[libvirt] Python listDefinedDomains broken?

[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.

> 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

> 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
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|