[DCCP]: Initial implementation

Development to this point was done on a subversion repository at:

http://oops.ghostprotocols.net:81/cgi-bin/viewcvs.cgi/dccp-2.6/

This repository will be kept at this site for the foreseable future,
so that interested parties can see the history of this code,
attributions, etc.

If I ever decide to take this offline I'll provide the full history at
some other suitable place.

Signed-off-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 763 insertions, 0 deletions

diff --git a/net/dccp/options.c b/net/dccp/options.c
new file mode 100644
index 000000000000..e1867767946c
--- /dev/null
+++ b/net/dccp/options.c
@@ -0,0 +1,763 @@
+/*
+ *  net/dccp/options.c
+ *
+ *  An implementation of the DCCP protocol
+ *  Aristeu Sergio Rozanski Filho <aris@cathedrallabs.org>
+ *  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; either version
+ *      2 of the License, or (at your option) any later version.
+ */
+#include <linux/config.h>
+#include <linux/dccp.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/skbuff.h>
+
+#include "ccid.h"
+#include "dccp.h"
+
+static void dccp_ackpkts_check_rcv_ackvector(struct dccp_ackpkts *ap,
+                                             struct sock *sk,
+                                             const u64 ackno,
+                                             const unsigned char len,
+                                             const unsigned char *vector);
+
+/* stores the default values for new connection. may be changed with sysctl */
+static const struct dccp_options dccpo_default_values = {
+        .dccpo_sequence_window    = DCCPF_INITIAL_SEQUENCE_WINDOW,
+        .dccpo_ccid               = DCCPF_INITIAL_CCID,
+        .dccpo_send_ack_vector    = DCCPF_INITIAL_SEND_ACK_VECTOR,
+        .dccpo_send_ndp_count     = DCCPF_INITIAL_SEND_NDP_COUNT,
+};
+
+void dccp_options_init(struct dccp_options *dccpo)
+{
+        memcpy(dccpo, &dccpo_default_values, sizeof(*dccpo));
+}
+
+static u32 dccp_decode_value_var(const unsigned char *bf, const u8 len)
+{
+        u32 value = 0;
+
+        if (len > 3)
+                value += *bf++ << 24;
+        if (len > 2)
+                value += *bf++ << 16;
+        if (len > 1)
+                value += *bf++ << 8;
+        if (len > 0)
+                value += *bf;
+
+        return value;
+}
+
+int dccp_parse_options(struct sock *sk, struct sk_buff *skb)
+{
+        struct dccp_sock *dp = dccp_sk(sk);
+#ifdef DCCP_DEBUG
+        const char *debug_prefix = dp->dccps_role == DCCP_ROLE_CLIENT ? "CLIENT rx opt: " :
+                                                                        "server rx opt: ";
+#endif
+        const struct dccp_hdr *dh = dccp_hdr(skb);
+        const u8 pkt_type = DCCP_SKB_CB(skb)->dccpd_type;
+        unsigned char *options = (unsigned char *)dh + dccp_hdr_len(skb);
+        unsigned char *opt_ptr = options;
+        const unsigned char *opt_end = (unsigned char *)dh + (dh->dccph_doff * 4);
+        struct dccp_options_received *opt_recv = &dp->dccps_options_received;
+        unsigned char opt, len;
+        unsigned char *value;
+
+        memset(opt_recv, 0, sizeof(*opt_recv));
+
+        while (opt_ptr != opt_end) {
+                opt   = *opt_ptr++;
+                len   = 0;
+                value = NULL;
+
+                /* Check if this isn't a single byte option */
+                if (opt > DCCPO_MAX_RESERVED) {
+                        if (opt_ptr == opt_end)
+                                goto out_invalid_option;
+
+                        len = *opt_ptr++;
+                        if (len < 3)
+                                goto out_invalid_option;
+                        /*
+                         * Remove the type and len fields, leaving
+                         * just the value size
+                         */
+                        len     -= 2;
+                        value   = opt_ptr;
+                        opt_ptr += len;
+
