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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 pipe provides the implementation of pipe-like data-link layer
// endpoints. Such endpoints allow packets to be sent between two interfaces.
package pipe
import (
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/buffer"
"gvisor.dev/gvisor/pkg/tcpip/header"
"gvisor.dev/gvisor/pkg/tcpip/stack"
)
var _ stack.LinkEndpoint = (*Endpoint)(nil)
// New returns both ends of a new pipe.
func New(linkAddr1, linkAddr2 tcpip.LinkAddress) (*Endpoint, *Endpoint) {
ep1 := &Endpoint{
linkAddr: linkAddr1,
}
ep2 := &Endpoint{
linkAddr: linkAddr2,
}
ep1.linked = ep2
ep2.linked = ep1
return ep1, ep2
}
// Endpoint is one end of a pipe.
type Endpoint struct {
dispatcher stack.NetworkDispatcher
linked *Endpoint
linkAddr tcpip.LinkAddress
}
func (e *Endpoint) deliverPackets(r stack.RouteInfo, proto tcpip.NetworkProtocolNumber, pkts stack.PacketBufferList) {
// Note that the local address from the perspective of this endpoint is the
// remote address from the perspective of the other end of the pipe
// (e.linked). Similarly, the remote address from the perspective of this
// endpoint is the local address on the other end.
//
// Deliver the packet in a new goroutine to escape this goroutine's stack and
// avoid a deadlock when a packet triggers a response which leads the stack to
// try and take a lock it already holds.
//
// As of writing, a deadlock may occur when performing link resolution as the
// neighbor table will send a solicitation while holding a lock and the
// response advertisement will be sent in the same stack that sent the
// solictation. When the response is received, the stack attempts to take the
// same lock it already took before sending the solicitation, leading to a
// deadlock. Basically, we attempt to lock the same lock twice in the same
// call stack.
//
// TODO(gvisor.dev/issue/5289): don't use a new goroutine once we support send
// and receive queues.
go func() {
for pkt := pkts.Front(); pkt != nil; pkt = pkt.Next() {
e.linked.dispatcher.DeliverNetworkPacket(r.LocalLinkAddress /* remote */, r.RemoteLinkAddress /* local */, proto, stack.NewPacketBuffer(stack.PacketBufferOptions{
Data: buffer.NewVectorisedView(pkt.Size(), pkt.Views()),
}))
}
}()
}
// WritePacket implements stack.LinkEndpoint.
func (e *Endpoint) WritePacket(r stack.RouteInfo, _ *stack.GSO, proto tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) *tcpip.Error {
if e.linked.IsAttached() {
var pkts stack.PacketBufferList
pkts.PushBack(pkt)
e.deliverPackets(r, proto, pkts)
}
return nil
}
// WritePackets implements stack.LinkEndpoint.
func (e *Endpoint) WritePackets(r stack.RouteInfo, _ *stack.GSO, pkts stack.PacketBufferList, proto tcpip.NetworkProtocolNumber) (int, *tcpip.Error) {
if e.linked.IsAttached() {
e.deliverPackets(r, proto, pkts)
}
return pkts.Len(), nil
}
// Attach implements stack.LinkEndpoint.
func (e *Endpoint) Attach(dispatcher stack.NetworkDispatcher) {
e.dispatcher = dispatcher
}
// IsAttached implements stack.LinkEndpoint.
func (e *Endpoint) IsAttached() bool {
return e.dispatcher != nil
}
// Wait implements stack.LinkEndpoint.
func (*Endpoint) Wait() {}
// MTU implements stack.LinkEndpoint.
func (*Endpoint) MTU() uint32 {
return header.IPv6MinimumMTU
}
// Capabilities implements stack.LinkEndpoint.
func (*Endpoint) Capabilities() stack.LinkEndpointCapabilities {
return 0
}
// MaxHeaderLength implements stack.LinkEndpoint.
func (*Endpoint) MaxHeaderLength() uint16 {
return 0
}
// LinkAddress implements stack.LinkEndpoint.
func (e *Endpoint) LinkAddress() tcpip.LinkAddress {
return e.linkAddr
}
// ARPHardwareType implements stack.LinkEndpoint.
func (*Endpoint) ARPHardwareType() header.ARPHardwareType {
return header.ARPHardwareNone
}
// AddHeader implements stack.LinkEndpoint.
func (*Endpoint) AddHeader(_, _ tcpip.LinkAddress, _ tcpip.NetworkProtocolNumber, _ *stack.PacketBuffer) {
}
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