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

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Message-ID: <4B0BB2A7.5040707@trash.net>
Date:	Tue, 24 Nov 2009 11:17:11 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	Stephen Hemminger <shemminger@...tta.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Patrick Mullaney <pmullaney@...ell.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Edge Virtual Bridging <evb@...oogroups.com>,
	Anna Fischer <anna.fischer@...com>,
	bridge@...ts.linux-foundation.org,
	virtualization@...ts.linux-foundation.org,
	Jens Osterkamp <jens@...ux.vnet.ibm.com>,
	Gerhard Stenzel <gerhard.stenzel@...ibm.com>,
	Mark Smith <lk-netdev@...netdev.nosense.org>
Subject: Re: [PATCH 1/4] veth: move loopback logic to common location

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 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.
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