diff --git a/qubes/core2migration.py b/qubes/core2migration.py
index fc2d669e..2286ad1b 100644
--- a/qubes/core2migration.py
+++ b/qubes/core2migration.py
@@ -24,6 +24,7 @@ import xml.parsers.expat
 import lxml.etree
 
 import qubes
+import qubes.devices
 import qubes.vm.appvm
 import qubes.vm.standalonevm
 import qubes.vm.templatevm
@@ -219,8 +220,10 @@ class Core2Qubes(qubes.Qubes):
                 pcidevs = ast.literal_eval(pcidevs)
             for pcidev in pcidevs:
                 try:
-                    vm.devices["pci"].attach(
-                        self.domains[0].devices['pci'][pcidev])
+                    dev = self.domains[0].devices['pci'][pcidev]
+                    assignment = qubes.devices.DeviceAssignment(
+                        backend_domain=dev.backend_domain, ident=dev.ident)
+                    vm.devices["pci"].attach(assignment)
                 except qubes.exc.QubesException as e:
                     self.log.error("VM {}: {}".format(vm.name, str(e)))
         except (ValueError, LookupError) as err:
diff --git a/qubes/devices.py b/qubes/devices.py
index 4fc24ebd..bd5f885d 100644
--- a/qubes/devices.py
+++ b/qubes/devices.py
@@ -47,7 +47,6 @@ Such extension should provide:
 
 import qubes.utils
 
-
 class DeviceNotAttached(qubes.exc.QubesException, KeyError):
     '''Trying to detach not attached device'''
     pass
@@ -57,6 +56,30 @@ class DeviceAlreadyAttached(qubes.exc.QubesException, KeyError):
     pass
 
 
+class DeviceAssignment(object): # pylint: disable=too-few-public-methods
+    ''' Maps a device to a frontend_domain. '''
+
+    def __init__(self, backend_domain, ident, options=None, persistent=False,
+                 frontend_domain=None):
+        self.backend_domain = backend_domain
+        self.ident = ident
+        self.options = options or {}
+        self.persistent = persistent
+        self.frontend_domain = frontend_domain
+
+    def __repr__(self):
+        return "[%s]:%s" % (self.backend_domain, self.ident)
+
+    def __hash__(self):
+        return hash((self.backend_domain, self.ident))
+
+    def __eq__(self, other):
+        if not isinstance(self, other.__class__):
+            raise NotImplementedError
+
+        return self.backend_domain == other.backend_domain \
+           and self.ident == other.ident
+
 class DeviceCollection(object):
     '''Bag for devices.
 
@@ -115,87 +138,117 @@ class DeviceCollection(object):
     def __init__(self, vm, class_):
         self._vm = vm
         self._class = class_
-        self._set = set()
+        self._set = PersistentCollection()
 
         self.devclass = qubes.utils.get_entry_point_one(
             'qubes.devices', self._class)
 
-    def attach(self, device, persistent=True):
+    def attach(self, device_assignment: DeviceAssignment):
         '''Attach (add) device to domain.
 
         :param DeviceInfo device: device object
         '''
 
-        if device in self.attached():
+        if not device_assignment.frontend_domain:
+            device_assignment.frontend_domain = self._vm
+        else:
+            assert device_assignment.frontend_domain == self._vm, \
+                "Trying to attach DeviceAssignment belonging to other domain"
+
+        if not device_assignment.persistent and self._vm.is_halted():
+            raise qubes.exc.QubesVMNotRunningError(self._vm,
+                "Devices can only be attached  non-persistent to a running vm")
+        device = self._device(device_assignment)
+        if device in self.assignments():
             raise DeviceAlreadyAttached(
-                'device {!r} of class {} already attached to {!r}'.format(
+                'device {!s} of class {} already attached to {!s}'.format(
                     device, self._class, self._vm))
         self._vm.fire_event_pre('device-pre-attach:'+self._class, device=device)
-        if persistent:
-            self._set.add(device)
+        if device_assignment.persistent:
+            self._set.add(device_assignment)
         self._vm.fire_event('device-attach:' + self._class, device=device)
 
-
-    def detach(self, device, persistent=True):
+    def detach(self, device_assignment: DeviceAssignment):
         '''Detach (remove) device from domain.
 
         :param DeviceInfo device: device object
         '''
 
-        if device not in self.attached():
+        if not device_assignment.frontend_domain:
+            device_assignment.frontend_domain = self._vm
+
+        if device_assignment in self._set and not self._vm.is_halted():
+            raise qubes.exc.QubesVMNotHaltedError(self._vm,
+                "Can not remove a persistent attachment from a non halted vm")
+        if device_assignment not in self.assignments():
             raise DeviceNotAttached(
                 'device {!s} of class {} not attached to {!s}'.format(
-                    device, self._class, self._vm))
+                    device_assignment.ident, self._class, self._vm))
+
+        device = self._device(device_assignment)
         self._vm.fire_event_pre('device-pre-detach:'+self._class, device=device)
-        if persistent:
-            self._set.remove(device)
+        if device in self._set:
+            device_assignment.persistent = True
+            self._set.discard(device_assignment)
+
         self._vm.fire_event('device-detach:' + self._class, device=device)
 
-    def attached(self, persistent=None):
-        '''List devices which are (or may be) attached to this vm
+    def attached(self):
+        '''List devices which are (or may be) attached to this vm '''
+        attached = self._vm.fire_event('device-list-attached:' + self._class)
+        if attached:
+            return [dev for dev, _ in attached]
+
+        return []
+
+    def persistent(self):
+        ''' Devices persistently attached and safe to access before libvirt
+            bootstrap.
+        '''
+        return [self._device(a) for a in self._set]
+
+    def assignments(self, persistent=None):
+        '''List assignments for devices which are (or may be) attached to the
+           vm.
 
         Devices may be attached persistently (so they are included in
         :file:`qubes.xml`) or not. Device can also be in :file:`qubes.xml`,
         but be temporarily detached.
 
-        :param bool persistent: only include devices which are (or are not) \
-        attached persistently - None means both
+        :param bool persistent: only include devices which are or are not
+        attached persistently.
         '''
-        seen = self._set.copy()
 
-        # ask for really attached devices only when requested not only
-        # persistent ones
-        if persistent is not True:
-            attached = self._vm.fire_event(
-                'device-list-attached:' + self._class,
-                persistent=persistent)
-            for device in attached:
-                device_persistent = device in self._set
-                if persistent is not None and device_persistent != persistent:
-                    continue
-                assert device.frontend_domain == self._vm, \
-                    '{!r} != {!r}'.format(device.frontend_domain, self._vm)
-
-                yield device
-
-                try:
-                    seen.remove(device)
-                except KeyError:
-                    pass
-
-        if persistent is False:
-            return
-
-        for device in seen:
-            # get fresh object - may contain updated information
-            device = device.backend_domain.devices[self._class][device.ident]
-            yield device
+        devices = self._vm.fire_event('device-list-attached:' + self._class,
+            persistent=persistent)
+        result = []
+        for dev, options in devices:
+            if dev in self._set and persistent is False:
+                continue
+            elif dev in self._set:
+                result.append(self._set.get(dev))
+            elif dev not in self._set and persistent is True:
+                continue
+            else:
+                result.append(
+                    DeviceAssignment(backend_domain=dev.backend_domain,
+                                     ident=dev.ident, options=options,
+                                     frontend_domain=self._vm))
+        if persistent is not False and not result:
+            result.extend(self._set)
+        return result
 
     def available(self):
         '''List devices exposed by this vm'''
         devices = self._vm.fire_event('device-list:' + self._class)
         return devices
 
+    def _device(self, assignment: DeviceAssignment):
+        ''' Helper method for geting a `qubes.devices.DeviceInfo` object from
+            `qubes.devices.DeviceAssignment`. '''
+
+        return assignment.backend_domain.devices[self._class][assignment.ident]
+
     def __iter__(self):
         return iter(self.available())
 
