/* SPDX-License-Identifier: GPL-2.0-only */

  #ifndef _ACKVEC_H
  #define _ACKVEC_H
  /*
   *  net/dccp/ackvec.h
   *

   *  An implementation of Ack Vectors for the DCCP protocol
   *  Copyright (c) 2007 University of Aberdeen, Scotland, UK

   *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@mandriva.com>

   */

  #include <linux/dccp.h>

  #include <linux/compiler.h>

  #include <linux/list.h>

  #include <linux/types.h>

  /*
   * Ack Vector buffer space is static, in multiples of %DCCP_SINGLE_OPT_MAXLEN,
   * the maximum size of a single Ack Vector. Setting %DCCPAV_NUM_ACKVECS to 1
   * will be sufficient for most cases of low Ack Ratios, using a value of 2 gives
   * more headroom if Ack Ratio is higher or when the sender acknowledges slowly.

   * The maximum value is bounded by the u16 types for indices and functions.

   */
  #define DCCPAV_NUM_ACKVECS	2
  #define DCCPAV_MAX_ACKVEC_LEN	(DCCP_SINGLE_OPT_MAXLEN * DCCPAV_NUM_ACKVECS)

  /* Estimated minimum average Ack Vector length - used for updating MPS */
  #define DCCPAV_MIN_OPTLEN	16

  /* Threshold for coping with large bursts of losses */
  #define DCCPAV_BURST_THRESH	(DCCPAV_MAX_ACKVEC_LEN / 8)

  enum dccp_ackvec_states {
  	DCCPAV_RECEIVED =	0x00,
  	DCCPAV_ECN_MARKED =	0x40,
  	DCCPAV_RESERVED =	0x80,
  	DCCPAV_NOT_RECEIVED =	0xC0
  };
  #define DCCPAV_MAX_RUNLEN	0x3F

  static inline u8 dccp_ackvec_runlen(const u8 *cell)
  {
  	return *cell & DCCPAV_MAX_RUNLEN;
  }

  static inline u8 dccp_ackvec_state(const u8 *cell)
  {
  	return *cell & ~DCCPAV_MAX_RUNLEN;
  }

  /**
   * struct dccp_ackvec - Ack Vector main data structure

   *

   * This implements a fixed-size circular buffer within an array and is largely
   * based on Appendix A of RFC 4340.

   *

   * @av_buf:	   circular buffer storage area
   * @av_buf_head:   head index; begin of live portion in @av_buf
   * @av_buf_tail:   tail index; first index _after_ the live portion in @av_buf
   * @av_buf_ackno:  highest seqno of acknowledgeable packet recorded in @av_buf

   * @av_tail_ackno: lowest  seqno of acknowledgeable packet recorded in @av_buf

   * @av_buf_nonce:  ECN nonce sums, each covering subsequent segments of up to
   *		   %DCCP_SINGLE_OPT_MAXLEN cells in the live portion of @av_buf

   * @av_overflow:   if 1 then buf_head == buf_tail indicates buffer wraparound

   * @av_records:	   list of %dccp_ackvec_record (Ack Vectors sent previously)

   */
  struct dccp_ackvec {

  	u8			av_buf[DCCPAV_MAX_ACKVEC_LEN];

  	u16			av_buf_head;

  	u16			av_buf_tail;
  	u64			av_buf_ackno:48;

  	u64			av_tail_ackno:48;

  	bool			av_buf_nonce[DCCPAV_NUM_ACKVECS];

  	u8			av_overflow:1;

  	struct list_head	av_records;

  };

  /**
   * struct dccp_ackvec_record - Records information about sent Ack Vectors

   *

   * These list entries define the additional information which the HC-Receiver
   * keeps about recently-sent Ack Vectors; again refer to RFC 4340, Appendix A.

   *

   * @avr_node:	    the list node in @av_records
   * @avr_ack_seqno:  sequence number of the packet the Ack Vector was sent on
   * @avr_ack_ackno:  the Ack number that this record/Ack Vector refers to
   * @avr_ack_ptr:    pointer into @av_buf where this record starts
   * @avr_ack_runlen: run length of @avr_ack_ptr at the time of sending
   * @avr_ack_nonce:  the sum of @av_buf_nonce's at the time this record was sent

   *

   * The list as a whole is sorted in descending order by @avr_ack_seqno.

   */
  struct dccp_ackvec_record {

  	struct list_head avr_node;

  	u64		 avr_ack_seqno:48;
  	u64		 avr_ack_ackno:48;

  	u16		 avr_ack_ptr;

  	u8		 avr_ack_runlen;
  	u8		 avr_ack_nonce:1;

  };

  int dccp_ackvec_init(void);
  void dccp_ackvec_exit(void);

  struct dccp_ackvec *dccp_ackvec_alloc(const gfp_t priority);
  void dccp_ackvec_free(struct dccp_ackvec *av);

  void dccp_ackvec_input(struct dccp_ackvec *av, struct sk_buff *skb);
  int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seq, u8 sum);
  void dccp_ackvec_clear_state(struct dccp_ackvec *av, const u64 ackno);
  u16 dccp_ackvec_buflen(const struct dccp_ackvec *av);

  static inline bool dccp_ackvec_is_empty(const struct dccp_ackvec *av)

  {

  	return av->av_overflow == 0 && av->av_buf_head == av->av_buf_tail;

  }

  
  /**
   * struct dccp_ackvec_parsed  -  Record offsets of Ack Vectors in skb
   * @vec:	start of vector (offset into skb)
   * @len:	length of @vec
   * @nonce:	whether @vec had an ECN nonce of 0 or 1
   * @node:	FIFO - arranged in descending order of ack_ackno

   *

   * This structure is used by CCIDs to access Ack Vectors in a received skb.
   */
  struct dccp_ackvec_parsed {
  	u8		 *vec,
  			 len,
  			 nonce:1;
  	struct list_head node;
  };

  int dccp_ackvec_parsed_add(struct list_head *head, u8 *vec, u8 len, u8 nonce);
  void dccp_ackvec_parsed_cleanup(struct list_head *parsed_chunks);

  #endif /* _ACKVEC_H */