Allow device drivers to show feedback to users if their open() methods fail

src/calibre/devices/errors.py

@@ -36,6 +36,11 @@ class UserFeedback(DeviceError):
        self.details = details
        self.msg = msg
 
+class OpenFeedback(DeviceError):
+    def __init__(self, msg):
+        self.feedback_msg = msg
+        DeviceError.__init__(self, msg)
+
 class DeviceBusy(ProtocolError):
     """ Raised when device is busy """
     def __init__(self, uerr=""):

src/calibre/devices/interface.py

@@ -216,6 +216,9 @@ class DevicePlugin(Plugin):
         an implementation of
         this function that should serve as a good example for USB Mass storage
         devices.
+
+        This method can raise an OpenFeedback exception to display a message to
+        the user.
         '''
         raise NotImplementedError()
 

src/calibre/gui2/device.py

@@ -12,7 +12,7 @@ from PyQt4.Qt import QMenu, QAction, QActionGroup, QIcon, SIGNAL, \
 from calibre.customize.ui import available_input_formats, available_output_formats, \
     device_plugins
 from calibre.devices.interface import DevicePlugin
-from calibre.devices.errors import UserFeedback
+from calibre.devices.errors import UserFeedback, OpenFeedback
 from calibre.gui2.dialogs.choose_format import ChooseFormatDialog
 from calibre.utils.ipc.job import BaseJob
 from calibre.devices.scanner import DeviceScanner
@@ -163,6 +163,9 @@ class DeviceManager(Thread): # {{{
                 dev.reset(detected_device=detected_device,
                     report_progress=self.report_progress)
                 dev.open()
+            except OpenFeedback, e:
+                self.open_feedback_slot(e.feedback_msg)
+                continue
             except:
                 tb = traceback.format_exc()
                 if DEBUG or tb not in self.reported_errors: