Re: [Qemu-devel] jumbo frames: needing some help

[Martin Rauh <martin.rauh@uni-ulm.de>]

Anthony Liguori wrote:
> Martin Rauh wrote:
>> Anthony Liguori wrote:
>>> martin.rauh@uni-ulm.de wrote:
>>>> Hello, everyone!
>>>>
>>>> Sorry for the inconvenience, but as a part of my diploma thesis, I 
>>>> am creating a virtual NIC for QEMU, in order to support a new 
>>>> cluster OS of the university. (Saving the overhead caused by 
>>>> emulating real hardware, it is not emulating an existing NIC.) 
>>>> Anyway, now it seems to be working correctly, except for handling 
>>>> jumbo frames, which I have to make available.
>>>
>>> You would have to post your patch.  We seem to be able to handle 
>>> jumbo frames nicely with virtio-net.
>>>
>>> BTW, are you aware of virtio-net?  It has all of the properties that 
>>> you are describing and it already exists for Linux and Windows.
>>>
>> No, I didn't know about virtio-net. Presumably it would be better to 
>> support this virtio-net in our OS, but I think there's not enough time 
>> left to develop a new driver now. I will recommend this for further 
>> proceeding, thank you for this hint!
>>
>> http://home.vrweb.de/mrauh/testnic.c
>> Here is the source file of my virtual NIC, which I modelled on then 
>> NE2000.c, but it is probably not very nice to read. I used 
>> qemu_send_packet for sending and registered my testnic_receive 
>> function via qemu_new_vlan_client. Do you agree in principle to this 
>> approach, in terms of proceeding jumbo frames?
> 
> Well if you don't have a patch to vl.c, that's probably your problem.  
> There are a number of spots in the VLAN send functions that use buffers 
> of 4096.  You won't be able to receive a packet larger than that.
> 
You are right, this was the Problem! I can't believe that I didn't see it, while I 
spent so many time on searching for. Thanks a lot!

Best wishes,
Martin Rauh.