dccp ccid-2: Algorithm to update buffer state

[deliverable/linux.git] / net / dccp / ackvec.c

/*
 *  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 "ackvec.h"
#include "dccp.h"

#include <linux/init.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/slab.h>

#include <net/sock.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)\n",
                      (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);
}

/*
 * If several packets are missing, the HC-Receiver may prefer to enter multiple
 * bytes with run length 0, rather than a single byte with a larger run length;
 * this simplifies table updates if one of the missing packets arrives.
 */
static inline int dccp_ackvec_set_buf_head_state(struct dccp_ackvec *av,
                                                 const unsigned int packets,
                                                 const unsigned char state)
{
        unsigned int gap;
        long new_head;

        if (av->av_vec_len + packets > DCCPAV_MAX_ACKVEC_LEN)
                return -ENOBUFS;

        gap      = packets - 1;
        new_head = av->av_buf_head - packets;

        if (new_head < 0) {
                if (gap > 0) {
                        memset(av->av_buf, DCCPAV_NOT_RECEIVED,
                               gap + new_head + 1);
                        gap = -new_head;
                }
                new_head += DCCPAV_MAX_ACKVEC_LEN;
        }

        av->av_buf_head = new_head;

        if (gap > 0)
                memset(av->av_buf + av->av_buf_head + 1,
                       DCCPAV_NOT_RECEIVED, gap);

        av->av_buf[av->av_buf_head] = state;
        av->av_vec_len += packets;
        return 0;
}

/*
 * Implements the RFC 4340, Appendix A
 */
int dccp_ackvec_add(struct dccp_ackvec *av, const struct sock *sk,
                    const u64 ackno, const u8 state)
{
        u8 *cur_head = av->av_buf + av->av_buf_head,
           *buf_end  = av->av_buf + DCCPAV_MAX_ACKVEC_LEN;
        /*
         * Check at the right places if the buffer is full, if it is, tell the
         * caller to start dropping packets till the HC-Sender acks our ACK
         * vectors, when we will free up space in av_buf.
         *
         * We may well decide to do buffer compression, etc, but for now lets
         * just drop.
         *
         * From Appendix A.1.1 (`New Packets'):
         *
         *      Of course, the circular buffer may overflow, either when the
         *      HC-Sender is sending data at a very high rate, when the
         *      HC-Receiver's acknowledgements are not reaching the HC-Sender,
         *      or when the HC-Sender is forgetting to acknowledge those acks
         *      (so the HC-Receiver is unable to clean up old state). In this
         *      case, the HC-Receiver should either compress the buffer (by
         *      increasing run lengths when possible), transfer its state to
         *      a larger buffer, or, as a last resort, drop all received
         *      packets, without processing them whatsoever, until its buffer
         *      shrinks again.
         */

        /* See if this is the first ackno being inserted */
        if (av->av_vec_len == 0) {
                *cur_head = state;
                av->av_vec_len = 1;
        } else if (after48(ackno, av->av_buf_ackno)) {
                const u64 delta = dccp_delta_seqno(av->av_buf_ackno, ackno);

                /*
                 * Look if the state of this packet is the same as the
                 * previous ackno and if so if we can bump the head len.
                 */
                if (delta == 1 && dccp_ackvec_state(cur_head) == state &&
                    dccp_ackvec_runlen(cur_head) < DCCPAV_MAX_RUNLEN)
                        *cur_head += 1;
                else if (dccp_ackvec_set_buf_head_state(av, delta, state))
                        return -ENOBUFS;
        } else {
                /*
                 * A.1.2.  Old Packets
                 *
                 *      When a packet with Sequence Number S <= buf_ackno
                 *      arrives, the HC-Receiver will scan the table for
                 *      the byte corresponding to S. (Indexing structures
                 *      could reduce the complexity of this scan.)
                 */
                u64 delta = dccp_delta_seqno(ackno, av->av_buf_ackno);

                while (1) {
                        const u8 len = dccp_ackvec_runlen(cur_head);
                        /*
                         * valid packets not yet in av_buf have a reserved
                         * entry, with a len equal to 0.
                         */
                        if (*cur_head == DCCPAV_NOT_RECEIVED && delta == 0) {
                                dccp_pr_debug("Found %llu reserved seat!\n",
                                              (unsigned long long)ackno);
                                *cur_head = state;
                                goto out;
                        }
                        /* len == 0 means one packet */
                        if (delta < len + 1)
                                goto out_duplicate;

