net/sched: act_police: Add extack messages for offload failure

For better error reporting to user space, add extack messages when
police action offload fails.

Example:

 # echo 1 > /sys/kernel/tracing/events/netlink/netlink_extack/enable

 # tc filter add dev dummy0 ingress pref 1 proto all matchall skip_sw action police rate 100Mbit burst 10000
 Error: cls_matchall: Failed to setup flow action.
 We have an error talking to the kernel

 # cat /sys/kernel/tracing/trace_pipe
       tc-182     [000] b..1.    21.592969: netlink_extack: msg=act_police: Offload not supported when conform/exceed action is "reclassify"
       tc-182     [000] .....    21.592982: netlink_extack: msg=cls_matchall: Failed to setup flow action

 # tc filter add dev dummy0 ingress pref 1 proto all matchall skip_sw action police rate 100Mbit burst 10000 conform-exceed drop/continue
 Error: cls_matchall: Failed to setup flow action.
 We have an error talking to the kernel

 # cat /sys/kernel/tracing/trace_pipe
       tc-184     [000] b..1.    38.882579: netlink_extack: msg=act_police: Offload not supported when conform/exceed action is "continue"
       tc-184     [000] .....    38.882593: netlink_extack: msg=cls_matchall: Failed to setup flow action
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_police.c

@@ -419,7 +419,8 @@ static int tcf_police_search(struct net *net, struct tc_action **a, u32 index)
 	return tcf_idr_search(tn, a, index);
 }
 
-static int tcf_police_act_to_flow_act(int tc_act, u32 *extval)
+static int tcf_police_act_to_flow_act(int tc_act, u32 *extval,
+				      struct netlink_ext_ack *extack)
 {
 	int act_id = -EOPNOTSUPP;
 
@@ -430,12 +431,20 @@ static int tcf_police_act_to_flow_act(int tc_act, u32 *extval)
 			act_id = FLOW_ACTION_DROP;
 		else if (tc_act == TC_ACT_PIPE)
 			act_id = FLOW_ACTION_PIPE;
+		else if (tc_act == TC_ACT_RECLASSIFY)
+			NL_SET_ERR_MSG_MOD(extack, "Offload not supported when conform/exceed action is \"reclassify\"");
+		else
+			NL_SET_ERR_MSG_MOD(extack, "Unsupported conform/exceed action offload");
 	} else if (TC_ACT_EXT_CMP(tc_act, TC_ACT_GOTO_CHAIN)) {
 		act_id = FLOW_ACTION_GOTO;
 		*extval = tc_act & TC_ACT_EXT_VAL_MASK;
 	} else if (TC_ACT_EXT_CMP(tc_act, TC_ACT_JUMP)) {
 		act_id = FLOW_ACTION_JUMP;
 		*extval = tc_act & TC_ACT_EXT_VAL_MASK;
+	} else if (tc_act == TC_ACT_UNSPEC) {
+		NL_SET_ERR_MSG_MOD(extack, "Offload not supported when conform/exceed action is \"continue\"");
+	} else {
+		NL_SET_ERR_MSG_MOD(extack, "Unsupported conform/exceed action offload");
 	}
 
 	return act_id;
@@ -467,14 +476,16 @@ static int tcf_police_offload_act_setup(struct tc_action *act, void *entry_data,
 		entry->police.mtu = tcf_police_tcfp_mtu(act);
 
 		act_id = tcf_police_act_to_flow_act(police->tcf_action,
-						    &entry->police.exceed.extval);
+						    &entry->police.exceed.extval,
+						    extack);
 		if (act_id < 0)
 			return act_id;
 
 		entry->police.exceed.act_id = act_id;
 
 		act_id = tcf_police_act_to_flow_act(p->tcfp_result,
-						    &entry->police.notexceed.extval);
+						    &entry->police.notexceed.extval,
+						    extack);
 		if (act_id < 0)
 			return act_id;