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137 lines
3.5 KiB
Go
137 lines
3.5 KiB
Go
// +build linux,cgo
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package loopback
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import (
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"errors"
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"fmt"
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"os"
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"github.com/sirupsen/logrus"
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"golang.org/x/sys/unix"
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)
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// Loopback related errors
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var (
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ErrAttachLoopbackDevice = errors.New("loopback attach failed")
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ErrGetLoopbackBackingFile = errors.New("Unable to get loopback backing file")
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ErrSetCapacity = errors.New("Unable set loopback capacity")
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)
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func stringToLoopName(src string) [LoNameSize]uint8 {
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var dst [LoNameSize]uint8
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copy(dst[:], src[:])
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return dst
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}
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func getNextFreeLoopbackIndex() (int, error) {
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f, err := os.OpenFile("/dev/loop-control", os.O_RDONLY, 0644)
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if err != nil {
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return 0, err
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}
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defer f.Close()
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index, err := ioctlLoopCtlGetFree(f.Fd())
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if index < 0 {
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index = 0
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}
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return index, err
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}
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func openNextAvailableLoopback(index int, sparseFile *os.File) (loopFile *os.File, err error) {
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// Start looking for a free /dev/loop
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for {
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target := fmt.Sprintf("/dev/loop%d", index)
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index++
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fi, err := os.Stat(target)
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if err != nil {
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if os.IsNotExist(err) {
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logrus.Error("There are no more loopback devices available.")
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}
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return nil, ErrAttachLoopbackDevice
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}
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if fi.Mode()&os.ModeDevice != os.ModeDevice {
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logrus.Errorf("Loopback device %s is not a block device.", target)
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continue
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}
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// OpenFile adds O_CLOEXEC
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loopFile, err = os.OpenFile(target, os.O_RDWR, 0644)
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if err != nil {
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logrus.Errorf("Error opening loopback device: %s", err)
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return nil, ErrAttachLoopbackDevice
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}
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// Try to attach to the loop file
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if err := ioctlLoopSetFd(loopFile.Fd(), sparseFile.Fd()); err != nil {
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loopFile.Close()
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// If the error is EBUSY, then try the next loopback
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if err != unix.EBUSY {
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logrus.Errorf("Cannot set up loopback device %s: %s", target, err)
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return nil, ErrAttachLoopbackDevice
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}
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// Otherwise, we keep going with the loop
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continue
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}
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// In case of success, we finished. Break the loop.
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break
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}
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// This can't happen, but let's be sure
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if loopFile == nil {
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logrus.Errorf("Unreachable code reached! Error attaching %s to a loopback device.", sparseFile.Name())
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return nil, ErrAttachLoopbackDevice
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}
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return loopFile, nil
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}
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// AttachLoopDevice attaches the given sparse file to the next
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// available loopback device. It returns an opened *os.File.
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func AttachLoopDevice(sparseName string) (loop *os.File, err error) {
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// Try to retrieve the next available loopback device via syscall.
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// If it fails, we discard error and start looping for a
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// loopback from index 0.
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startIndex, err := getNextFreeLoopbackIndex()
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if err != nil {
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logrus.Debugf("Error retrieving the next available loopback: %s", err)
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}
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// OpenFile adds O_CLOEXEC
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sparseFile, err := os.OpenFile(sparseName, os.O_RDWR, 0644)
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if err != nil {
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logrus.Errorf("Error opening sparse file %s: %s", sparseName, err)
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return nil, ErrAttachLoopbackDevice
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}
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defer sparseFile.Close()
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loopFile, err := openNextAvailableLoopback(startIndex, sparseFile)
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if err != nil {
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return nil, err
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}
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// Set the status of the loopback device
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loopInfo := &loopInfo64{
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loFileName: stringToLoopName(loopFile.Name()),
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loOffset: 0,
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loFlags: LoFlagsAutoClear,
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}
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if err := ioctlLoopSetStatus64(loopFile.Fd(), loopInfo); err != nil {
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logrus.Errorf("Cannot set up loopback device info: %s", err)
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// If the call failed, then free the loopback device
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if err := ioctlLoopClrFd(loopFile.Fd()); err != nil {
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logrus.Error("Error while cleaning up the loopback device")
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}
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loopFile.Close()
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return nil, ErrAttachLoopbackDevice
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}
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return loopFile, nil
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}
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