                        delta -= len + 1;
                        if (++cur_head == buf_end)
                                cur_head = av->av_buf;
                }
        }

        av->av_buf_ackno = ackno;
out:
        return 0;

out_duplicate:
        /* Duplicate packet */
        dccp_pr_debug("Received a dup or already considered lost "
                      "packet: %llu\n", (unsigned long long)ackno);
        return -EILSEQ;
}

static void dccp_ackvec_throw_record(struct dccp_ackvec *av,
                                     struct dccp_ackvec_record *avr)
{
        struct dccp_ackvec_record *next;

        /* sort out vector length */
        if (av->av_buf_head <= avr->avr_ack_ptr)
                av->av_vec_len = avr->avr_ack_ptr - av->av_buf_head;
        else
                av->av_vec_len = DCCPAV_MAX_ACKVEC_LEN - 1 -
                                 av->av_buf_head + avr->avr_ack_ptr;

        /* 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);
        }
}

void dccp_ackvec_check_rcv_ackno(struct dccp_ackvec *av, struct sock *sk,
                                 const u64 ackno)
{
        struct dccp_ackvec_record *avr;

        /*
         * If we traverse backwards, it should be faster when we have large
         * windows. We will be receiving ACKs for stuff we sent a while back
         * -sorbo.
         */
        list_for_each_entry_reverse(avr, &av->av_records, avr_node) {
                if (ackno == avr->avr_ack_seqno) {
                        dccp_pr_debug("%s ACK packet 0, len=%d, ack_seqno=%llu, "
                                      "ack_ackno=%llu, ACKED!\n",
                                      dccp_role(sk), avr->avr_ack_runlen,
                                      (unsigned long long)avr->avr_ack_seqno,
                                      (unsigned long long)avr->avr_ack_ackno);
                        dccp_ackvec_throw_record(av, avr);
                        break;
                } else if (avr->avr_ack_seqno > ackno)
                        break; /* old news */
        }
}

static void dccp_ackvec_check_rcv_ackvector(struct dccp_ackvec *av,
                                            struct sock *sk, u64 *ackno,
                                            const unsigned char len,
                                            const unsigned char *vector)
{
        unsigned char i;
        struct dccp_ackvec_record *avr;

        /* Check if we actually sent an ACK vector */
        if (list_empty(&av->av_records))
                return;

        i = len;
        /*
         * XXX
         * I think it might be more efficient to work backwards. See comment on
         * rcv_ackno. -sorbo.
         */
        avr = list_entry(av->av_records.next, struct dccp_ackvec_record, avr_node);
        while (i--) {
                const u8 rl = dccp_ackvec_runlen(vector);
                u64 ackno_end_rl;

                dccp_set_seqno(&ackno_end_rl, *ackno - rl);

                /*
                 * If our AVR sequence number is greater than the ack, go
                 * forward in the AVR list until it is not so.
                 */
                list_for_each_entry_from(avr, &av->av_records, avr_node) {
                        if (!after48(avr->avr_ack_seqno, *ackno))
                                goto found;
                }
                /* End of the av_records list, not found, exit */
                break;
found:
                if (between48(avr->avr_ack_seqno, ackno_end_rl, *ackno)) {
                        if (dccp_ackvec_state(vector) != DCCPAV_NOT_RECEIVED) {
                                dccp_pr_debug("%s ACK vector 0, len=%d, "
                                              "ack_seqno=%llu, ack_ackno=%llu, "
                                              "ACKED!\n",
                                              dccp_role(sk), len,
                                              (unsigned long long)
                                              avr->avr_ack_seqno,
                                              (unsigned long long)
                                              avr->avr_ack_ackno);
                                dccp_ackvec_throw_record(av, avr);
                                break;
                        }
                        /*
                         * If it wasn't received, continue scanning... we might
                         * find another one.
                         */
                }

                dccp_set_seqno(ackno, ackno_end_rl - 1);
                ++vector;
        }
}

int dccp_ackvec_parse(struct sock *sk, const struct sk_buff *skb,
                      u64 *ackno, const u8 opt, const u8 *value, const u8 len)
{
        if (len > DCCP_SINGLE_OPT_MAXLEN)
                return -1;

        /* dccp_ackvector_print(DCCP_SKB_CB(skb)->dccpd_ack_seq, value, len); */
        dccp_ackvec_check_rcv_ackvector(dccp_sk(sk)->dccps_hc_rx_ackvec, sk,
                                        ackno, len, value);
        return 0;
}

/**
 * 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);
        }
}

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;
        }
}