Anthony Liguori wrote:
> Jan Kiszka wrote:
>> That would only allow one such pair per VM.
>>   
> 
> id basically becomes another type of vlan id.  To have multiple nics,
> you do:
> 
> -net tap,vlan=off,id=1234 -net nic,model=virtio,vlan=off,id=1234
> -net tap,vlan=off,id=4321 -net nic,model=virtio,vlan=off,id=4321
> 
> And this goes back to the notion of having all device
> front-ends/back-ends have some sort of identifier to associate one to
> the other.
> 
>> Why not keeping all the existing infrastructure, just locking a vlan
>> against becoming more than a point-to-point link once some conflicting
>> optimization was applied? That should be easy to implement and to
>> explain to the user.
>>   
> 
> I think you're suggesting the same thing as me, except you are saying
> make vlan=off implicit, and use vlan=XXX instead of id=XXX.

Look like. :)

> 
> We can still make vlan=off implicit, and default id=0, so that -net tap
> net nic,model=virtio does the right thing.  However, if a user
> explicitly says -net tap,vlan=1 -net nic,model=virtio,vlan=1, it behaves
> like it used to.

That's my point. And if he tries "-net tap -net nic,model=virtio -net
nic", qemu will fall back to bus-like vlan. And if he tries do add the
third nic during runtime, there will be a descriptive error message.
That should be most elegant while not blocking optimizations (of the
common case).

Jan