src/internal/poll/sock_cloexec_accept.go

// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This file implements accept for platforms that provide a fast path for
// setting SetNonblock and CloseOnExec, but don't necessarily have accept4.
// This is the code we used for accept in Go 1.17 and earlier.
// On Linux the accept4 system call was introduced in 2.6.28 kernel,
// and our minimum requirement is 2.6.32, so we simplified the function.
// Unfortunately, on ARM accept4 wasn't added until 2.6.36, so for ARM
// only we continue using the older code.

//go:build linux && arm

package poll

import "syscall"

// Wrapper around the accept system call that marks the returned file
// descriptor as nonblocking and close-on-exec.
func accept(s int) (int, syscall.Sockaddr, string, error) {
	ns, sa, err := Accept4Func(s, syscall.SOCK_NONBLOCK|syscall.SOCK_CLOEXEC)
	switch err {
	case nil:
		return ns, sa, "", nil
	default: // errors other than the ones listed
		return -1, sa, "accept4", err
	case syscall.ENOSYS: // syscall missing
	case syscall.EINVAL: // some Linux use this instead of ENOSYS
	case syscall.EACCES: // some Linux use this instead of ENOSYS
	case syscall.EFAULT: // some Linux use this instead of ENOSYS
	}

	// See ../syscall/exec_unix.go for description of ForkLock.
	// It is probably okay to hold the lock across syscall.Accept
	// because we have put fd.sysfd into non-blocking mode.
	// However, a call to the File method will put it back into
	// blocking mode. We can't take that risk, so no use of ForkLock here.
	ns, sa, err = AcceptFunc(s)
	if err == nil {
		syscall.CloseOnExec(ns)
	}
	if err != nil {
		return -1, nil, "accept", err
	}
	if err = syscall.SetNonblock(ns, true); err != nil {
		CloseFunc(ns)
		return -1, nil, "setnonblock", err
	}
	return ns, sa, "", nil
}