Re: [Qemu-devel] [libvirt] [PATCH] qemu: Introduce VIRTIO_NET_F_STANDBY feature bit to virtio_net

["Ján Tomko" <jtomko@redhat.com>]

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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>


>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.

Jano

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