/*
   *  net/dccp/ackvec.c
   *
   *  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@ghostprotocols.net>
   *
   *      This program is free software; you can redistribute it and/or modify it
   *      under the terms of the GNU General Public License as published by the
   *      Free Software Foundation; version 2 of the License;
   */
  #include "dccp.h"
  #include <linux/kernel.h>
  #include <linux/slab.h>
  #include <linux/export.h>
  
  static struct kmem_cache *dccp_ackvec_slab;
  static struct kmem_cache *dccp_ackvec_record_slab;
  
  struct dccp_ackvec *dccp_ackvec_alloc(const gfp_t priority)
  {
  	struct dccp_ackvec *av = kmem_cache_zalloc(dccp_ackvec_slab, priority);
  
  	if (av != NULL) {
  		av->av_buf_head	= av->av_buf_tail = DCCPAV_MAX_ACKVEC_LEN - 1;
  		INIT_LIST_HEAD(&av->av_records);
  	}
  	return av;
  }
  
  static void dccp_ackvec_purge_records(struct dccp_ackvec *av)
  {
  	struct dccp_ackvec_record *cur, *next;
  
  	list_for_each_entry_safe(cur, next, &av->av_records, avr_node)
  		kmem_cache_free(dccp_ackvec_record_slab, cur);
  	INIT_LIST_HEAD(&av->av_records);
  }
  
  void dccp_ackvec_free(struct dccp_ackvec *av)
  {
  	if (likely(av != NULL)) {
  		dccp_ackvec_purge_records(av);
  		kmem_cache_free(dccp_ackvec_slab, av);
  	}
  }
  
  /**
   * dccp_ackvec_update_records  -  Record information about sent Ack Vectors
   * @av:		Ack Vector records to update
   * @seqno:	Sequence number of the packet carrying the Ack Vector just sent
   * @nonce_sum:	The sum of all buffer nonces contained in the Ack Vector
   */
  int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seqno, u8 nonce_sum)
  {
  	struct dccp_ackvec_record *avr;
  
  	avr = kmem_cache_alloc(dccp_ackvec_record_slab, GFP_ATOMIC);
  	if (avr == NULL)
  		return -ENOBUFS;
  
  	avr->avr_ack_seqno  = seqno;
  	avr->avr_ack_ptr    = av->av_buf_head;
  	avr->avr_ack_ackno  = av->av_buf_ackno;
  	avr->avr_ack_nonce  = nonce_sum;
  	avr->avr_ack_runlen = dccp_ackvec_runlen(av->av_buf + av->av_buf_head);
  	/*
  	 * When the buffer overflows, we keep no more than one record. This is
  	 * the simplest way of disambiguating sender-Acks dating from before the
  	 * overflow from sender-Acks which refer to after the overflow; a simple
  	 * solution is preferable here since we are handling an exception.
  	 */
  	if (av->av_overflow)
  		dccp_ackvec_purge_records(av);
  	/*
  	 * Since GSS is incremented for each packet, the list is automatically
  	 * arranged in descending order of @ack_seqno.
  	 */
  	list_add(&avr->avr_node, &av->av_records);
  
  	dccp_pr_debug("Added Vector, ack_seqno=%llu, ack_ackno=%llu (rl=%u)
  ",
  		      (unsigned long long)avr->avr_ack_seqno,
  		      (unsigned long long)avr->avr_ack_ackno,
  		      avr->avr_ack_runlen);
  	return 0;
  }
  
  static struct dccp_ackvec_record *dccp_ackvec_lookup(struct list_head *av_list,
  						     const u64 ackno)
  {
  	struct dccp_ackvec_record *avr;
  	/*
  	 * Exploit that records are inserted in descending order of sequence
  	 * number, start with the oldest record first. If @ackno is `before'
  	 * the earliest ack_ackno, the packet is too old to be considered.
  	 */
  	list_for_each_entry_reverse(avr, av_list, avr_node) {
  		if (avr->avr_ack_seqno == ackno)
  			return avr;
  		if (before48(ackno, avr->avr_ack_seqno))
  			break;
  	}
  	return NULL;
  }
  
