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

For better error reporting to user space, add extack messages when
skbedit 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 skbedit queue_mapping 1234
 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.    31.802414: netlink_extack: msg=act_skbedit: Offload not supported when "queue_mapping" option is used
       tc-185     [002] .....    31.802418: netlink_extack: msg=cls_matchall: Failed to setup flow action

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

 # cat /sys/kernel/tracing/trace_pipe
       tc-187     [002] b..1.    45.985145: netlink_extack: msg=act_skbedit: Offload not supported when "inheritdsfield" option is used
       tc-187     [002] .....    45.985160: 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_skbedit.h

@@ -94,4 +94,16 @@ static inline u32 tcf_skbedit_priority(const struct tc_action *a)
 	return priority;
 }
 
+/* Return true iff action is queue_mapping */
+static inline bool is_tcf_skbedit_queue_mapping(const struct tc_action *a)
+{
+	return is_tcf_skbedit_with_flag(a, SKBEDIT_F_QUEUE_MAPPING);
+}
+
+/* Return true iff action is inheritdsfield */
+static inline bool is_tcf_skbedit_inheritdsfield(const struct tc_action *a)
+{
+	return is_tcf_skbedit_with_flag(a, SKBEDIT_F_INHERITDSFIELD);
+}
+
 #endif /* __NET_TC_SKBEDIT_H */

net/sched/act_skbedit.c

@@ -343,7 +343,14 @@ static int tcf_skbedit_offload_act_setup(struct tc_action *act, void *entry_data
 		} else if (is_tcf_skbedit_priority(act)) {
 			entry->id = FLOW_ACTION_PRIORITY;
 			entry->priority = tcf_skbedit_priority(act);
+		} else if (is_tcf_skbedit_queue_mapping(act)) {
+			NL_SET_ERR_MSG_MOD(extack, "Offload not supported when \"queue_mapping\" option is used");
+			return -EOPNOTSUPP;
+		} else if (is_tcf_skbedit_inheritdsfield(act)) {
+			NL_SET_ERR_MSG_MOD(extack, "Offload not supported when \"inheritdsfield\" option is used");
+			return -EOPNOTSUPP;
 		} else {
+			NL_SET_ERR_MSG_MOD(extack, "Unsupported skbedit option offload");
 			return -EOPNOTSUPP;
 		}
 		*index_inc = 1;