+                        if (opt_ptr > opt_end)
+                                goto out_invalid_option;
+                }
+
+                switch (opt) {
+                case DCCPO_PADDING:
+                        break;
+                case DCCPO_NDP_COUNT:
+                        if (len > 3)
+                                goto out_invalid_option;
+
+                        opt_recv->dccpor_ndp = dccp_decode_value_var(value, len);
+                        dccp_pr_debug("%sNDP count=%d\n", debug_prefix, opt_recv->dccpor_ndp);
+                        break;
+                case DCCPO_ACK_VECTOR_0:
+                        if (len > DCCP_MAX_ACK_VECTOR_LEN)
+                                goto out_invalid_option;
+
+                        if (pkt_type == DCCP_PKT_DATA)
+                                continue;
+
+                        opt_recv->dccpor_ack_vector_len = len;
+                        opt_recv->dccpor_ack_vector_idx = value - options;
+
+                        dccp_pr_debug("%sACK vector 0, len=%d, ack_ackno=%llu\n",
+                                      debug_prefix, len, DCCP_SKB_CB(skb)->dccpd_ack_seq);
+                        dccp_ackvector_print(DCCP_SKB_CB(skb)->dccpd_ack_seq,
+                                             value, len);
+                        dccp_ackpkts_check_rcv_ackvector(dp->dccps_hc_rx_ackpkts, sk,
+                                                         DCCP_SKB_CB(skb)->dccpd_ack_seq,
+                                                         len, value);
+                        break;
+                case DCCPO_TIMESTAMP:
+                        if (len != 4)
+                                goto out_invalid_option;
+
+                        opt_recv->dccpor_timestamp = ntohl(*(u32 *)value);
+
+                        dp->dccps_timestamp_echo = opt_recv->dccpor_timestamp;
+                        dp->dccps_timestamp_time = jiffies;
+
+                        dccp_pr_debug("%sTIMESTAMP=%u, ackno=%llu\n",
+                                      debug_prefix, opt_recv->dccpor_timestamp,
+                                      DCCP_SKB_CB(skb)->dccpd_ack_seq);
+                        break;
+                case DCCPO_TIMESTAMP_ECHO:
+                        if (len < 4 || len > 8)
+                                goto out_invalid_option;
+
+                        opt_recv->dccpor_timestamp_echo = ntohl(*(u32 *)value);
+
+                        dccp_pr_debug("%sTIMESTAMP_ECHO=%u, len=%d, ackno=%llu, diff=%u\n",
+                                      debug_prefix, opt_recv->dccpor_timestamp_echo,
+                                      len + 2, DCCP_SKB_CB(skb)->dccpd_ack_seq,
+                                      tcp_time_stamp - opt_recv->dccpor_timestamp_echo);
+
+                        opt_recv->dccpor_elapsed_time = dccp_decode_value_var(value + 4, len - 4);
+                        dccp_pr_debug("%sTIMESTAMP_ECHO ELAPSED_TIME=%d\n", debug_prefix,
+                                      opt_recv->dccpor_elapsed_time);
+                        break;
+                case DCCPO_ELAPSED_TIME:
+                        if (len > 4)
+                                goto out_invalid_option;
+
+                        if (pkt_type == DCCP_PKT_DATA)
+                                continue;
+                        opt_recv->dccpor_elapsed_time = dccp_decode_value_var(value, len);
+                        dccp_pr_debug("%sELAPSED_TIME=%d\n", debug_prefix,
+                                      opt_recv->dccpor_elapsed_time);
+                        break;
+                        /*
+                         * From draft-ietf-dccp-spec-11.txt:
+                         *
+                         *      Option numbers 128 through 191 are for options sent from the HC-
+                         *      Sender to the HC-Receiver; option numbers 192 through 255 are for
+                         *      options sent from the HC-Receiver to the HC-Sender.
