Description of problem:

When adding a disk to the system or creating a logical volume, an exception is dropped as shown below:

-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
2019-01-29 17:18:33,003 INFO     tuned.plugins.hotplug: device 'dm-2' added
2019-01-29 17:18:33,004 INFO     tuned.plugins.hotplug: instance disk: adding new device dm-2
2019-01-29 17:18:33,004 ERROR    tuned.hardware.inventory: Exception occured in event handler of '<tuned.plugins.plugin_disk.DiskPlugin object at 0x7ff560840c50>'.
2019-01-29 17:18:33,004 ERROR    tuned.hardware.inventory: 
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/tuned/hardware/inventory.py", line 58, in _handle_udev_event
    callback(event, device)
  File "/usr/lib/python2.7/site-packages/tuned/plugins/plugin_disk.py", line 54, in _hardware_events_callback
    super(DiskPlugin, self)._hardware_events_callback(event, device)
  File "/usr/lib/python2.7/site-packages/tuned/plugins/hotplug.py", line 29, in _hardware_events_callback
    self._add_device(device)
  File "/usr/lib/python2.7/site-packages/tuned/plugins/hotplug.py", line 46, in _add_device
    self._added_device_apply_tuning(instance, device_name)
  File "/usr/lib/python2.7/site-packages/tuned/plugins/plugin_disk.py", line 58, in _added_device_apply_tuning
    instance._load_monitor.add_device(device_name)
  File "/usr/lib/python2.7/site-packages/tuned/monitors/base.py", line 102, in add_device
    assert isinstance(device, str)
AssertionError
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------


Version-Release number of selected component (if applicable):

tuned-2.10.0-6.el7.noarch


How reproducible:

Always


Steps to Reproduce:
1. Add a disk to a VM through hotplugging it or create a logical volume

  # vgcreate vg1 /dev/sdb
  # lvcreate -n vol1 -L 1G vg1


Actual results:

Exception above


Expected results:

No exception and device properly configured by tuned


Additional info:

Instrumenting the code, it appears that the device coming from udev is seen as "unicode" string, which can be seen by adding the log.info() line below:

/usr/lib/python2.7/site-packages/tuned/plugins/hotplug.py:
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
        def _add_device(self, device):
                device_name = device.sys_name
                log.info("DEVICE TYPE: %s" % type(device_name))
...
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

We then get the following log when creating a logical volume:

-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
2019-01-29 17:27:37,269 INFO     tuned.plugins.hotplug: device 'dm-3' added
2019-01-29 17:27:37,269 INFO     tuned.plugins.hotplug: DEVICE TYPE: <type 'unicode'>
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

Later, because of the following line, the assertion fails:

/usr/lib/python2.7/site-packages/tuned/monitors/base.py:
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
        def add_device(self, device):
                assert isinstance(device, str)
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

device.sys_name can probably be converted into a "str", but I'm not completely sure about that:

-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
        def _add_device(self, device):
                device_name = str(device.sys_name)
...
        def _remove_device(self, device):
                device_name = str(device.sys_name)
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------