@@ -216,6 +269,7 @@ class DeviceCollection(object):
         if dev:
             assert len(dev) == 1
             return dev[0]
+
         return UnknownDevice(self._vm, ident)
 
 
@@ -235,9 +289,10 @@ class DeviceManager(dict):
 
 
 class DeviceInfo(object):
+    ''' Holds all information about a device '''
     # pylint: disable=too-few-public-methods
     def __init__(self, backend_domain, ident, description=None,
-            frontend_domain=None, **kwargs):
+                 frontend_domain=None, options=None, **kwargs):
         #: domain providing this device
         self.backend_domain = backend_domain
         #: device identifier (unique for given domain and device type)
@@ -253,6 +308,7 @@ class DeviceInfo(object):
             self.frontend_domain = frontend_domain
         except AttributeError:
             pass
+        self.options = options or dict()
         self.data = kwargs
 
         if hasattr(self, 'regex'):
@@ -289,15 +345,52 @@ class UnknownDevice(DeviceInfo):
             frontend_domain, **kwargs)
 
 
-class BlockDevice(object):
-    # pylint: disable=too-few-public-methods
-    def __init__(self, path, name, script=None, rw=True, domain=None,
-                 devtype='disk'):
-        assert name, 'Missing device name'
-        assert path, 'Missing device path'
-        self.path = path
-        self.name = name
-        self.rw = rw
-        self.script = script
-        self.domain = domain
-        self.devtype = devtype
+class PersistentCollection(object):
+
+    ''' Helper object managing persistent `DeviceAssignment`s.
+    '''
+
+    def __init__(self):
+        self._dict = {}
+
+    def add(self, assignment: DeviceAssignment):
+        ''' Add assignment to collection '''
+        assert assignment.persistent and assignment.frontend_domain
+        vm = assignment.backend_domain
+        ident = assignment.ident
+        key = (vm, ident)
+        assert key not in self._dict
+
+        self._dict[key] = assignment
+
+    def discard(self, assignment):
+        ''' Discard assignment from collection '''
+        assert assignment.persistent and assignment.frontend_domain
+        vm = assignment.backend_domain
+        ident = assignment.ident
+        key = (vm, ident)
+        if key not in self._dict:
+            raise KeyError
+        del self._dict[key]
+
+    def __contains__(self, device) -> bool:
+        vm = device.backend_domain
+        ident = device.ident
+        key = (vm, ident)
+        return key in self._dict
+
+    def get(self, device: DeviceInfo) -> DeviceAssignment:
+        ''' Returns the corresponding `qubes.devices.DeviceAssignment` for the
+            device. '''
+        vm = device.backend_domain
+        ident = device.ident
+        key = (vm, ident)
+        if key not in self._dict:
+            raise KeyError
+        return self._dict[key]
+
+    def __iter__(self):
+        return self._dict.values().__iter__()
+
+    def __len__(self) -> int:
+        return len(self._dict.keys())
diff --git a/qubes/ext/pci.py b/qubes/ext/pci.py
index 5aaa60ab..3fa77f37 100644
--- a/qubes/ext/pci.py
+++ b/qubes/ext/pci.py
@@ -19,6 +19,9 @@
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 #
 
+''' Qubes PCI Extensions '''
+
+import functools
 import os
 import re
 import subprocess
@@ -34,7 +37,7 @@ pci_classes = None
 
 
 def load_pci_classes():
-    # List of known device classes, subclasses and programming interfaces
+    ''' List of known device classes, subclasses and programming interfaces. '''
     # Syntax:
     # C class       class_name
     #       subclass        subclass_name           <-- single tab
@@ -122,7 +125,6 @@ def _device_desc(hostdev_xml):
     )
 
 
-
 class PCIDevice(qubes.devices.DeviceInfo):
     # pylint: disable=too-few-public-methods
     regex = re.compile(
@@ -191,7 +193,7 @@ class PCIDeviceExtension(qubes.ext.Extension):
     def on_device_get_pci(self, vm, event, ident):
         # pylint: disable=unused-argument,no-self-use
         if not vm.app.vmm.offline_mode:
-            yield PCIDevice(vm, ident)
+            yield _cache_get(vm, ident)
 
     @qubes.ext.handler('device-list-attached:pci')
     def on_device_list_attached(self, vm, event, **kwargs):
@@ -213,7 +215,7 @@ class PCIDeviceExtension(qubes.ext.Extension):
                 device=device,
                 function=function,
             )
-            yield PCIDevice(vm.app.domains[0], ident)
+            yield (PCIDevice(vm.app.domains[0], ident), {})
 
     @qubes.ext.handler('device-pre-attach:pci')
     def on_device_pre_attached_pci(self, vm, event, device):
@@ -227,6 +229,7 @@ class PCIDeviceExtension(qubes.ext.Extension):
             return
 
         try:
+            device = _cache_get(vm, device.ident)
             self.bind_pci_to_pciback(vm.app, device)
             vm.libvirt_domain.attachDevice(
                 vm.app.env.get_template('libvirt/devices/pci.xml').render(
@@ -246,9 +249,10 @@ class PCIDeviceExtension(qubes.ext.Extension):
         # provision in libvirt for extracting device-side BDF; we need it for
         # qubes.DetachPciDevice, which unbinds driver, not to oops the kernel
 
+        device = _cache_get(vm, device.ident)
         p = subprocess.Popen(['xl', 'pci-list', str(vm.xid)],
                 stdout=subprocess.PIPE)
-        result = p.communicate()[0]
+        result = p.communicate()[0].decode()
         m = re.search(r'^(\d+.\d+)\s+0000:{}$'.format(device.ident), result,
             flags=re.MULTILINE)
         if not m:
@@ -270,8 +274,9 @@ class PCIDeviceExtension(qubes.ext.Extension):
     @qubes.ext.handler('domain-pre-start')
     def on_domain_pre_start(self, vm, _event, **_kwargs):
         # Bind pci devices to pciback driver
-        for pci in vm.devices['pci'].attached():
-            self.bind_pci_to_pciback(vm.app, pci)
+        for assignment in vm.devices['pci'].persistent():
+            device = _cache_get(vm, assignment.ident)
+            self.bind_pci_to_pciback(vm.app, device)
 
     @staticmethod
     def bind_pci_to_pciback(app, device):
@@ -300,3 +305,8 @@ class PCIDeviceExtension(qubes.ext.Extension):
                 pass
             else:
                 raise
+
+@functools.lru_cache(maxsize=None)
+def _cache_get(vm, ident):
+    ''' Caching wrapper around `PCIDevice(vm, ident)`. '''
+    return PCIDevice(vm, ident)
diff --git a/qubes/rngdoc.py b/qubes/rngdoc.py
index 5730f8b3..f35624d4 100755
--- a/qubes/rngdoc.py
+++ b/qubes/rngdoc.py
@@ -55,6 +55,7 @@ class Element(object):
         if wrap:
             return ''.join(self.schema.wrapper.fill(p) + '\n\n'
                 for p in textwrap.dedent(xml.text.strip('\n')).split('\n\n'))
+
         return ' '.join(xml.text.strip().split())
 
 
@@ -211,6 +212,7 @@ Quick example, worth thousands lines of specification:
 
 
 if __name__ == '__main__':
-    main(*sys.argv[1:])  # pylint: disable=no-value-for-parameter
+    # pylint: disable=no-value-for-parameter
+    main(*sys.argv[1:])
 
 # vim: ts=4 sw=4 et
diff --git a/qubes/storage/__init__.py b/qubes/storage/__init__.py
index fa8bc80d..5b29b5f0 100644
--- a/qubes/storage/__init__.py
+++ b/qubes/storage/__init__.py
@@ -34,7 +34,6 @@ from datetime import datetime
 import lxml.etree
 import pkg_resources
 import qubes
-import qubes.devices
 import qubes.exc
 import qubes.utils
 
@@ -46,6 +45,21 @@ class StoragePoolException(qubes.exc.QubesException):
     pass
 
