linux-kernel - Re: [PATCH 1/4] veth: move loopback logic to common location

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Message-ID: <4B0BB818.6090509@trash.net>
Date:	Tue, 24 Nov 2009 11:40:24 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Arnd Bergmann <arnd@...db.de>
CC:	virtualization@...ts.linux-foundation.org,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Anna Fischer <anna.fischer@...com>, netdev@...r.kernel.org,
	bridge@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Mark Smith <lk-netdev@...netdev.nosense.org>,
	Gerhard Stenzel <gerhard.stenzel@...ibm.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Jens Osterkamp <jens@...ux.vnet.ibm.com>,
	Patrick Mullaney <pmullaney@...ell.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Edge Virtual Bridging <evb@...oogroups.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH 1/4] veth: move loopback logic to common location

Arnd Bergmann wrote:
> On Tuesday 24 November 2009 10:17:11 Patrick McHardy wrote:
>> Arnd Bergmann wrote:
>>> On Tuesday 24 November 2009 09:51:19 Patrick McHardy wrote:
>>>>> +     skb_dst_drop(skb);
>>>>> +     skb->tstamp.tv64 = 0;
>>>>> +     skb->pkt_type = PACKET_HOST;
>>>>> +     skb->protocol = eth_type_trans(skb, dev);
>>>>> +     skb->mark = 0;
>>>> skb->mark clearing should stay private to veth since its usually
>>>> supposed to stay intact. The only exception is packets crossing
>>>> namespaces, where they should appear like a freshly received skbs.
>>> But isn't that what we want in macvlan as well when we're
>>> forwarding from one downstream interface to another?
>> In the TX direction you can use the mark for TC classification
>> on the underlying device.
> 
> I don't use dev_forward_skb for the case where the data is sent
> to the underlying device, so the TC classification should stay
> intact.

Right, I see. This looks fine.

>>> I did all my testing with macvlan interfaces in separate namespaces
>>> communicating with each other, so I'd assume that we should always
>>> clear skb->mark and skb->dst in this function.
>> Good point, in that case we probably should clear it as well. But
>> in the non-namespace case the TC classification currently works and
>> this is consistent with any other virtual device driver, so it
>> should continue to work.
> 
> Do you think we should be able to use TC to direct traffic between
> macvlans on the same underlying device in bridge mode? It does sound
> useful, but I'm not sure how to implement that or if you'd expect
> it to work with the current code. If we support that, it should probably
> also work with namespaces, by consuming the mark in the macvlan
> and veth drivers.

I don't think its necessary, we bypass outgoing queuing anyways.
But if you'd want to add it, just keeping the skb->mark clearing
in veth should work from what I can tell.
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