libvirt users - May 2010 - Better error codes when stopping a VM that is already stopped

Hi,

Sometimes when stopping a virtual domain using virDomainDestroy(), I come 
across a domain that is already stopped. (For example when someone already 
stopped the domain manually using virsh or because the guest OS issued a 
shutdown.) This is a special case that I absolutely need to catch and handle.

Unfortunately, when this happens, and I call virGetLastError() afterwards, I 
always just get the error code VIR_ERR_OPERATION_INVALID, which doesn't look
very precise to me...

Two questions about this:

Is the domain not running at that moment the only possible condition that can 
trigger this particular error code when calling virDomainDestroy()?

Can't we have a more obvious/precise error code in that case, like 
VIR_ERR_DOMAIN_NOT_RUNNING or something like that?

	Guido Winkelmann

On 05/21/2010 08:11 AM, Guido Winkelmann wrote:
> Hi,
> 
> Sometimes when stopping a virtual domain using virDomainDestroy(), I come 
> across a domain that is already stopped. (For example when someone already 
> stopped the domain manually using virsh or because the guest OS issued a 
> shutdown.) This is a special case that I absolutely need to catch and
handle.
> 
In virt-manager, we basically do:

def destroy(vm):
    if vm.is_running():
        vm.destroy()
    return

I'd recommend doing something similar in your app: no reason to run a
command if you can check ahead of time if it will fail. You can use
virDomainIsActive to check the domain status.
> Unfortunately, when this happens, and I call virGetLastError() afterwards,
I
> always just get the error code VIR_ERR_OPERATION_INVALID, which doesn't
look
> very precise to me...
> 
> Two questions about this:
> 
> Is the domain not running at that moment the only possible condition that
can
> trigger this particular error code when calling virDomainDestroy()?
> 
Yes, there are other errors but none that use OPERATION_INVALID.
> Can't we have a more obvious/precise error code in that case, like 
> VIR_ERR_DOMAIN_NOT_RUNNING or something like that?
> 
Sounds like a reasonable idea, won't help you though if your app needs
to support older versions.

- Cole

On Fri, May 21, 2010 at 02:11:47PM +0200, Guido Winkelmann
wrote:
> Hi,
> 
> Sometimes when stopping a virtual domain using virDomainDestroy(), I come 
> across a domain that is already stopped. (For example when someone already 
> stopped the domain manually using virsh or because the guest OS issued a 
> shutdown.) This is a special case that I absolutely need to catch and
handle.
> 
> Unfortunately, when this happens, and I call virGetLastError() afterwards,
I
> always just get the error code VIR_ERR_OPERATION_INVALID, which doesn't
look
> very precise to me...
> 
> Two questions about this:
> 
> Is the domain not running at that moment the only possible condition that
can
> trigger this particular error code when calling virDomainDestroy()?
The VIR_ERR_OPERATION_INVALID is a precise code that says the request
operation is not valid wrt the current state of the guest. So for the
virDomainDestroy() method, the only cause of this message is requesting
destroy of a guest that is not running.

Similarly you'll get it if you try to start a guest that is already
running.
> Can't we have a more obvious/precise error code in that case, like 
> VIR_ERR_DOMAIN_NOT_RUNNING or something like that?
The VIR_ERR_OPERATION_INVALID is already very precisely defined
as you need.


Daniel
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