[TFRC]: Ringbuffer to track loss interval history
A ringbuffer-based implementation of loss interval history is easier to maintain, allocate, and update. The `swap' routine to keep the RX history sorted is due to and was written by Arnaldo Carvalho de Melo, simplifying an earlier macro-based variant. Details: * access to the Loss Interval Records via macro wrappers (with safety checks); * simplified, on-demand allocation of entries (no extra memory consumption on lossless links); cache allocation is local to the module / exported as service; * provision of RFC-compliant algorithm to re-compute average loss interval; * provision of comprehensive, new loss detection algorithm - support for all cases of loss, including re-ordered/duplicate packets; - waiting for NDUPACK=3 packets to fill the hole; - updating loss records when a late-arriving packet fills a hole. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Gerrit Renker
committed by
David S. Miller
David S. Miller
parent
8995a238ef
commit
8a9c7e92e0
@@ -151,11 +151,10 @@ void tfrc_rx_packet_history_exit(void)
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}
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}
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void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h,
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const struct sk_buff *skb,
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const u32 ndp)
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static inline void tfrc_rx_hist_entry_from_skb(struct tfrc_rx_hist_entry *entry,
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const struct sk_buff *skb,
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const u32 ndp)
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{
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struct tfrc_rx_hist_entry *entry = tfrc_rx_hist_last_rcv(h);
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const struct dccp_hdr *dh = dccp_hdr(skb);
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entry->tfrchrx_seqno = DCCP_SKB_CB(skb)->dccpd_seq;
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@@ -164,6 +163,15 @@ void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h,
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entry->tfrchrx_ndp = ndp;
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entry->tfrchrx_tstamp = ktime_get_real();
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}
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void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h,
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const struct sk_buff *skb,
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const u32 ndp)
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{
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struct tfrc_rx_hist_entry *entry = tfrc_rx_hist_last_rcv(h);
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tfrc_rx_hist_entry_from_skb(entry, skb, ndp);
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}
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EXPORT_SYMBOL_GPL(tfrc_rx_hist_add_packet);
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/* has the packet contained in skb been seen before? */
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@@ -209,6 +217,208 @@ int tfrc_rx_hist_new_loss_indicated(struct tfrc_rx_hist *h,
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}
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EXPORT_SYMBOL_GPL(tfrc_rx_hist_new_loss_indicated);
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static void tfrc_rx_hist_swap(struct tfrc_rx_hist *h, const u8 a, const u8 b)
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{
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const u8 idx_a = tfrc_rx_hist_index(h, a),
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idx_b = tfrc_rx_hist_index(h, b);
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struct tfrc_rx_hist_entry *tmp = h->ring[idx_a];
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h->ring[idx_a] = h->ring[idx_b];
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h->ring[idx_b] = tmp;
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}
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/*
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* Private helper functions for loss detection.
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*
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* In the descriptions, `Si' refers to the sequence number of entry number i,
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* whose NDP count is `Ni' (lower case is used for variables).
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* Note: All __after_loss functions expect that a test against duplicates has
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* been performed already: the seqno of the skb must not be less than the
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* seqno of loss_prev; and it must not equal that of any valid hist_entry.
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*/
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static void __one_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n2)
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{
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u64 s0 = tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno,
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s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,
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s2 = DCCP_SKB_CB(skb)->dccpd_seq;
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int n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp,
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d12 = dccp_delta_seqno(s1, s2), d2;
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if (d12 > 0) { /* S1 < S2 */
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h->loss_count = 2;
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tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 2), skb, n2);
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return;
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}
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/* S0 < S2 < S1 */
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d2 = dccp_delta_seqno(s0, s2);
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if (d2 == 1 || n2 >= d2) { /* S2 is direct successor of S0 */
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int d21 = -d12;
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if (d21 == 1 || n1 >= d21) {
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/* hole is filled: S0, S2, and S1 are consecutive */
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h->loss_count = 0;
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h->loss_start = tfrc_rx_hist_index(h, 1);
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} else
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/* gap between S2 and S1: just update loss_prev */
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tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_loss_prev(h), skb, n2);
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} else { /* hole between S0 and S2 */
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/*
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* Reorder history to insert S2 between S0 and s1
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*/
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tfrc_rx_hist_swap(h, 0, 3);
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h->loss_start = tfrc_rx_hist_index(h, 3);
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tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 1), skb, n2);
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h->loss_count = 2;
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}
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}
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/* return 1 if a new loss event has been identified */
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static int __two_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n3)
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{
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u64 s0 = tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno,
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s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,
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s2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_seqno,
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s3 = DCCP_SKB_CB(skb)->dccpd_seq;
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int n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp,
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d23 = dccp_delta_seqno(s2, s3), d13, d3, d31;
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if (d23 > 0) { /* S2 < S3 */
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h->loss_count = 3;
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tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 3), skb, n3);
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return 1;
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}
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/* S3 < S2 */
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d13 = dccp_delta_seqno(s1, s3);
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if (d13 > 0) {
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/*
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* The sequence number order is S1, S3, S2
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* Reorder history to insert entry between S1 and S2
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*/
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tfrc_rx_hist_swap(h, 2, 3);
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tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 2), skb, n3);
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h->loss_count = 3;
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return 1;
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}
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/* S0 < S3 < S1 */
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d31 = -d13;
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d3 = dccp_delta_seqno(s0, s3);
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if (d3 == 1 || n3 >= d3) { /* S3 is a successor of S0 */
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if (d31 == 1 || n1 >= d31) {
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/* hole between S0 and S1 filled by S3 */
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int d2 = dccp_delta_seqno(s1, s2),
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n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp;
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if (d2 == 1 || n2 >= d2) {
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/* entire hole filled by S0, S3, S1, S2 */
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h->loss_start = tfrc_rx_hist_index(h, 2);
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h->loss_count = 0;
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} else {
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/* gap remains between S1 and S2 */
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h->loss_start = tfrc_rx_hist_index(h, 1);
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h->loss_count = 1;
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}
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} else /* gap exists between S3 and S1, loss_count stays at 2 */
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tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_loss_prev(h), skb, n3);
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return 0;
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}
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/*
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* The remaining case: S3 is not a successor of S0.
