netdev - Re: [PATCH 1/3] macvlan: Reflect macvlan packets meant for other macvlan devices

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Date:	Wed, 18 Nov 2009 06:37:50 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
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 McHardy <kaber@...sh.net>,
	Patrick Mullaney <pmullaney@...ell.com>,
	Edge Virtual Bridging <evb@...oogroups.com>,
	Anna Fischer <anna.fischer@...com>,
	bridge@...ts.linux-foundation.org,
	virtualization@...ux-foundation.com,
	Jens Osterkamp <jens@...ux.vnet.ibm.com>,
	Gerhard Stenzel <gerhard.stenzel@...ibm.com>
Subject: Re: [PATCH 1/3] macvlan: Reflect macvlan packets meant for other macvlan devices

Arnd Bergmann <arnd@...db.de> writes:

> On Wednesday 18 November 2009, Eric Dumazet wrote:
>> > -     skb->dev = dev;
>> > -     skb->pkt_type = PACKET_HOST;
>> > +     skb->protocol = eth_type_trans(skb, dev);
>> > +     eth = eth_hdr(skb);
>> >  
>> > -     netif_rx(skb);
>> > -     return NULL;
>> > +     skb_dst_drop(skb);
>> 
>> Why do you drop dst here ?
>> 
>> It seems strange, since this driver specifically masks out IFF_XMIT_DST_RELEASE
>> in its macvlan_setup() :
>> 
>> dev->priv_flags &= ~IFF_XMIT_DST_RELEASE;
>> 
>> If we really want to drop dst, it could be done by caller, if IFF_XMIT_DST_RELEASE
>> was not masked in macvlan_setup().
>> 
>
> That must be my fault, it is the only change I did to Eric B's patch when
> forward-porting to 2.6.32. The original patch did
>
> 	skb->protocol = eth_type_trans(skb, dev);
> 	eth = eth_hdr(skb);
> 	dst_release(skb->dst);
> 	skb->dst = NULL;
> 	skb->mark = 0;
>
> and I tried to convert that in the same way that other drivers did, but I
> have to admit that I did not understand the mechanics of IFF_XMIT_DST_RELEASE.

Please copy and ideally share code with the veth driver for recycling a skb.
There are bunch of little things you have to do to get it right.  As I recally
I was missing a few details in my original patch.

Eric
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