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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, sparseName string, sparseFile *os.File) (loopFile *os.File, err error) {
// Read information about the loopback file.
var st syscall.Stat_t
err = syscall.Fstat(int(sparseFile.Fd()), &st)
if err != nil {
logrus.Errorf("Error reading information about loopback file %s: %v", sparseName, err)
return nil, ErrAttachLoopbackDevice
}
// 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
}
// Check if the loopback driver and underlying filesystem agree on the loopback file's
// device and inode numbers.
dev, ino, err := getLoopbackBackingFile(loopFile)
if err != nil {
logrus.Errorf("Error getting loopback backing file: %s", err)
return nil, ErrGetLoopbackBackingFile
}
if dev != uint64(st.Dev) || ino != st.Ino {
logrus.Errorf("Loopback device and filesystem disagree on device/inode for %q: %#x(%d):%#x(%d) vs %#x(%d):%#x(%d)", sparseName, dev, dev, ino, ino, st.Dev, st.Dev, st.Ino, st.Ino)
}
// 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, sparseName, 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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