+                         */
+                case 128 ... 191: {
+                        const u16 idx = value - options;
+
+                        if (ccid_hc_rx_parse_options(dp->dccps_hc_rx_ccid, sk, opt, len, idx, value) != 0)
+                                goto out_invalid_option;
+                }
+                        break;
+                case 192 ... 255: {
+                        const u16 idx = value - options;
+
+                        if (ccid_hc_tx_parse_options(dp->dccps_hc_tx_ccid, sk, opt, len, idx, value) != 0)
+                                goto out_invalid_option;
+                }
+                        break;
+                default:
+                        pr_info("DCCP(%p): option %d(len=%d) not implemented, ignoring\n",
+                                sk, opt, len);
+                        break;
+                }
+        }
+
+        return 0;
+
+out_invalid_option:
+        DCCP_INC_STATS_BH(DCCP_MIB_INVALIDOPT);
+        DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_OPTION_ERROR;
+        pr_info("DCCP(%p): invalid option %d, len=%d\n", sk, opt, len);
+        return -1;
+}
+
+static void dccp_encode_value_var(const u32 value, unsigned char *to,
+                                  const unsigned int len)
+{
+        if (len > 3)
+                *to++ = (value & 0xFF000000) >> 24;
+        if (len > 2)
+                *to++ = (value & 0xFF0000) >> 16;
+        if (len > 1)
+                *to++ = (value & 0xFF00) >> 8;
+        if (len > 0)
+                *to++ = (value & 0xFF);
+}
+
+static inline int dccp_ndp_len(const int ndp)
+{
+        return likely(ndp <= 0xFF) ? 1 : ndp <= 0xFFFF ? 2 : 3;
+}
+
+void dccp_insert_option(struct sock *sk, struct sk_buff *skb,
+                        const unsigned char option,
+                        const void *value, const unsigned char len)
+{
+        unsigned char *to;
+
+        if (DCCP_SKB_CB(skb)->dccpd_opt_len + len + 2 > DCCP_MAX_OPT_LEN) {
+                LIMIT_NETDEBUG(pr_info("DCCP: packet too small to insert %d option!\n", option));
+                return;
+        }
+
+        DCCP_SKB_CB(skb)->dccpd_opt_len += len + 2;
+
+        to    = skb_push(skb, len + 2);
+        *to++ = option;
+        *to++ = len + 2;
+
+        memcpy(to, value, len);
+}
+
+EXPORT_SYMBOL_GPL(dccp_insert_option);
+
+static void dccp_insert_option_ndp(struct sock *sk, struct sk_buff *skb)
+{
+        struct dccp_sock *dp = dccp_sk(sk);
+        int ndp = dp->dccps_ndp_count;
+
+        if (dccp_non_data_packet(skb))
+                ++dp->dccps_ndp_count;
+        else
+                dp->dccps_ndp_count = 0;
+
+        if (ndp > 0) {
+                unsigned char *ptr;
+                const int ndp_len = dccp_ndp_len(ndp);
+                const int len = ndp_len + 2;
+
+                if (DCCP_SKB_CB(skb)->dccpd_opt_len + len > DCCP_MAX_OPT_LEN)
+                        return;
+
+                DCCP_SKB_CB(skb)->dccpd_opt_len += len;
+
+                ptr = skb_push(skb, len);
+                *ptr++ = DCCPO_NDP_COUNT;
+                *ptr++ = len;
+                dccp_encode_value_var(ndp, ptr, ndp_len);
+        }
+}
+
+static inline int dccp_elapsed_time_len(const u32 elapsed_time)
+{
+        return elapsed_time == 0 ? 0 :
+               elapsed_time <= 0xFF ? 1 :
+               elapsed_time <= 0xFFFF ? 2 :
+               elapsed_time <= 0xFFFFFF ? 3 : 4;
