loopback: separate loop logic from devicemapper

The loopback logic is not technically exclusive to the devicemapper
driver. This reorganizes the code such that the loopback code is usable
outside of the devicemapper package and driver.

Signed-off-by: Vincent Batts <vbatts@redhat.com>

daemon/graphdriver/devmapper/deviceset.go

@@ -24,6 +24,7 @@ import (
 	"github.com/docker/docker/daemon/graphdriver"
 	"github.com/docker/docker/pkg/devicemapper"
 	"github.com/docker/docker/pkg/idtools"
+	"github.com/docker/docker/pkg/loopback"
 	"github.com/docker/docker/pkg/mount"
 	"github.com/docker/docker/pkg/parsers"
 	"github.com/docker/go-units"
@@ -1170,7 +1171,7 @@ func (devices *DeviceSet) ResizePool(size int64) error {
 		return fmt.Errorf("devmapper: Can't shrink file")
 	}
 
-	dataloopback := devicemapper.FindLoopDeviceFor(datafile)
+	dataloopback := loopback.FindLoopDeviceFor(datafile)
 	if dataloopback == nil {
 		return fmt.Errorf("devmapper: Unable to find loopback mount for: %s", datafilename)
 	}
@@ -1182,7 +1183,7 @@ func (devices *DeviceSet) ResizePool(size int64) error {
 	}
 	defer metadatafile.Close()
 
-	metadataloopback := devicemapper.FindLoopDeviceFor(metadatafile)
+	metadataloopback := loopback.FindLoopDeviceFor(metadatafile)
 	if metadataloopback == nil {
 		return fmt.Errorf("devmapper: Unable to find loopback mount for: %s", metadatafilename)
 	}
@@ -1194,8 +1195,8 @@ func (devices *DeviceSet) ResizePool(size int64) error {
 	}
 
 	// Reload size for loopback device
-	if err := devicemapper.LoopbackSetCapacity(dataloopback); err != nil {
-		return fmt.Errorf("devmapper: Unable to update loopback capacity: %s", err)
+	if err := loopback.SetCapacity(dataloopback); err != nil {
+		return fmt.Errorf("Unable to update loopback capacity: %s", err)
 	}
 
 	// Suspend the pool
@@ -1414,7 +1415,7 @@ func getLoopFileDeviceMajMin(filename string) (string, uint64, uint64, error) {
 	}
 
 	defer file.Close()
-	loopbackDevice := devicemapper.FindLoopDeviceFor(file)
+	loopbackDevice := loopback.FindLoopDeviceFor(file)
 	if loopbackDevice == nil {
 		return "", 0, 0, fmt.Errorf("devmapper: Unable to find loopback mount for: %s", filename)
 	}
@@ -1622,7 +1623,7 @@ func (devices *DeviceSet) initDevmapper(doInit bool) error {
 				return err
 			}
 
-			dataFile, err = devicemapper.AttachLoopDevice(data)
+			dataFile, err = loopback.AttachLoopDevice(data)
 			if err != nil {
 				return err
 			}
@@ -1655,7 +1656,7 @@ func (devices *DeviceSet) initDevmapper(doInit bool) error {
 				return err
 			}
 
-			metadataFile, err = devicemapper.AttachLoopDevice(metadata)
+			metadataFile, err = loopback.AttachLoopDevice(metadata)
 			if err != nil {
 				return err
 			}

