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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 stack
import (
"fmt"
"gvisor.dev/gvisor/pkg/sync"
"gvisor.dev/gvisor/pkg/tcpip"
)
const (
// maxPendingResolutions is the maximum number of pending link-address
// resolutions.
maxPendingResolutions = 64
maxPendingPacketsPerResolution = 256
)
type pendingPacket struct {
nic *NIC
route *Route
proto tcpip.NetworkProtocolNumber
pkt tcpip.PacketBuffer
}
type forwardQueue struct {
sync.Mutex
// The packets to send once the resolver completes.
packets map[<-chan struct{}][]*pendingPacket
// FIFO of channels used to cancel the oldest goroutine waiting for
// link-address resolution.
cancelChans []chan struct{}
}
func newForwardQueue() *forwardQueue {
return &forwardQueue{packets: make(map[<-chan struct{}][]*pendingPacket)}
}
func (f *forwardQueue) enqueue(ch <-chan struct{}, n *NIC, r *Route, protocol tcpip.NetworkProtocolNumber, pkt tcpip.PacketBuffer) {
shouldWait := false
f.Lock()
packets, ok := f.packets[ch]
if !ok {
shouldWait = true
}
for len(packets) == maxPendingPacketsPerResolution {
p := packets[0]
packets = packets[1:]
p.nic.stack.stats.IP.OutgoingPacketErrors.Increment()
p.route.Release()
}
if l := len(packets); l >= maxPendingPacketsPerResolution {
panic(fmt.Sprintf("max pending packets for resolution reached; got %d packets, max = %d", l, maxPendingPacketsPerResolution))
}
f.packets[ch] = append(packets, &pendingPacket{
nic: n,
route: r,
proto: protocol,
pkt: pkt,
})
f.Unlock()
if !shouldWait {
return
}
// Wait for the link-address resolution to complete.
// Start a goroutine with a forwarding-cancel channel so that we can
// limit the maximum number of goroutines running concurrently.
cancel := f.newCancelChannel()
go func() {
cancelled := false
select {
case <-ch:
case <-cancel:
cancelled = true
}
f.Lock()
packets := f.packets[ch]
delete(f.packets, ch)
f.Unlock()
for _, p := range packets {
if cancelled {
p.nic.stack.stats.IP.OutgoingPacketErrors.Increment()
} else if _, err := p.route.Resolve(nil); err != nil {
p.nic.stack.stats.IP.OutgoingPacketErrors.Increment()
} else {
p.nic.forwardPacket(p.route, p.proto, p.pkt)
}
p.route.Release()
}
}()
}
// newCancelChannel creates a channel that can cancel a pending forwarding
// activity. The oldest channel is closed if the number of open channels would
// exceed maxPendingResolutions.
func (f *forwardQueue) newCancelChannel() chan struct{} {
f.Lock()
defer f.Unlock()
if len(f.cancelChans) == maxPendingResolutions {
ch := f.cancelChans[0]
f.cancelChans = f.cancelChans[1:]
close(ch)
}
if l := len(f.cancelChans); l >= maxPendingResolutions {
panic(fmt.Sprintf("max pending resolutions reached; got %d active resolutions, max = %d", l, maxPendingResolutions))
}
ch := make(chan struct{})
f.cancelChans = append(f.cancelChans, ch)
return ch
}
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