Re: [Qemu-devel] [PATCH] virtio-net: Do not filter VLANs without F_CTRL_VLAN

[Eric Blake <eblake@redhat.com>]

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On 02/16/2014 03:33 AM, Michael S. Tsirkin wrote:
> On Wed, Feb 12, 2014 at 10:46:28PM +0100, Stefan Fritsch wrote:
>> If VIRTIO_NET_F_CTRL_VLAN is not negotiated, do not filter out all
>> VLAN-tagged packets but send them to the guest.
>>
>> Signed-off-by: Stefan Fritsch <sf@sfritsch.de>
> 
> Thanks for the patch.
> I think there are still some issues after this
> patch: we need to notify management when
> this bit state changes.
> And I think libvirt still does not look at the filter info
> so it's probably not too late, and cleaner to simply tell it:
> "all-vlans".
> that is, add
>     '*vlan':          'RxState',
> to the schema.
> 
> (is it true that it needs to be * because old qemu does not produce it?
>  maybe not ...)

The following conversions are back-compat safe:

changing an input parameter from mandatory to optional
adding an optional input parameter
changing an output parameter from optional to mandatory
adding an output parameter (optional or always-present)

Regarding whether a parameter must be marked as optional: on input,
optional means the user can omit it.  On output, marking it as optional
means the current version of qemu will sometimes generate it, and
sometimes avoid it.  If qemu always generates it in the current version,
even if it was not generated in an previous version, then an output
parameter does not have to be marked optional (that is, behavior of
previous qemu versions should not impact the choice of whether the
current qemu marks an output as optional - only whether the current qemu
sometimes omits the parameter).  However, once an output parameter is
marked mandatory, you must never remove it in future qemu versions.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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