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

From: [email-masked] (Eric W. Biederman)
Date: Wed, 18 Nov 2009 06:37:50 -0800

Arnd Bergmann <[email-masked]> 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