pkg/devicemapper/devmapper.go

@@ -47,32 +47,29 @@ const (
 
 // List of errors returned when using devicemapper.
 var (
-	ErrTaskRun                = errors.New("dm_task_run failed")
-	ErrTaskSetName            = errors.New("dm_task_set_name failed")
-	ErrTaskSetMessage         = errors.New("dm_task_set_message failed")
-	ErrTaskSetAddNode         = errors.New("dm_task_set_add_node failed")
-	ErrTaskSetRo              = errors.New("dm_task_set_ro failed")
-	ErrTaskAddTarget          = errors.New("dm_task_add_target failed")
-	ErrTaskSetSector          = errors.New("dm_task_set_sector failed")
-	ErrTaskGetDeps            = errors.New("dm_task_get_deps failed")
-	ErrTaskGetInfo            = errors.New("dm_task_get_info failed")
-	ErrTaskGetDriverVersion   = errors.New("dm_task_get_driver_version failed")
-	ErrTaskDeferredRemove     = errors.New("dm_task_deferred_remove failed")
-	ErrTaskSetCookie          = errors.New("dm_task_set_cookie failed")
-	ErrNilCookie              = errors.New("cookie ptr can't be nil")
-	ErrAttachLoopbackDevice   = errors.New("loopback mounting failed")
-	ErrGetBlockSize           = errors.New("Can't get block size")
-	ErrUdevWait               = errors.New("wait on udev cookie failed")
-	ErrSetDevDir              = errors.New("dm_set_dev_dir failed")
-	ErrGetLibraryVersion      = errors.New("dm_get_library_version failed")
-	ErrCreateRemoveTask       = errors.New("Can't create task of type deviceRemove")
-	ErrRunRemoveDevice        = errors.New("running RemoveDevice failed")
-	ErrInvalidAddNode         = errors.New("Invalid AddNode type")
-	ErrGetLoopbackBackingFile = errors.New("Unable to get loopback backing file")
-	ErrLoopbackSetCapacity    = errors.New("Unable set loopback capacity")
-	ErrBusy                   = errors.New("Device is Busy")
-	ErrDeviceIDExists         = errors.New("Device Id Exists")
-	ErrEnxio                  = errors.New("No such device or address")
+	ErrTaskRun              = errors.New("dm_task_run failed")
+	ErrTaskSetName          = errors.New("dm_task_set_name failed")
+	ErrTaskSetMessage       = errors.New("dm_task_set_message failed")
+	ErrTaskSetAddNode       = errors.New("dm_task_set_add_node failed")
+	ErrTaskSetRo            = errors.New("dm_task_set_ro failed")
+	ErrTaskAddTarget        = errors.New("dm_task_add_target failed")
+	ErrTaskSetSector        = errors.New("dm_task_set_sector failed")
+	ErrTaskGetDeps          = errors.New("dm_task_get_deps failed")
+	ErrTaskGetInfo          = errors.New("dm_task_get_info failed")
+	ErrTaskGetDriverVersion = errors.New("dm_task_get_driver_version failed")
+	ErrTaskDeferredRemove   = errors.New("dm_task_deferred_remove failed")
+	ErrTaskSetCookie        = errors.New("dm_task_set_cookie failed")
+	ErrNilCookie            = errors.New("cookie ptr can't be nil")
+	ErrGetBlockSize         = errors.New("Can't get block size")
+	ErrUdevWait             = errors.New("wait on udev cookie failed")
+	ErrSetDevDir            = errors.New("dm_set_dev_dir failed")
+	ErrGetLibraryVersion    = errors.New("dm_get_library_version failed")
+	ErrCreateRemoveTask     = errors.New("Can't create task of type deviceRemove")
+	ErrRunRemoveDevice      = errors.New("running RemoveDevice failed")
+	ErrInvalidAddNode       = errors.New("Invalid AddNode type")
+	ErrBusy                 = errors.New("Device is Busy")
+	ErrDeviceIDExists       = errors.New("Device Id Exists")
+	ErrEnxio                = errors.New("No such device or address")
 )
 
 var (
@@ -257,58 +254,6 @@ func (t *Task) getNextTarget(next unsafe.Pointer) (nextPtr unsafe.Pointer, start
 		start, length, targetType, params
 }
 
