Hi,
this is the patch to check for device model (in XendConfig.py) when the 
device_model had no path specified, i.e. XenD was trying to read the 
file on the auxbin path. Without this patch applied the meaningless 
python error "coercing to Unicode: need string or buffer, NoneType 
found" occurred:

[2010-11-30 13:56:47 5255] ERROR (xmlrpclib2:181) Internal error 
handling xend.domain.create
Traceback (most recent call last):
   File "/usr/lib64/python2.4/site-packages/xen/util/xmlrpclib2.py", 
line 134, in _marshaled_dispatch
     response = self._dispatch(method, params)
   File "/usr/lib64/python2.4/SimpleXMLRPCServer.py", line 406, in _dispatch
     return func(*params)
   File 
"/usr/lib64/python2.4/site-packages/xen/xend/server/XMLRPCServer.py", 
line 80, in domain_create
     info = XendDomain.instance().domain_create(config)
   File "/usr/lib64/python2.4/site-packages/xen/xend/XendDomain.py", 
line 1001, in domain_create
     dominfo = XendDomainInfo.create(config)
   File "/usr/lib64/python2.4/site-packages/xen/xend/XendDomainInfo.py", 
line 97, in create
     domconfig = XendConfig.XendConfig(sxp_obj = config)
   File "/usr/lib64/python2.4/site-packages/xen/xend/XendConfig.py", 
line 367, in __init__
     self.validate()
   File "/usr/lib64/python2.4/site-packages/xen/xend/XendConfig.py", 
line 558, in validate
     self._platform_sanity_check()
   File "/usr/lib64/python2.4/site-packages/xen/xend/XendConfig.py", 
line 502, in _platform_sanity_check
     if not os.path.exists(self['platform']['device_model']):
   File "/usr/lib64/python2.4/posixpath.py", line 171, in exists
     st = os.stat(path)
TypeError: coercing to Unicode: need string or buffer, NoneType found

This patch raises VmError with message that no valid device model was 
specified if None type was found in the device_model specification.

It's been tested on non-existing device model where the message is being 
printed. If an invalid (but existing) device_model is set in the 
configuration file the domain was destroyed because it crashed. If there 
is a path specified (i.e. it's not using auxbin path) it bails with 
error that the device model was not found (which was already implemented 
there).

Michal

Signed-off-by: Michal Novotny <minovotn@redhat.com>

-- 
Michal Novotny<minovotn@redhat.com>, RHCE
Virtualization Team (xen userspace), Red Hat