pkg/loopback: use ioctl helpers from x/sys/unix

Use the IoctlRetInt, IoctlSetInt and IoctlLoopSetStatus64 helper
functions defined in the golang.org/x/sys/unix package instead of
manually wrapping these using a locally defined function.

Inspired by https://github.com/containerd/containerd/commit/3cc3d8a560a9d070466d7d58010beda61db5c1ba

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit c7c02eea8117347c5ebd43ef3b9192d43bcdd10b)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

pkg/loopback/attach_loopback.go

@@ -15,12 +15,12 @@ import (
 // Loopback related errors
 var (
 	ErrAttachLoopbackDevice   = errors.New("loopback attach failed")
-	ErrGetLoopbackBackingFile = errors.New("Unable to get loopback backing file")
-	ErrSetCapacity            = errors.New("Unable set loopback capacity")
+	ErrGetLoopbackBackingFile = errors.New("unable to get loopback backing file")
+	ErrSetCapacity            = errors.New("unable set loopback capacity")
 )
 
-func stringToLoopName(src string) [LoNameSize]uint8 {
-	var dst [LoNameSize]uint8
+func stringToLoopName(src string) [unix.LO_NAME_SIZE]uint8 {
+	var dst [unix.LO_NAME_SIZE]uint8
 	copy(dst[:], src[:])
 	return dst
 }
@@ -31,12 +31,7 @@ func getNextFreeLoopbackIndex() (int, error) {
 		return 0, err
 	}
 	defer f.Close()
-
-	index, err := ioctlLoopCtlGetFree(f.Fd())
-	if index < 0 {
-		index = 0
-	}
-	return index, err
+	return unix.IoctlRetInt(int(f.Fd()), unix.LOOP_CTL_GET_FREE)
 }
 
 func openNextAvailableLoopback(index int, sparseFile *os.File) (loopFile *os.File, err error) {
@@ -66,7 +61,7 @@ func openNextAvailableLoopback(index int, sparseFile *os.File) (loopFile *os.Fil
 		}
 
 		// Try to attach to the loop file
-		if err := ioctlLoopSetFd(loopFile.Fd(), sparseFile.Fd()); err != nil {
+		if err = unix.IoctlSetInt(int(loopFile.Fd()), unix.LOOP_SET_FD, int(sparseFile.Fd())); err != nil {
 			loopFile.Close()
 
 			// If the error is EBUSY, then try the next loopback
@@ -119,14 +114,14 @@ func AttachLoopDevice(sparseName string) (loop *os.File, err error) {
 	loopInfo := &unix.LoopInfo64{
 		File_name: stringToLoopName(loopFile.Name()),
 		Offset:    0,
-		Flags:     LoFlagsAutoClear,
+		Flags:     unix.LO_FLAGS_AUTOCLEAR,
 	}
 
-	if err := ioctlLoopSetStatus64(loopFile.Fd(), loopInfo); err != nil {
+	if err = unix.IoctlLoopSetStatus64(int(loopFile.Fd()), loopInfo); err != nil {
 		logrus.Errorf("Cannot set up loopback device info: %s", err)
 
 		// If the call failed, then free the loopback device
-		if err := ioctlLoopClrFd(loopFile.Fd()); err != nil {
+		if err = unix.IoctlSetInt(int(loopFile.Fd()), unix.LOOP_CLR_FD, 0); err != nil {
 			logrus.Error("Error while cleaning up the loopback device")
 		}
 		loopFile.Close()