+}
+
+void dccp_insert_option_elapsed_time(struct sock *sk,
+                                     struct sk_buff *skb,
+                                     u32 elapsed_time)
+{
+#ifdef DCCP_DEBUG
+        struct dccp_sock *dp = dccp_sk(sk);
+        const char *debug_prefix = dp->dccps_role == DCCP_ROLE_CLIENT ? "CLIENT TX opt: " :
+                                                                        "server TX opt: ";
+#endif
+        const int elapsed_time_len = dccp_elapsed_time_len(elapsed_time);
+        const int len = 2 + elapsed_time_len;
+        unsigned char *to;
+
+        /* If elapsed_time == 0... */
+        if (elapsed_time_len == 2)
+                return;
+
+        if (DCCP_SKB_CB(skb)->dccpd_opt_len + len > DCCP_MAX_OPT_LEN) {
+                LIMIT_NETDEBUG(pr_info("DCCP: packet too small to insert elapsed time!\n"));
+                return;
+        }
+
+        DCCP_SKB_CB(skb)->dccpd_opt_len += len;
+
+        to    = skb_push(skb, len);
+        *to++ = DCCPO_ELAPSED_TIME;
+        *to++ = len;
+
+        dccp_encode_value_var(elapsed_time, to, elapsed_time_len);
+
+        dccp_pr_debug("%sELAPSED_TIME=%u, len=%d, seqno=%llu\n",
+                      debug_prefix, elapsed_time,
+                      len, DCCP_SKB_CB(skb)->dccpd_seq);
+}
+
+EXPORT_SYMBOL(dccp_insert_option_elapsed_time);
+
+static void dccp_insert_option_ack_vector(struct sock *sk, struct sk_buff *skb)
+{
+        struct dccp_sock *dp = dccp_sk(sk);
+#ifdef DCCP_DEBUG
+        const char *debug_prefix = dp->dccps_role == DCCP_ROLE_CLIENT ? "CLIENT TX opt: " :
+                                                                        "server TX opt: ";
+#endif
+        struct dccp_ackpkts *ap = dp->dccps_hc_rx_ackpkts;
+        int len = ap->dccpap_buf_vector_len + 2;
+        const u32 elapsed_time = jiffies_to_usecs(jiffies - ap->dccpap_time) / 10;
+        unsigned char *to, *from;
+
+        if (elapsed_time != 0)
+                dccp_insert_option_elapsed_time(sk, skb, elapsed_time);
+
+        if (DCCP_SKB_CB(skb)->dccpd_opt_len + len > DCCP_MAX_OPT_LEN) {
+                LIMIT_NETDEBUG(pr_info("DCCP: packet too small to insert ACK Vector!\n"));
+                return;
+        }
+
+        /*
+         * XXX: now we have just one ack vector sent record, so
+         * we have to wait for it to be cleared.
+         *
+         * Of course this is not acceptable, but this is just for
+         * basic testing now.
+         */
+        if (ap->dccpap_ack_seqno != DCCP_MAX_SEQNO + 1)
+                return;
+
+        DCCP_SKB_CB(skb)->dccpd_opt_len += len;
+
+        to    = skb_push(skb, len);
+        *to++ = DCCPO_ACK_VECTOR_0;
+        *to++ = len;
+
+        len  = ap->dccpap_buf_vector_len;
+        from = ap->dccpap_buf + ap->dccpap_buf_head;
+
+        /* Check if buf_head wraps */
+        if (ap->dccpap_buf_head + len > ap->dccpap_buf_len) {
+                const unsigned int tailsize = ap->dccpap_buf_len - ap->dccpap_buf_head;
+
+                memcpy(to, from, tailsize);
+                to   += tailsize;
+                len  -= tailsize;
+                from = ap->dccpap_buf;
+        }
+
+        memcpy(to, from, len);
+        /*
+         *      From draft-ietf-dccp-spec-11.txt:
+         *
+         *      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.
+         *
+         * This implemention uses just one ack record for now.
