gvisor.dev/gvisor@v0.0.0-20240520182842-f9d4d51c7e0f/pkg/tcpip/link/stopfd/stopfd.go (about)

     1  // Copyright 2022 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  //go:build linux
    16  // +build linux
    17  
    18  // Package stopfd provides an type that can be used to signal the stop of a dispatcher.
    19  package stopfd
    20  
    21  import (
    22  	"fmt"
    23  
    24  	"golang.org/x/sys/unix"
    25  )
    26  
    27  // StopFD is an eventfd used to signal the stop of a dispatcher.
    28  type StopFD struct {
    29  	EFD int
    30  }
    31  
    32  // New returns a new, initialized StopFD.
    33  func New() (StopFD, error) {
    34  	efd, err := unix.Eventfd(0, unix.EFD_NONBLOCK)
    35  	if err != nil {
    36  		return StopFD{EFD: -1}, fmt.Errorf("failed to create eventfd: %w", err)
    37  	}
    38  	return StopFD{EFD: efd}, nil
    39  }
    40  
    41  // Stop writes to the eventfd and notifies the dispatcher to stop. It does not
    42  // block.
    43  func (sf *StopFD) Stop() {
    44  	increment := []byte{1, 0, 0, 0, 0, 0, 0, 0}
    45  	if n, err := unix.Write(sf.EFD, increment); n != len(increment) || err != nil {
    46  		// There are two possible errors documented in eventfd(2) for writing:
    47  		// 1. We are writing 8 bytes and not 0xffffffffffffff, thus no EINVAL.
    48  		// 2. stop is only supposed to be called once, it can't reach the limit,
    49  		// thus no EAGAIN.
    50  		panic(fmt.Sprintf("write(EFD) = (%d, %s), want (%d, nil)", n, err, len(increment)))
    51  	}
    52  }