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* Sequence order is S0, S3, S1, S2; reorder to insert between S0 and S1
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*/
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tfrc_rx_hist_swap(h, 0, 3);
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h->loss_start = tfrc_rx_hist_index(h, 3);
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tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 1), skb, n3);
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h->loss_count = 3;
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return 1;
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}
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/* return the signed modulo-2^48 sequence number distance from entry e1 to e2 */
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static s64 tfrc_rx_hist_delta_seqno(struct tfrc_rx_hist *h, u8 e1, u8 e2)
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{
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DCCP_BUG_ON(e1 > h->loss_count || e2 > h->loss_count);
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return dccp_delta_seqno(tfrc_rx_hist_entry(h, e1)->tfrchrx_seqno,
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tfrc_rx_hist_entry(h, e2)->tfrchrx_seqno);
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}
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/* recycle RX history records to continue loss detection if necessary */
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static void __three_after_loss(struct tfrc_rx_hist *h)
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{
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/*
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* The distance between S0 and S1 is always greater than 1 and the NDP
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* count of S1 is smaller than this distance. Otherwise there would
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* have been no loss. Hence it is only necessary to see whether there
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* are further missing data packets between S1/S2 and S2/S3.
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*/
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int d2 = tfrc_rx_hist_delta_seqno(h, 1, 2),
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d3 = tfrc_rx_hist_delta_seqno(h, 2, 3),
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n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp,
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n3 = tfrc_rx_hist_entry(h, 3)->tfrchrx_ndp;
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if (d2 == 1 || n2 >= d2) { /* S2 is successor to S1 */
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if (d3 == 1 || n3 >= d3) {
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/* S3 is successor of S2: entire hole is filled */
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h->loss_start = tfrc_rx_hist_index(h, 3);
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h->loss_count = 0;
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} else {
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/* gap between S2 and S3 */
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h->loss_start = tfrc_rx_hist_index(h, 2);
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h->loss_count = 1;
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}
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} else { /* gap between S1 and S2 */
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h->loss_start = tfrc_rx_hist_index(h, 1);
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h->loss_count = 2;
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}
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}
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/**
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* tfrc_rx_handle_loss - Loss detection and further processing
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* @h: The non-empty RX history object
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* @lh: Loss Intervals database to update
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* @skb: Currently received packet
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* @ndp: The NDP count belonging to @skb
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* @calc_first_li: Caller-dependent computation of first loss interval in @lh
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* @sk: Used by @calc_first_li (see tfrc_lh_interval_add)
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* Chooses action according to pending loss, updates LI database when a new
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* loss was detected, and does required post-processing. Returns 1 when caller
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* should send feedback, 0 otherwise.
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*/
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int tfrc_rx_handle_loss(struct tfrc_rx_hist *h,
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struct tfrc_loss_hist *lh,
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struct sk_buff *skb, u32 ndp,
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u32 (*calc_first_li)(struct sock *), struct sock *sk)
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{
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int is_new_loss = 0;
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if (h->loss_count == 1) {
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__one_after_loss(h, skb, ndp);
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} else if (h->loss_count != 2) {
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DCCP_BUG("invalid loss_count %d", h->loss_count);
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} else if (__two_after_loss(h, skb, ndp)) {
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/*
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* Update Loss Interval database and recycle RX records
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*/
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is_new_loss = tfrc_lh_interval_add(lh, h, calc_first_li, sk);
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__three_after_loss(h);
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}
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return is_new_loss;
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}
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EXPORT_SYMBOL_GPL(tfrc_rx_handle_loss);
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int tfrc_rx_hist_alloc(struct tfrc_rx_hist *h)
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{
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int i;
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