 
+class BlockDevice(object):
+    ''' Represents a storage block device. '''
+    # pylint: disable=too-few-public-methods
+    def __init__(self, path, name, script=None, rw=True, domain=None,
+                 devtype='disk'):
+        assert name, 'Missing device name'
+        assert path, 'Missing device path'
+        self.path = path
+        self.name = name
+        self.rw = rw
+        self.script = script
+        self.domain = domain
+        self.devtype = devtype
+
+
 class Volume(object):
     ''' Encapsulates all data about a volume for serialization to qubes.xml and
         libvirt config.
@@ -119,10 +133,10 @@ class Volume(object):
         return lxml.etree.Element('volume', **config)
 
     def block_device(self):
-        ''' Return :py:class:`qubes.devices.BlockDevice` for serialization in
+        ''' Return :py:class:`BlockDevice` for serialization in
             the libvirt XML template as <disk>.
         '''
-        return qubes.devices.BlockDevice(self.path, self.name, self.script,
+        return BlockDevice(self.path, self.name, self.script,
                                          self.rw, self.domain, self.devtype)
 
     @property
@@ -446,6 +460,7 @@ class Storage(object):
             "You need to pass a Volume or pool name as str"
         if isinstance(volume, Volume):
             return self.pools[volume.name]
+
         return self.vm.app.pools[volume]
 
     def commit(self):
@@ -475,6 +490,7 @@ class Storage(object):
             "You need to pass a Volume or pool name as str"
         if isinstance(volume, Volume):
             return self.pools[volume.name].export(volume)
+
         return self.pools[volume].export(self.vm.volumes[volume])
 
 
diff --git a/qubes/storage/file.py b/qubes/storage/file.py
index 1a07224c..6ab47283 100644
--- a/qubes/storage/file.py
+++ b/qubes/storage/file.py
@@ -30,7 +30,6 @@ import os.path
 import re
 import subprocess
 
-import qubes.devices
 import qubes.storage
 
 BLKSIZE = 512
@@ -358,7 +357,7 @@ class FileVolume(qubes.storage.Volume):
             return 'block-snapshot'
 
     def block_device(self):
-        ''' Return :py:class:`qubes.devices.BlockDevice` for serialization in
+        ''' Return :py:class:`qubes.storage.BlockDevice` for serialization in
             the libvirt XML template as <disk>.
         '''
         path = self.path
@@ -366,7 +365,7 @@ class FileVolume(qubes.storage.Volume):
             path += ":" + self.path_source_cow
         if self._is_origin or self._is_snapshot:
             path += ":" + self.path_cow
-        return qubes.devices.BlockDevice(path, self.name, self.script, self.rw,
+        return qubes.storage.BlockDevice(path, self.name, self.script, self.rw,
                                          self.domain, self.devtype)
 
     @property
@@ -378,6 +377,7 @@ class FileVolume(qubes.storage.Volume):
 
         if not os.path.exists(old_revision):
             return {}
+
         seconds = os.path.getctime(old_revision)
         iso_date = qubes.storage.isodate(seconds).split('.', 1)[0]
         return {iso_date: old_revision}
diff --git a/qubes/storage/lvm.py b/qubes/storage/lvm.py
index 051d75dc..4f3a4b56 100644
--- a/qubes/storage/lvm.py
+++ b/qubes/storage/lvm.py
@@ -394,13 +394,14 @@ class ThinVolume(qubes.storage.Volume):
             "You shouldn't use lvm size setter")
 
     def block_device(self):
-        ''' Return :py:class:`qubes.devices.BlockDevice` for serialization in
+        ''' Return :py:class:`qubes.storage.BlockDevice` for serialization in
             the libvirt XML template as <disk>.
         '''
         if self.snap_on_start:
-            return qubes.devices.BlockDevice(
+            return qubes.storage.BlockDevice(
                 '/dev/' + self._vid_snap, self.name, self.script,
                 self.rw, self.domain, self.devtype)
+
         return super(ThinVolume, self).block_device()
 
     @property
diff --git a/qubes/tests/devices.py b/qubes/tests/devices.py
index 1136199b..86a3926a 100644
--- a/qubes/tests/devices.py
+++ b/qubes/tests/devices.py
@@ -26,6 +26,7 @@ import qubes.devices
 import qubes.tests
 
 class TestDevice(qubes.devices.DeviceInfo):
+    # pylint: disable=too-few-public-methods
     pass
 
 
@@ -35,6 +36,7 @@ class TestVMCollection(dict):
 
 
 class TestApp(object):
+    # pylint: disable=too-few-public-methods
     def __init__(self):
         self.domains = TestVMCollection()
 
@@ -51,20 +53,25 @@ class TestVM(qubes.tests.TestEmitter):
         }
         self.app.domains[name] = self
         self.app.domains[self] = self
+        self.running = False
 
     def __str__(self):
         return self.name
 
     @qubes.events.handler('device-list-attached:testclass')
-    def dev_testclass_list_attached(self, event, persistent):
+    def dev_testclass_list_attached(self, event, persistent = False):
         for vm in self.app.domains:
             if vm.device.frontend_domain == self:
-                yield vm.device
+                yield (vm.device, {})
 
     @qubes.events.handler('device-list:testclass')
     def dev_testclass_list(self, event):
         yield self.device
 
+    def is_halted(self):
+        return not self.running
+
+
 
 class TC_00_DeviceCollection(qubes.tests.QubesTestCase):
     def setUp(self):
@@ -73,20 +80,25 @@ class TC_00_DeviceCollection(qubes.tests.QubesTestCase):
         self.app.domains['vm'] = self.emitter
         self.device = self.emitter.device
         self.collection = self.emitter.devices['testclass']
+        self.assignment = qubes.devices.DeviceAssignment(
+            backend_domain = self.device.backend_domain,
+            ident = self.device.ident,
+            persistent=True
+        )
 
     def test_000_init(self):
         self.assertFalse(self.collection._set)
 
     def test_001_attach(self):
-        self.collection.attach(self.device)
+        self.collection.attach(self.assignment)
         self.assertEventFired(self.emitter, 'device-pre-attach:testclass')
         self.assertEventFired(self.emitter, 'device-attach:testclass')
         self.assertEventNotFired(self.emitter, 'device-pre-detach:testclass')
         self.assertEventNotFired(self.emitter, 'device-detach:testclass')
 
     def test_002_detach(self):
-        self.collection.attach(self.device)
-        self.collection.detach(self.device)
+        self.collection.attach(self.assignment)
+        self.collection.detach(self.assignment)
         self.assertEventFired(self.emitter, 'device-pre-attach:testclass')
         self.assertEventFired(self.emitter, 'device-attach:testclass')
         self.assertEventFired(self.emitter, 'device-pre-detach:testclass')
@@ -94,41 +106,43 @@ class TC_00_DeviceCollection(qubes.tests.QubesTestCase):
 
     def test_010_empty_detach(self):
         with self.assertRaises(LookupError):
-            self.collection.detach(self.device)
+            self.collection.detach(self.assignment)
 
     def test_011_double_attach(self):
-        self.collection.attach(self.device)
+        self.collection.attach(self.assignment)
 
         with self.assertRaises(LookupError):
-            self.collection.attach(self.device)
+            self.collection.attach(self.assignment)
 
     def test_012_double_detach(self):
-        self.collection.attach(self.device)
-        self.collection.detach(self.device)
+        self.collection.attach(self.assignment)
+        self.collection.detach(self.assignment)
 
