unix/syscall_linux_test.go - sys - Git at Google

 // Copyright 2016 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.

 // +build linux

 package unix_test

 import (
 	"bufio"
 	"bytes"
 	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
 	"runtime"
 	"runtime/debug"
 	"strconv"
 	"strings"
 	"testing"
 	"time"

 	"golang.org/x/sys/unix"
 )

 func TestIoctlGetInt(t *testing.T) {
 	f, err := os.Open("/dev/random")
 	if err != nil {
 		t.Fatalf("failed to open device: %v", err)
 	}
 	defer f.Close()

 	v, err := unix.IoctlGetInt(int(f.Fd()), unix.RNDGETENTCNT)
 	if err != nil {
 		t.Fatalf("failed to perform ioctl: %v", err)
 	}

 	t.Logf("%d bits of entropy available", v)
 }

 func TestIoctlGetRTCTime(t *testing.T) {
 	f, err := os.Open("/dev/rtc0")
 	if err != nil {
 		t.Skipf("skipping test, %v", err)
 	}
 	defer f.Close()

 	v, err := unix.IoctlGetRTCTime(int(f.Fd()))
 	if err != nil {
 		t.Fatalf("failed to perform ioctl: %v", err)
 	}

 	t.Logf("RTC time: %04d-%02d-%02d %02d:%02d:%02d", v.Year+1900, v.Mon+1, v.Mday, v.Hour, v.Min, v.Sec)
 }

 func TestPpoll(t *testing.T) {
 	if runtime.GOOS == "android" {
 		t.Skip("mkfifo syscall is not available on android, skipping test")
 	}

 	defer chtmpdir(t)()
 	f, cleanup := mktmpfifo(t)
 	defer cleanup()

 	const timeout = 100 * time.Millisecond

 	ok := make(chan bool, 1)
 	go func() {
 		select {
 		case <-time.After(10 * timeout):
 			t.Errorf("Ppoll: failed to timeout after %d", 10*timeout)
 		case <-ok:
 		}
 	}()

 	fds := []unix.PollFd{{Fd: int32(f.Fd()), Events: unix.POLLIN}}
 	timeoutTs := unix.NsecToTimespec(int64(timeout))
 	n, err := unix.Ppoll(fds, &timeoutTs, nil)
 	ok <- true
 	if err != nil {
 		t.Errorf("Ppoll: unexpected error: %v", err)
 		return
 	}
 	if n != 0 {
 		t.Errorf("Ppoll: wrong number of events: got %v, expected %v", n, 0)
 		return
 	}
 }

 func TestTime(t *testing.T) {
 	var ut unix.Time_t
 	ut2, err := unix.Time(&ut)
 	if err != nil {
 		t.Fatalf("Time: %v", err)
 	}
 	if ut != ut2 {
 		t.Errorf("Time: return value %v should be equal to argument %v", ut2, ut)
 	}

 	var now time.Time

 	for i := 0; i < 10; i++ {
 		ut, err = unix.Time(nil)
 		if err != nil {
 			t.Fatalf("Time: %v", err)
 		}

 		now = time.Now()

 		if int64(ut) == now.Unix() {
 			return
 		}
 	}

 	t.Errorf("Time: return value %v should be nearly equal to time.Now().Unix() %v", ut, now.Unix())
 }

 func TestUtime(t *testing.T) {
 	defer chtmpdir(t)()

 	touch(t, "file1")

 	buf := &unix.Utimbuf{
 		Modtime: 12345,
 	}

 	err := unix.Utime("file1", buf)
 	if err != nil {
 		t.Fatalf("Utime: %v", err)
 	}

 	fi, err := os.Stat("file1")
 	if err != nil {
 		t.Fatal(err)
 	}

 	if fi.ModTime().Unix() != 12345 {
 		t.Errorf("Utime: failed to change modtime: expected %v, got %v", 12345, fi.ModTime().Unix())
 	}
 }

 func TestUtimesNanoAt(t *testing.T) {
 	defer chtmpdir(t)()

 	symlink := "symlink1"
 	os.Remove(symlink)
 	err := os.Symlink("nonexisting", symlink)
 	if err != nil {
 		t.Fatal(err)
 	}

 	ts := []unix.Timespec{
 		{Sec: 1111, Nsec: 2222},
 		{Sec: 3333, Nsec: 4444},
 	}
 	err = unix.UtimesNanoAt(unix.AT_FDCWD, symlink, ts, unix.AT_SYMLINK_NOFOLLOW)
 	if err != nil {
 		t.Fatalf("UtimesNanoAt: %v", err)
 	}

 	var st unix.Stat_t
 	err = unix.Lstat(symlink, &st)
 	if err != nil {
 		t.Fatalf("Lstat: %v", err)
 	}

 	// Only check Mtim, Atim might not be supported by the underlying filesystem
 	expected := ts[1]
 	if st.Mtim.Nsec == 0 {
 		// Some filesystems only support 1-second time stamp resolution
 		// and will always set Nsec to 0.
 		expected.Nsec = 0
 	}
 	if st.Mtim != expected {
 		t.Errorf("UtimesNanoAt: wrong mtime: expected %v, got %v", expected, st.Mtim)
 	}
 }

 func TestRlimitAs(t *testing.T) {
 	// disable GC during to avoid flaky test
 	defer debug.SetGCPercent(debug.SetGCPercent(-1))

 	var rlim unix.Rlimit
 	err := unix.Getrlimit(unix.RLIMIT_AS, &rlim)
 	if err != nil {
 		t.Fatalf("Getrlimit: %v", err)
 	}
 	var zero unix.Rlimit
 	if zero == rlim {
 		t.Fatalf("Getrlimit: got zero value %#v", rlim)
 	}
 	set := rlim
 	set.Cur = uint64(unix.Getpagesize())
 	err = unix.Setrlimit(unix.RLIMIT_AS, &set)
 	if err != nil {
 		t.Fatalf("Setrlimit: set failed: %#v %v", set, err)
 	}

 	// RLIMIT_AS was set to the page size, so mmap()'ing twice the page size
 	// should fail. See 'man 2 getrlimit'.
 	_, err = unix.Mmap(-1, 0, 2*unix.Getpagesize(), unix.PROT_NONE, unix.MAP_ANON|unix.MAP_PRIVATE)
 	if err == nil {
 		t.Fatal("Mmap: unexpectedly succeeded after setting RLIMIT_AS")
 	}

 	err = unix.Setrlimit(unix.RLIMIT_AS, &rlim)
 	if err != nil {
 		t.Fatalf("Setrlimit: restore failed: %#v %v", rlim, err)
 	}

 	b, err := unix.Mmap(-1, 0, 2*unix.Getpagesize(), unix.PROT_NONE, unix.MAP_ANON|unix.MAP_PRIVATE)
 	if err != nil {
 		t.Fatalf("Mmap: %v", err)
 	}
 	err = unix.Munmap(b)
 	if err != nil {
 		t.Fatalf("Munmap: %v", err)
 	}
 }

 func TestSelect(t *testing.T) {
 	_, err := unix.Select(0, nil, nil, nil, &unix.Timeval{Sec: 0, Usec: 0})
 	if err != nil {
 		t.Fatalf("Select: %v", err)
 	}

 	dur := 150 * time.Millisecond
 	tv := unix.NsecToTimeval(int64(dur))
 	start := time.Now()
 	_, err = unix.Select(0, nil, nil, nil, &tv)
 	took := time.Since(start)
 	if err != nil {
 		t.Fatalf("Select: %v", err)
 	}

 	if took < dur {
 		t.Errorf("Select: timeout should have been at least %v, got %v", dur, took)
 	}
 }

 func TestPselect(t *testing.T) {
 	_, err := unix.Pselect(0, nil, nil, nil, &unix.Timespec{Sec: 0, Nsec: 0}, nil)
 	if err != nil {
 		t.Fatalf("Pselect: %v", err)
 	}

 	dur := 2500 * time.Microsecond
 	ts := unix.NsecToTimespec(int64(dur))
 	start := time.Now()
 	_, err = unix.Pselect(0, nil, nil, nil, &ts, nil)
 	took := time.Since(start)
 	if err != nil {
 		t.Fatalf("Pselect: %v", err)
 	}

 	if took < dur {
 		t.Errorf("Pselect: timeout should have been at least %v, got %v", dur, took)
 	}
 }

 func TestSchedSetaffinity(t *testing.T) {
 	runtime.LockOSThread()
 	defer runtime.UnlockOSThread()

 	var oldMask unix.CPUSet
 	err := unix.SchedGetaffinity(0, &oldMask)
 	if err != nil {
 		t.Fatalf("SchedGetaffinity: %v", err)
 	}

 	var newMask unix.CPUSet
 	newMask.Zero()
 	if newMask.Count() != 0 {
 		t.Errorf("CpuZero: didn't zero CPU set: %v", newMask)
 	}
 	cpu := 1
 	newMask.Set(cpu)
 	if newMask.Count() != 1 || !newMask.IsSet(cpu) {
 		t.Errorf("CpuSet: didn't set CPU %d in set: %v", cpu, newMask)
 	}
 	cpu = 5
 	newMask.Set(cpu)
 	if newMask.Count() != 2 || !newMask.IsSet(cpu) {
 		t.Errorf("CpuSet: didn't set CPU %d in set: %v", cpu, newMask)
 	}
 	newMask.Clear(cpu)
 	if newMask.Count() != 1 || newMask.IsSet(cpu) {
 		t.Errorf("CpuClr: didn't clear CPU %d in set: %v", cpu, newMask)
 	}

 	if runtime.NumCPU() < 2 {
 		t.Skip("skipping setaffinity tests on single CPU system")
 	}
 	if runtime.GOOS == "android" {
 		t.Skip("skipping setaffinity tests on android")
 	}

 	// On a system like ppc64x where some cores can be disabled using ppc64_cpu,
 	// setaffinity should only be called with enabled cores. The valid cores
 	// are found from the oldMask, but if none are found then the setaffinity
 	// tests are skipped. Issue #27875.
 	if !oldMask.IsSet(cpu) {
 		newMask.Zero()
 		for i := 0; i < len(oldMask); i++ {
 			if oldMask.IsSet(i) {
 				newMask.Set(i)
 				break
 			}
 		}
 		if newMask.Count() == 0 {
 			t.Skip("skipping setaffinity tests if CPU not available")
 		}
 	}

 	err = unix.SchedSetaffinity(0, &newMask)
 	if err != nil {
 		t.Fatalf("SchedSetaffinity: %v", err)
 	}

 	var gotMask unix.CPUSet
 	err = unix.SchedGetaffinity(0, &gotMask)
 	if err != nil {
 		t.Fatalf("SchedGetaffinity: %v", err)
 	}

 	if gotMask != newMask {
 		t.Errorf("SchedSetaffinity: returned affinity mask does not match set affinity mask")
 	}

