xref: /linux/include/net/dropreason-qdisc.h (revision 91a4855d6c03e770e42f17c798a36a3c46e63de2)

/* SPDX-License-Identifier: GPL-2.0-or-later */

#ifndef _LINUX_DROPREASON_QDISC_H
#define _LINUX_DROPREASON_QDISC_H
#include <net/dropreason.h>

#define DEFINE_QDISC_DROP_REASON(FN, FNe)	\
	FN(UNSPEC)			\
	FN(GENERIC)			\
	FN(OVERLIMIT)			\
	FN(CONGESTED)			\
	FN(MAXFLOWS)			\
	FN(FLOOD_PROTECTION)		\
	FN(BAND_LIMIT)		\
	FN(HORIZON_LIMIT)		\
	FN(FLOW_LIMIT)			\
	FN(L4S_STEP_NON_ECN)		\
	FNe(MAX)

#undef FN
#undef FNe
#define FN(reason)	QDISC_DROP_##reason,
#define FNe(reason)	QDISC_DROP_##reason

/**
 * enum qdisc_drop_reason - reason why a qdisc dropped a packet
 *
 * Qdisc-specific drop reasons for packet drops that occur within the
 * traffic control (TC) queueing discipline layer. These reasons provide
 * detailed diagnostics about why packets were dropped by various qdisc
 * algorithms, enabling fine-grained monitoring and troubleshooting of
 * queue behavior.
 */
enum qdisc_drop_reason {
	/**
	 * @QDISC_DROP_UNSPEC: unspecified/invalid qdisc drop reason.
	 * Value 0 serves as analogous to SKB_NOT_DROPPED_YET for enum skb_drop_reason.
	 * Used for catching zero-initialized drop_reason fields.
	 */
	QDISC_DROP_UNSPEC = 0,
	/**
	 * @__QDISC_DROP_REASON: subsystem base value for qdisc drop reasons
	 */
	__QDISC_DROP_REASON = SKB_DROP_REASON_SUBSYS_QDISC <<
				SKB_DROP_REASON_SUBSYS_SHIFT,
	/**
	 * @QDISC_DROP_GENERIC: generic/default qdisc drop, used when no
	 * more specific reason applies
	 */
	QDISC_DROP_GENERIC,
	/**
	 * @QDISC_DROP_OVERLIMIT: packet dropped because the qdisc queue
	 * length exceeded its configured limit (sch->limit). This typically
	 * indicates the queue is full and cannot accept more packets.
	 */
	QDISC_DROP_OVERLIMIT,
	/**
	 * @QDISC_DROP_CONGESTED: packet dropped due to active congestion
	 * control algorithms (e.g., CoDel, PIE, RED) detecting network
	 * congestion. The qdisc proactively dropped the packet to signal
	 * congestion to the sender and prevent bufferbloat.
	 */
	QDISC_DROP_CONGESTED,
	/**
	 * @QDISC_DROP_MAXFLOWS: packet dropped because the qdisc's flow
	 * tracking table is full and no free slots are available to allocate
	 * for a new flow. This indicates flow table exhaustion in flow-based
	 * qdiscs that maintain per-flow state (e.g., SFQ).
	 */
	QDISC_DROP_MAXFLOWS,
	/**
	 * @QDISC_DROP_FLOOD_PROTECTION: packet dropped by flood protection
	 * mechanism detecting unresponsive flows (potential DoS/flood).
	 * Used by qdiscs implementing probabilistic drop algorithms like
	 * BLUE (e.g., CAKE's Cobalt AQM).
	 */
	QDISC_DROP_FLOOD_PROTECTION,
	/**
	 * @QDISC_DROP_BAND_LIMIT: packet dropped because the priority band's
	 * limit was reached. Used by qdiscs with priority bands that have
	 * per-band packet limits (e.g., FQ).
	 */
	QDISC_DROP_BAND_LIMIT,
	/**
	 * @QDISC_DROP_HORIZON_LIMIT: packet dropped because its timestamp
	 * is too far in the future (beyond the configured horizon).
	 * Used by qdiscs with time-based scheduling (e.g., FQ).
	 */
	QDISC_DROP_HORIZON_LIMIT,
	/**
	 * @QDISC_DROP_FLOW_LIMIT: packet dropped because an individual flow
	 * exceeded its per-flow packet/depth limit. Used by FQ and SFQ qdiscs
	 * to enforce per-flow fairness and prevent a single flow from
	 * monopolizing queue resources.
	 */
	QDISC_DROP_FLOW_LIMIT,
	/**
	 * @QDISC_DROP_L4S_STEP_NON_ECN: DualPI2 qdisc dropped a non-ECN-capable
	 * packet because the L4S queue delay exceeded the step threshold.
	 * Since the packet cannot be ECN-marked, it must be dropped to signal
	 * congestion. See RFC 9332 for the DualQ Coupled AQM step mechanism.
	 */
	QDISC_DROP_L4S_STEP_NON_ECN,
	/**
	 * @QDISC_DROP_MAX: the maximum of qdisc drop reasons, which
	 * shouldn't be used as a real 'reason' - only for tracing code gen
	 */
	QDISC_DROP_MAX,
};

#undef FN
#undef FNe

#endif