[PATCH 02/11] hyperv: implement domainUndefine and domainUndefineFlags

[Matt Coleman]

> On Nov 26, 2020, at 9:26 AM, Daniel P. Berrangé <berrange at redhat.com> wrote:
> 
> On Tue, Nov 24, 2020 at 02:48:31PM -0500, Matt Coleman wrote:
>> +    /* try to shut down the VM if it's not disabled, just to be safe */
>> +    if (computerSystem->data->EnabledState != MSVM_COMPUTERSYSTEM_ENABLEDSTATE_DISABLED &&
>> +        hypervDomainShutdown(domain) < 0) {
>> +        goto cleanup;
>> +    }
> 
> Many, but not all, drivers in libvirt allow undefining the cofig for a running
> VM. ie we can delete the config on disk, without affecting the running VM.
> This results in a so called "transient" VM - basically a VM which only exists
> as long as it is running - virDomainCreateXML creates such a beast, while
> virDomainDefineXML+virDomainCreate  creates a "persistent" VM and starts it.
> 
> If hyperv doesn't allow that, then shutting down the VM is likely to be
> surprising.
> 
> I'd suggest we report an error indicating undefine is not permitted for a
> running VM in such a case.

Hyper-V does not allow a VM's definition to be deleted if it's active, 
paused, or in state transition.

If I remove the check entirely, it displays an error including 
Hyper-V's method name, the error code from Hyper-V, and a string that's 
generated by hypervReturnCodeToString() from hyperv_wmi.c.

For example, `virsh undefine runningvm` would throw the error:

error: Failed to undefine domain runningvm
error: internal error: Invocation of DestroySystem returned an error: Invalid state for this operation (32775)

That simplifies the code significantly and provides details (the method 
name and error code) that users could look up in Microsoft's 
documentation. However, I don't think it's very clearly phrased. 
"Domain must not be active or in state transition" with the error code 
set to VIR_ERR_OPERATION_INVALID produces the following error output:

error: Failed to undefine domain testvm
error: Requested operation is not valid: Domain must not be active or in state transition

It's a difference of 18 lines (51 vs 33). The shorter version 
eliminates the result and computerSystem variables, does not use goto, 
and only sends a single WMI request to Hyper-V since it does not have 
to query the VM state before attempting to undefine it.

Would you prefer to have simpler code or a custom error message?

Thanks!
Matt