Store segment transmit count.

This will aid in segment reordering detection.

Updates #691

PiperOrigin-RevId: 301692638

2 files changed, 5 insertions, 4 deletions

diff --git a/pkg/tcpip/transport/tcp/segment.go b/pkg/tcpip/transport/tcp/segment.go
index 1c10da5ca..5d0bc4f72 100644
--- a/pkg/tcpip/transport/tcp/segment.go
+++ b/pkg/tcpip/transport/tcp/segment.go
@@ -56,9 +56,9 @@ type segment struct {
 	options        []byte `state:".([]byte)"`
 	hasNewSACKInfo bool
 	rcvdTime       time.Time `state:".(unixTime)"`
-	// xmitTime is the last transmit time of this segment. A zero value
-	// indicates that the segment has yet to be transmitted.
-	xmitTime time.Time `state:".(unixTime)"`
+	// xmitTime is the last transmit time of this segment.
+	xmitTime  time.Time `state:".(unixTime)"`
+	xmitCount uint32
 }
 
 func newSegment(r *stack.Route, id stack.TransportEndpointID, pkt tcpip.PacketBuffer) *segment {
diff --git a/pkg/tcpip/transport/tcp/snd.go b/pkg/tcpip/transport/tcp/snd.go
index b74b61e7d..657c3146e 100644
--- a/pkg/tcpip/transport/tcp/snd.go
+++ b/pkg/tcpip/transport/tcp/snd.go
@@ -1229,7 +1229,7 @@ func (s *sender) handleRcvdSegment(seg *segment) {
 
 // sendSegment sends the specified segment.
 func (s *sender) sendSegment(seg *segment) *tcpip.Error {
-	if !seg.xmitTime.IsZero() {
+	if seg.xmitCount > 0 {
 		s.ep.stack.Stats().TCP.Retransmits.Increment()
 		s.ep.stats.SendErrors.Retransmits.Increment()
 		if s.sndCwnd < s.sndSsthresh {
@@ -1237,6 +1237,7 @@ func (s *sender) sendSegment(seg *segment) *tcpip.Error {
 		}
 	}
 	seg.xmitTime = time.Now()
+	seg.xmitCount++
 	return s.sendSegmentFromView(seg.data, seg.flags, seg.sequenceNumber)
 }