github.com/docker/docker@v299999999.0.0-20200612211812-aaf470eca7b5+incompatible/pkg/loopback/loopback.go (about)

     1  // +build linux,cgo
     2  
     3  package loopback // import "github.com/docker/docker/pkg/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.Device, loopInfo.Inode, 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  	// the type is 32bit on mips
    41  	targetDevice := uint64(stat.Dev) // nolint: unconvert
    42  
    43  	for i := 0; true; i++ {
    44  		path := fmt.Sprintf("/dev/loop%d", i)
    45  
    46  		file, err := os.OpenFile(path, os.O_RDWR, 0)
    47  		if err != nil {
    48  			if os.IsNotExist(err) {
    49  				return nil
    50  			}
    51  
    52  			// Ignore all errors until the first not-exist
    53  			// we want to continue looking for the file
    54  			continue
    55  		}
    56  
    57  		dev, inode, err := getLoopbackBackingFile(file)
    58  		if err == nil && dev == targetDevice && inode == targetInode {
    59  			return file
    60  		}
    61  		file.Close()
    62  	}
    63  
    64  	return nil
    65  }