 	// Restore old mask so it doesn't affect successive tests
 	err = unix.SchedSetaffinity(0, &oldMask)
 	if err != nil {
 		t.Fatalf("SchedSetaffinity: %v", err)
 	}
 }

 func TestStatx(t *testing.T) {
 	var stx unix.Statx_t
 	err := unix.Statx(unix.AT_FDCWD, ".", 0, 0, &stx)
 	if err == unix.ENOSYS || err == unix.EPERM {
 		t.Skip("statx syscall is not available, skipping test")
 	} else if err != nil {
 		t.Fatalf("Statx: %v", err)
 	}

 	defer chtmpdir(t)()
 	touch(t, "file1")

 	var st unix.Stat_t
 	err = unix.Stat("file1", &st)
 	if err != nil {
 		t.Fatalf("Stat: %v", err)
 	}

 	flags := unix.AT_STATX_SYNC_AS_STAT
 	err = unix.Statx(unix.AT_FDCWD, "file1", flags, unix.STATX_ALL, &stx)
 	if err != nil {
 		t.Fatalf("Statx: %v", err)
 	}

 	if uint32(stx.Mode) != st.Mode {
 		t.Errorf("Statx: returned stat mode does not match Stat")
 	}

 	ctime := unix.StatxTimestamp{Sec: int64(st.Ctim.Sec), Nsec: uint32(st.Ctim.Nsec)}
 	mtime := unix.StatxTimestamp{Sec: int64(st.Mtim.Sec), Nsec: uint32(st.Mtim.Nsec)}

 	if stx.Ctime != ctime {
 		t.Errorf("Statx: returned stat ctime does not match Stat")
 	}
 	if stx.Mtime != mtime {
 		t.Errorf("Statx: returned stat mtime does not match Stat")
 	}

 	err = os.Symlink("file1", "symlink1")
 	if err != nil {
 		t.Fatal(err)
 	}

 	err = unix.Lstat("symlink1", &st)
 	if err != nil {
 		t.Fatalf("Lstat: %v", err)
 	}

 	err = unix.Statx(unix.AT_FDCWD, "symlink1", flags, unix.STATX_BASIC_STATS, &stx)
 	if err != nil {
 		t.Fatalf("Statx: %v", err)
 	}

 	// follow symlink, expect a regulat file
 	if stx.Mode&unix.S_IFREG == 0 {
 		t.Errorf("Statx: didn't follow symlink")
 	}

 	err = unix.Statx(unix.AT_FDCWD, "symlink1", flags|unix.AT_SYMLINK_NOFOLLOW, unix.STATX_ALL, &stx)
 	if err != nil {
 		t.Fatalf("Statx: %v", err)
 	}

 	// follow symlink, expect a symlink
 	if stx.Mode&unix.S_IFLNK == 0 {
 		t.Errorf("Statx: unexpectedly followed symlink")
 	}
 	if uint32(stx.Mode) != st.Mode {
 		t.Errorf("Statx: returned stat mode does not match Lstat")
 	}

 	ctime = unix.StatxTimestamp{Sec: int64(st.Ctim.Sec), Nsec: uint32(st.Ctim.Nsec)}
 	mtime = unix.StatxTimestamp{Sec: int64(st.Mtim.Sec), Nsec: uint32(st.Mtim.Nsec)}

 	if stx.Ctime != ctime {
 		t.Errorf("Statx: returned stat ctime does not match Lstat")
 	}
 	if stx.Mtime != mtime {
 		t.Errorf("Statx: returned stat mtime does not match Lstat")
 	}
 }

 // stringsFromByteSlice converts a sequence of attributes to a []string.
 // On Linux, each entry is a NULL-terminated string.
 func stringsFromByteSlice(buf []byte) []string {
 	var result []string
 	off := 0
 	for i, b := range buf {
 		if b == 0 {
 			result = append(result, string(buf[off:i]))
 			off = i + 1
 		}
 	}
 	return result
 }

 func TestFaccessat(t *testing.T) {
 	defer chtmpdir(t)()
 	touch(t, "file1")

 	err := unix.Faccessat(unix.AT_FDCWD, "file1", unix.R_OK, 0)
 	if err != nil {
 		t.Errorf("Faccessat: unexpected error: %v", err)
 	}

 	err = unix.Faccessat(unix.AT_FDCWD, "file1", unix.R_OK, 2)
 	if err != unix.EINVAL {
 		t.Errorf("Faccessat: unexpected error: %v, want EINVAL", err)
 	}

 	err = unix.Faccessat(unix.AT_FDCWD, "file1", unix.R_OK, unix.AT_EACCESS)
 	if err != nil {
 		t.Errorf("Faccessat: unexpected error: %v", err)
 	}

 	err = os.Symlink("file1", "symlink1")
 	if err != nil {
 		t.Fatal(err)
 	}

 	err = unix.Faccessat(unix.AT_FDCWD, "symlink1", unix.R_OK, unix.AT_SYMLINK_NOFOLLOW)
 	if err != nil {
 		t.Errorf("Faccessat SYMLINK_NOFOLLOW: unexpected error %v", err)
 	}

 	// We can't really test AT_SYMLINK_NOFOLLOW, because there
 	// doesn't seem to be any way to change the mode of a symlink.
 	// We don't test AT_EACCESS because such tests are only
 	// meaningful if run as root.

