[PATCH 12/14] [ACKVEC]: Update Ack Vector input routine

[Gerrit Renker <gerrit@erg.abdn.ac.uk>]

This patch updates the code which registers new packets as received, using the
new circular buffer interface, it now
	* supports both tail/head pointers and buffer wrap-around,
	* deals with overflow (head/tail move in lock-step), and
	* uses dynamic buffer-length computation.

The updated code is also partioned differently, into
	1. dealing with the empty buffer,
	2. adding new packets into non-empty buffer,
	3. reserving space when encountering a `hole' in the sequence space,
	4. updating old state and deciding when old state is irrelevant.

Much of the old code and naming is reused.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
---
 net/dccp/ackvec.c |  123 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 net/dccp/ackvec.h |    6 +++
 2 files changed, 129 insertions(+), 0 deletions(-)

--- a/net/dccp/ackvec.h
+++ b/net/dccp/ackvec.h
@@ -109,6 +109,7 @@ extern void dccp_ackvec_free(struct dccp_ackvec *av);
 extern int dccp_ackvec_add(struct dccp_ackvec *av, const struct sock *sk,
 			   const u64 ackno, const u8 state);
 
+extern void dccp_ackvec_input(struct dccp_ackvec *av, u64 seqno, u8 state);
 extern int  dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seq, u8 sum);
 extern void dccp_ackvec_clear_state(struct dccp_ackvec *av, const u64 ackno);
 extern u16  dccp_ackvec_buflen(const struct dccp_ackvec *av);
@@ -136,6 +137,11 @@ static inline void dccp_ackvec_free(struct dccp_ackvec *av)
 {
 }
 
+static inline void dccp_ackvec_input(struct dccp_ackvec *av, u64 seq, u8 state)
+{
+
+}
+
 static inline int dccp_ackvec_add(struct dccp_ackvec *av, const struct sock *sk,
 				  const u64 ackno, const u8 state)
 {
--- a/net/dccp/ackvec.c
+++ b/net/dccp/ackvec.c
@@ -134,6 +134,129 @@ u16 dccp_ackvec_buflen(const struct dccp_ackvec *av)
 	return dccp_ackvec_idx_sub(av->av_buf_tail, av->av_buf_head);
 }
 
+/* Mark @num entries after buf_head as "Not yet received". */
+static void dccp_ackvec_reserve_seats(struct dccp_ackvec *av, u16 num)
+{
+	u16 start = dccp_ackvec_idx_add(av->av_buf_head, 1),
+	    len	  = DCCPAV_MAX_ACKVEC_LEN - start;
+
+	/* check for buffer wrap-around */
+	if (num > len) {
+		memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, len);
+		start = 0;
+		num  -= len;
+	}
+	if (num)
+		memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, num);
+}
+
+/**
+ * dccp_ackvec_update_old  -  Update previous state as per RFC 4340, 11.4.1
+ * @av:		non-empty buffer to update
+ * @distance:   negative or zero distance of @seqno from buf_ackno downward
+ * @seqno:	the (old) sequence number whose record is to be updated
+ * @state:	state in which packet carrying @seqno was received
+ */
+static void dccp_ackvec_update_old(struct dccp_ackvec *av, s64 distance,
+				   u64 seqno, enum dccp_ackvec_states state)
+{
+	u16 ptr = av->av_buf_head;
+
+	BUG_ON(distance > 0);
+	if (unlikely(dccp_ackvec_is_empty(av)))
+		return;
+
+	do {
+		u8 runlen = dccp_ackvec_runlen(av->av_buf + ptr);
+
+		if (distance + runlen >= 0) {
+			/*
+			 * Only update the state if packet has not been received
+			 * yet. This is OK as per the second table in RFC 4340,
+			 * 11.4.1; i.e. here we are using the following table:
+			 *                     RECEIVED
+			 *                      0   1   3
+			 *              S     +---+---+---+
+			 *              T   0 | 0 | 0 | 0 |
+			 *              O     +---+---+---+
+			 *              R   1 | 1 | 1 | 1 |
+			 *              E     +---+---+---+
+			 *              D   3 | 0 | 1 | 3 |
+			 *                    +---+---+---+
+			 * The "Not Received" state was set by reserve_seats().
+			 */
+			if (av->av_buf[ptr] == DCCPAV_NOT_RECEIVED)
+				av->av_buf[ptr] = state;
+			else
+				dccp_pr_debug("Not changing %llu state to %u\n",
+					      (unsigned long long)seqno, state);
+			break;
+		}
+
+		distance += runlen + 1;
+		ptr	  = dccp_ackvec_idx_add(ptr, 1);
+
+	} while (ptr != av->av_buf_tail);
+}
+
+/**
+ * dccp_ackvec_add_new  -  Record one or more new entries in Ack Vector buffer
+ * @av:		 container of buffer to update (can be empty or non-empty)
+ * @num_packets: number of packets to register (must be >= 1)
+ * @seqno:	 sequence number of the first packet in @num_packets
+ * @state:	 state in which packet carrying @seqno was received
+ */
+static void dccp_ackvec_add_new(struct dccp_ackvec *av, u16 num_packets,
+				u64 seqno, enum dccp_ackvec_states state)
+{
+	if ((num_packets + dccp_ackvec_buflen(av)) >= DCCPAV_MAX_ACKVEC_LEN) {
+		DCCP_CRIT("Ack Vector buffer overflow: dropping old entries\n");
+		av->av_overflow = true;
+	}
+
+	av->av_buf_head = dccp_ackvec_idx_sub(av->av_buf_head, num_packets);
+	if (av->av_overflow)
+		av->av_buf_tail = av->av_buf_head;
+
+	av->av_buf[av->av_buf_head] = state;
+	av->av_buf_ackno	    = seqno;
+
+	if (num_packets > 1)
+		dccp_ackvec_reserve_seats(av, num_packets - 1);
+}
+
+/**
+ * dccp_ackvec_input  -  Register incoming packet in the buffer
+ * @av:		buffer/records to update
+ * @seqno:	sequence number to register as received
+ * @state:	how packet with @seqno was received, one of %dccp_ackvec_states
+ */
+void dccp_ackvec_input(struct dccp_ackvec *av, u64 seqno, u8 state)
+{
+	if (dccp_ackvec_is_empty(av)) {
+
+		dccp_ackvec_add_new(av, 1, seqno, state);
+		av->av_tail_ackno = seqno;
+
+	} else {
+		s64 num_packets = dccp_delta_seqno(av->av_buf_ackno, seqno);
+		u8 *current_head = av->av_buf + av->av_buf_head;
+
+		if (num_packets == 1 &&
+		    dccp_ackvec_state(current_head) == state &&
+		    dccp_ackvec_runlen(current_head) < DCCPAV_MAX_RUNLEN) {
+
+			*current_head   += 1;
+			av->av_buf_ackno = seqno;
+
+		} else if (num_packets > 0) {
+			dccp_ackvec_add_new(av, num_packets, seqno, state);
+		} else {
+			dccp_ackvec_update_old(av, num_packets, seqno, state);
+		}
+	}
+}
+
 /*
  * 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;
-- 
1.5.3.GIT