github.com/skanehira/moby@v17.12.1-ce-rc2+incompatible/pkg/loopback/loopback.go (about)

     1  // +build linux,cgo
     2  
     3  package loopback
     4  
     5  import (
     6  	"fmt"
     7  	"os"
     8  
     9  	"github.com/sirupsen/logrus"
    10  	"golang.org/x/sys/unix"
    11  )
    12  
    13  func getLoopbackBackingFile(file *os.File) (uint64, uint64, error) {
    14  	loopInfo, err := ioctlLoopGetStatus64(file.Fd())
    15  	if err != nil {
    16  		logrus.Errorf("Error get loopback backing file: %s", err)
    17  		return 0, 0, ErrGetLoopbackBackingFile
    18  	}
    19  	return loopInfo.loDevice, loopInfo.loInode, nil
    20  }
    21  
    22  // SetCapacity reloads the size for the loopback device.
    23  func SetCapacity(file *os.File) error {
    24  	if err := ioctlLoopSetCapacity(file.Fd(), 0); err != nil {
    25  		logrus.Errorf("Error loopbackSetCapacity: %s", err)
    26  		return ErrSetCapacity
    27  	}
    28  	return nil
    29  }
    30  
    31  // FindLoopDeviceFor returns a loopback device file for the specified file which
    32  // is backing file of a loop back device.
    33  func FindLoopDeviceFor(file *os.File) *os.File {
    34  	var stat unix.Stat_t
    35  	err := unix.Stat(file.Name(), &stat)
    36  	if err != nil {
    37  		return nil
    38  	}
    39  	targetInode := stat.Ino
    40  	targetDevice := stat.Dev
    41  
    42  	for i := 0; true; i++ {
    43  		path := fmt.Sprintf("/dev/loop%d", i)
    44  
    45  		file, err := os.OpenFile(path, os.O_RDWR, 0)
    46  		if err != nil {
    47  			if os.IsNotExist(err) {
    48  				return nil
    49  			}
    50  
    51  			// Ignore all errors until the first not-exist
    52  			// we want to continue looking for the file
    53  			continue
    54  		}
    55  
    56  		dev, inode, err := getLoopbackBackingFile(file)
    57  		if err == nil && dev == targetDevice && inode == targetInode {
    58  			return file
    59  		}
    60  		file.Close()
    61  	}
    62  
    63  	return nil
    64  }