-        with self.assertRaises(LookupError):
-            self.collection.detach(self.device)
+        with self.assertRaises(qubes.devices.DeviceNotAttached):
+            self.collection.detach(self.assignment)
 
     def test_013_list_attached_persistent(self):
-        self.assertEqual(set([]), set(self.collection.attached()))
+        self.assertEqual(set([]), set(self.collection.persistent()))
+        self.collection.attach(self.assignment)
         self.assertEventFired(self.emitter, 'device-list-attached:testclass')
-        self.collection.attach(self.device)
-        self.assertEqual({self.device}, set(self.collection.attached()))
+        self.assertEqual({self.device}, set(self.collection.persistent()))
         self.assertEqual({self.device},
-            set(self.collection.attached(persistent=True)))
+            set(self.collection.persistent()))
         self.assertEqual(set([]),
-            set(self.collection.attached(persistent=False)))
+            set(self.collection.attached()))
 
     def test_014_list_attached_non_persistent(self):
-        self.collection.attach(self.device, persistent=False)
+        self.assignment.persistent = False
+        self.emitter.running = True
+        self.collection.attach(self.assignment)
         # device-attach event not implemented, so manipulate object manually
         self.device.frontend_domain = self.emitter
         self.assertEqual({self.device},
             set(self.collection.attached()))
         self.assertEqual(set([]),
-            set(self.collection.attached(persistent=True)))
+            set(self.collection.persistent()))
         self.assertEqual({self.device},
-            set(self.collection.attached(persistent=False)))
+            set(self.collection.attached()))
         self.assertEventFired(self.emitter, 'device-list-attached:testclass')
 
     def test_015_list_available(self):
@@ -147,6 +161,7 @@ class TC_01_DeviceManager(qubes.tests.QubesTestCase):
 
     def test_001_missing(self):
         device = TestDevice(self.emitter.app.domains['vm'], 'testdev')
-        self.manager['testclass'].attach(device)
+        assignment = qubes.devices.DeviceAssignment(backend_domain=device.backend_domain, ident=device.ident, persistent=True)
+        self.manager['testclass'].attach(assignment)
         self.assertEventFired(self.emitter, 'device-attach:testclass')
 
diff --git a/qubes/tests/integ/devices_pci.py b/qubes/tests/integ/devices_pci.py
index ac36c113..8fa9e489 100644
--- a/qubes/tests/integ/devices_pci.py
+++ b/qubes/tests/integ/devices_pci.py
@@ -41,6 +41,7 @@ class TC_00_Devices_PCI(qubes.tests.SystemTestsMixin,
                 self.skipTest('Specify PCI device with QUBES_TEST_PCIDEV '
                               'environment variable')
             self.dev = self.app.domains[0].devices['pci'][pcidev]
+            self.assignment = qubes.devices.DeviceAssignment(backend_domain=self.dev.backend_domain, ident=self.dev.ident, persistent=True)
             if isinstance(self.dev, qubes.devices.UnknownDevice):
                 self.skipTest('Specified device {} does not exists'.format(pcidev))
             self.init_default_template()
@@ -64,110 +65,111 @@ class TC_00_Devices_PCI(qubes.tests.SystemTestsMixin,
             self.assertEqual(dev.backend_domain, self.app.domains[0])
             self.assertIn(dev.ident, actual_devices)
             self.assertEqual(dev.description, actual_devices[dev.ident])
-            self.assertIsInstance(dev.frontend_domain,
-                (qubes.vm.BaseVM, None.__class__))
             actual_devices.pop(dev.ident)
 
         if actual_devices:
             self.fail('Not all devices listed, missing: {}'.format(
                 actual_devices))
 
-    def test_010_attach_offline(self):
-        self.assertIsNone(self.dev.frontend_domain)
-        self.assertNotIn(self.dev, self.vm.devices['pci'].attached())
-        self.assertNotIn(self.dev, self.vm.devices['pci'].attached(
-            persistent=True))
-        self.assertNotIn(self.dev, self.vm.devices['pci'].attached(
-            persistent=False))
+    def assertDeviceNotInCollection(self, dev, dev_col):
+        self.assertNotIn(dev, dev_col.attached())
+        self.assertNotIn(dev, dev_col.persistent())
+        self.assertNotIn(dev, dev_col.assignments())
+        self.assertNotIn(dev, dev_col.assignments(persistent=True))
 
-        self.vm.devices['pci'].attach(self.dev)
+    def test_010_attach_offline_persistent(self):
+        dev_col = self.vm.devices['pci']
+        self.assertDeviceNotInCollection(self.dev, dev_col)
+        dev_col.attach(self.assignment)
         self.app.save()
+        self.assertNotIn(self.dev, dev_col.attached())
+        self.assertIn(self.dev, dev_col.persistent())
+        self.assertIn(self.dev, dev_col.assignments())
+        self.assertIn(self.dev, dev_col.assignments(persistent=True))
+        self.assertNotIn(self.dev, dev_col.assignments(persistent=False))
+
 
-        # still should be None, as domain is not started yet
-        self.assertIsNone(self.dev.frontend_domain)
-        self.assertIn(self.dev, self.vm.devices['pci'].attached())
-        self.assertIn(self.dev, self.vm.devices['pci'].attached(
-            persistent=True))
-        self.assertNotIn(self.dev, self.vm.devices['pci'].attached(
-            persistent=False))
         self.vm.start()
 
-        self.assertEqual(self.dev.frontend_domain, self.vm)
-        self.assertIn(self.dev, self.vm.devices['pci'].attached())
-        self.assertIn(self.dev, self.vm.devices['pci'].attached(
-            persistent=True))
-        self.assertNotIn(self.dev, self.vm.devices['pci'].attached(
-            persistent=False))
-
+        self.assertIn(self.dev, dev_col.attached())
         p = self.vm.run('lspci', passio_popen=True)
         (stdout, _) = p.communicate()
-        self.assertIn(self.dev.description, stdout)
+        self.assertIn(self.dev.description, stdout.decode())
 
-    def test_011_attach_online(self):
+
+    def test_011_attach_offline_temp_fail(self):
+        dev_col = self.vm.devices['pci']
+        self.assertDeviceNotInCollection(self.dev, dev_col)
+        self.assignment.persistent = False
+        with self.assertRaises(qubes.exc.QubesVMNotRunningError):
+            dev_col.attach(self.assignment)
+
+
+    def test_020_attach_online_persistent(self):
         self.vm.start()
-        self.vm.devices['pci'].attach(self.dev)
+        dev_col = self.vm.devices['pci']
+        self.assertDeviceNotInCollection(self.dev, dev_col)
+        dev_col.attach(self.assignment)
 
-        self.assertEqual(self.dev.frontend_domain, self.vm)
-        self.assertIn(self.dev, self.vm.devices['pci'].attached())
-        self.assertIn(self.dev, self.vm.devices['pci'].attached(
-            persistent=True))
-        self.assertNotIn(self.dev, self.vm.devices['pci'].attached(
-            persistent=False))
+        self.assertIn(self.dev, dev_col.attached())
+        self.assertIn(self.dev, dev_col.persistent())
+        self.assertIn(self.dev, dev_col.assignments())
+        self.assertIn(self.dev, dev_col.assignments(persistent=True))
+        self.assertNotIn(self.dev, dev_col.assignments(persistent=False))
 
         # give VM kernel some time to discover new device
         time.sleep(1)
         p = self.vm.run('lspci', passio_popen=True)
         (stdout, _) = p.communicate()
-        self.assertIn(self.dev.description, stdout)
+        self.assertIn(self.dev.description, stdout.decode())
 