-func getLoopbackBackingFile(file *os.File) (uint64, uint64, error) {
-	loopInfo, err := ioctlLoopGetStatus64(file.Fd())
-	if err != nil {
-		logrus.Errorf("devicemapper: Error get loopback backing file: %s", err)
-		return 0, 0, ErrGetLoopbackBackingFile
-	}
-	return loopInfo.loDevice, loopInfo.loInode, nil
-}
-
-// LoopbackSetCapacity reloads the size for the loopback device.
-func LoopbackSetCapacity(file *os.File) error {
-	if err := ioctlLoopSetCapacity(file.Fd(), 0); err != nil {
-		logrus.Errorf("devicemapper: Error loopbackSetCapacity: %s", err)
-		return ErrLoopbackSetCapacity
-	}
-	return nil
-}
-
-// FindLoopDeviceFor returns a loopback device file for the specified file which
-// is backing file of a loop back device.
-func FindLoopDeviceFor(file *os.File) *os.File {
-	stat, err := file.Stat()
-	if err != nil {
-		return nil
-	}
-	targetInode := stat.Sys().(*syscall.Stat_t).Ino
-	targetDevice := stat.Sys().(*syscall.Stat_t).Dev
-
-	for i := 0; true; i++ {
-		path := fmt.Sprintf("/dev/loop%d", i)
-
-		file, err := os.OpenFile(path, os.O_RDWR, 0)
-		if err != nil {
-			if os.IsNotExist(err) {
-				return nil
-			}
-
-			// Ignore all errors until the first not-exist
-			// we want to continue looking for the file
-			continue
-		}
-
-		dev, inode, err := getLoopbackBackingFile(file)
-		if err == nil && dev == targetDevice && inode == targetInode {
-			return file
-		}
-		file.Close()
-	}
-
-	return nil
-}
-
 // UdevWait waits for any processes that are waiting for udev to complete the specified cookie.
 func UdevWait(cookie *uint) error {
 	if res := DmUdevWait(*cookie); res != 1 {

pkg/devicemapper/devmapper_wrapper.go

@@ -5,17 +5,8 @@ package devicemapper
 /*
 #cgo LDFLAGS: -L. -ldevmapper
 #include <libdevmapper.h>
-#include <linux/loop.h> // FIXME: present only for defines, maybe we can remove it?
 #include <linux/fs.h>   // FIXME: present only for BLKGETSIZE64, maybe we can remove it?
 
-#ifndef LOOP_CTL_GET_FREE
-  #define LOOP_CTL_GET_FREE 0x4C82
-#endif
-
-#ifndef LO_FLAGS_PARTSCAN
-  #define LO_FLAGS_PARTSCAN 8
-#endif
-
 // FIXME: Can't we find a way to do the logging in pure Go?
 extern void DevmapperLogCallback(int level, char *file, int line, int dm_errno_or_class, char *str);
 
@@ -45,44 +36,12 @@ import (
 
 type (
 	cdmTask C.struct_dm_task
-
-	loopInfo64 struct {
-		loDevice         uint64 /* ioctl r/o */
-		loInode          uint64 /* ioctl r/o */
-		loRdevice        uint64 /* ioctl r/o */
-		loOffset         uint64
-		loSizelimit      uint64 /* bytes, 0 == max available */
-		loNumber         uint32 /* ioctl r/o */
-		loEncryptType    uint32
-		loEncryptKeySize uint32 /* ioctl w/o */
-		loFlags          uint32 /* ioctl r/o */
-		loFileName       [LoNameSize]uint8
-		loCryptName      [LoNameSize]uint8
-		loEncryptKey     [LoKeySize]uint8 /* ioctl w/o */
-		loInit           [2]uint64
-	}
 )
 
 // IOCTL consts
 const (
 	BlkGetSize64 = C.BLKGETSIZE64
 	BlkDiscard   = C.BLKDISCARD
-
-	LoopSetFd       = C.LOOP_SET_FD
-	LoopCtlGetFree  = C.LOOP_CTL_GET_FREE
-	LoopGetStatus64 = C.LOOP_GET_STATUS64
-	LoopSetStatus64 = C.LOOP_SET_STATUS64
-	LoopClrFd       = C.LOOP_CLR_FD
-	LoopSetCapacity = C.LOOP_SET_CAPACITY
-)
-
-// LOOP consts.
-const (
-	LoFlagsAutoClear = C.LO_FLAGS_AUTOCLEAR
-	LoFlagsReadOnly  = C.LO_FLAGS_READ_ONLY
-	LoFlagsPartScan  = C.LO_FLAGS_PARTSCAN
-	LoKeySize        = C.LO_KEY_SIZE
-	LoNameSize       = C.LO_NAME_SIZE
 )
 
