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

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Message-Id: <200911181047.07974.arnd@arndb.de>
Date:	Wed, 18 Nov 2009 10:47:07 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	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>,
	"Eric W. Biederman" <ebiederm@...ssion.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

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.

	Arnd <><
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