[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 00000000000..e1867767946
--- /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;
+	}
+}