github.com/demonoid81/containerd@v1.3.4/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  )
    27  
    28  // FindAssociatedLoopDevices returns a list of loop devices attached to a given image
    29  func FindAssociatedLoopDevices(imagePath string) ([]string, error) {
    30  	output, err := losetup("--list", "--output", "NAME", "--associated", imagePath)
    31  	if err != nil {
    32  		return nil, errors.Wrapf(err, "failed to get loop devices: '%s'", output)
    33  	}
    34  
    35  	if output == "" {
    36  		return []string{}, nil
    37  	}
    38  
    39  	items := strings.Split(output, "\n")
    40  	if len(items) <= 1 {
    41  		return []string{}, nil
    42  	}
    43  
    44  	// Skip header with column names
    45  	return items[1:], nil
    46  }
    47  
    48  // AttachLoopDevice finds first available loop device and associates it with an image.
    49  func AttachLoopDevice(imagePath string) (string, error) {
    50  	return losetup("--find", "--show", imagePath)
    51  }
    52  
    53  // DetachLoopDevice detaches loop devices
    54  func DetachLoopDevice(loopDevice ...string) error {
    55  	args := append([]string{"--detach"}, loopDevice...)
    56  	_, err := losetup(args...)
    57  	return err
    58  }
    59  
    60  // RemoveLoopDevicesAssociatedWithImage detaches all loop devices attached to a given sparse image
    61  func RemoveLoopDevicesAssociatedWithImage(imagePath string) error {
    62  	loopDevices, err := FindAssociatedLoopDevices(imagePath)
    63  	if err != nil {
    64  		return err
    65  	}
    66  
    67  	for _, loopDevice := range loopDevices {
    68  		if err = DetachLoopDevice(loopDevice); err != nil {
    69  			return err
    70  		}
    71  	}
    72  
    73  	return nil
    74  }
    75  
    76  // losetup is a wrapper around losetup command line tool
    77  func losetup(args ...string) (string, error) {
    78  	data, err := exec.Command("losetup", args...).CombinedOutput()
    79  	output := string(data)
    80  	if err != nil {
    81  		return "", errors.Wrapf(err, "losetup %s\nerror: %s\n", strings.Join(args, " "), output)
    82  	}
    83  
    84  	return strings.TrimSuffix(output, "\n"), err
    85  }