Brian: I tried your branch and it seems like the error I was getting before is fixed. But still snapshot of VM instance is not working. I am getting another error in the nova-compute.log.

nova-compute.log
----------------------------
2011-04-05 10:34:46,570 DEBUG nova.rpc [-] received {'_context_request_id': 'BJ8RO486PQEGIV8MF8PF', '_context_read_deleted': False, 'a                                  rgs': {'instance_id': 77, 'image_id': 32}, '_context_is_admin': True, '_context_timestamp': '2011-04-05T17:31:50Z', '_context_user': '                                  admin', 'method': 'snapshot_instance', '_context_project': 'admin', '_context_remote_address': None} from (pid=2189) _receive /home/tp                                  atil/nova/nova/rpc.py:167
2011-04-05 10:34:46,571 DEBUG nova.rpc [-] unpacked context: {'timestamp': '2011-04-05T17:31:50Z', 'remote_address': None, 'project':                                   'admin', 'is_admin': True, 'user': 'admin', 'request_id': 'BJ8RO486PQEGIV8MF8PF', 'read_deleted': False} from (pid=2189) _unpack_conte                                  xt /home/tpatil/nova/nova/rpc.py:331
2011-04-05 10:34:46,822 AUDIT nova.compute.manager [BJ8RO486PQEGIV8MF8PF admin admin] instance 77: snapshotting
2011-04-05 10:37:01,130 DEBUG nova.utils [-] Running cmd (subprocess): qemu-img convert -f qcow2 -O raw -s 67dfea6bc7314cad99a451dfb3b01981 /nova/instances/instance    -0000004d/disk /tmp/tmpVgnKrE/67dfea6bc7314cad99a451dfb3b01981 from (pid=2189) execute /home/tpatil/nova/nova/utils.py:150
2011-04-05 10:37:01,278 ERROR nova.exception [-] Uncaught exception
(nova.exception): TRACE: Traceback (most recent call last):
(nova.exception): TRACE:   File "/home/tpatil/nova/nova/exception.py", line 120, in _wrap
(nova.exception): TRACE:     return f(*args, **kw)
(nova.exception): TRACE:   File "/home/tpatil/nova/nova/virt/libvirt_conn.py", line 463, in snapshot
(nova.exception): TRACE:     utils.execute(qemu_img_cmd)
(nova.exception): TRACE:   File "/home/tpatil/nova/nova/utils.py", line 158, in execute
(nova.exception): TRACE:     env=env)
(nova.exception): TRACE:   File "/usr/lib/pymodules/python2.6/eventlet/green/subprocess.py", line 25, in __init__
(nova.exception): TRACE:     subprocess_orig.Popen.__init__(self, args, 0, *argss, **kwds)
(nova.exception): TRACE:   File "/usr/lib/python2.6/subprocess.py", line 623, in __init__
(nova.exception): TRACE:     errread, errwrite)
(nova.exception): TRACE:   File "/usr/lib/python2.6/subprocess.py", line 1141, in _execute_child
(nova.exception): TRACE:     raise child_exception
(nova.exception): TRACE: OSError: [Errno 2] No such file or directory
(nova.exception): TRACE:
2011-04-05 10:37:01,288 ERROR nova [-] Exception during message handling
(nova): TRACE: Traceback (most recent call last):
(nova): TRACE:   File "/home/tpatil/nova/nova/rpc.py", line 188, in _receive
(nova): TRACE:     rval = node_func(context=ctxt, **node_args)
(nova): TRACE:   File "/home/tpatil/nova/nova/exception.py", line 120, in _wrap
(nova): TRACE:     return f(*args, **kw)
(nova): TRACE:   File "/home/tpatil/nova/nova/compute/manager.py", line 342, in snapshot_instance
(nova): TRACE:     self.driver.snapshot(instance_ref, image_id)
(nova): TRACE:   File "/home/tpatil/nova/nova/exception.py", line 126, in _wrap
(nova): TRACE:     raise Error(str(e))
(nova): TRACE: Error: [Errno 2] No such file or directory
(nova): TRACE:

I have also tried installing qemu-img 0.14.0 version on the compute servers, but still I am getting same error as shown above.

Are you able to take snapshot of the vm instance successfully?