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// Copyright 2018 Google LLC
//
// 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 waitable provides the implementation of data-link layer endpoints
// that wrap other endpoints, and can wait for inflight calls to WritePacket or
// DeliverNetworkPacket to finish (and new ones to be prevented).
//
// Waitable endpoints can be used in the networking stack by calling New(eID) to
// create a new endpoint, where eID is the ID of the endpoint being wrapped,
// and then passing it as an argument to Stack.CreateNIC().
package waitable
import (
"gvisor.googlesource.com/gvisor/pkg/gate"
"gvisor.googlesource.com/gvisor/pkg/tcpip"
"gvisor.googlesource.com/gvisor/pkg/tcpip/buffer"
"gvisor.googlesource.com/gvisor/pkg/tcpip/stack"
)
// Endpoint is a waitable link-layer endpoint.
type Endpoint struct {
dispatchGate gate.Gate
dispatcher stack.NetworkDispatcher
writeGate gate.Gate
lower stack.LinkEndpoint
}
// New creates a new waitable link-layer endpoint. It wraps around another
// endpoint and allows the caller to block new write/dispatch calls and wait for
// the inflight ones to finish before returning.
func New(lower tcpip.LinkEndpointID) (tcpip.LinkEndpointID, *Endpoint) {
e := &Endpoint{
lower: stack.FindLinkEndpoint(lower),
}
return stack.RegisterLinkEndpoint(e), e
}
// DeliverNetworkPacket implements stack.NetworkDispatcher.DeliverNetworkPacket.
// It is called by the link-layer endpoint being wrapped when a packet arrives,
// and only forwards to the actual dispatcher if Wait or WaitDispatch haven't
// been called.
func (e *Endpoint) DeliverNetworkPacket(linkEP stack.LinkEndpoint, remote, local tcpip.LinkAddress, protocol tcpip.NetworkProtocolNumber, vv buffer.VectorisedView) {
if !e.dispatchGate.Enter() {
return
}
e.dispatcher.DeliverNetworkPacket(e, remote, local, protocol, vv)
e.dispatchGate.Leave()
}
// Attach implements stack.LinkEndpoint.Attach. It saves the dispatcher and
// registers with the lower endpoint as its dispatcher so that "e" is called
// for inbound packets.
func (e *Endpoint) Attach(dispatcher stack.NetworkDispatcher) {
e.dispatcher = dispatcher
e.lower.Attach(e)
}
// IsAttached implements stack.LinkEndpoint.IsAttached.
func (e *Endpoint) IsAttached() bool {
return e.dispatcher != nil
}
// MTU implements stack.LinkEndpoint.MTU. It just forwards the request to the
// lower endpoint.
func (e *Endpoint) MTU() uint32 {
return e.lower.MTU()
}
// Capabilities implements stack.LinkEndpoint.Capabilities. It just forwards the
// request to the lower endpoint.
func (e *Endpoint) Capabilities() stack.LinkEndpointCapabilities {
return e.lower.Capabilities()
}
// MaxHeaderLength implements stack.LinkEndpoint.MaxHeaderLength. It just
// forwards the request to the lower endpoint.
func (e *Endpoint) MaxHeaderLength() uint16 {
return e.lower.MaxHeaderLength()
}
// LinkAddress implements stack.LinkEndpoint.LinkAddress. It just forwards the
// request to the lower endpoint.
func (e *Endpoint) LinkAddress() tcpip.LinkAddress {
return e.lower.LinkAddress()
}
// WritePacket implements stack.LinkEndpoint.WritePacket. It is called by
// higher-level protocols to write packets. It only forwards packets to the
// lower endpoint if Wait or WaitWrite haven't been called.
func (e *Endpoint) WritePacket(r *stack.Route, hdr buffer.Prependable, payload buffer.VectorisedView, protocol tcpip.NetworkProtocolNumber) *tcpip.Error {
if !e.writeGate.Enter() {
return nil
}
err := e.lower.WritePacket(r, hdr, payload, protocol)
e.writeGate.Leave()
return err
}
// WaitWrite prevents new calls to WritePacket from reaching the lower endpoint,
// and waits for inflight ones to finish before returning.
func (e *Endpoint) WaitWrite() {
e.writeGate.Close()
}
// WaitDispatch prevents new calls to DeliverNetworkPacket from reaching the
// actual dispatcher, and waits for inflight ones to finish before returning.
func (e *Endpoint) WaitDispatch() {
e.dispatchGate.Close()
}
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