// TestFcntlFlock tests whether the file locking structure matches
// the calling convention of each kernel.
// On some Linux systems, glibc uses another set of values for the
// commands and translates them to the correct value that the kernel
// expects just before the actual fcntl syscall. As Go uses raw
// syscalls directly, it must use the real value, not the glibc value.
// Thus this test also verifies that the Flock_t structure can be
// roundtripped with F_SETLK and F_GETLK.
func TestFcntlFlock(t *testing.T) {
if runtime.GOOS == "darwin" && (runtime.GOARCH == "arm" || runtime.GOARCH == "arm64") {
t.Skip("skipping; no child processes allowed on iOS")
}
flock := syscall.Flock_t{
Type: syscall.F_WRLCK,
Start: 31415, Len: 271828, Whence: 1,
}
if os.Getenv("GO_WANT_HELPER_PROCESS") == "" {
// parent
name := filepath.Join(os.TempDir(), "TestFcntlFlock")
fd, err := syscall.Open(name, syscall.O_CREAT|syscall.O_RDWR|syscall.O_CLOEXEC, 0)
if err != nil {
t.Fatalf("Open failed: %v", err)
}
defer syscall.Unlink(name)
defer syscall.Close(fd)
if err := syscall.Ftruncate(fd, 1<<20); err != nil {
t.Fatalf("Ftruncate(1<<20) failed: %v", err)
}
if err := syscall.FcntlFlock(uintptr(fd), syscall.F_SETLK, &flock); err != nil {
t.Fatalf("FcntlFlock(F_SETLK) failed: %v", err)
}
cmd := exec.Command(os.Args[0], "-test.run=^TestFcntlFlock$")
cmd.Env = append(os.Environ(), "GO_WANT_HELPER_PROCESS=1")
cmd.ExtraFiles = []*os.File{os.NewFile(uintptr(fd), name)}
out, err := cmd.CombinedOutput()
if len(out) > 0 || err != nil {
t.Fatalf("child process: %q, %v", out, err)
}
} else {
// child
got := flock
// make sure the child lock is conflicting with the parent lock
got.Start--
got.Len++
if err := syscall.FcntlFlock(3, syscall.F_GETLK, &got); err != nil {
t.Fatalf("FcntlFlock(F_GETLK) failed: %v", err)
}
flock.Pid = int32(syscall.Getppid())
// Linux kernel always set Whence to 0
flock.Whence = 0
if got.Type == flock.Type && got.Start == flock.Start && got.Len == flock.Len && got.Pid == flock.Pid && got.Whence == flock.Whence {
os.Exit(0)
}
t.Fatalf("FcntlFlock got %v, want %v", got, flock)
}
}
// A wrapper around os.OpenFile() that locks the file after opening
// Will return an error if the file cannot be opened or the file cannot
// be locked
func SafeOpen(name string) (*os.File, *syscall.Flock_t, error) {
fi, err := os.OpenFile(name, os.O_RDWR, os.ModeExclusive)
if err != nil {
return nil, nil, err
}
// Lock the file so we're responsible
lk := syscall.Flock_t{
Type: syscall.F_WRLCK, // set write lock
Whence: 0, // SEEK_SET
Start: 0, // beginning of file
Len: 0, // until EOF
Pid: int32(os.Getpid()), // our PID
}
err = syscall.FcntlFlock(fi.Fd(), syscall.F_SETLKW, &lk)
// If we can't lock the file error out to prevent corruption
if err != nil {
return nil, nil, err
}
return fi, &lk, nil
}
func LockFile(file *os.File, lockType LockType) error {
if file == nil {
return fmt.Errorf("*os.File argument is nil.")
}
var syscallType int16
switch lockType {
case Read:
syscallType = syscall.F_RDLCK
case Write:
syscallType = syscall.F_WRLCK
default:
return fmt.Errorf("Invalid LockType %dv", lockType)
}
fd := file.Fd()
cmd := syscall.F_SETLK
lk := syscall.Flock_t{
Type: syscallType,
Whence: int16(os.SEEK_SET),
Start: 0,
Len: math.MaxInt64,
Pid: int32(os.Getpid()),
}
err := syscall.FcntlFlock(fd, cmd, &lk)
if err != nil {
return fmt.Errorf("Failed to lock %s: %s", file.Name(), err)
}
return nil
}
// flock acquires an advisory lock on a file descriptor.
func flock(f *os.File, exclusive bool, timeout time.Duration) error {
var t time.Time
for {
// If we're beyond our timeout then return an error.
