[Qemu-devel] Re: [PATCH 0/8] vlan cleanup

[Anthony Liguori <anthony@codemonkey.ws>]

On 07/13/2010 02:08 PM, Jan Kiszka wrote:
> Anthony Liguori wrote:
>    
>> On 07/13/2010 07:48 AM, Jan Kiszka wrote:
>>      
>>> Miguel Di Ciurcio Filho wrote:
>>>
>>>        
>>>> On Tue, Jul 13, 2010 at 3:16 AM, Jan Kiszka<jan.kiszka@web.de>   wrote:
>>>>
>>>>          
>>>>> Miguel Di Ciurcio Filho wrote:
>>>>>
>>>>>            
>>>>>> This series removes the vlan stuff without mercy. I've tried to
>>>>>> make the steps
>>>>>> as small as possible, but the last one is huge. I did some basic
>>>>>> tests and
>>>>>> networking is still working, so reviews are welcome :-D
>>>>>>
>>>>>>              
>>>>> Sorry, this is a bit too rude. This not only removes the vlan model,
>>>>> something one may talk about, but also the innocent socket back-ends
>>>>> and
>>>>> the useful pcap dump support.
>>>>>
>>>>> Socket back-ends allow quick and easy unprivileged inter-VM network
>>>>> setups. Nothing for production systems, but useful for testing purposes
>>>>> on boxes where taps are not allowed or unhandy to configure.
>>>>>
>>>>>
>>>>>            
>>>> I agree that it might be handy sometimes, but one could use VDE for
>>>> that too. Runs on user-space and can be tunneled over SSH or netcat
>>>> [1].
>>>>
>>>>          
>>> Yes, I know. But it requires yet another process as hop. In contrast,
>>> peer-to-peer sockets used to be as fast as taps in certain setup (now
>>> taps became faster again).
>>>
>>>        
>> Dump is critical to maintain.
>>
>> sockets is not terribly useful without vlan.  Honestly, I have a hard
>> time agreeing that it's terribly useful to begin with.  I don't buy an
>> argument about "ease-of-use" because how to properly configure the
>> sockets backend is not at all obvious.
>>      
> Old style:
>   -net socket,listen=:12345
> plus
>   -net socket,connect=127.0.0.1:12345
> and you have linked two VMs. New style would be less handy (unless we
> map -net on -netdev once vlans are gone), but still following the same
> pattern.
>    

For peer-to-peer.  But -net socket + vlan also supports multiple point.

And in this example, you're forwarding TCP over TCP which is pretty 
awful from a perf perspective.  Last time I did a quick sniff test with 
-net socket, it was amazingly slow (like 10s of KB/s).

> I bet there is only a minor bit missing to get "-netdev socket" working,
> given that slirp apparently works. If I had time, I would look into this.
>    

I'm sure you could, but the result is a tremendously crippled version of 
-net socket which leads me to wonder if it's still even worth supporting.

Regards,

Anthony Liguori

> Jan
>
>