-    def test_012_attach_online_temp(self):
+
+    def test_021_persist_detach_online_fail(self):
+        dev_col = self.vm.devices['pci']
+        self.assertDeviceNotInCollection(self.dev, dev_col)
+        dev_col.attach(self.assignment)
+        self.app.save()
         self.vm.start()
-        self.vm.devices['pci'].attach(self.dev, persistent=False)
+        with self.assertRaises(qubes.exc.QubesVMNotHaltedError):
+            self.vm.devices['pci'].detach(self.assignment)
+
+    def test_030_persist_attach_detach_offline(self):
+        dev_col = self.vm.devices['pci']
+        self.assertDeviceNotInCollection(self.dev, dev_col)
+        dev_col.attach(self.assignment)
+        self.app.save()
+        self.assertNotIn(self.dev, dev_col.attached())
+        self.assertIn(self.dev, dev_col.persistent())
+        self.assertIn(self.dev, dev_col.assignments())
+        self.assertIn(self.dev, dev_col.assignments(persistent=True))
+        self.assertNotIn(self.dev, dev_col.assignments(persistent=False))
+        dev_col.detach(self.assignment)
+        self.assertDeviceNotInCollection(self.dev, dev_col)
+
+    def test_031_attach_detach_online_temp(self):
+        dev_col = self.vm.devices['pci']
+        self.vm.start()
+        self.assignment.persistent = False
+        self.assertDeviceNotInCollection(self.dev, dev_col)
+        dev_col.attach(self.assignment)
+
+        self.assertIn(self.dev, dev_col.attached())
+        self.assertNotIn(self.dev, dev_col.persistent())
+        self.assertIn(self.dev, dev_col.assignments())
+        self.assertIn(self.dev, dev_col.assignments(persistent=False))
+        self.assertNotIn(self.dev, dev_col.assignments(persistent=True))
+        self.assertIn(self.dev, dev_col.assignments(persistent=False))
 
-        self.assertEqual(self.dev.frontend_domain, self.vm)
-        self.assertIn(self.dev, self.vm.devices['pci'].attached())
-        self.assertNotIn(self.dev, self.vm.devices['pci'].attached(
-            persistent=True))
-        self.assertIn(self.dev, self.vm.devices['pci'].attached(
-            persistent=False))
 
         # give VM kernel some time to discover new device
         time.sleep(1)
         p = self.vm.run('lspci', passio_popen=True)
         (stdout, _) = p.communicate()
-        self.assertIn(self.dev.description, stdout)
 
-    def test_020_detach_online(self):
-        self.vm.devices['pci'].attach(self.dev)
-        self.app.save()
-        self.vm.start()
-
-        self.assertIn(self.dev, self.vm.devices['pci'].attached())
-        self.assertIn(self.dev, self.vm.devices['pci'].attached(
-            persistent=True))
-        self.assertNotIn(self.dev, self.vm.devices['pci'].attached(
-            persistent=False))
-        self.assertEqual(self.dev.frontend_domain, self.vm)
-
-        self.vm.devices['pci'].detach(self.dev)
-
-        self.assertIsNone(self.dev.frontend_domain)
-        self.assertNotIn(self.dev, self.vm.devices['pci'].attached())
-        self.assertNotIn(self.dev, self.vm.devices['pci'].attached(
-            persistent=True))
-        self.assertNotIn(self.dev, self.vm.devices['pci'].attached(
-            persistent=False))
+        self.assertIn(self.dev.description, stdout.decode())
+        dev_col.detach(self.assignment)
+        self.assertDeviceNotInCollection(self.dev, dev_col)
 
         p = self.vm.run('lspci', passio_popen=True)
         (stdout, _) = p.communicate()
-        self.assertNotIn(self.dev.description, stdout)
-
-        # can't do this right now because of kernel bug - it cause the whole
-        # PCI bus being deregistered, which emit some warning in sysfs
-        # handling code (removing non-existing "0000:00" group)
-        #
-        # p = self.vm.run('dmesg', passio_popen=True)
-        # (stdout, _) = p.communicate()
-        # # check for potential oops
-        # self.assertNotIn('end trace', stdout)
-
+        self.assertNotIn(self.dev.description, stdout.decode())
diff --git a/qubes/tests/tools/qvm_device.py b/qubes/tests/tools/qvm_device.py
index e6611b96..2d7d88a5 100644
--- a/qubes/tests/tools/qvm_device.py
+++ b/qubes/tests/tools/qvm_device.py
@@ -1,4 +1,4 @@
-# pylint: disable=protected-access,pointless-statement
+# pylint: disable=protected-access
 
 #
 # The Qubes OS Project, https://www.qubes-os.org/
@@ -21,6 +21,8 @@
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 #
 
+''' Tests for the `qvm-device` tool. '''
+
 import qubes
 import qubes.devices
 import qubes.tools.qvm_device
@@ -30,82 +32,86 @@ import qubes.tests.devices
 import qubes.tests.tools
 
 class TestNamespace(object):
+    ''' A mock object for `argparse.Namespace`.
+    '''  # pylint: disable=too-few-public-methods
+
     def __init__(self, app, domains=None, device=None):
         super(TestNamespace, self).__init__()
         self.app = app
         self.devclass = 'testclass'
+        self.persistent = True
         if domains:
             self.domains = domains
         if device:
             self.device = device
+            self.device_assignment = qubes.devices.DeviceAssignment(
+                backend_domain=self.device.backend_domain,
+                ident=self.device.ident, persistent=self.persistent)
 
 
 class TC_00_Actions(qubes.tests.QubesTestCase):
+    ''' Tests the output logic of the qvm-device tool '''
     def setUp(self):
         super(TC_00_Actions, self).setUp()
         self.app = qubes.tests.devices.TestApp()
+        def save():
+            ''' A mock method for simulating a successful save '''
+            return True
+        self.app.save = save
         self.vm1 = qubes.tests.devices.TestVM(self.app, 'vm1')
         self.vm2 = qubes.tests.devices.TestVM(self.app, 'vm2')
         self.device = self.vm2.device
 
     def test_000_list_all(self):
+        ''' List all exposed vm devices. No devices are attached to other
+            domains.
+        '''
         args = TestNamespace(self.app)
         with qubes.tests.tools.StdoutBuffer() as buf:
             qubes.tools.qvm_device.list_devices(args)
-            self.assertEventFired(self.vm1,
-                'device-list:testclass')
-            self.assertEventFired(self.vm2,
-                'device-list:testclass')
-            self.assertEventNotFired(self.vm1,
-                'device-list-attached:testclass')
-            self.assertEventNotFired(self.vm2,
-                'device-list-attached:testclass')
             self.assertEqual(
                 [x.rstrip() for x in buf.getvalue().splitlines()],
                 ['vm1:testdev  Description',
                  'vm2:testdev  Description']
             )
 
-    def test_001_list_one(self):
+    def test_001_list_persistent_attach(self):
+        ''' Attach the device exposed by the `vm2` to the `vm1` persistently.
+        '''
         args = TestNamespace(self.app, [self.vm1])
         # simulate attach
+        assignment = qubes.devices.DeviceAssignment(backend_domain=self.vm2,
+            ident=self.device.ident, persistent=True, frontend_domain=self.vm1)
+
         self.vm2.device.frontend_domain = self.vm1
-        self.vm1.devices['testclass']._set.add(self.device)
+        self.vm1.devices['testclass']._set.add(assignment)
         with qubes.tests.tools.StdoutBuffer() as buf:
             qubes.tools.qvm_device.list_devices(args)
-            self.assertEventFired(self.vm1,
-                'device-list-attached:testclass')
-            self.assertEventNotFired(self.vm1,
-                'device-list:testclass')
-            self.assertEventNotFired(self.vm2,
-                'device-list:testclass')
-            self.assertEventNotFired(self.vm2,
-                'device-list-attached:testclass')
             self.assertEqual(
                 buf.getvalue(),
-                'vm2:testdev  Description  vm1\n'
+                'vm1:testdev  Description\n'
+                'vm2:testdev  Description  vm1  vm1\n'
             )
 
