transport: inject info about udev rules into io/os exception

trezorlib/transport/hid.py

@@ -19,6 +19,7 @@
 import time
 import hid
 import os
+import sys
 
 from ..protocol_v1 import ProtocolV1
 from ..protocol_v2 import ProtocolV2
@@ -39,7 +40,12 @@ def __init__(self, path):
     def open(self):
         if self.count == 0:
             self.handle = hid.device()
-            self.handle.open_path(self.path)
+            try:
+                self.handle.open_path(self.path)
+            except (IOError, OSError) as e:
+                if sys.platform.startswith('linux'):
+                    e.args = e.args + ('Do you have udev rules installed? https://github.com/trezor/trezor-common/blob/master/udev/51-trezor.rules', )
+                raise e
             self.handle.set_nonblocking(True)
         self.count += 1
 

trezorlib/transport/webusb.py

@@ -20,6 +20,7 @@
 import os
 import atexit
 import usb1
+import sys
 
 from ..protocol_v1 import ProtocolV1
 from ..protocol_v2 import ProtocolV2
@@ -46,7 +47,11 @@ def open(self, interface):
         if self.count == 0:
             self.handle = self.device.open()
             if self.handle is None:
-                raise Exception('Cannot open device')
+                if sys.platform.startswith('linux'):
+                    args = ('Do you have udev rules installed? https://github.com/trezor/trezor-common/blob/master/udev/51-trezor.rules', )
+                else:
+                    args = ()
+                raise IOError('Cannot open device', *args)
             self.handle.claimInterface(interface)
             self.count += 1