[PATCH net-next] selftests: openvswitch: add dec_ttl action support and test

[Minxi Hou <houminxi@gmail.com>]

Add dec_ttl action support to the OVS kernel datapath selftest
framework:

  - Add DecTtl nested NLA class to ovs-dpctl.py with proper
    OVS_DEC_TTL_ATTR_ACTION sub-attribute handling
  - Add parse support for dec_ttl(<inner_actions>) action string
    following the same pattern as clone()
  - Add dpstr output formatting for dec_ttl actions
  - Add test_dec_ttl() to openvswitch.sh that verifies:
    * Normal TTL packets are forwarded after decrement
    * TTL=1 packets are dropped (TTL expiry)
    * Graceful skip via ksft_skip if kernel lacks dec_ttl support

The DecTtl class uses late-binding type resolution to reference
ovsactions for its inner action list, avoiding circular references
at class definition time.

Tested with vng on x86_64, all OVS selftests pass.

Signed-off-by: Minxi Hou <houminxi@gmail.com>
---
 .../selftests/net/openvswitch/openvswitch.sh  | 55 +++++++++++++++++++
 .../selftests/net/openvswitch/ovs-dpctl.py    | 39 ++++++++++++-
 2 files changed, 92 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/net/openvswitch/openvswitch.sh b/tools/testing/selftests/net/openvswitch/openvswitch.sh
index 3cdd953f6813..200c36c4d7bf 100755
--- a/tools/testing/selftests/net/openvswitch/openvswitch.sh
+++ b/tools/testing/selftests/net/openvswitch/openvswitch.sh
@@ -28,6 +28,7 @@ tests="
 	tunnel_metadata				ovs: test extraction of tunnel metadata
 	tunnel_refcount				ovs: test tunnel vport reference cleanup
 	drop_reason				drop: test drop reasons are emitted
+	dec_ttl					ttl: dec_ttl action decrements IP TTL
 	psample					psample: Sampling packets with psample"
 
 info() {
@@ -244,6 +245,60 @@ usage() {
 }
 
 
+test_dec_ttl() {
+	sbx_add "test_dec_ttl" || return $?
+	ovs_add_dp "test_dec_ttl" decttl || return 1
+
+	info "create namespaces"
+	for ns in client server; do
+		ovs_add_netns_and_veths "test_dec_ttl" "decttl" "$ns" \
+			"${ns:0:1}0" "${ns:0:1}1" || return 1
+	done
+
+	ip netns exec client ip addr add 10.0.0.1/24 dev c1
+	ip netns exec client ip link set c1 up
+	ip netns exec server ip addr add 10.0.0.2/24 dev s1
+	ip netns exec server ip link set s1 up
+
+	# Probe: check if kernel supports dec_ttl action.
+	ovs_add_flow "test_dec_ttl" decttl \
+		'in_port(1),eth(),eth_type(0x0800),ipv4()' \
+		'dec_ttl()' &>/dev/null
+	if [ $? == 1 ]; then
+		info "no support for dec_ttl - skipping"
+		ovs_exit_sig
+		return $ksft_skip
+	fi
+
+	ovs_del_flows "test_dec_ttl" decttl
+
+	# ARP flows (bidirectional)
+	ovs_add_flow "test_dec_ttl" decttl \
+		'in_port(1),eth(),eth_type(0x0806),arp()' '2' || return 1
+	ovs_add_flow "test_dec_ttl" decttl \
+		'in_port(2),eth(),eth_type(0x0806),arp()' '1' || return 1
+
+	# IP flows with dec_ttl action
+	ovs_add_flow "test_dec_ttl" decttl \
+		'in_port(1),eth(),eth_type(0x0800),ipv4()' \
+		'dec_ttl(),2' || return 1
+	ovs_add_flow "test_dec_ttl" decttl \
+		'in_port(2),eth(),eth_type(0x0800),ipv4()' \
+		'dec_ttl(),1' || return 1
+
+	info "verify connectivity with dec_ttl"
+	ovs_sbx "test_dec_ttl" ip netns exec client ping -c 1 -W 2 \
+		10.0.0.2 || return 1
+
+	info "verify TTL=1 is dropped by dec_ttl"
+	ovs_sbx "test_dec_ttl" ip netns exec client ping -c 1 -W 2 \
+		-t 1 10.0.0.2 >/dev/null 2>&1 \
+		&& { info "FAIL: ping should fail with TTL=1 and dec_ttl"
+		     return 1; }
+
+	return 0
+}
+
 # psample test
 # - use psample to observe packets
 test_psample() {
diff --git a/tools/testing/selftests/net/openvswitch/ovs-dpctl.py b/tools/testing/selftests/net/openvswitch/ovs-dpctl.py
index bbe35e2718d2..a73ca98d7aef 100644
--- a/tools/testing/selftests/net/openvswitch/ovs-dpctl.py
+++ b/tools/testing/selftests/net/openvswitch/ovs-dpctl.py
@@ -388,11 +388,19 @@ class ovsactions(nla):
         ("OVS_ACTION_ATTR_CLONE", "recursive"),
         ("OVS_ACTION_ATTR_CHECK_PKT_LEN", "none"),
         ("OVS_ACTION_ATTR_ADD_MPLS", "none"),
-        ("OVS_ACTION_ATTR_DEC_TTL", "none"),
+        ("OVS_ACTION_ATTR_DEC_TTL", "DecTtl"),
         ("OVS_ACTION_ATTR_DROP", "uint32"),
         ("OVS_ACTION_ATTR_PSAMPLE", "psample"),
     )
 