+         */
+        ap->dccpap_ack_seqno      = DCCP_SKB_CB(skb)->dccpd_seq;
+        ap->dccpap_ack_ptr        = ap->dccpap_buf_head;
+        ap->dccpap_ack_ackno      = ap->dccpap_buf_ackno;
+        ap->dccpap_ack_nonce      = ap->dccpap_buf_nonce;
+        ap->dccpap_ack_vector_len = ap->dccpap_buf_vector_len;
+
+        dccp_pr_debug("%sACK Vector 0, len=%d, ack_seqno=%llu, ack_ackno=%llu\n",
+                      debug_prefix, ap->dccpap_ack_vector_len,
+                      ap->dccpap_ack_seqno, ap->dccpap_ack_ackno);
+}
+
+static inline void dccp_insert_option_timestamp(struct sock *sk, struct sk_buff *skb)
+{
+        const u32 now = htonl(tcp_time_stamp);
+        dccp_insert_option(sk, skb, DCCPO_TIMESTAMP, &now, sizeof(now));
+}
+
+static void dccp_insert_option_timestamp_echo(struct sock *sk, struct sk_buff *skb)
+{
+        struct dccp_sock *dp = dccp_sk(sk);
+#ifdef DCCP_DEBUG
+        const char *debug_prefix = dp->dccps_role == DCCP_ROLE_CLIENT ? "CLIENT TX opt: " :
+                                                                        "server TX opt: ";
+#endif
+        u32 tstamp_echo;
+        const u32 elapsed_time = jiffies_to_usecs(jiffies - dp->dccps_timestamp_time) / 10;
+        const int elapsed_time_len = dccp_elapsed_time_len(elapsed_time);
+        const int len = 6 + elapsed_time_len;
+        unsigned char *to;
+
+        if (DCCP_SKB_CB(skb)->dccpd_opt_len + len > DCCP_MAX_OPT_LEN) {
+                LIMIT_NETDEBUG(pr_info("DCCP: packet too small to insert timestamp echo!\n"));
+                return;
+        }
+
+        DCCP_SKB_CB(skb)->dccpd_opt_len += len;
+
+        to    = skb_push(skb, len);
+        *to++ = DCCPO_TIMESTAMP_ECHO;
+        *to++ = len;
+
+        tstamp_echo = htonl(dp->dccps_timestamp_echo);
+        memcpy(to, &tstamp_echo, 4);
+        to += 4;
+        dccp_encode_value_var(elapsed_time, to, elapsed_time_len);
+
+        dccp_pr_debug("%sTIMESTAMP_ECHO=%u, len=%d, seqno=%llu\n",
+                      debug_prefix, dp->dccps_timestamp_echo,
+                      len, DCCP_SKB_CB(skb)->dccpd_seq);
+
+        dp->dccps_timestamp_echo = 0;
+        dp->dccps_timestamp_time = 0;
+}
+
+void dccp_insert_options(struct sock *sk, struct sk_buff *skb)
+{
+        struct dccp_sock *dp = dccp_sk(sk);
+
+        DCCP_SKB_CB(skb)->dccpd_opt_len = 0;
+
+        if (dp->dccps_options.dccpo_send_ndp_count)
+                dccp_insert_option_ndp(sk, skb);
+
+        if (!dccp_packet_without_ack(skb)) {
+                if (dp->dccps_options.dccpo_send_ack_vector &&
+                    dp->dccps_hc_rx_ackpkts->dccpap_buf_ackno != DCCP_MAX_SEQNO + 1)
+                        dccp_insert_option_ack_vector(sk, skb);
+
+                dccp_insert_option_timestamp(sk, skb);
+                if (dp->dccps_timestamp_echo != 0)
+                        dccp_insert_option_timestamp_echo(sk, skb);
+        }
+
+        ccid_hc_rx_insert_options(dp->dccps_hc_rx_ccid, sk, skb);
+        ccid_hc_tx_insert_options(dp->dccps_hc_tx_ccid, sk, skb);
+
+        /* XXX: insert other options when appropriate */
+
+        if (DCCP_SKB_CB(skb)->dccpd_opt_len != 0) {
+                /* The length of all options has to be a multiple of 4 */