// This can only occur after we've attempted a flock once.
if t.IsZero() {
t = time.Now()
} else if timeout > 0 && time.Since(t) > timeout {
return ErrTimeout
}
var lock syscall.Flock_t
lock.Start = 0
lock.Len = 0
lock.Pid = 0
lock.Whence = 0
lock.Pid = 0
if exclusive {
lock.Type = syscall.F_WRLCK
} else {
lock.Type = syscall.F_RDLCK
}
err := syscall.FcntlFlock(f.Fd(), syscall.F_SETLK, &lock)
if err == nil {
return nil
} else if err != syscall.EAGAIN {
return err
}
// Wait for a bit and try again.
time.Sleep(50 * time.Millisecond)
}
}
// Unlock an open file. Unlocking errors are ignored.
func Unlock(file *os.File, lk *syscall.Flock_t) error {
if lk == nil || file == nil {
return fmt.Errorf("file or lock are nil file: %s lk: %v", file.Name(), lk)
}
lk.Type = syscall.F_UNLCK
return syscall.FcntlFlock(file.Fd(), syscall.F_SETLK, lk)
}
// funlock releases an advisory lock on a file descriptor.
func funlock(f *os.File) error {
var lock syscall.Flock_t
lock.Start = 0
lock.Len = 0
lock.Type = syscall.F_UNLCK
lock.Whence = 0
return syscall.FcntlFlock(uintptr(f.Fd()), syscall.F_SETLK, &lock)
}
func init() {
// use open file descriptor locks if the system supports it
getlk := syscall.Flock_t{Type: syscall.F_RDLCK}
if err := syscall.FcntlFlock(0, F_OFD_GETLK, &getlk); err == nil {
linuxTryLockFile = ofdTryLockFile
linuxLockFile = ofdLockFile
}
}
func open(path string) (*os.File, error) {
var f *os.File
var err error
for {
f, err = os.OpenFile(path,
syscall.O_RDWR|syscall.O_CREAT|syscall.O_EXCL, 0644)
if err != nil {
if !os.IsExist(err) {
return nil, err
}
f, err = os.OpenFile(path, syscall.O_RDWR, 0644)
if err != nil {
if os.IsNotExist(err) {
continue
}
return nil, err
}
}
err = syscall.FcntlFlock(f.Fd(), syscall.F_SETLK, &syscall.Flock_t{
Type: syscall.F_WRLCK,
})
if err != nil {
f.Close()
return nil, err
}
st1 := syscall.Stat_t{}
err = syscall.Fstat(int(f.Fd()), &st1) // ffs
if err != nil {
f.Close()
return nil, err
}
st2 := syscall.Stat_t{}
err = syscall.Stat(path, &st2)
if err != nil {
f.Close()
if os.IsNotExist(err) {
continue
}
return nil, err
}
if st1.Ino != st2.Ino {
f.Close()
continue
}
break
}
return f, nil
}
// Lock acquires exclusivity on the lock without blocking
func (l *lock) Lock() error {
var lock syscall.Flock_t
lock.Start = 0
lock.Len = 0
lock.Type = syscall.F_WRLCK
lock.Whence = 0
lock.Pid = 0
return syscall.FcntlFlock(uintptr(l.fd), syscall.F_SETLK, &lock)
}
func (l *FcntlLockfile) unlock(offset int64, whence int, len int64) {
l.ft.Len = len
l.ft.Start = offset
l.ft.Whence = int16(whence)
l.ft.Type = syscall.F_UNLCK
syscall.FcntlFlock(l.file.Fd(), syscall.F_SETLK, l.ft)
if l.maintainFile {
l.file.Close()
}
}
// Unlock unlocks the lock
func (l *lock) Unlock() error {
var lock syscall.Flock_t
lock.Start = 0
lock.Len = 0
lock.Type = syscall.F_UNLCK
lock.Whence = 0
err := syscall.FcntlFlock(uintptr(l.fd), syscall.F_SETLK, &lock)
if err != nil && err == syscall.EAGAIN {
return ErrLocked
}
return err
}
func setFileLock(f *os.File, lock bool) error {
flock := syscall.Flock_t{
Type: syscall.F_UNLCK,
Start: 0,
Len: 0,
Whence: 1,
}
if lock {
flock.Type = syscall.F_WRLCK
}
return syscall.FcntlFlock(f.Fd(), syscall.F_SETLK, &flock)
}
func (l *unixLock) set(lock bool) error {
flock := syscall.Flock_t{
Type: syscall.F_UNLCK,
Start: 0,
Len: 0,
Whence: 1,
}
if lock {
flock.Type = syscall.F_WRLCK
}
return syscall.FcntlFlock(l.f.Fd(), syscall.F_SETLK, &flock)
}
func lockFile(file string) error {
fd, err := syscall.Open(file, syscall.O_CREAT|syscall.O_RDWR|syscall.O_CLOEXEC, 0660)
if err != nil {
return err
}
lock := syscall.Flock_t{
Start: 0,
Len: 0,
Type: syscall.F_WRLCK,
Whence: int16(os.SEEK_SET),
}
return syscall.FcntlFlock(uintptr(fd), syscall.F_SETLK, &lock)
}
func ofdLockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
f, err := os.OpenFile(path, flag, perm)
if err != nil {
return nil, err
}
flock := wrlck
err = syscall.FcntlFlock(f.Fd(), F_OFD_SETLKW, &flock)
if err != nil {
f.Close()
return nil, err
}
return &LockedFile{f}, err
}
// TestFcntlFlock tests whether the file locking structure matches
// the calling convention of each kernel.
