mirror of
https://github.com/moby/moby.git
synced 2022-11-09 12:21:53 -05:00
129 lines
3.2 KiB
Go
129 lines
3.2 KiB
Go
// +build linux
|
|
|
|
package devicemapper
|
|
|
|
import (
|
|
"fmt"
|
|
"os"
|
|
"syscall"
|
|
|
|
"github.com/Sirupsen/logrus"
|
|
)
|
|
|
|
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.Errorf("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.Errorf("Error while cleaning up the loopback device")
|
|
}
|
|
loopFile.Close()
|
|
return nil, ErrAttachLoopbackDevice
|
|
}
|
|
|
|
return loopFile, nil
|
|
}
|