/*
 *  net/dccp/ackvec.c
 *
 *  An implementation of the DCCP protocol
 *  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;

static struct dccp_ackvec_record *dccp_ackvec_record_new(void)
{
        struct dccp_ackvec_record *avr =
                        kmem_cache_alloc(dccp_ackvec_record_slab, GFP_ATOMIC);

        if (avr != NULL)
                INIT_LIST_HEAD(&avr->avr_node);

        return avr;
}

static void dccp_ackvec_record_delete(struct dccp_ackvec_record *avr)
{
        if (unlikely(avr == NULL))
                return;
        /* Check if deleting a linked record */
        WARN_ON(!list_empty(&avr->avr_node));
        kmem_cache_free(dccp_ackvec_record_slab, avr);
}

static void dccp_ackvec_insert_avr(struct dccp_ackvec *av,
                                   struct dccp_ackvec_record *avr)
{
        /*
         * AVRs are sorted by seqno. Since we are sending them in order, we
         * just add the AVR at the head of the list.
         * -sorbo.
         */
        if (!list_empty(&av->av_records)) {
                const struct dccp_ackvec_record *head =
                                        list_entry(av->av_records.next,
                                                   struct dccp_ackvec_record,
                                                   avr_node);
                BUG_ON(before48(avr->avr_ack_seqno, head->avr_ack_seqno));
        }

        list_add(&avr->avr_node, &av->av_records);
}

int dccp_insert_option_ackvec(struct sock *sk, struct sk_buff *skb)
{
        struct dccp_sock *dp = dccp_sk(sk);
        struct dccp_ackvec *av = dp->dccps_hc_rx_ackvec;
        /* Figure out how many options do we need to represent the ackvec */
        const u8 nr_opts = DIV_ROUND_UP(av->av_vec_len, DCCP_SINGLE_OPT_MAXLEN);
        u16 len = av->av_vec_len + 2 * nr_opts, i;
        u32 elapsed_time;
        const unsigned char *tail, *from;
        unsigned char *to;
        struct dccp_ackvec_record *avr;
        suseconds_t delta;

        if (DCCP_SKB_CB(skb)->dccpd_opt_len + len > DCCP_MAX_OPT_LEN)
                return -1;

        delta = ktime_us_delta(ktime_get_real(), av->av_time);
        elapsed_time = delta / 10;

        if (elapsed_time != 0 &&
            dccp_insert_option_elapsed_time(sk, skb, elapsed_time))
                return -1;

        avr = dccp_ackvec_record_new();
        if (avr == NULL)
                return -1;

        DCCP_SKB_CB(skb)->dccpd_opt_len += len;

        to   = skb_push(skb, len);
        len  = av->av_vec_len;
        from = av->av_buf + av->av_buf_head;
        tail = av->av_buf + DCCP_MAX_ACKVEC_LEN;

        for (i = 0; i < nr_opts; ++i) {
                int copylen = len;

                if (len > DCCP_SINGLE_OPT_MAXLEN)
                        copylen = DCCP_SINGLE_OPT_MAXLEN;

                *to++ = DCCPO_ACK_VECTOR_0;
                *to++ = copylen + 2;

                /* Check if buf_head wraps */
                if (from + copylen > tail) {
                        const u16 tailsize = tail - from;

                        memcpy(to, from, tailsize);
                        to      += tailsize;
                        len     -= tailsize;
                        copylen -= tailsize;
                        from    = av->av_buf;
                }

                memcpy(to, from, copylen);
                from += copylen;
                to   += copylen;
                len  -= copylen;
        }

