devmapper: implement dmsetup status

Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>

snapshots/devmapper/dmsetup/dmsetup.go

@@ -263,6 +263,53 @@ func Version() (string, error) {
 	return dmsetup("version")
 }
 
+// DeviceStatus represents devmapper device status information
+type DeviceStatus struct {
+	Offset int64
+	Length int64
+	Target string
+	Params []string
+}
+
+// Status provides status information for devmapper device
+func Status(deviceName string) (*DeviceStatus, error) {
+	var (
+		err    error
+		status DeviceStatus
+	)
+
+	output, err := dmsetup("status", deviceName)
+	if err != nil {
+		return nil, err
+	}
+
+	// Status output format:
+	//  Offset (int64)
+	//  Length (int64)
+	//  Target type (string)
+	//  Params (Array of strings)
+	const MinParseCount = 4
+	parts := strings.Split(output, " ")
+	if len(parts) < MinParseCount {
+		return nil, errors.Errorf("failed to parse output: %q", output)
+	}
+
+	status.Offset, err = strconv.ParseInt(parts[0], 10, 64)
+	if err != nil {
+		return nil, errors.Wrapf(err, "failed to parse offset: %q", parts[0])
+	}
+
+	status.Length, err = strconv.ParseInt(parts[1], 10, 64)
+	if err != nil {
+		return nil, errors.Wrapf(err, "failed to parse length: %q", parts[1])
+	}
+
+	status.Target = parts[2]
+	status.Params = parts[3:]
+
+	return &status, nil
+}
+
 // GetFullDevicePath returns full path for the given device name (like "/dev/mapper/name")
 func GetFullDevicePath(deviceName string) string {
 	if strings.HasPrefix(deviceName, DevMapperDir) {

snapshots/devmapper/dmsetup/dmsetup_test.go

@@ -24,12 +24,13 @@ import (
 	"strings"
 	"testing"
 
-	"github.com/containerd/containerd/pkg/testutil"
-	"github.com/containerd/containerd/snapshots/devmapper/losetup"
 	"github.com/docker/go-units"
 	"golang.org/x/sys/unix"
 	"gotest.tools/assert"
 	is "gotest.tools/assert/cmp"
+
+	"github.com/containerd/containerd/pkg/testutil"
+	"github.com/containerd/containerd/snapshots/devmapper/losetup"
 )
 
 const (
@@ -83,6 +84,7 @@ func TestDMSetup(t *testing.T) {
 	t.Run("DeleteSnapshot", testDeleteSnapshot)
 
 	t.Run("ActivateDevice", testActivateDevice)
+	t.Run("DeviceStatus", testDeviceStatus)
 	t.Run("SuspendResumeDevice", testSuspendResumeDevice)
 	t.Run("RemoveDevice", testRemoveDevice)
 
@@ -139,6 +141,16 @@ func testActivateDevice(t *testing.T) {
 	assert.Assert(t, info.TableLive)
 }
 
+func testDeviceStatus(t *testing.T) {
+	status, err := Status(testDeviceName)
+	assert.NilError(t, err)
+
+	assert.Equal(t, int64(0), status.Offset)
+	assert.Equal(t, int64(2), status.Length)
+	assert.Equal(t, "thin", status.Target)
+	assert.DeepEqual(t, status.Params, []string{"0", "-"})
+}
+
 func testSuspendResumeDevice(t *testing.T) {
 	err := SuspendDevice(testDeviceName)
 	assert.NilError(t, err)