Re: [Libvirt-cim] [PATCH 1 of 2] Initialize libvirt early so that we avoid the backend register race
Dan Smith wrote:
HE> A CIMOM does not have the possibility to return different
return
HE> codes, meaning the error for Xen_ComputerSystem and the instances
HE> for KVM_ComputerSystem. In the case where one request returned
HE> with an error, this one is reported back to the client and all
HE> returned instances are revoked.
Ah, okay. It seems a little weird to solve this by not returning
failure if you try to enumerate a class that can't possibly exist on a
particular system.
That's how the providers also behave with the lv_connect()
approach.
However, I'm not sure there is any reasonable way
around this.
The question a client is asking is - are there instances of
Xen_ComputerSystems on this machine. If there are none, than a result of
0 instances is valid. If the client is interested in the question "why
there are none", then he has to ask the VirtualSystemManagementService,
if Xen is running or not. If Xen is not running on this machine, then
also here no instance for Xen is returned. Then the client knows, that
Xen is not available on this machine and all requests against Xen
classes will return 0 instances. If VirtualSystemManagementService
returns an instance for Xen, then the client knows, that currently no
Xen_ComputerSystems are defined, but he can work on this machine to
create one/some Xen instances.
So the question for a provider is - are there instances of the class I'm
responsible for or not ? This one is answered with yes (returning
instances) or no (returning no instances). The reason why there are no
instances, is resolved by the client itself with the evaluation of the
model for existing and non-existing instances. This means for the
provider programmer that he has to tolerate a - at a first view -
light-weight error reporting. To answer your question - no, there is no
reasonable way around this ;). Its the clients responsibility to
traverse and interpret the model and instances.
--
Regards
Heidi Eckhart
Software Engineer
Linux Technology Center - Open Hypervisor
heidieck(a)linux.vnet.ibm.com
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