 	err = unix.Fchmodat(unix.AT_FDCWD, "file1", 0, 0)
 	if err != nil {
 		t.Errorf("Fchmodat: unexpected error %v", err)
 	}

 	err = unix.Faccessat(unix.AT_FDCWD, "file1", unix.F_OK, unix.AT_SYMLINK_NOFOLLOW)
 	if err != nil {
 		t.Errorf("Faccessat: unexpected error: %v", err)
 	}

 	err = unix.Faccessat(unix.AT_FDCWD, "file1", unix.R_OK, unix.AT_SYMLINK_NOFOLLOW)
 	if err != unix.EACCES {
 		if unix.Getuid() != 0 {
 			t.Errorf("Faccessat: unexpected error: %v, want EACCES", err)
 		}
 	}
 }

 func TestSyncFileRange(t *testing.T) {
 	file, err := ioutil.TempFile("", "TestSyncFileRange")
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer os.Remove(file.Name())
 	defer file.Close()

 	err = unix.SyncFileRange(int(file.Fd()), 0, 0, 0)
 	if err == unix.ENOSYS || err == unix.EPERM {
 		t.Skip("sync_file_range syscall is not available, skipping test")
 	} else if err != nil {
 		t.Fatalf("SyncFileRange: %v", err)
 	}

 	// invalid flags
 	flags := 0xf00
 	err = unix.SyncFileRange(int(file.Fd()), 0, 0, flags)
 	if err != unix.EINVAL {
 		t.Fatalf("SyncFileRange: unexpected error: %v, want EINVAL", err)
 	}
 }

 func TestClockNanosleep(t *testing.T) {
 	delay := 100 * time.Millisecond

 	// Relative timespec.
 	start := time.Now()
 	rel := unix.NsecToTimespec(delay.Nanoseconds())
 	err := unix.ClockNanosleep(unix.CLOCK_MONOTONIC, 0, &rel, nil)
 	if err == unix.ENOSYS || err == unix.EPERM {
 		t.Skip("clock_nanosleep syscall is not available, skipping test")
 	} else if err != nil {
 		t.Errorf("ClockNanosleep(CLOCK_MONOTONIC, 0, %#v, nil) = %v", &rel, err)
 	} else if slept := time.Now().Sub(start); slept < delay {
 		t.Errorf("ClockNanosleep(CLOCK_MONOTONIC, 0, %#v, nil) slept only %v", &rel, slept)
 	}

 	// Absolute timespec.
 	start = time.Now()
 	until := start.Add(delay)
 	abs := unix.NsecToTimespec(until.UnixNano())
 	err = unix.ClockNanosleep(unix.CLOCK_REALTIME, unix.TIMER_ABSTIME, &abs, nil)
 	if err != nil {
 		t.Errorf("ClockNanosleep(CLOCK_REALTIME, TIMER_ABSTIME, %#v (=%v), nil) = %v", &abs, until, err)
 	} else if slept := time.Now().Sub(start); slept < delay {
 		t.Errorf("ClockNanosleep(CLOCK_REALTIME, TIMER_ABSTIME, %#v (=%v), nil) slept only %v", &abs, until, slept)
 	}

 	// Invalid clock. clock_nanosleep(2) says EINVAL, but it’s actually EOPNOTSUPP.
 	err = unix.ClockNanosleep(unix.CLOCK_THREAD_CPUTIME_ID, 0, &rel, nil)
 	if err != unix.EINVAL && err != unix.EOPNOTSUPP {
 		t.Errorf("ClockNanosleep(CLOCK_THREAD_CPUTIME_ID, 0, %#v, nil) = %v, want EINVAL or EOPNOTSUPP", &rel, err)
 	}
 }

 func TestOpenByHandleAt(t *testing.T) {
 	skipIfNotSupported := func(t *testing.T, name string, err error) {
 		if err == unix.EPERM {
 			t.Skipf("skipping %s test without CAP_DAC_READ_SEARCH", name)
 		}
 		if err == unix.ENOSYS {
 			t.Skipf("%s system call not available", name)
 		}
 		if err == unix.EOPNOTSUPP {
 			t.Skipf("%s not supported on this filesystem", name)
 		}
 	}

 	h, mountID, err := unix.NameToHandleAt(unix.AT_FDCWD, "syscall_linux_test.go", 0)
 	if err != nil {
 		skipIfNotSupported(t, "name_to_handle_at", err)
 		t.Fatalf("NameToHandleAt: %v", err)
 	}
 	t.Logf("mountID: %v, handle: size=%d, type=%d, bytes=%q", mountID,
 		h.Size(), h.Type(), h.Bytes())
 	mount, err := openMountByID(mountID)
 	if err != nil {
 		t.Fatalf("openMountByID: %v", err)
 	}
 	defer mount.Close()

 	for _, clone := range []bool{false, true} {
 		t.Run("clone="+strconv.FormatBool(clone), func(t *testing.T) {
 			if clone {
 				h = unix.NewFileHandle(h.Type(), h.Bytes())
 			}
 			fd, err := unix.OpenByHandleAt(int(mount.Fd()), h, unix.O_RDONLY)
 			skipIfNotSupported(t, "open_by_handle_at", err)
 			if err != nil {
 				t.Fatalf("OpenByHandleAt: %v", err)
 			}
 			defer unix.Close(fd)

 			t.Logf("opened fd %v", fd)
 			f := os.NewFile(uintptr(fd), "")
 			slurp, err := ioutil.ReadAll(f)
 			if err != nil {
 				t.Fatal(err)
 			}
 			const substr = "Some substring for a test."
 			if !strings.Contains(string(slurp), substr) {
 				t.Errorf("didn't find substring %q in opened file; read %d bytes", substr, len(slurp))
 			}
 		})
 	}
 }

 func openMountByID(mountID int) (f *os.File, err error) {
 	mi, err := os.Open("/proc/self/mountinfo")
 	if err != nil {
 		return nil, err
 	}
 	defer mi.Close()
 	bs := bufio.NewScanner(mi)
 	wantPrefix := []byte(fmt.Sprintf("%v ", mountID))
 	for bs.Scan() {
 		if !bytes.HasPrefix(bs.Bytes(), wantPrefix) {
 			continue
 		}
 		fields := strings.Fields(bs.Text())
 		dev := fields[4]
 		return os.Open(dev)
 	}
 	if err := bs.Err(); err != nil {
 		return nil, err
 	}
 	return nil, errors.New("mountID not found")
 }
	// Copyright 2016 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.