+                int padding = DCCP_SKB_CB(skb)->dccpd_opt_len % 4;
+
+                if (padding != 0) {
+                        padding = 4 - padding;
+                        memset(skb_push(skb, padding), 0, padding);
+                        DCCP_SKB_CB(skb)->dccpd_opt_len += padding;
+                }
+        }
+}
+
+struct dccp_ackpkts *dccp_ackpkts_alloc(unsigned int len, int priority)
+{
+        struct dccp_ackpkts *ap = kmalloc(sizeof(*ap) + len, priority);
+
+        if (ap != NULL) {
+#ifdef DCCP_DEBUG
+                memset(ap->dccpap_buf, 0xFF, len);
+#endif
+                ap->dccpap_buf_len        = len;
+                ap->dccpap_buf_head       = ap->dccpap_buf_tail = ap->dccpap_buf_len - 1;
+                ap->dccpap_buf_ackno      = ap->dccpap_ack_ackno = ap->dccpap_ack_seqno = DCCP_MAX_SEQNO + 1;
+                ap->dccpap_buf_nonce      = ap->dccpap_buf_nonce = 0;
+                ap->dccpap_ack_ptr        = 0;
+                ap->dccpap_time           = 0;
+                ap->dccpap_buf_vector_len = ap->dccpap_ack_vector_len = 0;
+        }
+
+        return ap;
+}
+
+void dccp_ackpkts_free(struct dccp_ackpkts *ap)
+{
+        if (ap != NULL) {
+#ifdef DCCP_DEBUG
+                memset(ap, 0xFF, sizeof(*ap) + ap->dccpap_buf_len);
+#endif
+                kfree(ap);
+        }
+}
+
+static inline u8 dccp_ackpkts_state(const struct dccp_ackpkts *ap,
+                                    const unsigned int index)
+{
+        return ap->dccpap_buf[index] & DCCP_ACKPKTS_STATE_MASK;
+}
+
+static inline u8 dccp_ackpkts_len(const struct dccp_ackpkts *ap,
+                                  const unsigned int index)
+{
+        return ap->dccpap_buf[index] & DCCP_ACKPKTS_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_ackpkts_set_buf_head_state(struct dccp_ackpkts *ap,
+                                                  const unsigned int packets,
+                                                  const unsigned char state)
+{
+        unsigned int gap;
+        signed long new_head;
+
+        if (ap->dccpap_buf_vector_len + packets > ap->dccpap_buf_len)
+                return -ENOBUFS;
+
+        gap      = packets - 1;
+        new_head = ap->dccpap_buf_head - packets;
+
+        if (new_head < 0) {
+                if (gap > 0) {
+                        memset(ap->dccpap_buf, DCCP_ACKPKTS_STATE_NOT_RECEIVED,
+                               gap + new_head + 1);
+                        gap = -new_head;
+                }
+                new_head += ap->dccpap_buf_len;
+        } 
+
+        ap->dccpap_buf_head = new_head;
+
+        if (gap > 0)
+                memset(ap->dccpap_buf + ap->dccpap_buf_head + 1,
+                       DCCP_ACKPKTS_STATE_NOT_RECEIVED, gap);
+
+        ap->dccpap_buf[ap->dccpap_buf_head] = state;
+        ap->dccpap_buf_vector_len += packets;
+        return 0;
+}
+
+/*
+ * Implements the draft-ietf-dccp-spec-11.txt Appendix A
+ */
+int dccp_ackpkts_add(struct dccp_ackpkts *ap, u64 ackno, 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 dccpap_buf.
+         *
+         * We may well decide to do buffer compression, etc, but for now lets
+         * just drop.
