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

For better error reporting to user space, add extack messages when gact
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 continue
 Error: cls_matchall: Failed to setup flow action.
 We have an error talking to the kernel

 # cat /sys/kernel/tracing/trace_pipe
       tc-181     [002] b..1.   105.493450: netlink_extack: msg=act_gact: Offload of "continue" action is not supported
       tc-181     [002] .....   105.493466: netlink_extack: msg=cls_matchall: Failed to setup flow action

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

 # cat /sys/kernel/tracing/trace_pipe
       tc-183     [002] b..1.   124.126477: netlink_extack: msg=act_gact: Offload of "reclassify" action is not supported
       tc-183     [002] .....   124.126489: netlink_extack: msg=cls_matchall: Failed to setup flow action

 # tc filter add dev dummy0 ingress pref 1 proto all matchall skip_sw action pipe action drop
 Error: cls_matchall: Failed to setup flow action.
 We have an error talking to the kernel

 # cat /sys/kernel/tracing/trace_pipe
       tc-185     [002] b..1.   137.097791: netlink_extack: msg=act_gact: Offload of "pipe" action is not supported
       tc-185     [002] .....   137.097804: 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>

include/net/tc_act/tc_gact.h

@@ -59,4 +59,19 @@ static inline u32 tcf_gact_goto_chain_index(const struct tc_action *a)
 	return READ_ONCE(a->tcfa_action) & TC_ACT_EXT_VAL_MASK;
 }
 
+static inline bool is_tcf_gact_continue(const struct tc_action *a)
+{
+	return __is_tcf_gact_act(a, TC_ACT_UNSPEC, false);
+}
+
+static inline bool is_tcf_gact_reclassify(const struct tc_action *a)
+{
+	return __is_tcf_gact_act(a, TC_ACT_RECLASSIFY, false);
+}
+
+static inline bool is_tcf_gact_pipe(const struct tc_action *a)
+{
+	return __is_tcf_gact_act(a, TC_ACT_PIPE, false);
+}
+
 #endif /* __NET_TC_GACT_H */

net/sched/act_gact.c

@@ -268,7 +268,17 @@ static int tcf_gact_offload_act_setup(struct tc_action *act, void *entry_data,
 		} else if (is_tcf_gact_goto_chain(act)) {
 			entry->id = FLOW_ACTION_GOTO;
 			entry->chain_index = tcf_gact_goto_chain_index(act);
+		} else if (is_tcf_gact_continue(act)) {
+			NL_SET_ERR_MSG_MOD(extack, "Offload of \"continue\" action is not supported");
+			return -EOPNOTSUPP;
+		} else if (is_tcf_gact_reclassify(act)) {
+			NL_SET_ERR_MSG_MOD(extack, "Offload of \"reclassify\" action is not supported");
+			return -EOPNOTSUPP;
+		} else if (is_tcf_gact_pipe(act)) {
+			NL_SET_ERR_MSG_MOD(extack, "Offload of \"pipe\" action is not supported");
+			return -EOPNOTSUPP;
 		} else {
+			NL_SET_ERR_MSG_MOD(extack, "Unsupported generic action offload");
 			return -EOPNOTSUPP;
 		}
 		*index_inc = 1;