	// +build linux

	package unix_test

	import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"io/ioutil"
	"os"
	"runtime"
	"runtime/debug"
	"strconv"
	"strings"
	"testing"
	"time"

	"golang.org/x/sys/unix"
	)

	func TestIoctlGetInt(t *testing.T) {
	f, err := os.Open("/dev/random")
	if err != nil {
	t.Fatalf("failed to open device: %v", err)
	}
	defer f.Close()

	v, err := unix.IoctlGetInt(int(f.Fd()), unix.RNDGETENTCNT)
	if err != nil {
	t.Fatalf("failed to perform ioctl: %v", err)
	}

	t.Logf("%d bits of entropy available", v)
	}

	func TestIoctlGetRTCTime(t *testing.T) {
	f, err := os.Open("/dev/rtc0")
	if err != nil {
	t.Skipf("skipping test, %v", err)
	}
	defer f.Close()

	v, err := unix.IoctlGetRTCTime(int(f.Fd()))
	if err != nil {
	t.Fatalf("failed to perform ioctl: %v", err)
	}

	t.Logf("RTC time: %04d-%02d-%02d %02d:%02d:%02d", v.Year+1900, v.Mon+1, v.Mday, v.Hour, v.Min, v.Sec)
	}

	func TestPpoll(t *testing.T) {
	if runtime.GOOS == "android" {
	t.Skip("mkfifo syscall is not available on android, skipping test")
	}

	defer chtmpdir(t)()
	f, cleanup := mktmpfifo(t)
	defer cleanup()

	const timeout = 100 * time.Millisecond

	ok := make(chan bool, 1)
	go func() {
	select {
	case <-time.After(10 * timeout):
	t.Errorf("Ppoll: failed to timeout after %d", 10*timeout)
	case <-ok:
	}
	}()

	fds := []unix.PollFd{{Fd: int32(f.Fd()), Events: unix.POLLIN}}
	timeoutTs := unix.NsecToTimespec(int64(timeout))
	n, err := unix.Ppoll(fds, &timeoutTs, nil)
	ok <- true
	if err != nil {
	t.Errorf("Ppoll: unexpected error: %v", err)
	return
	}
	if n != 0 {
	t.Errorf("Ppoll: wrong number of events: got %v, expected %v", n, 0)
	return
	}
	}

	func TestTime(t *testing.T) {
	var ut unix.Time_t
	ut2, err := unix.Time(&ut)
	if err != nil {
	t.Fatalf("Time: %v", err)
	}
	if ut != ut2 {
	t.Errorf("Time: return value %v should be equal to argument %v", ut2, ut)
	}

	var now time.Time

	for i := 0; i < 10; i++ {
	ut, err = unix.Time(nil)
	if err != nil {
	t.Fatalf("Time: %v", err)
	}

	now = time.Now()

	if int64(ut) == now.Unix() {
	return
	}
	}

	t.Errorf("Time: return value %v should be nearly equal to time.Now().Unix() %v", ut, now.Unix())
	}

	func TestUtime(t *testing.T) {
	defer chtmpdir(t)()

	touch(t, "file1")

	buf := &unix.Utimbuf{
	Modtime: 12345,
	}

	err := unix.Utime("file1", buf)
	if err != nil {
	t.Fatalf("Utime: %v", err)
	}

	fi, err := os.Stat("file1")
	if err != nil {
	t.Fatal(err)
	}

	if fi.ModTime().Unix() != 12345 {
	t.Errorf("Utime: failed to change modtime: expected %v, got %v", 12345, fi.ModTime().Unix())
	}
	}

	func TestUtimesNanoAt(t *testing.T) {
	defer chtmpdir(t)()

	symlink := "symlink1"
	os.Remove(symlink)
	err := os.Symlink("nonexisting", symlink)
	if err != nil {
	t.Fatal(err)
	}

	ts := []unix.Timespec{
	{Sec: 1111, Nsec: 2222},
	{Sec: 3333, Nsec: 4444},
	}
	err = unix.UtimesNanoAt(unix.AT_FDCWD, symlink, ts, unix.AT_SYMLINK_NOFOLLOW)
	if err != nil {
	t.Fatalf("UtimesNanoAt: %v", err)
	}

	var st unix.Stat_t
	err = unix.Lstat(symlink, &st)
	if err != nil {
	t.Fatalf("Lstat: %v", err)
	}

	// Only check Mtim, Atim might not be supported by the underlying filesystem
	expected := ts[1]
	if st.Mtim.Nsec == 0 {
	// Some filesystems only support 1-second time stamp resolution
	// and will always set Nsec to 0.
	expected.Nsec = 0
	}
	if st.Mtim != expected {
	t.Errorf("UtimesNanoAt: wrong mtime: expected %v, got %v", expected, st.Mtim)
	}
	}

	func TestRlimitAs(t *testing.T) {
	// disable GC during to avoid flaky test
	defer debug.SetGCPercent(debug.SetGCPercent(-1))

	var rlim unix.Rlimit
	err := unix.Getrlimit(unix.RLIMIT_AS, &rlim)
	if err != nil {
	t.Fatalf("Getrlimit: %v", err)
	}
	var zero unix.Rlimit
	if zero == rlim {
	t.Fatalf("Getrlimit: got zero value %#v", rlim)
	}
	set := rlim
	set.Cur = uint64(unix.Getpagesize())
	err = unix.Setrlimit(unix.RLIMIT_AS, &set)
	if err != nil {
	t.Fatalf("Setrlimit: set failed: %#v %v", set, err)
	}