+         *
+         * From Appendix A:
+         *
+         *      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 (ap->dccpap_buf_vector_len == 0) {
+                ap->dccpap_buf[ap->dccpap_buf_head] = state;
+                ap->dccpap_buf_vector_len = 1;
+        } else if (after48(ackno, ap->dccpap_buf_ackno)) {
+                const u64 delta = dccp_delta_seqno(ap->dccpap_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_ackpkts_state(ap, ap->dccpap_buf_head) == state &&
+                    dccp_ackpkts_len(ap, ap->dccpap_buf_head) < DCCP_ACKPKTS_LEN_MASK)
+                        ap->dccpap_buf[ap->dccpap_buf_head]++;
+                else if (dccp_ackpkts_set_buf_head_state(ap, delta, state))
+                        return -ENOBUFS;
+        } else {
+                /*
+                 * A.1.2.  Old Packets
+                 *
+                 *      When a packet with Sequence Number S arrives, and S <= buf_ackno,
+                 *      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, ap->dccpap_buf_ackno);
+                unsigned int index = ap->dccpap_buf_head;
+
+                while (1) {
+                        const u8 len = dccp_ackpkts_len(ap, index);
+                        const u8 state = dccp_ackpkts_state(ap, index);
+                        /*
+                         * valid packets not yet in dccpap_buf have a reserved entry, with
+                         * a len equal to 0
+                         */
+                        if (state == DCCP_ACKPKTS_STATE_NOT_RECEIVED &&
+                            len == 0 && delta == 0) { /* Found our reserved seat! */
+                                dccp_pr_debug("Found %llu reserved seat!\n", ackno);
+                                ap->dccpap_buf[index] = state;
+                                goto out;
+                        }
+                        /* len == 0 means one packet */
+                        if (delta < len + 1)
+                                goto out_duplicate;
+
+                        delta -= len + 1;
+                        if (++index == ap->dccpap_buf_len)
+                                index = 0;
+                }
+        }
+
+        ap->dccpap_buf_ackno = ackno;
+        ap->dccpap_time = jiffies;
+out:
+        dccp_pr_debug("");
+        dccp_ackpkts_print(ap);
+        return 0;
+
+out_duplicate:
+        /* Duplicate packet */
+        dccp_pr_debug("Received a dup or already considered lost packet: %llu\n", ackno);
+        return -EILSEQ;
+}
+
+#ifdef DCCP_DEBUG
+void dccp_ackvector_print(const u64 ackno, const unsigned char *vector, int len)
+{
+        if (!dccp_debug)
+                return;
+
+        printk("ACK vector len=%d, ackno=%llu |", len, ackno);
+
+        while (len--) {
+                const u8 state = (*vector & DCCP_ACKPKTS_STATE_MASK) >> 6;
+                const u8 rl = (*vector & DCCP_ACKPKTS_LEN_MASK);
+
+                printk("%d,%d|", state, rl);
+                ++vector;
+        }
+
+        printk("\n");
+}
+
+void dccp_ackpkts_print(const struct dccp_ackpkts *ap)
+{
+        dccp_ackvector_print(ap->dccpap_buf_ackno,
+                             ap->dccpap_buf + ap->dccpap_buf_head,
+                             ap->dccpap_buf_vector_len);
+}
+#endif
+
+static void dccp_ackpkts_trow_away_ack_record(struct dccp_ackpkts *ap)
+{
+        /*
+         * As we're keeping track of the ack vector size
+         * (dccpap_buf_vector_len) and the sent ack vector size
+         * (dccpap_ack_vector_len) we don't need dccpap_buf_tail at all, but
+         * keep this code here as in the future we'll implement a vector of ack
+         * records, as suggested in draft-ietf-dccp-spec-11.txt Appendix A. -acme
+         */
+#if 0
+        ap->dccpap_buf_tail = ap->dccpap_ack_ptr + 1;
+        if (ap->dccpap_buf_tail >= ap->dccpap_buf_len)
+                ap->dccpap_buf_tail -= ap->dccpap_buf_len;
