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// Copyright 2014 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.
//go:build dragonfly || freebsd || linux || netbsd
package unix
import "unsafe"
// fcntl64Syscall is usually SYS_FCNTL, but is overridden on 32-bit Linux
// systems by fcntl_linux_32bit.go to be SYS_FCNTL64.
var fcntl64Syscall uintptr = SYS_FCNTL
func fcntl(fd int, cmd, arg int) (int, error) {
valptr, _, errno := Syscall(fcntl64Syscall, uintptr(fd), uintptr(cmd), uintptr(arg))
var err error
if errno != 0 {
err = errno
return int(valptr), err
// FcntlInt performs a fcntl syscall on fd with the provided command and argument.
func FcntlInt(fd uintptr, cmd, arg int) (int, error) {
return fcntl(int(fd), cmd, arg)
// FcntlFlock performs a fcntl syscall for the F_GETLK, F_SETLK or F_SETLKW command.
func FcntlFlock(fd uintptr, cmd int, lk *Flock_t) error {
_, _, errno := Syscall(fcntl64Syscall, fd, uintptr(cmd), uintptr(unsafe.Pointer(lk)))
if errno == 0 {
return nil
return errno