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// Copyright 2019 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.
// +build linux
package flipcall
import (
"fmt"
"math"
"sync/atomic"
"syscall"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/log"
)
func (ep *Endpoint) doFutexRoundTrip() error {
ourSeq, err := ep.doFutexNotifySeq()
if err != nil {
return err
}
return ep.doFutexWaitSeq(ourSeq)
}
func (ep *Endpoint) doFutexWaitFirst() error {
return ep.doFutexWaitSeq(0)
}
func (ep *Endpoint) doFutexNotifyLast() error {
_, err := ep.doFutexNotifySeq()
return err
}
func (ep *Endpoint) doFutexNotifySeq() (uint32, error) {
ourSeq := atomic.AddUint32(ep.seq(), 1)
if err := ep.futexWake(1); err != nil {
return ourSeq, fmt.Errorf("failed to FUTEX_WAKE peer Endpoint: %v", err)
}
return ourSeq, nil
}
func (ep *Endpoint) doFutexWaitSeq(prevSeq uint32) error {
nextSeq := prevSeq + 1
for {
if ep.isShutdown() {
return endpointShutdownError{}
}
if err := ep.futexWait(prevSeq); err != nil {
return fmt.Errorf("failed to FUTEX_WAIT for peer Endpoint: %v", err)
}
seq := atomic.LoadUint32(ep.seq())
if seq == nextSeq {
return nil
}
if seq != prevSeq {
return fmt.Errorf("invalid packet sequence number %d (expected %d or %d)", seq, prevSeq, nextSeq)
}
}
}
func (ep *Endpoint) doFutexInterruptForShutdown() {
// Wake MaxInt32 threads to prevent a malicious or broken peer from
// swallowing our wakeup by FUTEX_WAITing from multiple threads.
if err := ep.futexWake(math.MaxInt32); err != nil {
log.Warningf("failed to FUTEX_WAKE Endpoint: %v", err)
}
}
func (ep *Endpoint) futexWake(numThreads int32) error {
if _, _, e := syscall.RawSyscall(syscall.SYS_FUTEX, uintptr(ep.packet), linux.FUTEX_WAKE, uintptr(numThreads)); e != 0 {
return e
}
return nil
}
func (ep *Endpoint) futexWait(seq uint32) error {
_, _, e := syscall.Syscall6(syscall.SYS_FUTEX, uintptr(ep.packet), linux.FUTEX_WAIT, uintptr(seq), 0, 0, 0)
if e != 0 && e != syscall.EAGAIN && e != syscall.EINTR {
return e
}
return nil
}
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