github.com/rawahars/moby@v24.0.4+incompatible/pkg/loopback/loopback.go (about)

     1  //go:build linux && cgo
     2  // +build linux,cgo
     3  
     4  package loopback // import "github.com/docker/docker/pkg/loopback"
     5  
     6  import (
     7  	"fmt"
     8  	"os"
     9  
    10  	"github.com/sirupsen/logrus"
    11  	"golang.org/x/sys/unix"
    12  )
    13  
    14  func getLoopbackBackingFile(file *os.File) (uint64, uint64, error) {
    15  	loopInfo, err := unix.IoctlLoopGetStatus64(int(file.Fd()))
    16  	if err != nil {
    17  		logrus.Errorf("Error get loopback backing file: %s", err)
    18  		return 0, 0, ErrGetLoopbackBackingFile
    19  	}
    20  	return loopInfo.Device, loopInfo.Inode, nil
    21  }
    22  
    23  // SetCapacity reloads the size for the loopback device.
    24  func SetCapacity(file *os.File) error {
    25  	if err := unix.IoctlSetInt(int(file.Fd()), unix.LOOP_SET_CAPACITY, 0); err != nil {
    26  		logrus.Errorf("Error loopbackSetCapacity: %s", err)
    27  		return ErrSetCapacity
    28  	}
    29  	return nil
    30  }
    31  
    32  // FindLoopDeviceFor returns a loopback device file for the specified file which
    33  // is backing file of a loop back device.
    34  func FindLoopDeviceFor(file *os.File) *os.File {
    35  	var stat unix.Stat_t
    36  	err := unix.Stat(file.Name(), &stat)
    37  	if err != nil {
    38  		return nil
    39  	}
    40  	targetInode := stat.Ino
    41  	targetDevice := uint64(stat.Dev) //nolint: unconvert // the type is 32bit on mips
    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  }