devlink: Add early_drop trap

Add the packet trap that can report packets that were ECN marked due to RED
AQM.

Signed-off-by: Amit Cohen <[e-mail]>
Signed-off-by: Petr Machata <[e-mail]>
Reviewed-by: Jiri Pirko <[e-mail]>
Signed-off-by: Ido Schimmel <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/networking/devlink/devlink-trap.rst

···
      - ``control``
      - Traps packets logged during processing of flow action trap (e.g., via
        tc's trap action)
+   * - ``early_drop``
+     - ``drop``
+     - Traps packets dropped due to the RED (Random Early Detection) algorithm
+       (i.e., early drops)
 
 Driver-specific Packet Traps
 ============================

include/net/devlink.h

···
 	DEVLINK_TRAP_GENERIC_ID_PTP_GENERAL,
 	DEVLINK_TRAP_GENERIC_ID_FLOW_ACTION_SAMPLE,
 	DEVLINK_TRAP_GENERIC_ID_FLOW_ACTION_TRAP,
+	DEVLINK_TRAP_GENERIC_ID_EARLY_DROP,
 
 	/* Add new generic trap IDs above */
 	__DEVLINK_TRAP_GENERIC_ID_MAX,
···
 	"flow_action_sample"
 #define DEVLINK_TRAP_GENERIC_NAME_FLOW_ACTION_TRAP \
 	"flow_action_trap"
+#define DEVLINK_TRAP_GENERIC_NAME_EARLY_DROP \
+	"early_drop"
 
 #define DEVLINK_TRAP_GROUP_GENERIC_NAME_L2_DROPS \
 	"l2_drops"

net/core/devlink.c

···
 	DEVLINK_TRAP(PTP_GENERAL, CONTROL),
 	DEVLINK_TRAP(FLOW_ACTION_SAMPLE, CONTROL),
 	DEVLINK_TRAP(FLOW_ACTION_TRAP, CONTROL),
+	DEVLINK_TRAP(EARLY_DROP, DROP),
 };
 
 #define DEVLINK_TRAP_GROUP(_id)						      \