+#endif
+        ap->dccpap_buf_vector_len -= ap->dccpap_ack_vector_len;
+}
+
+void dccp_ackpkts_check_rcv_ackno(struct dccp_ackpkts *ap, struct sock *sk,
+                                 u64 ackno)
+{
+        /* Check if we actually sent an ACK vector */
+        if (ap->dccpap_ack_seqno == DCCP_MAX_SEQNO + 1)
+                return;
+
+        if (ackno == ap->dccpap_ack_seqno) {
+#ifdef DCCP_DEBUG
+                struct dccp_sock *dp = dccp_sk(sk);
+                const char *debug_prefix = dp->dccps_role == DCCP_ROLE_CLIENT ? "CLIENT rx ack: " :
+                                                                                "server rx ack: ";
+#endif
+                dccp_pr_debug("%sACK packet 0, len=%d, ack_seqno=%llu, ack_ackno=%llu, ACKED!\n",
+                              debug_prefix, 1,
+                              ap->dccpap_ack_seqno, ap->dccpap_ack_ackno);
+                dccp_ackpkts_trow_away_ack_record(ap);
+                ap->dccpap_ack_seqno = DCCP_MAX_SEQNO + 1;
+        }
+}
+
+static void dccp_ackpkts_check_rcv_ackvector(struct dccp_ackpkts *ap,
+                                             struct sock *sk, u64 ackno,
+                                             const unsigned char len,
+                                             const unsigned char *vector)
+{
+        unsigned char i;
+
+        /* Check if we actually sent an ACK vector */
+        if (ap->dccpap_ack_seqno == DCCP_MAX_SEQNO + 1)
+                return;
+        /*
+         * We're in the receiver half connection, so if the received an ACK vector
+         * ackno (e.g. 50) before dccpap_ack_seqno (e.g. 52), we're not interested.
+         *
+         * Extra explanation with example:
+         * 
+         * if we received an ACK vector with ackno 50, it can only be acking
+         * 50, 49, 48, etc, not 52 (the seqno for the ACK vector we sent).
+         */
+        // dccp_pr_debug("is %llu < %llu? ", ackno, ap->dccpap_ack_seqno);
+        if (before48(ackno, ap->dccpap_ack_seqno)) {
+                // dccp_pr_debug_cat("yes\n");
+                return;
+        }
+        // dccp_pr_debug_cat("no\n");
+
+        i = len;
+        while (i--) {
+                const u8 rl = (*vector & DCCP_ACKPKTS_LEN_MASK);
+                u64 ackno_end_rl;
+
+                dccp_set_seqno(&ackno_end_rl, ackno - rl);
+
+                // dccp_pr_debug("is %llu <= %llu <= %llu? ", ackno_end_rl, ap->dccpap_ack_seqno, ackno);
+                if (between48(ap->dccpap_ack_seqno, ackno_end_rl, ackno)) {
+                        const u8 state = (*vector & DCCP_ACKPKTS_STATE_MASK) >> 6;
+                        // dccp_pr_debug_cat("yes\n");
+
+                        if (state != DCCP_ACKPKTS_STATE_NOT_RECEIVED) {
+#ifdef DCCP_DEBUG
+                                struct dccp_sock *dp = dccp_sk(sk);
+                                const char *debug_prefix = dp->dccps_role == DCCP_ROLE_CLIENT ? "CLIENT rx ack: " :
+                                                                                                "server rx ack: ";
+#endif
+                                dccp_pr_debug("%sACK vector 0, len=%d, ack_seqno=%llu, ack_ackno=%llu, ACKED!\n",
+                                              debug_prefix, len,
+                                              ap->dccpap_ack_seqno, ap->dccpap_ack_ackno);
+                                dccp_ackpkts_trow_away_ack_record(ap);
+                        }
+                        /*
+                         * If dccpap_ack_seqno was not received, no problem we'll
+                         * send another ACK vector.
+                         */
+                        ap->dccpap_ack_seqno = DCCP_MAX_SEQNO + 1;
+                        break;
+                }
+                // dccp_pr_debug_cat("no\n");
+
+                dccp_set_seqno(&ackno, ackno_end_rl - 1);
+                ++vector;
+        }
+}