-    def test_002_list_one_non_persistent(self):
+    def test_002_list_list_temp_attach(self):
+        ''' Attach the device exposed by the `vm2` to the `vm1`
+            non-persistently.
+        '''
         args = TestNamespace(self.app, [self.vm1])
         # simulate attach
+        assignment = qubes.devices.DeviceAssignment(backend_domain=self.vm2,
+            ident=self.device.ident, persistent=True, frontend_domain=self.vm1)
+
         self.vm2.device.frontend_domain = self.vm1
+        self.vm1.devices['testclass']._set.add(assignment)
         with qubes.tests.tools.StdoutBuffer() as buf:
             qubes.tools.qvm_device.list_devices(args)
-            self.assertEventFired(self.vm1,
-                'device-list-attached:testclass')
-            self.assertEventNotFired(self.vm1,
-                'device-list:testclass')
-            self.assertEventNotFired(self.vm2,
-                'device-list:testclass')
-            self.assertEventNotFired(self.vm2,
-                'device-list-attached:testclass')
-            self.assertEqual(
-                buf.getvalue(),
-                'vm2:testdev  Description  vm1\n'
-            )
+            self.assertEqual(buf.getvalue(),
+                            'vm1:testdev  Description\n'
+                            'vm2:testdev  Description  vm1  vm1\n')
 
     def test_010_attach(self):
+        ''' Test attach action '''
         args = TestNamespace(
             self.app,
             [self.vm1],
@@ -118,6 +124,7 @@ class TC_00_Actions(qubes.tests.QubesTestCase):
             'device-attach:testclass', kwargs={'device': self.device})
 
     def test_011_double_attach(self):
+        ''' Double attach should not be possible '''
         args = TestNamespace(
             self.app,
             [self.vm1],
@@ -128,6 +135,7 @@ class TC_00_Actions(qubes.tests.QubesTestCase):
             qubes.tools.qvm_device.attach_device(args)
 
     def test_020_detach(self):
+        ''' Test detach action '''
         args = TestNamespace(
             self.app,
             [self.vm1],
@@ -135,10 +143,12 @@ class TC_00_Actions(qubes.tests.QubesTestCase):
         )
         # simulate attach
         self.vm2.device.frontend_domain = self.vm1
-        self.vm1.devices['testclass']._set.add(self.device)
+        args.device_assignment.frontend_domain = self.vm1
+        self.vm1.devices['testclass']._set.add(args.device_assignment)
         qubes.tools.qvm_device.detach_device(args)
 
     def test_021_detach_not_attached(self):
+        ''' Invalid detach action should not be possible '''
         args = TestNamespace(
             self.app,
             [self.vm1],
diff --git a/qubes/tests/vm/init.py b/qubes/tests/vm/init.py
index 072271ae..d5439a4c 100644
--- a/qubes/tests/vm/init.py
+++ b/qubes/tests/vm/init.py
@@ -108,7 +108,7 @@ class TC_10_BaseVM(qubes.tests.QubesTestCase):
         })
 
         self.assertCountEqual(vm.devices.keys(), ('pci',))
-        self.assertCountEqual(list(vm.devices['pci'].attached(persistent=True)),
+        self.assertCountEqual(list(vm.devices['pci'].persistent()),
             [qubes.ext.pci.PCIDevice(vm, '00:11.22')])
 
         self.assertXMLIsValid(vm.__xml__(), 'domain.rng')
diff --git a/qubes/tools/__init__.py b/qubes/tools/__init__.py
index 3fc5e794..5ee69f0b 100644
--- a/qubes/tools/__init__.py
+++ b/qubes/tools/__init__.py
@@ -257,7 +257,7 @@ class VolumeAction(QubesAction):
             try:
                 pool = app.pools[pool_name]
                 volume = [v for v in pool.volumes if v.vid == vid]
-                assert volume > 1, 'Duplicate vids in pool %s' % pool_name
+                assert len(volume) == 1, 'Duplicate vids in pool %s' % pool_name
                 if not volume:
                     parser.error_runtime(
                         'no volume with id {!r} pool: {!r}'.format(vid,
@@ -352,9 +352,8 @@ class QubesArgumentParser(argparse.ArgumentParser):
 
         self.set_defaults(verbose=1, quiet=0)
 
-    def parse_args(self, *args, **kwargs):
-        # pylint: disable=arguments-differ
-        namespace = super(QubesArgumentParser, self).parse_args(*args, **kwargs)
+    def parse_args(self, args=None, namespace=None):
+        namespace = super(QubesArgumentParser, self).parse_args(args, namespace)
 
         if self._want_app and not self._want_app_no_instance:
             self.set_qubes_verbosity(namespace)
@@ -442,8 +441,8 @@ class AliasedSubParsersAction(argparse._SubParsersAction):
             sup = super(AliasedSubParsersAction._AliasedPseudoAction, self)
             sup.__init__(option_strings=[], dest=dest, help=help)
 
-        def __call__(self, **kwargs):
-            pass
+        def __call__(self, parser, namespace, values, option_string=None):
+            raise NotImplementedError
 
     def add_parser(self, name, **kwargs):
         if 'aliases' in kwargs:
diff --git a/qubes/tools/qubesd.py b/qubes/tools/qubesd.py
index 65e5138b..91f18732 100644
--- a/qubes/tools/qubesd.py
+++ b/qubes/tools/qubesd.py
@@ -41,8 +41,7 @@ class QubesDaemonProtocol(asyncio.Protocol):
         print('connection_lost(exc={!r})'.format(exc))
         self.untrusted_buffer.close()
 
-    def data_received(self, untrusted_data):
-        # pylint: disable=arguments-differ
+    def data_received(self, untrusted_data):  # pylint: disable=arguments-differ
         print('data_received(untrusted_data={!r})'.format(untrusted_data))
         if self.len_untrusted_buffer + len(untrusted_data) > self.buffer_size:
             self.app.log.warning('request too long')
diff --git a/qubes/tools/qvm_check.py b/qubes/tools/qvm_check.py
index 756e4695..bf6e97fc 100644
--- a/qubes/tools/qvm_check.py
+++ b/qubes/tools/qvm_check.py
@@ -38,8 +38,7 @@ parser.add_argument("--template", action="store_true", dest="template",
 
 
 def print_msg(domains, what_single, what_plural):
-    # pylint: disable=len-as-condition
-    if len(domains) == 0:
+    if not domains:
         print("None of given VM {!s}".format(what_single))
     elif len(domains) == 1:
         print("VM {!s} {!s}".format(domains[0], what_single))
diff --git a/qubes/tools/qvm_device.py b/qubes/tools/qvm_device.py
index 6f6a79a9..a51972fd 100644
--- a/qubes/tools/qvm_device.py
+++ b/qubes/tools/qvm_device.py
@@ -49,17 +49,30 @@ def prepare_table(dev_list):
     output = []
     header = []
     if sys.stdout.isatty():
-        header += [('BACKEND:DEVID', 'DESCRIPTION', 'USED BY')]  # NOQA
+        header += [('VMNAME:DEVID', 'DESCRIPTION', 'USED BY', 'ASSIGNED')]  # NOQA
 
     for dev in dev_list:
         output += [(
-            "{!s}:{!s}".format(dev.backend_domain, dev.ident),
+            dev.id,
             dev.description,
-            str(dev.frontend_domain) if dev.frontend_domain else "",
+            str(dev.attached_to),
+            dev.assignments
         )]
 
     return header + sorted(output)
 
+class Line(object):
+
+    def __init__(self, device: qubes.devices.DeviceInfo, attached_to = None):
+        self.id = "{!s}:{!s}".format(device.backend_domain, device.ident)
+        self.description = device.description
+        self.attached_to = attached_to if attached_to else ""
+        self.frontends = []
+
+    @property
+    def assignments(self):
+        return ', '.join(self.frontends)
+
 
 def list_devices(args):
     ''' Called by the parser to execute the qubes-devices list
@@ -67,32 +80,60 @@ def list_devices(args):
     app = args.app
 
     result = []
+    devices = set()
     if hasattr(args, 'domains') and args.domains:
         for domain in args.domains:
-            result.extend(domain.devices[args.devclass].attached())
-    else:
-        for backend in app.domains:
-            result.extend(backend.devices[args.devclass])
+            for dev in domain.devices[args.devclass].attached():
+                devices.add(dev)
+            for dev in domain.devices[args.devclass].available():
+                devices.add(dev)
 