+    class DecTtl(nla):
+        nla_flags = NLA_F_NESTED
+
+        nla_map = (
+            ("OVS_DEC_TTL_ATTR_UNSPEC", "none"),
+            ("OVS_DEC_TTL_ATTR_ACTION", "actions"),
+        )
+
     class psample(nla):
         nla_flags = NLA_F_NESTED
 
@@ -632,6 +640,13 @@ class ovsactions(nla):
                 print_str += "ct_clear"
             elif field[0] == "OVS_ACTION_ATTR_POP_VLAN":
                 print_str += "pop_vlan"
+            elif field[0] == "OVS_ACTION_ATTR_DEC_TTL":
+                datum = self.get_attr(field[0])
+                print_str += "dec_ttl("
+                subacts = datum.get_attr("OVS_DEC_TTL_ATTR_ACTION")
+                if subacts and subacts.get("attrs"):
+                    print_str += subacts.dpstr(more)
+                print_str += ")"
             elif field[0] == "OVS_ACTION_ATTR_POP_ETH":
                 print_str += "pop_eth"
             elif field[0] == "OVS_ACTION_ATTR_POP_NSH":
@@ -725,7 +740,21 @@ class ovsactions(nla):
                     actstr = actstr[strspn(actstr, ", ") :]
                     parsed = True
 
-            if parse_starts_block(actstr, "clone(", False):
+            if parse_starts_block(actstr, "dec_ttl(", False):
+                parencount += 1
+                subacts = ovsactions()
+                actstr = actstr[len("dec_ttl("):]
+                parsedLen = subacts.parse(actstr)
+                decttl = ovsactions.DecTtl()
+                decttl["attrs"].append(
+                    ("OVS_DEC_TTL_ATTR_ACTION", subacts)
+                )
+                self["attrs"].append(
+                    ("OVS_ACTION_ATTR_DEC_TTL", decttl)
+                )
+                actstr = actstr[parsedLen:]
+                parsed = True
+            elif parse_starts_block(actstr, "clone(", False):
                 parencount += 1
                 subacts = ovsactions()
                 actstr = actstr[len("clone("):]
@@ -896,6 +925,12 @@ class ovsactions(nla):
         return (totallen - len(actstr))
 
 
+# pyroute2 resolves nla_map types via getattr(self, name).
+# DecTtl needs "actions" to resolve to ovsactions, but
+# ovsactions is not defined when DecTtl class body runs.
+ovsactions.DecTtl.actions = ovsactions
+
+
 class ovskey(nla):
     nla_flags = NLA_F_NESTED
     nla_map = (
-- 
2.53.0