan_match+='vlan(vid=10),'
+       vlan_match+='encap(eth_type(0x0800),'
+       vlan_match+='ipv4(src=198.51.100.1,proto=1),icmp())'
+       ovs_add_flow "$sbx" vlandp "$vlan_match" '2' || return 1
+
+       local pcap_no_pop
+       pcap_no_pop=$(mktemp --suffix=.pcap)
+       on_exit "rm -f $pcap_no_pop"
+       local tpid tlog
+       start_capture ns2 ns2veth "$pcap_no_pop" tpid tlog || return $?
+
+       ip netns exec ns1 ping -I ns1veth.10 -c 3 -W 1 198.51.100.2 \
+               >/dev/null 2>&1 || true
+       stop_capture "$tpid" "$tlog"
+
+       # assert: VLAN tag still present (no pop_vlan in action)
+       tcpdump -nr "$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 "$vlan_match" 'pop_vlan,2' || return 1
+       ovs_add_flow "$sbx" vlandp \
+               'in_port(2),eth(),eth_type(0x0800),ipv4()' '1' || return 1
+
+       local pcap
+       pcap=$(mktemp --suffix=.pcap)
+       on_exit "rm -f $pcap"
+       local tpid2 tlog2
+       start_capture ns2 ns2veth "$pcap" tpid2 tlog2 || return $?
+
+       # ns1veth.10 only accepts tagged frames;
+       # ns2 sends untagged reply → dropped by ns1
+       local ping_rc=0
+       ip netns exec ns1 ping -I ns1veth.10 -c 3 -W 1 198.51.100.2 \
+               >/dev/null 2>&1 || ping_rc=$?
+       stop_capture "$tpid2" "$tlog2"
+
+       # ping failure is expected (reply path asymmetric)
+       [ "$ping_rc" -ne 0 ] || {
+               info "FAIL: ping succeeded unexpectedly"
+               return 1
+       }
+
+       # assert: no VLAN tag (POP succeeded), untagged ICMP arrived
+       tcpdump -nr "$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
+       }
+
+       return 0
+}
+
 run_test() {
        (
        tname="$1"
-- 
2.53.0

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