Attach volume on a used device

Attach a volume on a device already used by the system isn't correctly handled.
It's reproducible in the current bazaar branch.

Ubuntu Lucid
Nova Bexar release

Environment:

Request Method: POST
Request URL: http://p-novamaster/project/project1/volumes/attach
Django Version: 1.2.3
Python Version: 2.6.5
Installed Applications:
['dashboard',
 'django.contrib.auth',
 'django.contrib.admin',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.comments',
 'django.contrib.sites',
 'django.contrib.markup',
 'django.contrib.syndication',
 'django_nose',
 'django_nova',
 'registration']
Installed Middleware:
('django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.middleware.doc.XViewMiddleware')

Traceback:
File "/root/openstack-dashboard/trunk/.dashboard-venv/lib/python2.6/site-packages/django/core/handlers/base.py" in get_response
  100. response = callback(request, *callback_args, **callback_kwargs)
File "/root/openstack-dashboard/trunk/.dashboard-venv/lib/python2.6/site-packages/django/contrib/auth/decorators.py" in _wrapped_view
  25. return view_func(request, *args, **kwargs)
File "/root/django-nova/trunk/src/django_nova/exceptions.py" in decorator
  90. return func(*args, **kwargs)
File "/root/django-nova/trunk/src/django_nova/views/volumes.py" in attach
  112. form.cleaned_data['device']
File "/root/django-nova/trunk/src/django_nova/exceptions.py" in decorator
  80. raise NovaServerError(e)

Exception Type: NovaServerError at /project/project1/volumes/attach
Exception Value: Bad Request

The Nova-compute log :

2011-02-07 17:01:12,895 AUDIT nova.compute.manager [0ZETSPQNZNGVYD0R48NO user1 project1] instance 7: attaching volume 2 to /dev/vdb
libvir: QEMU error : operation failed: target vdb already exists
2011-02-07 17:01:13,116 ERROR nova.exception [-] Uncaught exception
(nova.exception): TRACE: Traceback (most recent call last):
(nova.exception): TRACE: File "/usr/lib/pymodules/python2.6/nova/exception.py", line 116, in _wrap
(nova.exception): TRACE: return f(*args, **kw)
(nova.exception): TRACE: File "/usr/lib/pymodules/python2.6/nova/virt/libvirt_conn.py", line 285, in attach_volume
(nova.exception): TRACE: virt_dom.attachDevice(xml)
(nova.exception): TRACE: File "/usr/lib/python2.6/dist-packages/libvirt.py", line 266, in attachDevice
(nova.exception): TRACE: if ret == -1: raise libvirtError ('virDomainAttachDevice() failed', dom=self)
(nova.exception): TRACE: libvirtError: operation failed: target vdb already exists
(nova.exception): TRACE:
2011-02-07 17:01:13,117 ERROR nova.compute.manager [0ZETSPQNZNGVYD0R48NO user1 project1] instance 7: attach failed /dev/vdb, removing
(nova.compute.manager): TRACE: Traceback (most recent call last):
(nova.compute.manager): TRACE: File "/usr/lib/pymodules/python2.6/nova/compute/manager.py", line 531, in attach_volume
(nova.compute.manager): TRACE: mountpoint)
(nova.compute.manager): TRACE: File "/usr/lib/pymodules/python2.6/nova/exception.py", line 122, in _wrap
(nova.compute.manager): TRACE: raise Error(str(e))
(nova.compute.manager): TRACE: Error: operation failed: target vdb already exists
(nova.compute.manager): TRACE:
2011-02-07 17:01:13,140 ERROR nova.root [-] Exception during message handling
(nova.root): TRACE: Traceback (most recent call last):
(nova.root): TRACE: File "/usr/lib/pymodules/python2.6/nova/rpc.py", line 192, in receive
(nova.root): TRACE: rval = node_func(context=ctxt, **node_args)
(nova.root): TRACE: File "/usr/lib/pymodules/python2.6/nova/compute/manager.py", line 92, in decorated_function
(nova.root): TRACE: function(self, context, instance_id, *args, **kwargs)
(nova.root): TRACE: File "/usr/lib/pymodules/python2.6/nova/compute/manager.py", line 544, in attach_volume
(nova.root): TRACE: raise exc
(nova.root): TRACE: Error: operation failed: target vdb already exists
(nova.root): TRACE: