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- // +build linux,cgo
- package loopback
- import (
- "errors"
- "fmt"
- "os"
- "syscall"
- "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[:])
- return dst
- }
- func getNextFreeLoopbackIndex() (int, error) {
- f, err := os.OpenFile("/dev/loop-control", os.O_RDONLY, 0644)
- if err != nil {
- return 0, err
- }
- defer f.Close()
- index, err := ioctlLoopCtlGetFree(f.Fd())
- if index < 0 {
- index = 0
- }
- return index, err
- }
- func openNextAvailableLoopback(index int, sparseFile *os.File) (loopFile *os.File, err error) {
- // Start looking for a free /dev/loop
- for {
- target := fmt.Sprintf("/dev/loop%d", index)
- index++
- fi, err := os.Stat(target)
- if err != nil {
- if os.IsNotExist(err) {
- logrus.Error("There are no more loopback devices available.")
- }
- return nil, ErrAttachLoopbackDevice
- }
- if fi.Mode()&os.ModeDevice != os.ModeDevice {
- logrus.Errorf("Loopback device %s is not a block device.", target)
- continue
- }
- // OpenFile adds O_CLOEXEC
- loopFile, err = os.OpenFile(target, os.O_RDWR, 0644)
- if err != nil {
- logrus.Errorf("Error opening loopback device: %s", err)
- return nil, ErrAttachLoopbackDevice
- }
- // Try to attach to the loop file
- if err := ioctlLoopSetFd(loopFile.Fd(), sparseFile.Fd()); err != nil {
- loopFile.Close()
- // If the error is EBUSY, then try the next loopback
- if err != syscall.EBUSY {
- logrus.Errorf("Cannot set up loopback device %s: %s", target, err)
- return nil, ErrAttachLoopbackDevice
- }
- // Otherwise, we keep going with the loop
- continue
- }
- // In case of success, we finished. Break the loop.
- break
- }
- // This can't happen, but let's be sure
- if loopFile == nil {
- logrus.Errorf("Unreachable code reached! Error attaching %s to a loopback device.", sparseFile.Name())
- return nil, ErrAttachLoopbackDevice
- }
- return loopFile, nil
- }
- // AttachLoopDevice attaches the given sparse file to the next
- // available loopback device. It returns an opened *os.File.
- func AttachLoopDevice(sparseName string) (loop *os.File, err error) {
- // Try to retrieve the next available loopback device via syscall.
- // If it fails, we discard error and start looping for a
- // loopback from index 0.
- startIndex, err := getNextFreeLoopbackIndex()
- if err != nil {
- logrus.Debugf("Error retrieving the next available loopback: %s", err)
- }
- // OpenFile adds O_CLOEXEC
- sparseFile, err := os.OpenFile(sparseName, os.O_RDWR, 0644)
- if err != nil {
- logrus.Errorf("Error opening sparse file %s: %s", sparseName, err)
- return nil, ErrAttachLoopbackDevice
- }
- defer sparseFile.Close()
- loopFile, err := openNextAvailableLoopback(startIndex, sparseFile)
- if err != nil {
- return nil, err
- }
- // Set the status of the loopback device
- loopInfo := &loopInfo64{
- loFileName: stringToLoopName(loopFile.Name()),
- loOffset: 0,
- loFlags: LoFlagsAutoClear,
- }
- if err := ioctlLoopSetStatus64(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 {
- logrus.Error("Error while cleaning up the loopback device")
- }
- loopFile.Close()
- return nil, ErrAttachLoopbackDevice
- }
- return loopFile, nil
- }
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