Re: [Qemu-devel] [QEMU] net: adapt dump to support the new syntax

[Benjamin <mlspirat42@gmail.com>]

On 01/24/12 20:58, Markus Armbruster wrote:
> Stefan Hajnoczi<stefanha@gmail.com>  writes:
>
>> On Tue, Jan 24, 2012 at 6:22 PM, Benjamin<mlspirat42@gmail.com>  wrote:
>>> Hello Stefan,
>>
>> Hi,
>> Please send QEMU development emails to the mailing list so others can
>> help or we can avoid duplicating work in case someone else is already
>> looking into this.  I have CCed the mailing list.
>>
>>> I've seen your blog and I hope you can help me address the issue of
>>> -net dump not being compatible with the new -netdev syntax.
>>
>> The reason is because packet capture is implemented as a net client -
>> it receives packets on the "VLAN" and writes them to the pcap file.
>> In the -netdev model each client has a peer (another net client that
>> is communicates with).  So it's not possible to plug the "dump" net
>> client together with an emulated NIC client and a host tap client, for
>> example.  Since "VLANs" broadcast packets to all attached net clients
>> it works there.
>>
>>> I think it is possible to achieve but I've had a lot of trouble
>>> understanding the code, VLANs are everywhere and even though the new
>>> syntax doesn't use them it looks like the code still uses a VLAN logic.
>>>
>>> Before I really start to get serious about this task, do you have any
>>> advice or recommendation?
>>
>> I refactored the network subsystem to drop the "VLAN" concept a while
>> back but never got around to submitting the patches:
>>
>> http://repo.or.cz/w/qemu/stefanha.git/shortlog/refs/heads/vlan-hub
>>
>> This branch completely removes the "VLAN" feature.  Instead it
>> introduces hubs, which are net clients that have multiple ports and
>> broadcast packets between them.  This allows you to achieve the same
>> behavior as "VLANs" except we remove all the hardcoded special cases
>> in the net subsystem and instead push that feature out into the hub
>> net client.
>
> Sounds more advanced than my experimental hackery to kill VLANs.
>
>> If you rebase the vlan-hub branch onto a recent qemu.git, then you can
>> use -netdev syntax to create an emulated NIC, host device, dump
>> device, and a hub.  The three clients must be attached to the hub.
>>
>> I think the code is already there, it should work.  I didn't submit
>> this because I wanted to implement automated tests to ensure that
>> these changes don't brake the old syntax for "VLANs".
>>
>> Feel free to play around with the vlan-hub branch, test it, and push
>> it upstream along with changes that you make.
>
> Yes, please.


I will rebase it and test it then. Thanks.