-    qubes.tools.print_table(prepare_table(result))
+    else:
+        for domain in app.domains:
+            for dev in domain.devices[args.devclass].available():
+                devices.add(dev)
+
+    result = {dev: Line(dev) for dev in devices}
+
+    for dev in result:
+        for domain in app.domains:
+            if domain == dev.backend_domain:
+                continue
+            elif dev in domain.devices[args.devclass].attached():
+                result[dev].attached_to = str(domain)
+
+            if dev in domain.devices[args.devclass].assignments():
+                if dev in domain.devices[args.devclass].persistent():
+                    result[dev].frontends.append(str(domain))
+
+
+    qubes.tools.print_table(prepare_table(result.values()))
 
 
 def attach_device(args):
     ''' Called by the parser to execute the :program:`qvm-devices attach`
         subcommand.
     '''
-    device = args.device
+    device_assignment = args.device_assignment
     vm = args.domains[0]
-    vm.devices[args.devclass].attach(device)
+    app = args.app
+    device_assignment.persistent = args.persistent
+    vm.devices[args.devclass].attach(device_assignment)
+    if device_assignment.persistent:
+        app.save()
 
 
 def detach_device(args):
     ''' Called by the parser to execute the :program:`qvm-devices detach`
         subcommand.
     '''
-    device = args.device
+    device_assignment = args.device_assignment
     vm = args.domains[0]
-    vm.devices[args.devclass].detach(device)
+    before = len(vm.devices[args.devclass].persistent())
+    vm.devices[args.devclass].detach(device_assignment)
+    after = len(vm.devices[args.devclass].persistent())
+    if after < before:
+        args.app.save()
 
 
 def init_list_parser(sub_parsers):
@@ -110,44 +151,48 @@ def init_list_parser(sub_parsers):
 
 class DeviceAction(qubes.tools.QubesAction):
     ''' Action for argument parser that gets the
-        :py:class:``qubes.storage.Volume`` from a POOL_NAME:VOLUME_ID string.
-    '''
-    # pylint: disable=too-few-public-methods
+        :py:class:``qubes.device.DeviceInfo`` from a BACKEND:DEVICE_ID string.
+    '''  # pylint: disable=too-few-public-methods
 
-    def __init__(self, help='A domain & device id combination',
-                 required=True, allow_unknown=False, **kwargs):
+    def __init__(self, help='A pool & volume id combination',
+                 required=True, **kwargs):
         # pylint: disable=redefined-builtin
         super(DeviceAction, self).__init__(help=help, required=required,
                                            **kwargs)
-        self.allow_unknown = allow_unknown
 
     def __call__(self, parser, namespace, values, option_string=None):
-        ''' Set ``namespace.device`` to ``values`` '''
+        ''' Set ``namespace.vmname`` to ``values`` '''
         setattr(namespace, self.dest, values)
 
     def parse_qubes_app(self, parser, namespace):
-        ''' Acquire the :py:class:``qubes.devices.DeviceInfo`` object from
-            ``namespace.app``.
-        '''
         assert hasattr(namespace, 'app')
-        assert hasattr(namespace, 'devclass')
         app = namespace.app
+
+        assert hasattr(namespace, 'device')
+        backend_device_id = getattr(namespace, self.dest)
+
+        assert hasattr(namespace, 'devclass')
         devclass = namespace.devclass
 
         try:
-            backend_name, devid = getattr(namespace, self.dest).split(':', 1)
+            vmname, device_id = backend_device_id.split(':', 1)
             try:
-                backend = app.domains[backend_name]
-                dev = backend.devices[devclass][devid]
-                if not self.allow_unknown and isinstance(dev,
-                        qubes.devices.UnknownDevice):
-                    parser.error_runtime('no device {!r} in qube {!r}'.format(
-                        backend_name, devid))
+                vm = app.domains[vmname]
             except KeyError:
-                parser.error_runtime('no domain {!r}'.format(backend_name))
+                parser.error_runtime("no backend vm {!r}".format(vmname))
+
+            try:
+                vm.devices[devclass][device_id]
+            except KeyError:
+                parser.error_runtime(
+                    "backend vm {!r} doesn't expose device {!r}"
+                    .format(vmname, device_id))
+            device_assignment = qubes.devices.DeviceAssignment(vm, device_id,)
+            setattr(namespace, 'device_assignment', device_assignment)
         except ValueError:
-            parser.error('expected a domain & device id combination like '
-                         'foo:bar')
+            parser.error('expected a backend vm & device id combination ' \
+                         'like foo:bar got %s' % backend_device_id)
+
 
 def get_parser(device_class=None):
     '''Create :py:class:`argparse.ArgumentParser` suitable for
@@ -169,15 +214,29 @@ def get_parser(device_class=None):
     init_list_parser(sub_parsers)
     attach_parser = sub_parsers.add_parser(
         'attach', help="Attach device to domain", aliases=('at', 'a'))
-    attach_parser.add_argument('VMNAME', action=qubes.tools.RunningVmNameAction)
-    attach_parser.add_argument(metavar='BACKEND:DEVICE_ID', dest='device',
-                               action=qubes.tools.VolumeAction)
-    attach_parser.set_defaults(func=detach_device)
     detach_parser = sub_parsers.add_parser(
         "detach", help="Detach device from domain", aliases=('d', 'dt'))
-    detach_parser.add_argument('VMNAME', action=qubes.tools.RunningVmNameAction)
-    detach_parser.add_argument(metavar='BACKEND:DEVICE_ID', dest='device',
-                               action=qubes.tools.VolumeAction)
+
+    attach_parser.add_argument('VMNAME', action=qubes.tools.VmNameAction)
+    detach_parser.add_argument('VMNAME', action=qubes.tools.VmNameAction)
+
+    if device_class == 'block':
+        attach_parser.add_argument(metavar='BACKEND:DEVICE_ID', dest='device',
+                                action=qubes.tools.VolumeAction)
+        detach_parser.add_argument(metavar='BACKEND:DEVICE_ID', dest='device',
+                                    action=qubes.tools.VolumeAction)
+    else:
+        attach_parser.add_argument(metavar='BACKEND:DEVICE_ID',
+                                   dest='device',
+                                   action=DeviceAction)
+        attach_parser.add_argument('-p', '--persistent', default=False,
+                                   help='device will attached on each start of the VMNAME',
+                                   action='store_true')
+        detach_parser.add_argument(metavar='BACKEND:DEVICE_ID',
+                                   dest='device',
+                                   action=DeviceAction)
+
+    attach_parser.set_defaults(func=attach_device)
     detach_parser.set_defaults(func=detach_device)
 
     return parser
diff --git a/qubes/tools/qvm_ls.py b/qubes/tools/qvm_ls.py
index c477346f..352f1bed 100644
--- a/qubes/tools/qvm_ls.py
+++ b/qubes/tools/qvm_ls.py
@@ -309,6 +309,7 @@ class StatusColumn(Column):
         if ret is not None:
             if getattr(vm, 'hvm', False):
                 return ret.upper()
+
             return ret
 
 
@@ -477,6 +478,7 @@ class Table(object):
         '''Format single table row (all columns for one domain).'''
         if self.raw_data:
             return '|'.join(col.format(vm) for col in self.columns)
+
         return ''.join(col.cell(vm) for col in self.columns)
 
 
diff --git a/qubes/utils.py b/qubes/utils.py
index d15300dc..1bd1fadb 100644
--- a/qubes/utils.py
+++ b/qubes/utils.py
@@ -111,18 +111,21 @@ def parse_size(size):
 def mbytes_to_kmg(size):
     if size > 1024:
         return "%d GiB" % (size / 1024)
+
     return "%d MiB" % size
 
 
 def kbytes_to_kmg(size):
     if size > 1024:
         return mbytes_to_kmg(size / 1024)
+
     return "%d KiB" % size
 
 
 def bytes_to_kmg(size):
     if size > 1024:
         return kbytes_to_kmg(size / 1024)
+
     return "%d B" % size
 
