netdev - Re: [patch net-next-2.6] net: vlan: make non-hw-accel rx path similar to hw-accel

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Date:	Mon, 04 Apr 2011 21:00:00 +0200
From:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
To:	Jiri Pirko <jpirko@...hat.com>
CC:	Jesse Gross <jesse@...nel.org>, netdev@...r.kernel.org,
	davem@...emloft.net, shemminger@...ux-foundation.org,
	kaber@...sh.net, fubar@...ibm.com, eric.dumazet@...il.com,
	andy@...yhouse.net, xiaosuo@...il.com,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [patch net-next-2.6] net: vlan: make non-hw-accel rx path similar
 to hw-accel

Le 04/04/2011 09:14, Jiri Pirko a écrit :
> Mon, Apr 04, 2011 at 08:54:40AM CEST, nicolas.2p.debian@...il.com wrote:
>> Le 03/04/2011 22:38, Jesse Gross a écrit :
<snip>
>>> It would be nice to merge all of this together.  One complication is
>>> the interaction of bridging and vlan on the same device.  Some people
>>> want to have a bridge for each vlan and a bridge for untagged packets.
>>>   On older kernels with vlan accelerated hardware this was possible
>>> because vlan devices would get packets before bridging and on current
>>> kernels it is possible with ebtables rules.  If we use rx_handler for
>>> both I believe we would need to extend it some to allow multiple
>>> handlers.
>>
>> I totally agree.
>
> I do not. The reason I do vlan_untag early is so actually emulates
> hw acceleration. The reason is to make rx path of hwaccel an
> nonhwaccel similar. If you move vlan untag to rx_handler, this goal
> wouldn't be achieved.

Need to think more about that point.

>> Remember that Jiri's original proposal (last summer) was to have
>> several rx_handlers per net_device. I still think we need several of
>> them, because the network stack need to be generic and allow for any
>> complex stacking setup. The rx_handler framework may need to be
>> enhanced for that, but I think it is the right tool to do all those
>> per net_device specific features.
>>
>>>> This would also cause protocol handlers to receive the untouched (tagged)
>>>> frame, if no setup required the frame to be untagged, which I think is the
>>>> right thing to do.
>>>
>>> At the very least we need to make sure that these packets are marked
>>> as PACKET_OTHERHOST because protocol handlers don't pay attention to
>>> the vlan field.
>>
>> Agreed.
>>
>>>>> @@ -3177,7 +3183,7 @@ ncls:
>>>>>                        ret = deliver_skb(skb, pt_prev, orig_dev);
>>>>>                        pt_prev = NULL;
>>>>>                }
>>>>> -             if (vlan_hwaccel_do_receive(&skb)) {
>>>>> +             if (vlan_do_receive(&skb)) {
>>>>>                        ret = __netif_receive_skb(skb);
>>>>>                        goto out;
>>>>>                } else if (unlikely(!skb))
>>>>
>>>> Why are you calling __netif_receive_skb here? Can't we simply goto
>>>> another_round?
>>>
>>> This code (other than the name change) predates the
>>> another_round/rx_handler changes.
>>
>> Yes, you are right. Let's keep this for a possible follow-up patch,
>> to avoid skb reinjection when it is not strictly necessary.
>
> To do another round here was my attention do do in follow up patch (I'm
> still figuring out how to move this effectively into rx_handlers)

So you want to move vlan_do_receive into an rx_handler, but want untagging to stay hard-coded at the 
beginning of __netif_receive_skb. I don't think I understand the rational behind that.
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