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fd_unix.go
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fd_unix.go
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// Copyright (c) 2020 Andy Pan
//
// 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.
//go:build linux || freebsd || dragonfly || darwin
// +build linux freebsd dragonfly darwin
package netpoll
import (
"sync/atomic"
"syscall"
"golang.org/x/sys/unix"
)
// Dup is the wrapper for dupCloseOnExec.
func Dup(fd int) (int, string, error) {
return dupCloseOnExec(fd)
}
// tryDupCloexec indicates whether F_DUPFD_CLOEXEC should be used.
// If the kernel doesn't support it, this is set to 0.
var tryDupCloexec = int32(1)
// dupCloseOnExec dups fd and marks it close-on-exec.
func dupCloseOnExec(fd int) (int, string, error) {
if atomic.LoadInt32(&tryDupCloexec) == 1 {
r, err := unix.FcntlInt(uintptr(fd), unix.F_DUPFD_CLOEXEC, 0)
if err == nil {
return r, "", nil
}
switch err.(syscall.Errno) {
case unix.EINVAL, unix.ENOSYS:
// Old kernel, or js/wasm (which returns
// ENOSYS). Fall back to the portable way from
// now on.
atomic.StoreInt32(&tryDupCloexec, 0)
default:
return -1, "fcntl", err
}
}
return dupCloseOnExecOld(fd)
}
// dupCloseOnExecOld is the traditional way to dup an fd and
// set its O_CLOEXEC bit, using two system calls.
func dupCloseOnExecOld(fd int) (int, string, error) {
syscall.ForkLock.RLock()
defer syscall.ForkLock.RUnlock()
newFD, err := syscall.Dup(fd)
if err != nil {
return -1, "dup", err
}
syscall.CloseOnExec(newFD)
return newFD, "", nil
}