[libvirt] Python listDefinedDomains broken?

[Marc Richter]

Hi Daniel,

thanks for that nice answer!


Am 01.06.2016 um 15:03 schrieb Daniel P. Berrange:
> On Wed, Jun 01, 2016 at 02:49:26PM +0200, Marc Richter wrote:
>> Hi everyone,
>>
>> please, don't roast me if I'm asking stupid things or fail to provide info,
>> since I'm a freshman, using libvirt.
> No problem, we're a friendly lot here :-)
>
>> Then a domain named "winxp_ausgeschaltet" is within that list:
>>
>>
>>   Id    Name                           State
>> ----------------------------------------------------
>> ...
>>   -     winxp_ausgeschaltet            shut off
>>
>>
>> When I do the same for the second host, it is also in that list:
>>
>>
>>   Id    Name                           State
>> ----------------------------------------------------
>> ...
>>   7     winxp_ausgeschaltet            running
>>
>>
>> When I do the following in Python, this domain is listed for the first host
>> (where it's state is "shut off"), but not for the second one:
>>
>>
>> import libvirt
>> import sys
>>
>> class kvmhost:
>>      def __init__(self, host, keyfile):
>>          self.conn = self.connect_kvm(host, keyfile)
>>          self.doms = sorted(self.get_doms())
>>      def connect_kvm(self, host, keyfile):
>>          try:
>>              conn = libvirt.openReadOnly('qemu+ssh://root@' + host +
>> '/system?keyfile=' + keyfile)
>>          except libvirt.libvirtError as lve:
>>              print('Error: ' + str(lve))
>>              sys.exit(1)
>>          return conn
>>      def get_doms(self):
>>          try:
>>              alldoms = self.conn.listDefinedDomains()
>>          except libvirt.libvirtError as lve:
>>              print('Error: ' + str(lve))
>>              self.conn.close()
>>              sys.exit(1)
>>          return alldoms
>>
>> host1 = kvmhost('host1', '/path/to/ssh_keyfile')
>> host2 = kvmhost('host2', '/path/to/ssh_keyfile')
>>
>> print(host1.doms)
>> print(host2.doms)
>>
>>
>> What am I doing wrong here or: is there a missbehavior in libvirt or the
>> python module?
> This is expected behaviour of the listDefinedDomains() API call - though
> admittedly somewhat stupid behaviour.
>
> Originally libvirt has a listDomainsIDs API call that only listed guests
> that were running.
>
> We then added  listDefinedDomains() call that only listed guests that
> were *not* running.
>
> So to get a complete list of guests on the host you had to use *both*
> listDomainsIDs and listDefinedDomains().
>
> This had a built-in race condition if a guest started or stopped in
> betweeen the 2 API calls. So we introduced 'listAllDomains' as a better
> API that can give you a list of *all* domains whether running or stopped.

Great, thanks for explaining this to me!
Then listAllDomains seems like the way to go for me; but even the 
workaround of combining listDomainsIDs and listDefinedDomains() seems 
OK, if I cannot resolve the unknown procedure issue.

>> Using listAllDomains instead of listDefinedDomains gives:
>>
>> libvirt: Remote Driver error : unknown procedure: 273
> I'm really surprised to see that error - this API call has existed
> since libvirt 0.9.13 and you say you have 1.3.1 which is more than
> new enough

I'm very sorry, my bad: I've queried the wrong server from out of 
python. You are right: The Host which has this issue is of libvirt 
version 0.9.2. Testing the call against more recent libvirt works.
Thank you for helping me identifying this fail.

>> What is the difference between listAllDomains and listDefinedDomains at all?
> Essentially listAllDomains() is what any app using modern libvirt should
> be using. We recommend ignoring listDefinedDomains & listDomainIDs unless
> you need to work with older (ancient) libvirt
>
> Regards,
> Daniel

Best regars,
Marc

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