selftests: openvswitch: Skip drop testing on older kernels

Kernels that don't have support for openvswitch drop reasons also
won't have the drop counter reasons, so we should skip the test
completely.  It previously wasn't possible to build a test case
for this without polluting the datapath, so we introduce a mechanism
to clear all the flows from a datapath allowing us to test for
explicit drop actions, and then clear the flows to build the
original test case.

Fixes: 4242029164 ("selftests: openvswitch: add explicit drop testcase")
Signed-off-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/openvswitch/openvswitch.sh

@@ -144,6 +144,12 @@ ovs_add_flow () {
 	return 0
 }
 
+ovs_del_flows () {
+	info "Deleting all flows from DP: sbx:$1 br:$2"
+	ovs_sbx "$1" python3 $ovs_base/ovs-dpctl.py del-flows "$2"
+	return 0
+}
+
 ovs_drop_record_and_run () {
 	local sbx=$1
 	shift
@@ -200,6 +206,17 @@ test_drop_reason() {
 	ip netns exec server ip addr add 172.31.110.20/24 dev s1
 	ip netns exec server ip link set s1 up
 
+	# Check if drop reasons can be sent
+	ovs_add_flow "test_drop_reason" dropreason \
+		'in_port(1),eth(),eth_type(0x0806),arp()' 'drop(10)' 2>/dev/null
+	if [ $? == 1 ]; then
+		info "no support for drop reasons - skipping"
+		ovs_exit_sig
+		return $ksft_skip
+	fi
+
+	ovs_del_flows "test_drop_reason" dropreason
+
 	# Allow ARP
 	ovs_add_flow "test_drop_reason" dropreason \
 		'in_port(1),eth(),eth_type(0x0806),arp()' '2' || return 1

tools/testing/selftests/net/openvswitch/ovs-dpctl.py

@@ -1906,6 +1906,32 @@ class OvsFlow(GenericNetlinkSocket):
             raise ne
         return reply
 
+    def del_flows(self, dpifindex):
+        """
+        Send a del message to the kernel that will drop all flows.
+
+        dpifindex should be a valid datapath obtained by calling
+        into the OvsDatapath lookup
+        """
+
+        flowmsg = OvsFlow.ovs_flow_msg()
+        flowmsg["cmd"] = OVS_FLOW_CMD_DEL
+        flowmsg["version"] = OVS_DATAPATH_VERSION
+        flowmsg["reserved"] = 0
+        flowmsg["dpifindex"] = dpifindex
+
+        try:
+            reply = self.nlm_request(
+                flowmsg,
+                msg_type=self.prid,
+                msg_flags=NLM_F_REQUEST | NLM_F_ACK,
+            )
+            reply = reply[0]
+        except NetlinkError as ne:
+            print(flowmsg)
+            raise ne
+        return reply
+
     def dump(self, dpifindex, flowspec=None):
         """
         Returns a list of messages containing flows.
@@ -2068,6 +2094,9 @@ def main(argv):
     addflcmd.add_argument("flow", help="Flow specification")
     addflcmd.add_argument("acts", help="Flow actions")
 
+    delfscmd = subparsers.add_parser("del-flows")
+    delfscmd.add_argument("flsbr", help="Datapath name")
+
     args = parser.parse_args()
 
     if args.verbose > 0:
@@ -2151,6 +2180,11 @@ def main(argv):
         flow = OvsFlow.ovs_flow_msg()
         flow.parse(args.flow, args.acts, rep["dpifindex"])
         ovsflow.add_flow(rep["dpifindex"], flow)
+    elif hasattr(args, "flsbr"):
+        rep = ovsdp.info(args.flsbr, 0)
+        if rep is None:
+            print("DP '%s' not found." % args.flsbr)
+        ovsflow.del_flows(rep["dpifindex"])
 
     return 0