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fifo.go
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fifo.go
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// 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 fifo provides the implementation of FIFO queuing discipline that
// queues all outbound packets and asynchronously dispatches them to the
// lower link endpoint in the order that they were queued.
package fifo
import (
"github.com/ttpreport/gvisor-ligolo/pkg/atomicbitops"
"github.com/ttpreport/gvisor-ligolo/pkg/sleep"
"github.com/ttpreport/gvisor-ligolo/pkg/sync"
"github.com/ttpreport/gvisor-ligolo/pkg/tcpip"
"github.com/ttpreport/gvisor-ligolo/pkg/tcpip/stack"
)
var _ stack.QueueingDiscipline = (*discipline)(nil)
const (
// BatchSize is the number of packets to write in each syscall. It is 47
// because when GvisorGSO is in use then a single 65KB TCP segment can get
// split into 46 segments of 1420 bytes and a single 216 byte segment.
BatchSize = 47
qDiscClosed = 1
)
// discipline represents a QueueingDiscipline which implements a FIFO queue for
// all outgoing packets. discipline can have 1 or more underlying
// queueDispatchers. All outgoing packets are consistenly hashed to a single
// underlying queue using the PacketBuffer.Hash if set, otherwise all packets
// are queued to the first queue to avoid reordering in case of missing hash.
type discipline struct {
wg sync.WaitGroup
dispatchers []queueDispatcher
closed atomicbitops.Int32
}
// queueDispatcher is responsible for dispatching all outbound packets in its
// queue. It will also smartly batch packets when possible and write them
// through the lower LinkWriter.
type queueDispatcher struct {
lower stack.LinkWriter
mu sync.Mutex
// +checklocks:mu
queue packetBufferCircularList
newPacketWaker sleep.Waker
closeWaker sleep.Waker
}
// New creates a new fifo queuing discipline with the n queues with maximum
// capacity of queueLen.
//
// +checklocksignore: we don't have to hold locks during initialization.
func New(lower stack.LinkWriter, n int, queueLen int) stack.QueueingDiscipline {
d := &discipline{
dispatchers: make([]queueDispatcher, n),
}
// Create the required dispatchers
for i := range d.dispatchers {
qd := &d.dispatchers[i]
qd.lower = lower
qd.queue.init(queueLen)
d.wg.Add(1)
go func() {
defer d.wg.Done()
qd.dispatchLoop()
}()
}
return d
}
func (qd *queueDispatcher) dispatchLoop() {
s := sleep.Sleeper{}
s.AddWaker(&qd.newPacketWaker)
s.AddWaker(&qd.closeWaker)
defer s.Done()
var batch stack.PacketBufferList
for {
switch w := s.Fetch(true); w {
case &qd.newPacketWaker:
case &qd.closeWaker:
qd.mu.Lock()
for p := qd.queue.removeFront(); !p.IsNil(); p = qd.queue.removeFront() {
p.DecRef()
}
qd.queue.decRef()
qd.mu.Unlock()
return
default:
panic("unknown waker")
}
qd.mu.Lock()
for pkt := qd.queue.removeFront(); !pkt.IsNil(); pkt = qd.queue.removeFront() {
batch.PushBack(pkt)
if batch.Len() < BatchSize && !qd.queue.isEmpty() {
continue
}
qd.mu.Unlock()
_, _ = qd.lower.WritePackets(batch)
batch.Reset()
qd.mu.Lock()
}
qd.mu.Unlock()
}
}
// WritePacket implements stack.QueueingDiscipline.WritePacket.
//
// The packet must have the following fields populated:
// - pkt.EgressRoute
// - pkt.GSOOptions
// - pkt.NetworkProtocolNumber
func (d *discipline) WritePacket(pkt stack.PacketBufferPtr) tcpip.Error {
if d.closed.Load() == qDiscClosed {
return &tcpip.ErrClosedForSend{}
}
qd := &d.dispatchers[int(pkt.Hash)%len(d.dispatchers)]
qd.mu.Lock()
haveSpace := qd.queue.hasSpace()
if haveSpace {
qd.queue.pushBack(pkt.IncRef())
}
qd.mu.Unlock()
if !haveSpace {
return &tcpip.ErrNoBufferSpace{}
}
qd.newPacketWaker.Assert()
return nil
}
func (d *discipline) Close() {
d.closed.Store(qDiscClosed)
for i := range d.dispatchers {
d.dispatchers[i].closeWaker.Assert()
}
d.wg.Wait()
}