 // Devicemapper cookie flags.

pkg/devicemapper/ioctl.go

@@ -7,51 +7,6 @@ import (
 	"unsafe"
 )
 
-func ioctlLoopCtlGetFree(fd uintptr) (int, error) {
-	index, _, err := syscall.Syscall(syscall.SYS_IOCTL, fd, LoopCtlGetFree, 0)
-	if err != 0 {
-		return 0, err
-	}
-	return int(index), nil
-}
-
-func ioctlLoopSetFd(loopFd, sparseFd uintptr) error {
-	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, loopFd, LoopSetFd, sparseFd); err != 0 {
-		return err
-	}
-	return nil
-}
-
-func ioctlLoopSetStatus64(loopFd uintptr, loopInfo *loopInfo64) error {
-	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, loopFd, LoopSetStatus64, uintptr(unsafe.Pointer(loopInfo))); err != 0 {
-		return err
-	}
-	return nil
-}
-
-func ioctlLoopClrFd(loopFd uintptr) error {
-	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, loopFd, LoopClrFd, 0); err != 0 {
-		return err
-	}
-	return nil
-}
-
-func ioctlLoopGetStatus64(loopFd uintptr) (*loopInfo64, error) {
-	loopInfo := &loopInfo64{}
-
-	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, loopFd, LoopGetStatus64, uintptr(unsafe.Pointer(loopInfo))); err != 0 {
-		return nil, err
-	}
-	return loopInfo, nil
-}
-
-func ioctlLoopSetCapacity(loopFd uintptr, value int) error {
-	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, loopFd, LoopSetCapacity, uintptr(value)); err != 0 {
-		return err
-	}
-	return nil
-}
-
 func ioctlBlkGetSize64(fd uintptr) (int64, error) {
 	var size int64
 	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, fd, BlkGetSize64, uintptr(unsafe.Pointer(&size))); err != 0 {

pkg/loopback/attach_loopback.go

@@ -1,8 +1,9 @@
 // +build linux
 
-package devicemapper
+package loopback
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"syscall"
@@ -10,6 +11,13 @@ import (
 	"github.com/Sirupsen/logrus"
 )
 
+// 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")
+)
+
 func stringToLoopName(src string) [LoNameSize]uint8 {
 	var dst [LoNameSize]uint8
 	copy(dst[:], src[:])

pkg/loopback/ioctl.go

@@ -0,0 +1,53 @@
+// +build linux
+
+package loopback
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+func ioctlLoopCtlGetFree(fd uintptr) (int, error) {
+	index, _, err := syscall.Syscall(syscall.SYS_IOCTL, fd, LoopCtlGetFree, 0)
+	if err != 0 {
+		return 0, err
+	}
+	return int(index), nil
+}
+
+func ioctlLoopSetFd(loopFd, sparseFd uintptr) error {
+	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, loopFd, LoopSetFd, sparseFd); err != 0 {
+		return err
+	}
+	return nil
+}
+
+func ioctlLoopSetStatus64(loopFd uintptr, loopInfo *loopInfo64) error {
+	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, loopFd, LoopSetStatus64, uintptr(unsafe.Pointer(loopInfo))); err != 0 {
+		return err
+	}
+	return nil
+}
+
+func ioctlLoopClrFd(loopFd uintptr) error {
+	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, loopFd, LoopClrFd, 0); err != 0 {
+		return err
+	}
+	return nil
+}
+
+func ioctlLoopGetStatus64(loopFd uintptr) (*loopInfo64, error) {
+	loopInfo := &loopInfo64{}
+
+	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, loopFd, LoopGetStatus64, uintptr(unsafe.Pointer(loopInfo))); err != 0 {
+		return nil, err
+	}
+	return loopInfo, nil
+}
+
+func ioctlLoopSetCapacity(loopFd uintptr, value int) error {
+	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, loopFd, LoopSetCapacity, uintptr(value)); err != 0 {
+		return err
+	}
+	return nil
+}