 
@@ -134,6 +137,7 @@ def size_to_human(size):
         return str(round(size / 1024.0, 1)) + ' KiB'
     elif size < 1024 * 1024 * 1024:
         return str(round(size / (1024.0 * 1024), 1)) + ' MiB'
+
     return str(round(size / (1024.0 * 1024 * 1024), 1)) + ' GiB'
 
 
diff --git a/qubes/vm/__init__.py b/qubes/vm/__init__.py
index 90b2362c..1efedd79 100644
--- a/qubes/vm/__init__.py
+++ b/qubes/vm/__init__.py
@@ -217,11 +217,17 @@ class BaseVM(qubes.PropertyHolder, metaclass=BaseVMMeta):
         for parent in self.xml.xpath('./devices'):
             devclass = parent.get('class')
             for node in parent.xpath('./device'):
-                device = self.devices[devclass].devclass(
+                options = {}
+                if node.get('options'):
+                    options = node.get('options').attribs(),
+
+                device_assignment = qubes.devices.DeviceAssignment(
                     self.app.domains[node.get('backend-domain')],
-                    node.get('id')
+                    node.get('id'),
+                    options,
+                    persistent=True
                 )
-                self.devices[devclass].attach(device)
+                self.devices[devclass].attach(device_assignment)
 
         # tags
         for node in self.xml.xpath('./tags/tag'):
@@ -250,10 +256,14 @@ class BaseVM(qubes.PropertyHolder, metaclass=BaseVMMeta):
         for devclass in self.devices:
             devices = lxml.etree.Element('devices')
             devices.set('class', devclass)
-            for device in self.devices[devclass].attached(persistent=True):
+            for device in self.devices[devclass].assignments(persistent=True):
                 node = lxml.etree.Element('device')
                 node.set('backend-domain', device.backend_domain.name)
                 node.set('id', device.ident)
+                options_node = lxml.etree.Element('options')
+                for key, val in device.options:
+                    options_node.set(key, val)
+                node.append(options_node)
                 devices.append(node)
             element.append(devices)
 
diff --git a/qubes/vm/adminvm.py b/qubes/vm/adminvm.py
index cd852ceb..88710280 100644
--- a/qubes/vm/adminvm.py
+++ b/qubes/vm/adminvm.py
@@ -115,8 +115,7 @@ class AdminVM(qubes.vm.qubesvm.QubesVM):
             try:
                 return self.app.vmm.libvirt_conn.getInfo()[1]
             except libvirt.libvirtError as e:
-                self.log.warning(
-                    'Failed to get memory limit for dom0: {}'.format(e))
+                self.log.warning('Failed to get memory limit for dom0: %s', e)
                 return 4096
 
     def verify_files(self):
@@ -127,7 +126,8 @@ class AdminVM(qubes.vm.qubesvm.QubesVM):
         '''  # pylint: disable=no-self-use
         return True
 
-    def start(self, **kwargs):
+    def start(self, preparing_dvm=False, start_guid=True, notify_function=None,
+            mem_required=None):
         '''Always raises an exception.
 
         .. seealso:
diff --git a/qubes/vm/mix/net.py b/qubes/vm/mix/net.py
index d2f82370..7d1913d3 100644
--- a/qubes/vm/mix/net.py
+++ b/qubes/vm/mix/net.py
@@ -49,6 +49,7 @@ def _default_ip(self):
         return None
     if self.netvm is not None:
         return self.netvm.get_ip_for_vm(self)  # pylint: disable=no-member
+
     return self.get_ip_for_vm(self)
 
 
@@ -172,6 +173,7 @@ class NetVMMixin(qubes.events.Emitter):
                 '10.139.1.1',
                 '10.139.1.2',
             )
+
         return None
 
     def __init__(self, *args, **kwargs):
diff --git a/qubes/vm/qubesvm.py b/qubes/vm/qubesvm.py
index ca5377aa..5454133f 100644
--- a/qubes/vm/qubesvm.py
+++ b/qubes/vm/qubesvm.py
@@ -430,7 +430,8 @@ class QubesVM(qubes.vm.mix.net.NetVMMixin, qubes.vm.BaseVM):
     # pylint: disable=no-member
     kernelopts = qubes.property('kernelopts', type=str, load_stage=4,
         default=(lambda self: qubes.config.defaults['kernelopts_pcidevs']
-            if list(self.devices['pci'].attached(persistent=True))
+            # pylint: disable=no-member
+            if list(self.devices['pci'].persistent())
             else self.template.kernelopts if hasattr(self, 'template')
             else qubes.config.defaults['kernelopts']),
         ls_width=30,
@@ -444,6 +445,7 @@ class QubesVM(qubes.vm.mix.net.NetVMMixin, qubes.vm.BaseVM):
     # XXX shouldn't this go to standalone VM and TemplateVM, and leave here
     #     only plain property?
     default_user = qubes.property('default_user', type=str,
+        # pylint: disable=no-member
         default=(lambda self: self.template.default_user
             if hasattr(self, 'template') else 'user'),
         setter=_setter_default_user,
@@ -570,7 +572,7 @@ class QubesVM(qubes.vm.mix.net.NetVMMixin, qubes.vm.BaseVM):
 
     @property
     def block_devices(self):
-        ''' Return all :py:class:`qubes.devices.BlockDevice`s for current domain
+        ''' Return all :py:class:`qubes.storage.BlockDevice`s for current domain
             for serialization in the libvirt XML template as <disk>.
         '''
         return [v.block_device() for v in self.volumes.values()]
@@ -1435,7 +1437,9 @@ class QubesVM(qubes.vm.mix.net.NetVMMixin, qubes.vm.BaseVM):
                 else:
                     if not self.is_fully_usable():
                         return "Transient"
+
                     return "Running"
+
             return 'Halted'
         except libvirt.libvirtError as e:
             if e.get_error_code() == libvirt.VIR_ERR_NO_DOMAIN:
@@ -1614,6 +1618,7 @@ class QubesVM(qubes.vm.mix.net.NetVMMixin, qubes.vm.BaseVM):
             '/vm/{}/start_time'.format(self.uuid))
         if start_time != '':
             return datetime.datetime.fromtimestamp(float(start_time))
+
         return None
 
     def is_outdated(self):
diff --git a/relaxng/qubes.rng b/relaxng/qubes.rng
index 7197aa28..02c43f22 100644
--- a/relaxng/qubes.rng
+++ b/relaxng/qubes.rng
@@ -212,8 +212,8 @@ the parser will complain about missing combine= attribute on the second <start>.
                             </doc:description>
                             <attribute name="backend-domain">
                                 <doc:description>
-                                    Backend domain name.
-                                </doc:description>
+                                  Backend domain name.
+                              </doc:description>
                                 <data type="string">
                                     <param name="pattern">[a-z0-9_]+</param>
                                 </data>
@@ -224,6 +224,15 @@ the parser will complain about missing combine= attribute on the second <start>.
                                     <param name="pattern">[0-9a-f]{2}:[0-9a-f]{2}.[0-9a-f]{2}</param>
                                 </data>
                             </attribute>
+                              <optional>
+                                <element name="options">
+                                    <doc:description>
+                                      Options
+                                  </doc:description>
+                                <data type="string">
+                                </data>
+                              </element>
+                            </optional>
                         </element>
                     </oneOrMore>
                 </element>
diff --git a/templates/libvirt/xen.xml b/templates/libvirt/xen.xml
index b5d2ae00..c6480cac 100644
--- a/templates/libvirt/xen.xml
+++ b/templates/libvirt/xen.xml
@@ -32,7 +32,7 @@
                 <viridian/>
             {% endif %}
 
-            {% if vm.devices['pci'].attached(persistent=True) | list
+            {% if vm.devices['pci'].persistent() | list
                     and vm.features.get('pci-e820-host', True) %}
                 <xen>
                     <e820_host state="on"/>
@@ -106,7 +106,7 @@
                 {% include 'libvirt/devices/net.xml' with context %}
             {% endif %}
 
-            {% for device in vm.devices.pci.attached(persistent=True) %}
+            {% for device in vm.devices.pci.persistent() %}
                 {% include 'libvirt/devices/pci.xml' %}
             {% endfor %}