func TestPassFD(t *testing.T) {
	if os.Getenv("GO_WANT_HELPER_PROCESS") == "1" {
		passFDChild()
		return
	}
	tempDir, err := ioutil.TempDir("", "TestPassFD")
	if err != nil {
		t.Fatal(err)
	}
	defer os.RemoveAll(tempDir)
	fds, err := unix.Socketpair(unix.AF_LOCAL, unix.SOCK_STREAM, 0)
	if err != nil {
		t.Fatalf("Socketpair: %v", err)
	}
	defer unix.Close(fds[0])
	defer unix.Close(fds[1])
	writeFile := os.NewFile(uintptr(fds[0]), "child-writes")
	readFile := os.NewFile(uintptr(fds[1]), "parent-reads")
	defer writeFile.Close()
	defer readFile.Close()
	cmd := exec.Command(os.Args[0], "-test.run=^TestPassFD$", "--", tempDir)
	cmd.Env = []string{"GO_WANT_HELPER_PROCESS=1"}
	if lp := os.Getenv("LD_LIBRARY_PATH"); lp != "" {
		cmd.Env = append(cmd.Env, "LD_LIBRARY_PATH="+lp)
	}
	cmd.ExtraFiles = []*os.File{writeFile}
	out, err := cmd.CombinedOutput()
	if len(out) > 0 || err != nil {
		t.Fatalf("child process: %q, %v", out, err)
	}
	c, err := net.FileConn(readFile)
	if err != nil {
		t.Fatalf("FileConn: %v", err)
	}
	defer c.Close()
	uc, ok := c.(*net.UnixConn)
	if !ok {
		t.Fatalf("unexpected FileConn type; expected UnixConn, got %T", c)
	}
	buf := make([]byte, 32)  
	oob := make([]byte, 32)  
	closeUnix := time.AfterFunc(5*time.Second, func() {
		t.Logf("timeout reading from unix socket")
		uc.Close()
	})
	_, oobn, _, _, err := uc.ReadMsgUnix(buf, oob)
	if err != nil {
		t.Fatalf("ReadMsgUnix: %v", err)
	}
	closeUnix.Stop()
	scms, err := unix.ParseSocketControlMessage(oob[:oobn])
	if err != nil {
		t.Fatalf("ParseSocketControlMessage: %v", err)
	}
	if len(scms) != 1 {
		t.Fatalf("expected 1 SocketControlMessage; got scms = %#v", scms)
	}
	scm := scms[0]
	gotFds, err := unix.ParseUnixRights(&scm)
	if err != nil {
		t.Fatalf("unix.ParseUnixRights: %v", err)
	}
	if len(gotFds) != 1 {
		t.Fatalf("wanted 1 fd; got %#v", gotFds)
	}
	f := os.NewFile(uintptr(gotFds[0]), "fd-from-child")
	defer f.Close()
	got, err := ioutil.ReadAll(f)
	want := "Hello from child process!\n"
	if string(got) != want {
		t.Errorf("child process ReadAll: %q, %v; want %q", got, err, want)
	}
}
TestPassFD tests passing a file descriptor over a Unix socket.

This test involved both a parent and child process. The parent
process is invoked as a normal test, with "go test", which then
runs the child process by running the current test binary with args
"-test.run=^TestPassFD$" and an environment variable used to signal
that the test should become the child process instead.
package unix_test
import (
	"flag"
	"fmt"
	"io/ioutil"
	"net"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"testing"
	"time"
	"golang.org/x/sys/unix"
)
func _() {
	var (
		_ func(int, int, int) error   = unix.Setpriority
		_ func(int, int) (int, error) = unix.Getpriority
	)
	const (
		_ int = unix.PRIO_USER
		_ int = unix.PRIO_PROCESS
		_ int = unix.PRIO_PGRP
	)
	const (
		_ int = unix.TCIFLUSH
		_ int = unix.TCIOFLUSH
		_ int = unix.TCOFLUSH
	)
	var (
		_ = unix.Flock_t{
			Type:   int16(0),
			Whence: int16(0),
			Start:  int64(0),
			Len:    int64(0),
			Pid:    int32(0),
		}
	)
	const (
		_ = unix.F_GETLK
		_ = unix.F_SETLK
		_ = unix.F_SETLKW
	)
}
func TestFcntlFlock(t *testing.T) {
	name := filepath.Join(os.TempDir(), "TestFcntlFlock")
	fd, err := unix.Open(name, unix.O_CREAT|unix.O_RDWR|unix.O_CLOEXEC, 0)
	if err != nil {
		t.Fatalf("Open failed: %v", err)
	}
	defer unix.Unlink(name)
	defer unix.Close(fd)
	flock := unix.Flock_t{
		Type:  unix.F_RDLCK,
		Start: 0, Len: 0, Whence: 1,
	}
	if err := unix.FcntlFlock(uintptr(fd), unix.F_GETLK, &flock); err != nil {
		t.Fatalf("FcntlFlock failed: %v", err)
	}
}