dccp ccid-2: Update code for the Ack Vector input/registration routine
This patch updates the code which registers new packets as received, using the new circular buffer interface. It contributes a new algorithm which * supports both tail/head pointers and buffer wrap-around and * deals with overflow (head/tail move in lock-step). Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
This commit is contained in:
Gerrit Renker
parent
5753fdfe8b
commit
3802408644
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@ -131,6 +131,156 @@ u16 dccp_ackvec_buflen(const struct dccp_ackvec *av)
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return __ackvec_idx_sub(av->av_buf_tail, av->av_buf_head);
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}
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/**
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* dccp_ackvec_update_old - Update previous state as per RFC 4340, 11.4.1
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* @av: non-empty buffer to update
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* @distance: negative or zero distance of @seqno from buf_ackno downward
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* @seqno: the (old) sequence number whose record is to be updated
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* @state: state in which packet carrying @seqno was received
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*/
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static void dccp_ackvec_update_old(struct dccp_ackvec *av, s64 distance,
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u64 seqno, enum dccp_ackvec_states state)
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{
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u16 ptr = av->av_buf_head;
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BUG_ON(distance > 0);
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if (unlikely(dccp_ackvec_is_empty(av)))
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return;
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do {
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u8 runlen = dccp_ackvec_runlen(av->av_buf + ptr);
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if (distance + runlen >= 0) {
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/*
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* Only update the state if packet has not been received
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* yet. This is OK as per the second table in RFC 4340,
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* 11.4.1; i.e. here we are using the following table:
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* RECEIVED
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* 0 1 3
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* S +---+---+---+
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* T 0 | 0 | 0 | 0 |
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* O +---+---+---+
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* R 1 | 1 | 1 | 1 |
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* E +---+---+---+
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* D 3 | 0 | 1 | 3 |
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* +---+---+---+
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* The "Not Received" state was set by reserve_seats().
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*/
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if (av->av_buf[ptr] == DCCPAV_NOT_RECEIVED)
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av->av_buf[ptr] = state;
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else
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dccp_pr_debug("Not changing %llu state to %u\n",
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(unsigned long long)seqno, state);
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break;
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}
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distance += runlen + 1;
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ptr = __ackvec_idx_add(ptr, 1);
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} while (ptr != av->av_buf_tail);
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}
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/* Mark @num entries after buf_head as "Not yet received". */
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static void dccp_ackvec_reserve_seats(struct dccp_ackvec *av, u16 num)
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{
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u16 start = __ackvec_idx_add(av->av_buf_head, 1),
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len = DCCPAV_MAX_ACKVEC_LEN - start;
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/* check for buffer wrap-around */
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if (num > len) {
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memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, len);
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start = 0;
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num -= len;
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}
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if (num)
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memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, num);
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}
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/**
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* dccp_ackvec_add_new - Record one or more new entries in Ack Vector buffer
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* @av: container of buffer to update (can be empty or non-empty)
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* @num_packets: number of packets to register (must be >= 1)
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* @seqno: sequence number of the first packet in @num_packets
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* @state: state in which packet carrying @seqno was received
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*/
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static void dccp_ackvec_add_new(struct dccp_ackvec *av, u32 num_packets,
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u64 seqno, enum dccp_ackvec_states state)
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{
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u32 num_cells = num_packets;
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if (num_packets > DCCPAV_BURST_THRESH) {
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u32 lost_packets = num_packets - 1;
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DCCP_WARN("Warning: large burst loss (%u)\n", lost_packets);
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/*
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* We received 1 packet and have a loss of size "num_packets-1"
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* which we squeeze into num_cells-1 rather than reserving an
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* entire byte for each lost packet.
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* The reason is that the vector grows in O(burst_length); when
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* it grows too large there will no room left for the payload.
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* This is a trade-off: if a few packets out of the burst show
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* up later, their state will not be changed; it is simply too
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* costly to reshuffle/reallocate/copy the buffer each time.
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* Should such problems persist, we will need to switch to a
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* different underlying data structure.
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*/
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for (num_packets = num_cells = 1; lost_packets; ++num_cells) {
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u8 len = min(lost_packets, (u32)DCCPAV_MAX_RUNLEN);
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av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, 1);
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av->av_buf[av->av_buf_head] = DCCPAV_NOT_RECEIVED | len;
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lost_packets -= len;
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}
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}
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if (num_cells + dccp_ackvec_buflen(av) >= DCCPAV_MAX_ACKVEC_LEN) {
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DCCP_CRIT("Ack Vector buffer overflow: dropping old entries\n");
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av->av_overflow = true;
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}
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av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, num_packets);
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if (av->av_overflow)
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av->av_buf_tail = av->av_buf_head;
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av->av_buf[av->av_buf_head] = state;
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av->av_buf_ackno = seqno;
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if (num_packets > 1)
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dccp_ackvec_reserve_seats(av, num_packets - 1);
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}
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/**
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* dccp_ackvec_input - Register incoming packet in the buffer
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*/
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void dccp_ackvec_input(struct dccp_ackvec *av, struct sk_buff *skb)
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{
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u64 seqno = DCCP_SKB_CB(skb)->dccpd_seq;
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enum dccp_ackvec_states state = DCCPAV_RECEIVED;
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if (dccp_ackvec_is_empty(av)) {
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dccp_ackvec_add_new(av, 1, seqno, state);
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av->av_tail_ackno = seqno;
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} else {
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s64 num_packets = dccp_delta_seqno(av->av_buf_ackno, seqno);
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u8 *current_head = av->av_buf + av->av_buf_head;
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if (num_packets == 1 &&
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dccp_ackvec_state(current_head) == state &&
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dccp_ackvec_runlen(current_head) < DCCPAV_MAX_RUNLEN) {
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*current_head += 1;
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av->av_buf_ackno = seqno;
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} else if (num_packets > 0) {
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dccp_ackvec_add_new(av, num_packets, seqno, state);
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} else {
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dccp_ackvec_update_old(av, num_packets, seqno, state);
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}
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}
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}
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/*
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* If several packets are missing, the HC-Receiver may prefer to enter multiple
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* bytes with run length 0, rather than a single byte with a larger run length;
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@ -29,6 +29,9 @@
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/* Estimated minimum average Ack Vector length - used for updating MPS */
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#define DCCPAV_MIN_OPTLEN 16
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/* Threshold for coping with large bursts of losses */
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#define DCCPAV_BURST_THRESH (DCCPAV_MAX_ACKVEC_LEN / 8)
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enum dccp_ackvec_states {
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DCCPAV_RECEIVED = 0x00,
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DCCPAV_ECN_MARKED = 0x40,
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@ -116,6 +119,7 @@ extern int dccp_ackvec_parse(struct sock *sk, const struct sk_buff *skb,
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u64 *ackno, const u8 opt,
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const u8 *value, const u8 len);
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extern void dccp_ackvec_input(struct dccp_ackvec *av, struct sk_buff *skb);
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extern int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seq, u8 sum);
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extern void dccp_ackvec_clear_state(struct dccp_ackvec *av, const u64 ackno);
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extern u16 dccp_ackvec_buflen(const struct dccp_ackvec *av);
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