diff --git a/qubesadmin/tests/tools/qvm_start.py b/qubesadmin/tests/tools/qvm_start.py
index e91651f8..338cdb42 100644
--- a/qubesadmin/tests/tools/qvm_start.py
+++ b/qubesadmin/tests/tools/qvm_start.py
@@ -78,17 +78,17 @@ def test_010_drive_cdrom(self):
         self.app.expected_calls[
             ('some-vm', 'admin.vm.CurrentState', None, None)] = \
             b'0\x00power_state=Halted'
-        self.app.expected_calls[
-            ('dom0', 'admin.vm.device.block.Available', None, None)] = \
-            b'0\x00sr0\n'
         self.app.expected_calls[
             ('some-vm', 'admin.vm.Start', None, None)] = b'0\x00'
         self.app.expected_calls[
-            ('some-vm', 'admin.vm.device.block.Attach', 'dom0+sr0',
-                b'devtype=cdrom required=True read-only=True')] = b'0\x00'
+            ('some-vm', 'admin.vm.device.block.Assign', 'dom0+sr0',
+             b"required='yes' attach_automatically='yes' ident='sr0' "
+             b"devclass='block' backend_domain='dom0' "
+             b"frontend_domain='some-vm' _devtype='cdrom' "
+             b"_read-only='True'")] = b'0\x00'
         self.app.expected_calls[
-            ('some-vm', 'admin.vm.device.block.Set.assignment', 'dom0+sr0',
-            b'False')] = b'0\x00'
+            ('some-vm', 'admin.vm.device.block.Unassign', 'dom0+sr0', None)] = \
+            b'0\x00'
         qubesadmin.tools.qvm_start.main(['--cdrom=dom0:sr0', 'some-vm'],
             app=self.app)
         self.assertAllCalled()
@@ -101,17 +101,17 @@ def test_011_drive_disk(self):
         self.app.expected_calls[
             ('some-vm', 'admin.vm.CurrentState', None, None)] = \
             b'0\x00power_state=Halted'
-        self.app.expected_calls[
-            ('dom0', 'admin.vm.device.block.Available', None, None)] = \
-            b'0\x00sdb1\n'
         self.app.expected_calls[
             ('some-vm', 'admin.vm.Start', None, None)] = b'0\x00'
         self.app.expected_calls[
-            ('some-vm', 'admin.vm.device.block.Attach', 'dom0+sdb1',
-                b'devtype=disk required=True read-only=False')] = b'0\x00'
+            ('some-vm', 'admin.vm.device.block.Assign', 'dom0+sdb1',
+             b"required='yes' attach_automatically='yes' ident='sdb1' "
+             b"devclass='block' backend_domain='dom0' "
+             b"frontend_domain='some-vm' _devtype='disk' "
+             b"_read-only='False'")] = b'0\x00'
         self.app.expected_calls[
-            ('some-vm', 'admin.vm.device.block.Set.assignment', 'dom0+sdb1',
-            b'False')] = b'0\x00'
+            ('some-vm', 'admin.vm.device.block.Unassign', 'dom0+sdb1',
+             None)] = b'0\x00'
         qubesadmin.tools.qvm_start.main(['--hd=dom0:sdb1', 'some-vm'],
             app=self.app)
         self.assertAllCalled()
@@ -124,17 +124,17 @@ def test_012_drive_disk(self):
         self.app.expected_calls[
             ('some-vm', 'admin.vm.CurrentState', None, None)] = \
             b'0\x00power_state=Halted'
-        self.app.expected_calls[
-            ('dom0', 'admin.vm.device.block.Available', None, None)] = \
-            b'0\x00sdb1\n'
         self.app.expected_calls[
             ('some-vm', 'admin.vm.Start', None, None)] = b'0\x00'
         self.app.expected_calls[
-            ('some-vm', 'admin.vm.device.block.Attach', 'dom0+sdb1',
-                b'devtype=disk required=True read-only=False')] = b'0\x00'
+            ('some-vm', 'admin.vm.device.block.Assign', 'dom0+sdb1',
+             b"required='yes' attach_automatically='yes' ident='sdb1' "
+             b"devclass='block' backend_domain='dom0' "
+             b"frontend_domain='some-vm' _devtype='disk' "
+             b"_read-only='False'")] = b'0\x00'
         self.app.expected_calls[
-            ('some-vm', 'admin.vm.device.block.Set.assignment', 'dom0+sdb1',
-            b'False')] = b'0\x00'
+            ('some-vm', 'admin.vm.device.block.Unassign', 'dom0+sdb1',
+             None)] = b'0\x00'
         qubesadmin.tools.qvm_start.main(['--drive=hd:dom0:sdb1', 'some-vm'],
             app=self.app)
         self.assertAllCalled()
@@ -154,12 +154,15 @@ def test_013_drive_loop_local(self, mock_subprocess):
         self.app.expected_calls[
             ('some-vm', 'admin.vm.Start', None, None)] = b'0\x00'
         self.app.expected_calls[
