github.com/containerd/Containerd@v1.4.13/snapshots/devmapper/losetup/losetup.go (about)

     1  // +build linux
     2  
     3  /*
     4     Copyright The containerd Authors.
     5  
     6     Licensed under the Apache License, Version 2.0 (the "License");
     7     you may not use this file except in compliance with the License.
     8     You may obtain a copy of the License at
     9  
    10         http://www.apache.org/licenses/LICENSE-2.0
    11  
    12     Unless required by applicable law or agreed to in writing, software
    13     distributed under the License is distributed on an "AS IS" BASIS,
    14     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    15     See the License for the specific language governing permissions and
    16     limitations under the License.
    17  */
    18  
    19  package losetup
    20  
    21  import (
    22  	"os/exec"
    23  	"strings"
    24  
    25  	"github.com/pkg/errors"
    26  	"golang.org/x/sys/unix"
    27  )
    28  
    29  // FindAssociatedLoopDevices returns a list of loop devices attached to a given image
    30  func FindAssociatedLoopDevices(imagePath string) ([]string, error) {
    31  	output, err := losetup("--list", "--output", "NAME", "--associated", imagePath)
    32  	if err != nil {
    33  		return nil, errors.Wrapf(err, "failed to get loop devices: '%s'", output)
    34  	}
    35  
    36  	if output == "" {
    37  		return []string{}, nil
    38  	}
    39  
    40  	items := strings.Split(output, "\n")
    41  	if len(items) <= 1 {
    42  		return []string{}, nil
    43  	}
    44  
    45  	// Skip header with column names
    46  	return items[1:], nil
    47  }
    48  
    49  // AttachLoopDevice finds first available loop device and associates it with an image.
    50  func AttachLoopDevice(imagePath string) (string, error) {
    51  	return losetup("--find", "--show", imagePath)
    52  }
    53  
    54  // DetachLoopDevice detaches loop devices
    55  func DetachLoopDevice(loopDevice ...string) error {
    56  	args := append([]string{"--detach"}, loopDevice...)
    57  	_, err := losetup(args...)
    58  	return err
    59  }
    60  
    61  // RemoveLoopDevicesAssociatedWithImage detaches all loop devices attached to a given sparse image
    62  func RemoveLoopDevicesAssociatedWithImage(imagePath string) error {
    63  	loopDevices, err := FindAssociatedLoopDevices(imagePath)
    64  	if err != nil {
    65  		return err
    66  	}
    67  
    68  	for _, loopDevice := range loopDevices {
    69  		if err = DetachLoopDevice(loopDevice); err != nil && err != unix.ENOENT {
    70  			return err
    71  		}
    72  	}
    73  
    74  	return nil
    75  }
    76  
    77  // losetup is a wrapper around losetup command line tool
    78  func losetup(args ...string) (string, error) {
    79  	cmd := exec.Command("losetup", args...)
    80  	cmd.Env = append(cmd.Env, "LANG=C")
    81  	data, err := cmd.CombinedOutput()
    82  	output := string(data)
    83  	if err != nil {
    84  		if strings.Contains(output, "No such file or directory") || strings.Contains(output, "No such device") {
    85  			return "", unix.ENOENT
    86  		}
    87  
    88  		return "", errors.Wrapf(err, "losetup %s\nerror: %s\n", strings.Join(args, " "), output)
    89  	}
    90  
    91  	return strings.TrimSuffix(output, "\n"), err
    92  }