pkg/loopback/ioctl.go

@@ -1,53 +0,0 @@
-//go:build linux
-// +build linux
-
-package loopback // import "github.com/docker/docker/pkg/loopback"
-
-import (
-	"unsafe"
-
-	"golang.org/x/sys/unix"
-)
-
-func ioctlLoopCtlGetFree(fd uintptr) (int, error) {
-	// The ioctl interface for /dev/loop-control (since Linux 3.1) is a bit
-	// off compared to what you'd expect: instead of writing an integer to a
-	// parameter pointer like unix.IoctlGetInt() expects, it returns the first
-	// available loop device index directly.
-	ioctlReturn, _, err := unix.Syscall(unix.SYS_IOCTL, fd, LoopCtlGetFree, 0)
-	if err != 0 {
-		return 0, err
-	}
-	return int(ioctlReturn), nil
-}
-
-func ioctlLoopSetFd(loopFd, sparseFd uintptr) error {
-	return unix.IoctlSetInt(int(loopFd), unix.LOOP_SET_FD, int(sparseFd))
-}
-
-func ioctlLoopSetStatus64(loopFd uintptr, loopInfo *unix.LoopInfo64) error {
-	if _, _, err := unix.Syscall(unix.SYS_IOCTL, loopFd, unix.LOOP_SET_STATUS64, uintptr(unsafe.Pointer(loopInfo))); err != 0 {
-		return err
-	}
-	return nil
-}
-
-func ioctlLoopClrFd(loopFd uintptr) error {
-	if _, _, err := unix.Syscall(unix.SYS_IOCTL, loopFd, unix.LOOP_CLR_FD, 0); err != 0 {
-		return err
-	}
-	return nil
-}
-
-func ioctlLoopGetStatus64(loopFd uintptr) (*unix.LoopInfo64, error) {
-	loopInfo := &unix.LoopInfo64{}
-
-	if _, _, err := unix.Syscall(unix.SYS_IOCTL, loopFd, unix.LOOP_GET_STATUS64, uintptr(unsafe.Pointer(loopInfo))); err != 0 {
-		return nil, err
-	}
-	return loopInfo, nil
-}
-
-func ioctlLoopSetCapacity(loopFd uintptr, value int) error {
-	return unix.IoctlSetInt(int(loopFd), unix.LOOP_SET_CAPACITY, value)
-}

pkg/loopback/loop_wrapper.go

@@ -1,25 +0,0 @@
-//go:build linux
-// +build linux
-
-package loopback // import "github.com/docker/docker/pkg/loopback"
-
-import "golang.org/x/sys/unix"
-
-// IOCTL consts
-const (
-	LoopSetFd       = unix.LOOP_SET_FD
-	LoopCtlGetFree  = unix.LOOP_CTL_GET_FREE
-	LoopGetStatus64 = unix.LOOP_GET_STATUS64
-	LoopSetStatus64 = unix.LOOP_SET_STATUS64
-	LoopClrFd       = unix.LOOP_CLR_FD
-	LoopSetCapacity = unix.LOOP_SET_CAPACITY
-)
-
-// LOOP consts.
-const (
-	LoFlagsAutoClear = unix.LO_FLAGS_AUTOCLEAR
-	LoFlagsReadOnly  = unix.LO_FLAGS_READ_ONLY
-	LoFlagsPartScan  = unix.LO_FLAGS_PARTSCAN
-	LoKeySize        = unix.LO_KEY_SIZE
-	LoNameSize       = unix.LO_NAME_SIZE
-)

pkg/loopback/loopback.go

@@ -12,7 +12,7 @@ import (
 )
 
 func getLoopbackBackingFile(file *os.File) (uint64, uint64, error) {
-	loopInfo, err := ioctlLoopGetStatus64(file.Fd())
+	loopInfo, err := unix.IoctlLoopGetStatus64(int(file.Fd()))
 	if err != nil {
 		logrus.Errorf("Error get loopback backing file: %s", err)
 		return 0, 0, ErrGetLoopbackBackingFile
@@ -22,7 +22,7 @@ func getLoopbackBackingFile(file *os.File) (uint64, uint64, error) {
 
 // SetCapacity reloads the size for the loopback device.
 func SetCapacity(file *os.File) error {
-	if err := ioctlLoopSetCapacity(file.Fd(), 0); err != nil {
+	if err := unix.IoctlSetInt(int(file.Fd()), unix.LOOP_SET_CAPACITY, 0); err != nil {
 		logrus.Errorf("Error loopbackSetCapacity: %s", err)
 		return ErrSetCapacity
 	}
@@ -38,8 +38,7 @@ func FindLoopDeviceFor(file *os.File) *os.File {
 		return nil
 	}
 	targetInode := stat.Ino
-	// the type is 32bit on mips
-	targetDevice := uint64(stat.Dev) //nolint: unconvert
+	targetDevice := uint64(stat.Dev) //nolint: unconvert // the type is 32bit on mips
 
 	for i := 0; true; i++ {
 		path := fmt.Sprintf("/dev/loop%d", i)