Re: [Qemu-devel] [PATCH 3/3] Unified Datagram Socket Transport - raw support

[Anton Ivanov]

On 24/07/17 05:03, Jason Wang wrote:
>
>
> On 2017年07月22日 02:50, Anton Ivanov wrote:
>>
>> [snip]
>>
>>>> +    "-netdev raw,id=str,ifname=ifname\n"
>>>> +    "                configure a network backend with ID 'str'
>>>> connected to\n"
>>>> +    "                an Ethernet interface named ifname via raw
>>>> socket.\n"
>>>> +    "                This backend does not change the interface
>>>> settings.\n"
>>>> +    "                Most interfaces will require being set into
>>>> promisc mode,\n"
>>>> +    "                as well having most offloads (TSO, etc)
>>>> turned off.\n"
>>>> +    "                Some virtual interfaces like tap support only
>>>> RX.\n"
>>>
>>> Pay attention that qemu supports vnet header. So any reason to turn
>>> off e.g TSO here?
>>
>> I am not aware of any means to get extra info like checksums, etc
>> show up on raw socket read.
>>
>> If you know a way to make them show up, this is worth investigating.
>
> See packet_rcv_vnet(). But a known 'issue' for raw socket is that it
> forbids change vnet header length after creation, we may need some
> workaround in qemu.

There are a couple of other issues - if I understand the situation
correctly, probing the vnet header size relies on tap ioctls.

I have some support for this working now. I will try to get around to
redo the patches as per your last comments + initial vnet header support
and re-submit.

One definitive advantage of having it is that it allows to detect if
GSO/TSO is enabled on the interface as this is not something that gets
along very well with fixed buffer size vector IO.

A.

[snip]
>>>
>
>


-- 
Anton R. Ivanov
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