[libvirt] RFC: Detaching interface from guest fails with improper error message if no mac given in xml

[Madhu Pavan]

On 09/29/2017 01:27 PM, Peter Krempa wrote:
> On Fri, Sep 29, 2017 at 12:45:30 +0530, Madhu Pavan wrote:
>> This RFC is regarding https://bugzilla.redhat.com/show_bug.cgi?id=1497054
>>
>> Let's say we have a network interface
>>      <interface type='network'>
>>        <mac address='52:54:00:fe:10:57'/>
>>        <source network='vfnetwork'/>
>>        <model type='virtio'/>
>>        <address type='pci' domain='0x0000' bus='0x01' slot='0x01'
>> function='0x0'/>
>>      </interface>
>>
>> and we are trying to detach the above interface with the following
>> xml(vfpool.xml):
>>      <interface type='network'>
>>        <source network='vfnetwork'/>
>>        <model type='virtio'/>
>>        <address type='pci' domain='0x0000' bus='0x01' slot='0x01'
>> function='0x0'/>
>>      </interface>
>> Detaching the interface returns error:
>> # virsh detach-device vffuest vfpool.xml
>> error: Failed to detach device from vfpool.xml
>> error: operation failed: no device matching mac address 52:54:00:54:f6:61
>> found
>>
>> Here the mac address is auto-generated as we haven't given in the
>> vfpool.xml.
>> And virDomainNetFindIdx will try to match the auto-generated mac address
>> with
>> the domain xml. It fails as there will be no match and the error message
>> says
>> "no device matching mac address 52:54:00:54:f6:61 found".
>>
>> Here in this scenario I see two possible improvements.
>> 1. As virDomainNetFindIdx search according to mac address and guest side
>>     PCI address (if specified), we can search for PCI address and avoid
>>     mac address search if mac is not given in the xml. As the PCI address
>>     is unique we don't compromise in performance.
>> 2. Improve error message by saying mac address is missing in the device xml.
> I think the problem is that the mac address is always generated in the
> device XML parser. Auto assignment of the mac address is necessary when
> the device is added to the VM. When removing, generating the mac address
> is bogus.
>
> I think we need to make sure that no unique ids are added to the parser
> at least in the cases when the XML is parsed for the unplug code path.
I have a patch ready to search according to PCI address in the absence
of mac address. I can make changes to it so that mac address is not
auto-generated. Is this good to proceed in this direction?