RACK: Update reorder window.

After receiving an ACK(cumulative or selective), RACK will update the reorder
window which is used as a settling time before marking the packet as lost.
This change will add an init function to initialize the variables in RACK and
also store the reference to sender in rackControl.
The reorder window is calculated as per rfc:
https://tools.ietf.org/html/draft-ietf-tcpm-rack-08#section-7.2 Step 4.

PiperOrigin-RevId: 354453528

1 files changed, 16 insertions, 9 deletions

diff --git a/pkg/tcpip/transport/tcp/snd.go b/pkg/tcpip/transport/tcp/snd.go
index 2967c9f97..dfc8fd248 100644
--- a/pkg/tcpip/transport/tcp/snd.go
+++ b/pkg/tcpip/transport/tcp/snd.go
@@ -258,14 +258,9 @@ func newSender(ep *endpoint, iss, irs seqnum.Value, sndWnd seqnum.Size, mss uint
 			highRxt:   iss,
 			rescueRxt: iss,
 		},
-		rc: rackControl{
-			fack: iss,
-		},
 		gso: ep.gso != nil,
 	}
 
-	s.rc.init()
-
 	if s.gso {
 		s.ep.gso.MSS = uint16(maxPayloadSize)
 	}
@@ -273,6 +268,7 @@ func newSender(ep *endpoint, iss, irs seqnum.Value, sndWnd seqnum.Size, mss uint
 	s.cc = s.initCongestionControl(ep.cc)
 
 	s.lr = s.initLossRecovery()
+	s.rc.init(s, iss)
 
 	// A negative sndWndScale means that no scaling is in use, otherwise we
 	// store the scaling value.
@@ -1058,7 +1054,6 @@ func (s *sender) leaveRecovery() {
 
 	// Deflate cwnd. It had been artificially inflated when new dups arrived.
 	s.sndCwnd = s.sndSsthresh
-
 	s.cc.PostRecovery()
 }
 
@@ -1195,11 +1190,13 @@ func (s *sender) isDupAck(seg *segment) bool {
 // See: https://tools.ietf.org/html/draft-ietf-tcpm-rack-08#section-7.2
 // steps 2 and 3.
 func (s *sender) walkSACK(rcvdSeg *segment) {
+	s.rc.setDSACKSeen(false)
+
 	// Look for DSACK block.
 	idx := 0
 	n := len(rcvdSeg.parsedOptions.SACKBlocks)
 	if checkDSACK(rcvdSeg) {
-		s.rc.setDSACKSeen()
+		s.rc.setDSACKSeen(true)
 		idx = 1
 		n--
 	}
@@ -1220,7 +1217,7 @@ func (s *sender) walkSACK(rcvdSeg *segment) {
 	for _, sb := range sackBlocks {
 		for seg != nil && seg.sequenceNumber.LessThan(sb.End) && seg.xmitCount != 0 {
 			if sb.Start.LessThanEq(seg.sequenceNumber) && !seg.acked {
-				s.rc.update(seg, rcvdSeg, s.ep.tsOffset)
+				s.rc.update(seg, rcvdSeg)
 				s.rc.detectReorder(seg)
 				seg.acked = true
 				s.sackedOut += s.pCount(seg, s.maxPayloadSize)
@@ -1424,7 +1421,7 @@ func (s *sender) handleRcvdSegment(rcvdSeg *segment) {
 
 			// Update the RACK fields if SACK is enabled.
 			if s.ep.sackPermitted && !seg.acked {
-				s.rc.update(seg, rcvdSeg, s.ep.tsOffset)
+				s.rc.update(seg, rcvdSeg)
 				s.rc.detectReorder(seg)
 			}
 
@@ -1454,6 +1451,10 @@ func (s *sender) handleRcvdSegment(rcvdSeg *segment) {
 			s.cc.Update(originalOutstanding - s.outstanding)
 			if s.fr.last.LessThan(s.sndUna) {
 				s.state = tcpip.Open
+				// Update RACK when we are exiting fast or RTO
+				// recovery as described in the RFC
+				// draft-ietf-tcpm-rack-08 Section-7.2 Step 4.
+				s.rc.exitRecovery()
 			}
 		}
 
@@ -1477,6 +1478,12 @@ func (s *sender) handleRcvdSegment(rcvdSeg *segment) {
 		}
 	}
 
+	// Update RACK reorder window.
+	// See: https://tools.ietf.org/html/draft-ietf-tcpm-rack-08#section-7.2
+	// * Upon receiving an ACK:
+	// * Step 4: Update RACK reordering window
+	s.rc.updateRACKReorderWindow(rcvdSeg)
+
 	// Now that we've popped all acknowledged data from the retransmit
 	// queue, retransmit if needed.
 	if s.fr.active {