  /*
   * Buffer index and length computation using modulo-buffersize arithmetic.
   * Note that, as pointers move from right to left, head is `before' tail.
   */
  static inline u16 __ackvec_idx_add(const u16 a, const u16 b)
  {
  	return (a + b) % DCCPAV_MAX_ACKVEC_LEN;
  }
  
  static inline u16 __ackvec_idx_sub(const u16 a, const u16 b)
  {
  	return __ackvec_idx_add(a, DCCPAV_MAX_ACKVEC_LEN - b);
  }
  
  u16 dccp_ackvec_buflen(const struct dccp_ackvec *av)
  {
  	if (unlikely(av->av_overflow))
  		return DCCPAV_MAX_ACKVEC_LEN;
  	return __ackvec_idx_sub(av->av_buf_tail, av->av_buf_head);
  }
  
  /**
   * dccp_ackvec_update_old  -  Update previous state as per RFC 4340, 11.4.1
   * @av:		non-empty buffer to update
   * @distance:   negative or zero distance of @seqno from buf_ackno downward
   * @seqno:	the (old) sequence number whose record is to be updated
   * @state:	state in which packet carrying @seqno was received
   */
  static void dccp_ackvec_update_old(struct dccp_ackvec *av, s64 distance,
  				   u64 seqno, enum dccp_ackvec_states state)
  {
  	u16 ptr = av->av_buf_head;
  
  	BUG_ON(distance > 0);
  	if (unlikely(dccp_ackvec_is_empty(av)))
  		return;
  
  	do {
  		u8 runlen = dccp_ackvec_runlen(av->av_buf + ptr);
  
  		if (distance + runlen >= 0) {
  			/*
  			 * Only update the state if packet has not been received
  			 * yet. This is OK as per the second table in RFC 4340,
  			 * 11.4.1; i.e. here we are using the following table:
  			 *                     RECEIVED
  			 *                      0   1   3
  			 *              S     +---+---+---+
  			 *              T   0 | 0 | 0 | 0 |
  			 *              O     +---+---+---+
  			 *              R   1 | 1 | 1 | 1 |
  			 *              E     +---+---+---+
  			 *              D   3 | 0 | 1 | 3 |
  			 *                    +---+---+---+
  			 * The "Not Received" state was set by reserve_seats().
  			 */
  			if (av->av_buf[ptr] == DCCPAV_NOT_RECEIVED)
  				av->av_buf[ptr] = state;
  			else
  				dccp_pr_debug("Not changing %llu state to %u
  ",
  					      (unsigned long long)seqno, state);
  			break;
  		}
  
  		distance += runlen + 1;
  		ptr	  = __ackvec_idx_add(ptr, 1);
  
  	} while (ptr != av->av_buf_tail);
  }
  
  /* Mark @num entries after buf_head as "Not yet received". */
  static void dccp_ackvec_reserve_seats(struct dccp_ackvec *av, u16 num)
  {
  	u16 start = __ackvec_idx_add(av->av_buf_head, 1),
  	    len	  = DCCPAV_MAX_ACKVEC_LEN - start;
  
  	/* check for buffer wrap-around */
  	if (num > len) {
  		memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, len);
  		start = 0;
  		num  -= len;
  	}
  	if (num)
  		memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, num);
  }
  
  /**
   * dccp_ackvec_add_new  -  Record one or more new entries in Ack Vector buffer
   * @av:		 container of buffer to update (can be empty or non-empty)
   * @num_packets: number of packets to register (must be >= 1)
   * @seqno:	 sequence number of the first packet in @num_packets
   * @state:	 state in which packet carrying @seqno was received
   */
  static void dccp_ackvec_add_new(struct dccp_ackvec *av, u32 num_packets,
  				u64 seqno, enum dccp_ackvec_states state)
  {
  	u32 num_cells = num_packets;
  
  	if (num_packets > DCCPAV_BURST_THRESH) {
  		u32 lost_packets = num_packets - 1;
  