pkg/loopback/loop_wrapper.go

@@ -0,0 +1,52 @@
+// +build linux
+
+package loopback
+
+/*
+#include <linux/loop.h> // FIXME: present only for defines, maybe we can remove it?
+
+#ifndef LOOP_CTL_GET_FREE
+  #define LOOP_CTL_GET_FREE 0x4C82
+#endif
+
+#ifndef LO_FLAGS_PARTSCAN
+  #define LO_FLAGS_PARTSCAN 8
+#endif
+
+*/
+import "C"
+
+type loopInfo64 struct {
+	loDevice         uint64 /* ioctl r/o */
+	loInode          uint64 /* ioctl r/o */
+	loRdevice        uint64 /* ioctl r/o */
+	loOffset         uint64
+	loSizelimit      uint64 /* bytes, 0 == max available */
+	loNumber         uint32 /* ioctl r/o */
+	loEncryptType    uint32
+	loEncryptKeySize uint32 /* ioctl w/o */
+	loFlags          uint32 /* ioctl r/o */
+	loFileName       [LoNameSize]uint8
+	loCryptName      [LoNameSize]uint8
+	loEncryptKey     [LoKeySize]uint8 /* ioctl w/o */
+	loInit           [2]uint64
+}
+
+// IOCTL consts
+const (
+	LoopSetFd       = C.LOOP_SET_FD
+	LoopCtlGetFree  = C.LOOP_CTL_GET_FREE
+	LoopGetStatus64 = C.LOOP_GET_STATUS64
+	LoopSetStatus64 = C.LOOP_SET_STATUS64
+	LoopClrFd       = C.LOOP_CLR_FD
+	LoopSetCapacity = C.LOOP_SET_CAPACITY
+)
+
+// LOOP consts.
+const (
+	LoFlagsAutoClear = C.LO_FLAGS_AUTOCLEAR
+	LoFlagsReadOnly  = C.LO_FLAGS_READ_ONLY
+	LoFlagsPartScan  = C.LO_FLAGS_PARTSCAN
+	LoKeySize        = C.LO_KEY_SIZE
+	LoNameSize       = C.LO_NAME_SIZE
+)

pkg/loopback/loopback.go

@@ -0,0 +1,63 @@
+// +build linux
+
+package loopback
+
+import (
+	"fmt"
+	"os"
+	"syscall"
+
+	"github.com/Sirupsen/logrus"
+)
+
+func getLoopbackBackingFile(file *os.File) (uint64, uint64, error) {
+	loopInfo, err := ioctlLoopGetStatus64(file.Fd())
+	if err != nil {
+		logrus.Errorf("Error get loopback backing file: %s", err)
+		return 0, 0, ErrGetLoopbackBackingFile
+	}
+	return loopInfo.loDevice, loopInfo.loInode, nil
+}
+
+// SetCapacity reloads the size for the loopback device.
+func SetCapacity(file *os.File) error {
+	if err := ioctlLoopSetCapacity(file.Fd(), 0); err != nil {
+		logrus.Errorf("Error loopbackSetCapacity: %s", err)
+		return ErrSetCapacity
+	}
+	return nil
+}
+
+// FindLoopDeviceFor returns a loopback device file for the specified file which
+// is backing file of a loop back device.
+func FindLoopDeviceFor(file *os.File) *os.File {
+	stat, err := file.Stat()
+	if err != nil {
+		return nil
+	}
+	targetInode := stat.Sys().(*syscall.Stat_t).Ino
+	targetDevice := stat.Sys().(*syscall.Stat_t).Dev
+
+	for i := 0; true; i++ {
+		path := fmt.Sprintf("/dev/loop%d", i)
+
+		file, err := os.OpenFile(path, os.O_RDWR, 0)
+		if err != nil {
+			if os.IsNotExist(err) {
+				return nil
+			}
+
+			// Ignore all errors until the first not-exist
+			// we want to continue looking for the file
+			continue
+		}
+
+		dev, inode, err := getLoopbackBackingFile(file)
+		if err == nil && dev == targetDevice && inode == targetInode {
+			return file
+		}
+		file.Close()
+	}
+
+	return nil
+}