diff options
Diffstat (limited to 'runtime/graphdriver/devmapper/attach_loopback.go')
-rw-r--r-- | runtime/graphdriver/devmapper/attach_loopback.go | 126 |
1 files changed, 126 insertions, 0 deletions
diff --git a/runtime/graphdriver/devmapper/attach_loopback.go b/runtime/graphdriver/devmapper/attach_loopback.go new file mode 100644 index 0000000000..23339076e8 --- /dev/null +++ b/runtime/graphdriver/devmapper/attach_loopback.go @@ -0,0 +1,126 @@ +// +build linux,amd64 + +package devmapper + +import ( + "fmt" + "github.com/dotcloud/docker/utils" +) + +func stringToLoopName(src string) [LoNameSize]uint8 { + var dst [LoNameSize]uint8 + copy(dst[:], src[:]) + return dst +} + +func getNextFreeLoopbackIndex() (int, error) { + f, err := osOpenFile("/dev/loop-control", osORdOnly, 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 *osFile) (loopFile *osFile, err error) { + // Start looking for a free /dev/loop + for { + target := fmt.Sprintf("/dev/loop%d", index) + index++ + + fi, err := osStat(target) + if err != nil { + if osIsNotExist(err) { + utils.Errorf("There are no more loopback device available.") + } + return nil, ErrAttachLoopbackDevice + } + + if fi.Mode()&osModeDevice != osModeDevice { + utils.Errorf("Loopback device %s is not a block device.", target) + continue + } + + // OpenFile adds O_CLOEXEC + loopFile, err = osOpenFile(target, osORdWr, 0644) + if err != nil { + utils.Errorf("Error openning 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 != sysEBusy { + utils.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 { + utils.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 *osFile. +func attachLoopDevice(sparseName string) (loop *osFile, err error) { + + // Try to retrieve the next available loopback device via syscall. + // If it fails, we discard error and start loopking for a + // loopback from index 0. + startIndex, err := getNextFreeLoopbackIndex() + if err != nil { + utils.Debugf("Error retrieving the next available loopback: %s", err) + } + + // OpenFile adds O_CLOEXEC + sparseFile, err := osOpenFile(sparseName, osORdWr, 0644) + if err != nil { + utils.Errorf("Error openning 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 { + utils.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 { + utils.Errorf("Error while cleaning up the loopback device") + } + loopFile.Close() + return nil, ErrAttachLoopbackDevice + } + + return loopFile, nil +} |