devmapper: add losetup

Signed-off-by: Maksym Pavlenko <makpav@amazon.com>

snapshots/devmapper/losetup/losetup.go

@@ -0,0 +1,83 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package losetup
+
+import (
+	"os/exec"
+	"strings"
+
+	"github.com/pkg/errors"
+)
+
+// FindAssociatedLoopDevices returns a list of loop devices attached to a given image
+func FindAssociatedLoopDevices(imagePath string) ([]string, error) {
+	output, err := losetup("--list", "--output", "NAME", "--associated", imagePath)
+	if err != nil {
+		return nil, errors.Wrapf(err, "failed to get loop devices: '%s'", output)
+	}
+
+	if output == "" {
+		return []string{}, nil
+	}
+
+	items := strings.Split(output, "\n")
+	if len(items) <= 1 {
+		return []string{}, nil
+	}
+
+	// Skip header with column names
+	return items[1:], nil
+}
+
+// AttachLoopDevice finds first available loop device and associates it with an image.
+func AttachLoopDevice(imagePath string) (string, error) {
+	return losetup("--find", "--show", imagePath)
+}
+
+// DetachLoopDevice detaches loop devices
+func DetachLoopDevice(loopDevice ...string) error {
+	args := append([]string{"--detach"}, loopDevice...)
+	_, err := losetup(args...)
+	return err
+}
+
+// RemoveLoopDevicesAssociatedWithImage detaches all loop devices attached to a given sparse image
+func RemoveLoopDevicesAssociatedWithImage(imagePath string) error {
+	loopDevices, err := FindAssociatedLoopDevices(imagePath)
+	if err != nil {
+		return err
+	}
+
+	for _, loopDevice := range loopDevices {
+		if err = DetachLoopDevice(loopDevice); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// losetup is a wrapper around losetup command line tool
+func losetup(args ...string) (string, error) {
+	data, err := exec.Command("losetup", args...).CombinedOutput()
+	output := string(data)
+	if err != nil {
+		return "", errors.Wrapf(err, "losetup %s\nerror: %s\n", strings.Join(args, " "), output)
+	}
+
+	return strings.TrimSuffix(output, "\n"), err
+}

snapshots/devmapper/losetup/losetup_test.go

@@ -0,0 +1,115 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package losetup
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"github.com/containerd/containerd/pkg/testutil"
+	"github.com/docker/go-units"
+	"gotest.tools/assert"
+	is "gotest.tools/assert/cmp"
+)
+
+func TestLosetup(t *testing.T) {
+	testutil.RequiresRoot(t)
+
+	var (
+		imagePath   = createSparseImage(t)
+		loopDevice1 string
+		loopDevice2 string
+	)
+
+	defer func() {
+		err := os.Remove(imagePath)
+		assert.NilError(t, err)
+	}()
+
+	t.Run("AttachLoopDevice", func(t *testing.T) {
+		dev1, err := AttachLoopDevice(imagePath)
+		assert.NilError(t, err)
+		assert.Assert(t, dev1 != "")
+
+		dev2, err := AttachLoopDevice(imagePath)
+		assert.NilError(t, err)
+		assert.Assert(t, dev2 != dev1, "should attach different loop device")
+
+		loopDevice1 = dev1
+		loopDevice2 = dev2
+	})
+
+	t.Run("AttachEmptyLoopDevice", func(t *testing.T) {
+		_, err := AttachLoopDevice("")
+		assert.Assert(t, err != nil, "shouldn't attach empty path")
+	})
+
+	t.Run("FindAssociatedLoopDevices", func(t *testing.T) {
+		devices, err := FindAssociatedLoopDevices(imagePath)
+		assert.NilError(t, err)
+		assert.Assert(t, is.Len(devices, 2), "unexpected number of attached devices")
+		assert.Assert(t, is.Contains(devices, loopDevice1))
+		assert.Assert(t, is.Contains(devices, loopDevice2))
+	})
+
+	t.Run("FindAssociatedLoopDevicesForInvalidImage", func(t *testing.T) {
+		devices, err := FindAssociatedLoopDevices("")
+		assert.NilError(t, err)
+		assert.Assert(t, is.Len(devices, 0))
+	})
+
+	t.Run("DetachLoopDevice", func(t *testing.T) {
+		err := DetachLoopDevice(loopDevice2)
+		assert.NilError(t, err, "failed to detach %q", loopDevice2)
+	})
+
+	t.Run("DetachEmptyDevice", func(t *testing.T) {
+		err := DetachLoopDevice("")
+		assert.Assert(t, err != nil, "shouldn't detach empty path")
+	})
+
+	t.Run("RemoveLoopDevicesAssociatedWithImage", func(t *testing.T) {
+		err := RemoveLoopDevicesAssociatedWithImage(imagePath)
+		assert.NilError(t, err)
+
+		devices, err := FindAssociatedLoopDevices(imagePath)
+		assert.NilError(t, err)
+		assert.Assert(t, is.Len(devices, 0))
+	})
+
+	t.Run("RemoveLoopDevicesAssociatedWithInvalidImage", func(t *testing.T) {
+		err := RemoveLoopDevicesAssociatedWithImage("")
+		assert.NilError(t, err)
+	})
+}
+
+func createSparseImage(t *testing.T) string {
+	file, err := ioutil.TempFile("", "losetup-tests-")
+	assert.NilError(t, err)
+
+	size, err := units.RAMInBytes("16Mb")
+	assert.NilError(t, err)
+
+	err = file.Truncate(size)
+	assert.NilError(t, err)
+
+	err = file.Close()
+	assert.NilError(t, err)
+
+	return file.Name()
+}