        /*
         *      From RFC 4340, A.2:
         *
         *      For each acknowledgement it sends, the HC-Receiver will add an
         *      acknowledgement record.  ack_seqno will equal the HC-Receiver
         *      sequence number it used for the ack packet; ack_ptr will equal
         *      buf_head; ack_ackno will equal buf_ackno; and ack_nonce will
         *      equal buf_nonce.
         */
        avr->avr_ack_seqno = DCCP_SKB_CB(skb)->dccpd_seq;
        avr->avr_ack_ptr   = av->av_buf_head;
        avr->avr_ack_ackno = av->av_buf_ackno;
        avr->avr_ack_nonce = av->av_buf_nonce;
        avr->avr_sent_len  = av->av_vec_len;

        dccp_ackvec_insert_avr(av, avr);

        dccp_pr_debug("%s ACK Vector 0, len=%d, ack_seqno=%llu, "
                      "ack_ackno=%llu\n",
                      dccp_role(sk), avr->avr_sent_len,
                      (unsigned long long)avr->avr_ack_seqno,
                      (unsigned long long)avr->avr_ack_ackno);
        return 0;
}

struct dccp_ackvec *dccp_ackvec_alloc(const gfp_t priority)
{
        struct dccp_ackvec *av = kmem_cache_alloc(dccp_ackvec_slab, priority);

        if (av != NULL) {
                av->av_buf_head  = DCCP_MAX_ACKVEC_LEN - 1;
                av->av_buf_ackno = UINT48_MAX + 1;
                av->av_buf_nonce = 0;
                av->av_time      = ktime_set(0, 0);
                av->av_vec_len   = 0;
                INIT_LIST_HEAD(&av->av_records);
        }

        return av;
}

void dccp_ackvec_free(struct dccp_ackvec *av)
{
        if (unlikely(av == NULL))
                return;

        if (!list_empty(&av->av_records)) {
                struct dccp_ackvec_record *avr, *next;

                list_for_each_entry_safe(avr, next, &av->av_records, avr_node) {
                        list_del_init(&avr->avr_node);
                        dccp_ackvec_record_delete(avr);
                }
        }

        kmem_cache_free(dccp_ackvec_slab, av);
}

static inline u8 dccp_ackvec_state(const struct dccp_ackvec *av,
                                   const u32 index)
{
        return av->av_buf[index] & DCCP_ACKVEC_STATE_MASK;
}

static inline u8 dccp_ackvec_len(const struct dccp_ackvec *av,
                                 const u32 index)
{
        return av->av_buf[index] & DCCP_ACKVEC_LEN_MASK;
}

/*
 * 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 > DCCP_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, DCCP_ACKVEC_STATE_NOT_RECEIVED,
                               gap + new_head + 1);
                        gap = -new_head;
                }
                new_head += DCCP_MAX_ACKVEC_LEN;
        }

        av->av_buf_head = new_head;

        if (gap > 0)
                memset(av->av_buf + av->av_buf_head + 1,
                       DCCP_ACKVEC_STATE_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)
{
        /*
         * 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) {
                av->av_buf[av->av_buf_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(av, av->av_buf_head) == state &&
                    dccp_ackvec_len(av, av->av_buf_head) < DCCP_ACKVEC_LEN_MASK)
                        av->av_buf[av->av_buf_head]++;
                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);
                u32 index = av->av_buf_head;

                while (1) {
                        const u8 len = dccp_ackvec_len(av, index);
                        const u8 av_state = dccp_ackvec_state(av, index);
                        /*
                         * valid packets not yet in av_buf have a reserved
                         * entry, with a len equal to 0.
                         */
                        if (av_state == DCCP_ACKVEC_STATE_NOT_RECEIVED &&
                            len == 0 && delta == 0) { /* Found our
                                                         reserved seat! */
                                dccp_pr_debug("Found %llu reserved seat!\n",
                                              (unsigned long long)ackno);
                                av->av_buf[index] = state;
                                goto out;
                        }
                        /* len == 0 means one packet */
                        if (delta < len + 1)
                                goto out_duplicate;

                        delta -= len + 1;
                        if (++index == DCCP_MAX_ACKVEC_LEN)
                                index = 0;
                }
        }

        av->av_buf_ackno = ackno;
        av->av_time = ktime_get_real();
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 = DCCP_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_init(&avr->avr_node);
                dccp_ackvec_record_delete(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), 1,
                                      (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 = *vector & DCCP_ACKVEC_LEN_MASK;
                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)) {
                        const u8 state = *vector & DCCP_ACKVEC_STATE_MASK;
                        if (state != DCCP_ACKVEC_STATE_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;
}

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;
        }
}