	// RLIMIT_AS was set to the page size, so mmap()'ing twice the page size
	// should fail. See 'man 2 getrlimit'.
	_, err = unix.Mmap(-1, 0, 2*unix.Getpagesize(), unix.PROT_NONE, unix.MAP_ANON\|unix.MAP_PRIVATE)
	if err == nil {
	t.Fatal("Mmap: unexpectedly succeeded after setting RLIMIT_AS")
	}

	err = unix.Setrlimit(unix.RLIMIT_AS, &rlim)
	if err != nil {
	t.Fatalf("Setrlimit: restore failed: %#v %v", rlim, err)
	}

	b, err := unix.Mmap(-1, 0, 2*unix.Getpagesize(), unix.PROT_NONE, unix.MAP_ANON\|unix.MAP_PRIVATE)
	if err != nil {
	t.Fatalf("Mmap: %v", err)
	}
	err = unix.Munmap(b)
	if err != nil {
	t.Fatalf("Munmap: %v", err)
	}
	}

	func TestSelect(t *testing.T) {
	_, err := unix.Select(0, nil, nil, nil, &unix.Timeval{Sec: 0, Usec: 0})
	if err != nil {
	t.Fatalf("Select: %v", err)
	}

	dur := 150 * time.Millisecond
	tv := unix.NsecToTimeval(int64(dur))
	start := time.Now()
	_, err = unix.Select(0, nil, nil, nil, &tv)
	took := time.Since(start)
	if err != nil {
	t.Fatalf("Select: %v", err)
	}

	if took < dur {
	t.Errorf("Select: timeout should have been at least %v, got %v", dur, took)
	}
	}

	func TestPselect(t *testing.T) {
	_, err := unix.Pselect(0, nil, nil, nil, &unix.Timespec{Sec: 0, Nsec: 0}, nil)
	if err != nil {
	t.Fatalf("Pselect: %v", err)
	}

	dur := 2500 * time.Microsecond
	ts := unix.NsecToTimespec(int64(dur))
	start := time.Now()
	_, err = unix.Pselect(0, nil, nil, nil, &ts, nil)
	took := time.Since(start)
	if err != nil {
	t.Fatalf("Pselect: %v", err)
	}

	if took < dur {
	t.Errorf("Pselect: timeout should have been at least %v, got %v", dur, took)
	}
	}

	func TestSchedSetaffinity(t *testing.T) {
	runtime.LockOSThread()
	defer runtime.UnlockOSThread()

	var oldMask unix.CPUSet
	err := unix.SchedGetaffinity(0, &oldMask)
	if err != nil {
	t.Fatalf("SchedGetaffinity: %v", err)
	}

	var newMask unix.CPUSet
	newMask.Zero()
	if newMask.Count() != 0 {
	t.Errorf("CpuZero: didn't zero CPU set: %v", newMask)
	}
	cpu := 1
	newMask.Set(cpu)
	if newMask.Count() != 1 \|\| !newMask.IsSet(cpu) {
	t.Errorf("CpuSet: didn't set CPU %d in set: %v", cpu, newMask)
	}
	cpu = 5
	newMask.Set(cpu)
	if newMask.Count() != 2 \|\| !newMask.IsSet(cpu) {
	t.Errorf("CpuSet: didn't set CPU %d in set: %v", cpu, newMask)
	}
	newMask.Clear(cpu)
	if newMask.Count() != 1 \|\| newMask.IsSet(cpu) {
	t.Errorf("CpuClr: didn't clear CPU %d in set: %v", cpu, newMask)
	}

	if runtime.NumCPU() < 2 {
	t.Skip("skipping setaffinity tests on single CPU system")
	}
	if runtime.GOOS == "android" {
	t.Skip("skipping setaffinity tests on android")
	}

	// On a system like ppc64x where some cores can be disabled using ppc64_cpu,
	// setaffinity should only be called with enabled cores. The valid cores
	// are found from the oldMask, but if none are found then the setaffinity
	// tests are skipped. Issue #27875.
	if !oldMask.IsSet(cpu) {
	newMask.Zero()
	for i := 0; i < len(oldMask); i++ {
	if oldMask.IsSet(i) {
	newMask.Set(i)
	break
	}
	}
	if newMask.Count() == 0 {
	t.Skip("skipping setaffinity tests if CPU not available")
	}
	}

	err = unix.SchedSetaffinity(0, &newMask)
	if err != nil {
	t.Fatalf("SchedSetaffinity: %v", err)
	}

	var gotMask unix.CPUSet
	err = unix.SchedGetaffinity(0, &gotMask)
	if err != nil {
	t.Fatalf("SchedGetaffinity: %v", err)
	}

	if gotMask != newMask {
	t.Errorf("SchedSetaffinity: returned affinity mask does not match set affinity mask")
	}

