[Qemu-devel] jumbo frames: needing some help

[Qemu-devel] jumbo frames: needing some help

[martin.rauh]

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.

I connected two QEMU instances by -net socket,listen and -net  
socket,connect options and I can send and receive packets in the  
guests. If I'm sending a 9000 byte packet, or bigger than 4 kByte, it  
is received completely by the other instance, but then QEMU crashes.

I didn't find an according bug in the code of my NIC.
MTU of 127.0.0.1 is 16436...

Is there something special that I have to take care of, dealing with  
jumbo frames? Unfortunately I'm no expert in networking...

Thank you in advance!

Regards,

Martin Rauh.

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

[Anthony Liguori]

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.

Regards,

Anthony Liguori

> I connected two QEMU instances by -net socket,listen and -net 
> socket,connect options and I can send and receive packets in the 
> guests. If I'm sending a 9000 byte packet, or bigger than 4 kByte, it 
> is received completely by the other instance, but then QEMU crashes.
>
> I didn't find an according bug in the code of my NIC.
> MTU of 127.0.0.1 is 16436...
>
> Is there something special that I have to take care of, dealing with 
> jumbo frames? Unfortunately I'm no expert in networking...
>
> Thank you in advance!
>
> Regards,
>
> Martin Rauh.
>
>
>
>

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

[Martin Rauh]

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?

Thanks!

Martin Rauh.

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

[Anthony Liguori]

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.

Regards,

Anthony Liguori

> Thanks!
>
> Martin Rauh.
>
>

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

[Martin Rauh]

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.