  		DCCP_WARN("Warning: large burst loss (%u)
  ", lost_packets);
  		/*
  		 * We received 1 packet and have a loss of size "num_packets-1"
  		 * which we squeeze into num_cells-1 rather than reserving an
  		 * entire byte for each lost packet.
  		 * The reason is that the vector grows in O(burst_length); when
  		 * it grows too large there will no room left for the payload.
  		 * This is a trade-off: if a few packets out of the burst show
  		 * up later, their state will not be changed; it is simply too
  		 * costly to reshuffle/reallocate/copy the buffer each time.
  		 * Should such problems persist, we will need to switch to a
  		 * different underlying data structure.
  		 */
  		for (num_packets = num_cells = 1; lost_packets; ++num_cells) {
  			u8 len = min(lost_packets, (u32)DCCPAV_MAX_RUNLEN);
  
  			av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, 1);
  			av->av_buf[av->av_buf_head] = DCCPAV_NOT_RECEIVED | len;
  
  			lost_packets -= len;
  		}
  	}
  
  	if (num_cells + dccp_ackvec_buflen(av) >= DCCPAV_MAX_ACKVEC_LEN) {
  		DCCP_CRIT("Ack Vector buffer overflow: dropping old entries
  ");
  		av->av_overflow = true;
  	}
  
  	av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, num_packets);
  	if (av->av_overflow)
  		av->av_buf_tail = av->av_buf_head;
  
  	av->av_buf[av->av_buf_head] = state;
  	av->av_buf_ackno	    = seqno;
  
  	if (num_packets > 1)
  		dccp_ackvec_reserve_seats(av, num_packets - 1);
  }
  
  /**
   * dccp_ackvec_input  -  Register incoming packet in the buffer
   */
  void dccp_ackvec_input(struct dccp_ackvec *av, struct sk_buff *skb)
  {
  	u64 seqno = DCCP_SKB_CB(skb)->dccpd_seq;
  	enum dccp_ackvec_states state = DCCPAV_RECEIVED;
  
  	if (dccp_ackvec_is_empty(av)) {
  		dccp_ackvec_add_new(av, 1, seqno, state);
  		av->av_tail_ackno = seqno;
  
  	} else {
  		s64 num_packets = dccp_delta_seqno(av->av_buf_ackno, seqno);
  		u8 *current_head = av->av_buf + av->av_buf_head;
  
  		if (num_packets == 1 &&
  		    dccp_ackvec_state(current_head) == state &&
  		    dccp_ackvec_runlen(current_head) < DCCPAV_MAX_RUNLEN) {
  
  			*current_head   += 1;
  			av->av_buf_ackno = seqno;
  
  		} else if (num_packets > 0) {
  			dccp_ackvec_add_new(av, num_packets, seqno, state);
  		} else {
  			dccp_ackvec_update_old(av, num_packets, seqno, state);
  		}
  	}
  }
  
  /**
   * dccp_ackvec_clear_state  -  Perform house-keeping / garbage-collection
   * This routine is called when the peer acknowledges the receipt of Ack Vectors
   * up to and including @ackno. While based on on section A.3 of RFC 4340, here
   * are additional precautions to prevent corrupted buffer state. In particular,
   * we use tail_ackno to identify outdated records; it always marks the earliest
   * packet of group (2) in 11.4.2.
   */
  void dccp_ackvec_clear_state(struct dccp_ackvec *av, const u64 ackno)
  {
  	struct dccp_ackvec_record *avr, *next;
  	u8 runlen_now, eff_runlen;
  	s64 delta;
  
  	avr = dccp_ackvec_lookup(&av->av_records, ackno);
  	if (avr == NULL)
  		return;
  	/*
  	 * Deal with outdated acknowledgments: this arises when e.g. there are
  	 * several old records and the acks from the peer come in slowly. In
  	 * that case we may still have records that pre-date tail_ackno.
  	 */
  	delta = dccp_delta_seqno(av->av_tail_ackno, avr->avr_ack_ackno);
  	if (delta < 0)
  		goto free_records;
  	/*
  	 * Deal with overlapping Ack Vectors: don't subtract more than the
  	 * number of packets between tail_ackno and ack_ackno.
  	 */
  	eff_runlen = delta < avr->avr_ack_runlen ? delta : avr->avr_ack_runlen;
  