	// Restore old mask so it doesn't affect successive tests
	err = unix.SchedSetaffinity(0, &oldMask)
	if err != nil {
	t.Fatalf("SchedSetaffinity: %v", err)
	}
	}

	func TestStatx(t *testing.T) {
	var stx unix.Statx_t
	err := unix.Statx(unix.AT_FDCWD, ".", 0, 0, &stx)
	if err == unix.ENOSYS \|\| err == unix.EPERM {
	t.Skip("statx syscall is not available, skipping test")
	} else if err != nil {
	t.Fatalf("Statx: %v", err)
	}

	defer chtmpdir(t)()
	touch(t, "file1")

	var st unix.Stat_t
	err = unix.Stat("file1", &st)
	if err != nil {
	t.Fatalf("Stat: %v", err)
	}

	flags := unix.AT_STATX_SYNC_AS_STAT
	err = unix.Statx(unix.AT_FDCWD, "file1", flags, unix.STATX_ALL, &stx)
	if err != nil {
	t.Fatalf("Statx: %v", err)
	}

	if uint32(stx.Mode) != st.Mode {
	t.Errorf("Statx: returned stat mode does not match Stat")
	}

	ctime := unix.StatxTimestamp{Sec: int64(st.Ctim.Sec), Nsec: uint32(st.Ctim.Nsec)}
	mtime := unix.StatxTimestamp{Sec: int64(st.Mtim.Sec), Nsec: uint32(st.Mtim.Nsec)}

	if stx.Ctime != ctime {
	t.Errorf("Statx: returned stat ctime does not match Stat")
	}
	if stx.Mtime != mtime {
	t.Errorf("Statx: returned stat mtime does not match Stat")
	}

	err = os.Symlink("file1", "symlink1")
	if err != nil {
	t.Fatal(err)
	}

	err = unix.Lstat("symlink1", &st)
	if err != nil {
	t.Fatalf("Lstat: %v", err)
	}

	err = unix.Statx(unix.AT_FDCWD, "symlink1", flags, unix.STATX_BASIC_STATS, &stx)
	if err != nil {
	t.Fatalf("Statx: %v", err)
	}

	// follow symlink, expect a regulat file
	if stx.Mode&unix.S_IFREG == 0 {
	t.Errorf("Statx: didn't follow symlink")
	}

	err = unix.Statx(unix.AT_FDCWD, "symlink1", flags\|unix.AT_SYMLINK_NOFOLLOW, unix.STATX_ALL, &stx)
	if err != nil {
	t.Fatalf("Statx: %v", err)
	}

	// follow symlink, expect a symlink
	if stx.Mode&unix.S_IFLNK == 0 {
	t.Errorf("Statx: unexpectedly followed symlink")
	}
	if uint32(stx.Mode) != st.Mode {
	t.Errorf("Statx: returned stat mode does not match Lstat")
	}

	ctime = unix.StatxTimestamp{Sec: int64(st.Ctim.Sec), Nsec: uint32(st.Ctim.Nsec)}
	mtime = unix.StatxTimestamp{Sec: int64(st.Mtim.Sec), Nsec: uint32(st.Mtim.Nsec)}

	if stx.Ctime != ctime {
	t.Errorf("Statx: returned stat ctime does not match Lstat")
	}
	if stx.Mtime != mtime {
	t.Errorf("Statx: returned stat mtime does not match Lstat")
	}
	}

	// stringsFromByteSlice converts a sequence of attributes to a []string.
	// On Linux, each entry is a NULL-terminated string.
	func stringsFromByteSlice(buf []byte) []string {
	var result []string
	off := 0
	for i, b := range buf {
	if b == 0 {
	result = append(result, string(buf[off:i]))
	off = i + 1
	}
	}
	return result
	}

	func TestFaccessat(t *testing.T) {
	defer chtmpdir(t)()
	touch(t, "file1")

	err := unix.Faccessat(unix.AT_FDCWD, "file1", unix.R_OK, 0)
	if err != nil {
	t.Errorf("Faccessat: unexpected error: %v", err)
	}

	err = unix.Faccessat(unix.AT_FDCWD, "file1", unix.R_OK, 2)
	if err != unix.EINVAL {
	t.Errorf("Faccessat: unexpected error: %v, want EINVAL", err)
	}

	err = unix.Faccessat(unix.AT_FDCWD, "file1", unix.R_OK, unix.AT_EACCESS)
	if err != nil {
	t.Errorf("Faccessat: unexpected error: %v", err)
	}

	err = os.Symlink("file1", "symlink1")
	if err != nil {
	t.Fatal(err)
	}

	err = unix.Faccessat(unix.AT_FDCWD, "symlink1", unix.R_OK, unix.AT_SYMLINK_NOFOLLOW)
	if err != nil {
	t.Errorf("Faccessat SYMLINK_NOFOLLOW: unexpected error %v", err)
	}

	// We can't really test AT_SYMLINK_NOFOLLOW, because there
	// doesn't seem to be any way to change the mode of a symlink.
	// We don't test AT_EACCESS because such tests are only
	// meaningful if run as root.

	err = unix.Fchmodat(unix.AT_FDCWD, "file1", 0, 0)
	if err != nil {
	t.Errorf("Fchmodat: unexpected error %v", err)
	}

	err = unix.Faccessat(unix.AT_FDCWD, "file1", unix.F_OK, unix.AT_SYMLINK_NOFOLLOW)
	if err != nil {
	t.Errorf("Faccessat: unexpected error: %v", err)
	}

	err = unix.Faccessat(unix.AT_FDCWD, "file1", unix.R_OK, unix.AT_SYMLINK_NOFOLLOW)
	if err != unix.EACCES {
	if unix.Getuid() != 0 {
	t.Errorf("Faccessat: unexpected error: %v, want EACCES", err)
	}
	}
	}

	func TestSyncFileRange(t *testing.T) {
	file, err := ioutil.TempFile("", "TestSyncFileRange")
	if err != nil {
	t.Fatal(err)
	}
	defer os.Remove(file.Name())
	defer file.Close()

	err = unix.SyncFileRange(int(file.Fd()), 0, 0, 0)
	if err == unix.ENOSYS \|\| err == unix.EPERM {
	t.Skip("sync_file_range syscall is not available, skipping test")
	} else if err != nil {
	t.Fatalf("SyncFileRange: %v", err)
	}