-            ('some-vm', 'admin.vm.device.block.Attach', 'dom0+loop12',
-                b'devtype=cdrom required=True read-only=True')] = b'0\x00'
+            ('some-vm', 'admin.vm.device.block.Assign', 'dom0+loop12',
+             b"required='yes' attach_automatically='yes' ident='loop12' "
+             b"devclass='block' backend_domain='dom0' "
+             b"frontend_domain='some-vm' _devtype='cdrom' "
+             b"_read-only='True'")] = b'0\x00'
         self.app.expected_calls[
-            ('some-vm', 'admin.vm.device.block.Set.assignment', 'dom0+loop12',
-            b'False')] = b'0\x00'
-        mock_subprocess.return_value = b'/dev/loop12'
+            ('some-vm', 'admin.vm.device.block.Unassign', 'dom0+loop12', None
+             )] = b'0\x00loop12\n'
+        mock_subprocess.return_value = b"/dev/loop12"
         qubesadmin.tools.qvm_start.main([
             '--cdrom=dom0:/home/some/image.iso',
             'some-vm'],
@@ -183,12 +186,14 @@ def test_014_drive_loop_remote(self):
         self.app.expected_calls[
             ('some-vm', 'admin.vm.Start', None, None)] = b'0\x00'
         self.app.expected_calls[
-            ('some-vm', 'admin.vm.device.block.Attach', 'other-vm+loop7',
-                b'devtype=cdrom required=True read-only=True')] = b'0\x00'
+            ('some-vm', 'admin.vm.device.block.Assign', 'other-vm+loop7',
+             b"required='yes' attach_automatically='yes' ident='loop7' "
+             b"devclass='block' backend_domain='other-vm' "
+             b"frontend_domain='some-vm' _devtype='cdrom' "
+             b"_read-only='True'")] = b'0\x00'
         self.app.expected_calls[
-            ('some-vm', 'admin.vm.device.block.Set.assignment',
-            'other-vm+loop7',
-            b'False')] = b'0\x00'
+            ('some-vm', 'admin.vm.device.block.Unassign', 'other-vm+loop7',
+             None)] = b'0\x00'
         self.app.expected_calls[
             ('other-vm', 'admin.vm.feature.CheckWithTemplate', 'vmexec',
              None)] = b'2\x00QubesFeatureNotFoundError\x00\x00Feature \'vmexec\' not set\x00'
@@ -215,8 +220,11 @@ def test_015_drive_failed_start(self):
             ('some-vm', 'admin.vm.CurrentState', None, None)] = \
             b'0\x00power_state=Halted'
         self.app.expected_calls[
-            ('some-vm', 'admin.vm.device.block.Attach', 'other-vm+loop7',
-                b'devtype=cdrom required=True read-only=True')] = b'0\x00'
+            ('some-vm', 'admin.vm.device.block.Assign', 'other-vm+loop7',
+             b"required='yes' attach_automatically='yes' ident='loop7' "
+             b"devclass='block' backend_domain='other-vm' "
+             b"frontend_domain='some-vm' _devtype='cdrom' "
+             b"_read-only='True'")] = b'0\x00'
         self.app.expected_calls[
             ('some-vm', 'admin.vm.Start', None, None)] = \
             b'2\x00QubesException\x00\x00An error occurred\x00'
@@ -239,8 +247,11 @@ def test_016_drive_failed_attach(self):
             ('some-vm', 'admin.vm.CurrentState', None, None)] = \
             b'0\x00power_state=Halted'
         self.app.expected_calls[
-            ('some-vm', 'admin.vm.device.block.Attach', 'other-vm+loop7',
-                b'devtype=cdrom required=True read-only=True')] = \
+            ('some-vm', 'admin.vm.device.block.Assign', 'other-vm+loop7',
+             b"required='yes' attach_automatically='yes' ident='loop7' "
+             b"devclass='block' backend_domain='other-vm' "
+             b"frontend_domain='some-vm' _devtype='cdrom' "
+             b"_read-only='True'")] = \
             b'2\x00QubesException\x00\x00An error occurred\x00'
         retcode = qubesadmin.tools.qvm_start.main([
             '--cdrom=other-vm:loop7',
diff --git a/qubesadmin/tools/qvm_start.py b/qubesadmin/tools/qvm_start.py
index 27de91ff..39fca0cd 100644
--- a/qubesadmin/tools/qvm_start.py
+++ b/qubesadmin/tools/qvm_start.py
@@ -157,8 +157,9 @@ def get_drive_assignment(app, drive_str):
         'read-only': devtype == 'cdrom'
     }
     assignment = qubesadmin.device_protocol.DeviceAssignment(
-        backend_domain,
-        ident,
+        backend_domain=backend_domain,
+        ident=ident,
+        devclass='block',
         options=options,
         attach_automatically=True,
         required=True)