sys/netinet/tcp_sack.c

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205 			/* pkt left to sack blk */
209 			/* pkt right to sack blk */
551  * Process cumulative ACK and the TCP SACK option to update the scoreboard.
552  * tp->snd_holes is an ordered list of holes (oldest to newest, in terms of
559 tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack)
582 	 * Account changes to SND.UNA always in delivered data.
590 		 * due to DSACK blocks
599 	 * Append received valid SACK blocks to sack_blocks[], but only if we
602 	if (to->to_flags & TOF_SACK) {
603 		for (i = 0; i < to->to_nsacks; i++) {
604 			bcopy((to->to_sacks + i * TCPOLEN_SACK),
635 	 * pass. The overhead of sorting up to 4+1 elements is less than
636 	 * making up to 4+1 passes over the scoreboard.
649 		 * Empty scoreboard. Need to initialize snd_fack (it may be
652 		 * (in the logic that adds holes to the tail of the
662 	 * one pass in order to reduce the number of compares especially when
678 		 * is always to the right of the end.
705 				/* Go to the previous sack block. */
710 				 * We failed to add a new hole based on the current
712 				 * fall completely to the right of snd_fack and
713 				 * proceed to trim the scoreboard based on the
727 					 * some SACK data had to be dismissed.
765 			 * SACKs data beyond the current hole.  Go to the
773 			 * SACKs data before the current hole.  Go to the
825 				 * to split current hole
879 	if (!(to->to_flags & TOF_SACK))
898  * Free all SACK holes to clear the scoreboard.
921  * the scoreboard. This is in line with the Errata to
923  * an RTO to good effect typically.
940  * simple for now.  When a partial ack is received, force snd_cwnd to a value
941  * that will allow the sender to transmit no more than 2 segments.  If
943  * the goal is to prevent the sender from bursting a large amount of data in
988 	 * compared to RFC6675.
990 	 * segments to be retransmitted. This addresses a corner case, when
1021  * Returns the next hole to retransmit and the number of retransmitted bytes
1027  * the loop to traverse more than 1 link before finding the next hole to
1028  * retransmit, we would need to have at least 1 node following the current
1031  * Therefore, in order to traverse more 1 link in the loop below, we need to
1077  * should be used to avoid retransmitting SACKed data.  This function
1078  * traverses the SACK list to see if snd_nxt should be moved forward.
1095 	 * Two cases for which we want to advance snd_nxt:
1145 		 * Remember the old ssthresh, to deduct the beta factor used
1146 		 * by the CC module. Finally, set cwnd to ssthresh just
1147 		 * prior to invoking another cwnd reduction by the CC
1148 		 * module, to not shrink it excessively.
1161 		 * subsequently, only set it to a safe value here.