	// invalid flags
	flags := 0xf00
	err = unix.SyncFileRange(int(file.Fd()), 0, 0, flags)
	if err != unix.EINVAL {
	t.Fatalf("SyncFileRange: unexpected error: %v, want EINVAL", err)
	}
	}

	func TestClockNanosleep(t *testing.T) {
	delay := 100 * time.Millisecond

	// Relative timespec.
	start := time.Now()
	rel := unix.NsecToTimespec(delay.Nanoseconds())
	err := unix.ClockNanosleep(unix.CLOCK_MONOTONIC, 0, &rel, nil)
	if err == unix.ENOSYS \|\| err == unix.EPERM {
	t.Skip("clock_nanosleep syscall is not available, skipping test")
	} else if err != nil {
	t.Errorf("ClockNanosleep(CLOCK_MONOTONIC, 0, %#v, nil) = %v", &rel, err)
	} else if slept := time.Now().Sub(start); slept < delay {
	t.Errorf("ClockNanosleep(CLOCK_MONOTONIC, 0, %#v, nil) slept only %v", &rel, slept)
	}

	// Absolute timespec.
	start = time.Now()
	until := start.Add(delay)
	abs := unix.NsecToTimespec(until.UnixNano())
	err = unix.ClockNanosleep(unix.CLOCK_REALTIME, unix.TIMER_ABSTIME, &abs, nil)
	if err != nil {
	t.Errorf("ClockNanosleep(CLOCK_REALTIME, TIMER_ABSTIME, %#v (=%v), nil) = %v", &abs, until, err)
	} else if slept := time.Now().Sub(start); slept < delay {
	t.Errorf("ClockNanosleep(CLOCK_REALTIME, TIMER_ABSTIME, %#v (=%v), nil) slept only %v", &abs, until, slept)
	}

	// Invalid clock. clock_nanosleep(2) says EINVAL, but it’s actually EOPNOTSUPP.
	err = unix.ClockNanosleep(unix.CLOCK_THREAD_CPUTIME_ID, 0, &rel, nil)
	if err != unix.EINVAL && err != unix.EOPNOTSUPP {
	t.Errorf("ClockNanosleep(CLOCK_THREAD_CPUTIME_ID, 0, %#v, nil) = %v, want EINVAL or EOPNOTSUPP", &rel, err)
	}
	}

	func TestOpenByHandleAt(t *testing.T) {
	skipIfNotSupported := func(t *testing.T, name string, err error) {
	if err == unix.EPERM {
	t.Skipf("skipping %s test without CAP_DAC_READ_SEARCH", name)
	}
	if err == unix.ENOSYS {
	t.Skipf("%s system call not available", name)
	}
	if err == unix.EOPNOTSUPP {
	t.Skipf("%s not supported on this filesystem", name)
	}
	}

	h, mountID, err := unix.NameToHandleAt(unix.AT_FDCWD, "syscall_linux_test.go", 0)
	if err != nil {
	skipIfNotSupported(t, "name_to_handle_at", err)
	t.Fatalf("NameToHandleAt: %v", err)
	}
	t.Logf("mountID: %v, handle: size=%d, type=%d, bytes=%q", mountID,
	h.Size(), h.Type(), h.Bytes())
	mount, err := openMountByID(mountID)
	if err != nil {
	t.Fatalf("openMountByID: %v", err)
	}
	defer mount.Close()

	for _, clone := range []bool{false, true} {
	t.Run("clone="+strconv.FormatBool(clone), func(t *testing.T) {
	if clone {
	h = unix.NewFileHandle(h.Type(), h.Bytes())
	}
	fd, err := unix.OpenByHandleAt(int(mount.Fd()), h, unix.O_RDONLY)
	skipIfNotSupported(t, "open_by_handle_at", err)
	if err != nil {
	t.Fatalf("OpenByHandleAt: %v", err)
	}
	defer unix.Close(fd)

	t.Logf("opened fd %v", fd)
	f := os.NewFile(uintptr(fd), "")
	slurp, err := ioutil.ReadAll(f)
	if err != nil {
	t.Fatal(err)
	}
	const substr = "Some substring for a test."
	if !strings.Contains(string(slurp), substr) {
	t.Errorf("didn't find substring %q in opened file; read %d bytes", substr, len(slurp))
	}
	})
	}
	}

	func openMountByID(mountID int) (f *os.File, err error) {
	mi, err := os.Open("/proc/self/mountinfo")
	if err != nil {
	return nil, err
	}
	defer mi.Close()
	bs := bufio.NewScanner(mi)
	wantPrefix := []byte(fmt.Sprintf("%v ", mountID))
	for bs.Scan() {
	if !bytes.HasPrefix(bs.Bytes(), wantPrefix) {
	continue
	}
	fields := strings.Fields(bs.Text())
	dev := fields[4]
	return os.Open(dev)
	}
	if err := bs.Err(); err != nil {
	return nil, err
	}
	return nil, errors.New("mountID not found")
	}