[libvirt] [PATCH] qemu: Introduce VIRTIO_NET_F_STANDBY feature bit to virtio_net

[Samudrala, Sridhar]

On 6/6/2018 11:52 AM, Ján Tomko wrote:
> On Wed, Jun 06, 2018 at 11:17:36AM -0700, Samudrala, Sridhar wrote:
>> On 6/4/2018 7:06 PM, Jason Wang wrote:
>>>
>>>
>>> On 2018年06月05日 09:41, Samudrala, Sridhar wrote:
>>>> Ping on this patch now that the kernel patches are accepted into
>>>> davem's net-next tree.
>>>> https://patchwork.ozlabs.org/cover/920005/
>>>>
>>>>
>>>> On 5/7/2018 4:09 PM, Sridhar Samudrala wrote:
>>>>> This feature bit can be used by hypervisor to indicate virtio_net
>>>>> device to
>>>>> act as a standby for another device with the same MAC address.
>>>>>
>>>>> I tested this with a small change to the patch to mark the STANDBY
>>>>> feature 'true'
>>>>> by default as i am using libvirt to start the VMs.
>>>>> Is there a way to pass the newly added feature bit 'standby' to qemu
>>>>> via libvirt
>>>>> XML file?
>>>>>
>>>
>>> Maybe you can try qemu command line passthrough:
>>>
>>> https://libvirt.org/drvqemu.html#qemucommand
>>
>> It looks like this can be used to pass command line arguments to qemu.
>> Is it possible to specify a virtio specific attribute via this method?
>>
>
> Yes, for testing purposes you should be able to do this via using QEMU's
> -set command line argument:
> http://blog.vmsplice.net/2011/04/how-to-pass-qemu-command-line-options.html 
>
> i.e.:
>
> <domain type='kvm' 
> xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
>  ...
>  <qemu:commandline>
>    <qemu:arg value='-set'/>
>    <qemu:arg value='device.net0.standby=on'/>
>  </qemu:commandline>
> </domain>

Thanks. Will try this.

>
>> For ex: to say mrg_rxbuf is off we can add the following line to virtio
>> section of the domain xml file.
>>   <host mrg_rxbuf='off'/>
>>
>> I think libvirt needs to be extended to to support the new 'standby' 
>> attribute
>> via this mechanism.
>> Adding Liane Stump and libvirt to the CC list.
>
> *Laine
>
>>
>> Michael,
>> Can we start with getting this patch into Qemu and an update to 
>> libvirt to
>> support the 'standby' feature so that this feature can be enabled via
>> some scripts/orchestration layer for now.
>>
>> We could improve this solution by enhancing Qemu to do automatic 
>> management of the
>> addition/deletion of the primary device based on feature negotiation 
>> as a later patch.
>>
>
> If that means the libvirt attribute would no longer be needed, I don't
> see the reason to add it to libvirt in the first place.

I think we still need this attribute supported via libvirt so that a user/admin
can enable this feature via domain XML specification.