1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
|
// Copyright 2020 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package tcp
import "gvisor.dev/gvisor/pkg/tcpip/seqnum"
// sackRecovery stores the variables related to TCP SACK loss recovery
// algorithm.
//
// +stateify savable
type sackRecovery struct {
s *sender
}
func newSACKRecovery(s *sender) *sackRecovery {
return &sackRecovery{s: s}
}
// handleSACKRecovery implements the loss recovery phase as described in RFC6675
// section 5, step C.
// +checklocks:sr.s.ep.mu
func (sr *sackRecovery) handleSACKRecovery(limit int, end seqnum.Value) (dataSent bool) {
snd := sr.s
snd.SetPipe()
if smss := int(snd.ep.scoreboard.SMSS()); limit > smss {
// Cap segment size limit to s.smss as SACK recovery requires
// that all retransmissions or new segments send during recovery
// be of <= SMSS.
limit = smss
}
nextSegHint := snd.writeList.Front()
for snd.Outstanding < snd.SndCwnd {
var nextSeg *segment
var rescueRtx bool
nextSeg, nextSegHint, rescueRtx = snd.NextSeg(nextSegHint)
if nextSeg == nil {
return dataSent
}
if !snd.isAssignedSequenceNumber(nextSeg) || snd.SndNxt.LessThanEq(nextSeg.sequenceNumber) {
// New data being sent.
// Step C.3 described below is handled by
// maybeSendSegment which increments sndNxt when
// a segment is transmitted.
//
// Step C.3 "If any of the data octets sent in
// (C.1) are above HighData, HighData must be
// updated to reflect the transmission of
// previously unsent data."
//
// We pass s.smss as the limit as the Step 2) requires that
// new data sent should be of size s.smss or less.
if sent := snd.maybeSendSegment(nextSeg, limit, end); !sent {
return dataSent
}
dataSent = true
snd.Outstanding++
snd.updateWriteNext(nextSeg.Next())
continue
}
// Now handle the retransmission case where we matched either step 1,3 or 4
// of the NextSeg algorithm.
// RFC 6675, Step C.4.
//
// "The estimate of the amount of data outstanding in the network
// must be updated by incrementing pipe by the number of octets
// transmitted in (C.1)."
snd.Outstanding++
dataSent = true
snd.sendSegment(nextSeg)
segEnd := nextSeg.sequenceNumber.Add(nextSeg.logicalLen())
if rescueRtx {
// We do the last part of rule (4) of NextSeg here to update
// RescueRxt as until this point we don't know if we are going
// to use the rescue transmission.
snd.FastRecovery.RescueRxt = snd.FastRecovery.Last
} else {
// RFC 6675, Step C.2
//
// "If any of the data octets sent in (C.1) are below
// HighData, HighRxt MUST be set to the highest sequence
// number of the retransmitted segment unless NextSeg ()
// rule (4) was invoked for this retransmission."
snd.FastRecovery.HighRxt = segEnd - 1
}
}
return dataSent
}
// +checklocks:sr.s.ep.mu
func (sr *sackRecovery) DoRecovery(rcvdSeg *segment, fastRetransmit bool) {
snd := sr.s
if fastRetransmit {
snd.resendSegment()
}
// We are in fast recovery mode. Ignore the ack if it's out of range.
if ack := rcvdSeg.ackNumber; !ack.InRange(snd.SndUna, snd.SndNxt+1) {
return
}
// RFC 6675 recovery algorithm step C 1-5.
end := snd.SndUna.Add(snd.SndWnd)
dataSent := sr.handleSACKRecovery(snd.MaxPayloadSize, end)
snd.postXmit(dataSent, true /* shouldScheduleProbe */)
}
|
