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124 lines
3.3 KiB
Go
124 lines
3.3 KiB
Go
package devmapper
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import (
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"fmt"
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"github.com/dotcloud/docker/utils"
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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 := osOpenFile("/dev/loop-control", osORdOnly, 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 *osFile) (loopFile *osFile, 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 := osStat(target)
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if err != nil {
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if osIsNotExist(err) {
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utils.Errorf("There are no more loopback device available.")
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}
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return nil, ErrAttachLoopbackDevice
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}
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if fi.Mode()&osModeDevice != osModeDevice {
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utils.Errorf("Loopback device %s is not a block device.", target)
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continue
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}
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// Open the targeted loopback (use OpenFile because Open sets O_CLOEXEC)
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loopFile, err = osOpenFile(target, osORdWr, 0644)
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if err != nil {
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utils.Errorf("Error openning 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 != sysEBusy {
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utils.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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utils.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 *osFile.
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func attachLoopDevice(sparseName string) (loop *osFile, 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 loopking 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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utils.Debugf("Error retrieving the next available loopback: %s", err)
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}
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// Open the given sparse file (use OpenFile because Open sets O_CLOEXEC)
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sparseFile, err := osOpenFile(sparseName, osORdWr, 0644)
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if err != nil {
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utils.Errorf("Error openning 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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utils.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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utils.Errorf("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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