Add function to retrieve real device path of mapped device

Signed-off-by: Daniel Weiße <dw@edgeless.systems>

go.mod

@@ -221,4 +221,4 @@ require (
 	sigs.k8s.io/structured-merge-diff/v4 v4.2.1 // indirect
 )
 
-replace github.com/martinjungblut/go-cryptsetup => github.com/daniel-weisse/go-cryptsetup v0.0.0-20220510090142-d35a60c619db
+replace github.com/martinjungblut/go-cryptsetup => github.com/daniel-weisse/go-cryptsetup v0.0.0-20220511084044-b537356aa24b

go.sum

@@ -512,8 +512,8 @@ github.com/d2g/dhcp4 v0.0.0-20170904100407-a1d1b6c41b1c/go.mod h1:Ct2BUK8SB0YC1S
 github.com/d2g/dhcp4client v1.0.0/go.mod h1:j0hNfjhrt2SxUOw55nL0ATM/z4Yt3t2Kd1mW34z5W5s=
 github.com/d2g/dhcp4server v0.0.0-20181031114812-7d4a0a7f59a5/go.mod h1:Eo87+Kg/IX2hfWJfwxMzLyuSZyxSoAug2nGa1G2QAi8=
 github.com/d2g/hardwareaddr v0.0.0-20190221164911-e7d9fbe030e4/go.mod h1:bMl4RjIciD2oAxI7DmWRx6gbeqrkoLqv3MV0vzNad+I=
-github.com/daniel-weisse/go-cryptsetup v0.0.0-20220510090142-d35a60c619db h1:MgKZLtrp/goZpLnshCnx7j5YwjfibjCt60Sl/pPJHtg=
+github.com/daniel-weisse/go-cryptsetup v0.0.0-20220511084044-b537356aa24b h1:YGmoG92uSwGnXqoYYIAAXZSJ33Ogc13GXgnBbDr8p5o=
-github.com/daniel-weisse/go-cryptsetup v0.0.0-20220510090142-d35a60c619db/go.mod h1:gZoZ0+POlM1ge/VUxWpMmZVNPzzMJ7l436CgkQ5+qzU=
+github.com/daniel-weisse/go-cryptsetup v0.0.0-20220511084044-b537356aa24b/go.mod h1:gZoZ0+POlM1ge/VUxWpMmZVNPzzMJ7l436CgkQ5+qzU=
 github.com/davecgh/go-spew v0.0.0-20161028175848-04cdfd42973b/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=

mount/cryptmapper/cryptmapper.go

@@ -63,6 +63,8 @@ type DeviceMapper interface {
 	Format(deviceType cryptsetup.DeviceType, genericParams cryptsetup.GenericParams) error
 	// Free releases crypt device context and used memory.
 	Free() bool
+	// GetDeviceName gets the path to the underlying device.
+	GetDeviceName() string
 	// Load loads crypt device parameters from the on-disk header.
 	// Returns nil on success, or an error otherwise.
 	Load(cryptsetup.DeviceType) error
@@ -195,6 +197,11 @@ func (c *CryptMapper) ResizeCryptDevice(ctx context.Context, volumeID string) (s
 	return cryptPrefix + volumeID, nil
 }
 
+// GetDeviceName returns the real device name of a mapped crypt device.
+func (c *CryptMapper) GetDevicePath(volumeID string) (string, error) {
+	return getDevicePath(c.mapper, strings.TrimPrefix(volumeID, cryptPrefix))
+}
+
 // closeCryptDevice closes the crypt device mapped for volumeID.
 func closeCryptDevice(device DeviceMapper, source, volumeID, deviceType string) error {
 	packageLock.Lock()
@@ -389,6 +396,22 @@ func resizeCryptDevice(device DeviceMapper, name, passphrase string) error {
 	return nil
 }
 
+func getDevicePath(device DeviceMapper, name string) (string, error) {
+	packageLock.Lock()
+	defer packageLock.Unlock()
+
+	if err := device.InitByName(name); err != nil {
+		return "", fmt.Errorf("initializing device: %w", err)
+	}
+	defer device.Free()
+
+	deviceName := device.GetDeviceName()
+	if deviceName == "" {
+		return "", errors.New("unable to determine device name")
+	}
+	return deviceName, nil
+}
+
 // IsIntegrityFS checks if the fstype string contains an integrity suffix.
 // If yes, returns the trimmed fstype and true, fstype and false otherwise.
 func IsIntegrityFS(fstype string) (string, bool) {

mount/cryptmapper/cryptmapper_test.go

@@ -64,6 +64,10 @@ func (c *stubCryptDevice) Free() bool {
 	return true
 }
 
+func (c *stubCryptDevice) GetDeviceName() string {
+	return c.deviceName
+}
+
 func (c *stubCryptDevice) Load(cryptsetup.DeviceType) error {
 	return c.loadErr
 }
@@ -314,6 +318,49 @@ func TestResizeCryptDevice(t *testing.T) {
 	}
 }
 
+func TestGetDevicePath(t *testing.T) {
+	volumeID := "pvc-123"
+	someErr := errors.New("error")
+	testCases := map[string]struct {
+		volumeID string
+		device   *stubCryptDevice
+		wantErr  bool
+	}{
+		"success": {
+			volumeID: volumeID,
+			device:   &stubCryptDevice{deviceName: volumeID},
+		},
+		"InitByName fails": {
+			volumeID: volumeID,
+			device:   &stubCryptDevice{initByNameErr: someErr},
+			wantErr:  true,
+		},
+		"GetDeviceName returns nothing": {
+			volumeID: volumeID,
+			device:   &stubCryptDevice{},
+			wantErr:  true,
+		},
+	}
+
+	for name, tc := range testCases {
+		t.Run(name, func(t *testing.T) {
+			assert := assert.New(t)
+
+			mapper := &CryptMapper{
+				mapper: tc.device,
+			}
+
+			res, err := mapper.GetDevicePath(tc.volumeID)
+			if tc.wantErr {
+				assert.Error(err)
+			} else {
+				assert.NoError(err)
+				assert.Equal(tc.device.deviceName, res)
+			}
+		})
+	}
+}
+
 func TestIsIntegrityFS(t *testing.T) {
 	testCases := map[string]struct {
 		wantIntegrity bool