device: Add new FP_DEVICE_ERROR_UNTRUSTED error code

Throw a specific error when we are unable to verify the integrety of the
device.

libfprint/fp-device.h

@@ -118,6 +118,7 @@ typedef enum {
  * @FP_DEVICE_ERROR_DATA_FULL: No space on device available for operation
  * @FP_DEVICE_ERROR_DATA_DUPLICATE: Enrolling template duplicates storaged templates
  * @FP_DEVICE_ERROR_REMOVED: The device has been removed.
+ * @FP_DEVICE_ERROR_UNTRUSTED: Device cannot be trusted
  *
  * Error codes for device operations. More specific errors from other domains
  * such as #G_IO_ERROR or #G_USB_DEVICE_ERROR may also be reported.
@@ -135,6 +136,7 @@ typedef enum {
   FP_DEVICE_ERROR_DATA_DUPLICATE,
   /* Leave some room to add more DATA related errors */
   FP_DEVICE_ERROR_REMOVED = 0x100,
+  FP_DEVICE_ERROR_UNTRUSTED,
 } FpDeviceError;
 
 GQuark fp_device_retry_quark (void);

libfprint/fpi-device.c

@@ -177,6 +177,10 @@ fpi_device_error_new (FpDeviceError error)
       msg = "This device has been removed from the system.";
       break;
 
+    case FP_DEVICE_ERROR_UNTRUSTED:
+      msg = "Could not verify integrity of the device, it cannot be trusted!";
+      break;
+
     default:
       g_warning ("Unsupported error, returning general error instead!");
       error = FP_DEVICE_ERROR_GENERAL;