  	runlen_now = dccp_ackvec_runlen(av->av_buf + avr->avr_ack_ptr);
  	/*
  	 * The run length of Ack Vector cells does not decrease over time. If
  	 * the run length is the same as at the time the Ack Vector was sent, we
  	 * free the ack_ptr cell. That cell can however not be freed if the run
  	 * length has increased: in this case we need to move the tail pointer
  	 * backwards (towards higher indices), to its next-oldest neighbour.
  	 */
  	if (runlen_now > eff_runlen) {
  
  		av->av_buf[avr->avr_ack_ptr] -= eff_runlen + 1;
  		av->av_buf_tail = __ackvec_idx_add(avr->avr_ack_ptr, 1);
  
  		/* This move may not have cleared the overflow flag. */
  		if (av->av_overflow)
  			av->av_overflow = (av->av_buf_head == av->av_buf_tail);
  	} else {
  		av->av_buf_tail	= avr->avr_ack_ptr;
  		/*
  		 * We have made sure that avr points to a valid cell within the
  		 * buffer. This cell is either older than head, or equals head
  		 * (empty buffer): in both cases we no longer have any overflow.
  		 */
  		av->av_overflow	= 0;
  	}
  
  	/*
  	 * The peer has acknowledged up to and including ack_ackno. Hence the
  	 * first packet in group (2) of 11.4.2 is the successor of ack_ackno.
  	 */
  	av->av_tail_ackno = ADD48(avr->avr_ack_ackno, 1);
  
  free_records:
  	list_for_each_entry_safe_from(avr, next, &av->av_records, avr_node) {
  		list_del(&avr->avr_node);
  		kmem_cache_free(dccp_ackvec_record_slab, avr);
  	}
  }
  
  /*
   *	Routines to keep track of Ack Vectors received in an skb
   */
  int dccp_ackvec_parsed_add(struct list_head *head, u8 *vec, u8 len, u8 nonce)
  {
  	struct dccp_ackvec_parsed *new = kmalloc(sizeof(*new), GFP_ATOMIC);
  
  	if (new == NULL)
  		return -ENOBUFS;
  	new->vec   = vec;
  	new->len   = len;
  	new->nonce = nonce;
  
  	list_add_tail(&new->node, head);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_add);
  
  void dccp_ackvec_parsed_cleanup(struct list_head *parsed_chunks)
  {
  	struct dccp_ackvec_parsed *cur, *next;
  
  	list_for_each_entry_safe(cur, next, parsed_chunks, node)
  		kfree(cur);
  	INIT_LIST_HEAD(parsed_chunks);
  }
  EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_cleanup);
  
  int __init dccp_ackvec_init(void)
  {
  	dccp_ackvec_slab = kmem_cache_create("dccp_ackvec",
  					     sizeof(struct dccp_ackvec), 0,
  					     SLAB_HWCACHE_ALIGN, NULL);
  	if (dccp_ackvec_slab == NULL)
  		goto out_err;
  
  	dccp_ackvec_record_slab = kmem_cache_create("dccp_ackvec_record",
  					     sizeof(struct dccp_ackvec_record),
  					     0, SLAB_HWCACHE_ALIGN, NULL);
  	if (dccp_ackvec_record_slab == NULL)
  		goto out_destroy_slab;
  
  	return 0;
  
  out_destroy_slab:
  	kmem_cache_destroy(dccp_ackvec_slab);
  	dccp_ackvec_slab = NULL;
  out_err:
  	DCCP_CRIT("Unable to create Ack Vector slab cache");
  	return -ENOBUFS;
  }
  
  void dccp_ackvec_exit(void)
  {
  	if (dccp_ackvec_slab != NULL) {
  		kmem_cache_destroy(dccp_ackvec_slab);
  		dccp_ackvec_slab = NULL;
  	}
  	if (dccp_ackvec_record_slab != NULL) {
  		kmem_cache_destroy(dccp_ackvec_record_slab);
  		dccp_ackvec_record_slab = NULL;
  	}
  }