func TestFcntlFlock(t *testing.T) {
name := filepath.Join(os.TempDir(), "TestFcntlFlock")
fd, err := syscall.Open(name, syscall.O_CREAT|syscall.O_RDWR|syscall.O_CLOEXEC, 0)
if err != nil {
t.Fatalf("Open failed: %v", err)
}
defer syscall.Unlink(name)
defer syscall.Close(fd)
flock := syscall.Flock_t{
Type: syscall.F_RDLCK,
Start: 0, Len: 0, Whence: 1,
}
if err := syscall.FcntlFlock(uintptr(fd), syscall.F_GETLK, &flock); err != nil {
t.Fatalf("FcntlFlock failed: %v", err)
}
}
func ofdTryLockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
f, err := os.OpenFile(path, flag, perm)
if err != nil {
return nil, err
}
flock := wrlck
if err = syscall.FcntlFlock(f.Fd(), F_OFD_SETLK, &flock); err != nil {
f.Close()
if err == syscall.EWOULDBLOCK {
err = ErrLocked
}
return nil, err
}
return &LockedFile{f}, nil
}
// Owner will return the pid of the process that owns an fcntl based
// lock on the file. If the file is not locked it will return -1. If
// a lock is owned by the current process, it will return -1.
func (l *FcntlLockfile) Owner() int {
ft := &syscall.Flock_t{}
*ft = *l.ft
err := syscall.FcntlFlock(l.file.Fd(), syscall.F_GETLK, ft)
if err != nil {
fmt.Println(err)
return -1
}
if ft.Type == syscall.F_UNLCK {
fmt.Println(err)
return -1
}
return int(ft.Pid)
}
func LockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
var lock syscall.Flock_t
lock.Start = 0
lock.Len = 0
lock.Pid = 0
lock.Type = syscall.F_WRLCK
lock.Whence = 0
f, err := os.OpenFile(path, flag, perm)
if err != nil {
return nil, err
}
if err = syscall.FcntlFlock(f.Fd(), syscall.F_SETLKW, &lock); err != nil {
f.Close()
return nil, err
}
return &LockedFile{f}, nil
}
func (defFS) Lock(name string) (io.Closer, error) {
f, err := os.Create(name)
if err != nil {
return nil, err
}
spec := syscall.Flock_t{
Type: syscall.F_WRLCK,
Whence: int16(os.SEEK_SET),
Start: 0,
Len: 0, // 0 means to lock the entire file.
Pid: int32(os.Getpid()),
}
if err := syscall.FcntlFlock(f.Fd(), syscall.F_SETLK, &spec); err != nil {
f.Close()
return nil, err
}
return lockCloser{f}, nil
}
// Control the lock of file.
func fcntlFlock(lockType int16, path ...string) error {
var err error
if lockType != syscall.F_UNLCK {
mode := syscall.O_CREAT | syscall.O_WRONLY
mask := syscall.Umask(0)
lockFile, err = os.OpenFile(path[0], mode, 0666)
syscall.Umask(mask)
if err != nil {
return err
}
}
lock := syscall.Flock_t{
Start: 0,
Len: 1,
Type: lockType,
Whence: int16(os.SEEK_SET),
}
return syscall.FcntlFlock(lockFile.Fd(), syscall.F_SETLK, &lock)
}
func (l *FcntlLockfile) lock(exclusive, blocking bool, offset int64, whence int, len int64) error {
if l.file == nil {
f, err := os.OpenFile(l.Path, os.O_CREATE|os.O_RDWR, 0666)
if err != nil {
return err
}
l.file = f
}
ft := &syscall.Flock_t{
Whence: int16(whence),
Start: offset,
Len: len,
Pid: int32(os.Getpid()),
}
l.ft = ft
if exclusive {
ft.Type = syscall.F_WRLCK
} else {
ft.Type = syscall.F_RDLCK
}
var flags int
if blocking {
flags = syscall.F_SETLKW
} else {
flags = syscall.F_SETLK
}
err := syscall.FcntlFlock(l.file.Fd(), flags, l.ft)
if err != nil {
if l.maintainFile {
l.file.Close()
}
return ErrFailedToLock
}
return nil
}
func UnlockFile(file *os.File) error {
if file == nil {
return fmt.Errorf("*os.File argument is nil.")
}
fd := file.Fd()
cmd := syscall.F_SETLK
lk := syscall.Flock_t{
Type: syscall.F_UNLCK,
Whence: int16(os.SEEK_SET),
Start: 0,
Len: math.MaxInt64,
Pid: int32(os.Getpid()),
}
err := syscall.FcntlFlock(fd, cmd, &lk)
if err != nil {
return fmt.Errorf("Failed to unlock %s: %s", file.Name(), err)
}
return nil
}
func unlockFileImpl(file *os.File) (err error) {
return syscall.FcntlFlock(
file.Fd(),
syscall.F_SETLK,
createLockParams(syscall.F_UNLCK))
}
