netdev - Re: [PATCH net-next-2.6] bonding: allow arp_ip_targets to be on a separate vlan from bond device

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Date:	Mon, 30 Nov 2009 15:53:34 -0500
From:	Andy Gospodarek <andy@...yhouse.net>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Andy Gospodarek <andy@...yhouse.net>, netdev@...r.kernel.org,
	fubar@...ibm.com
Subject: Re: [PATCH net-next-2.6] bonding: allow arp_ip_targets to be on a
	separate vlan from bond device

On Mon, Nov 30, 2009 at 09:22:33PM +0100, Patrick McHardy wrote:
> Andy Gospodarek wrote:
> > diff --git a/net/8021q/vlan_core.c b/net/8021q/vlan_core.c
> > index e75a2f3..8d8a778 100644
> > --- a/net/8021q/vlan_core.c
> > +++ b/net/8021q/vlan_core.c
> > @@ -14,6 +14,7 @@ int __vlan_hwaccel_rx(struct sk_buff *skb, struct vlan_group *grp,
> >  	if (skb_bond_should_drop(skb))
> >  		goto drop;
> >  
> > +	skb->skb_iif = skb->dev->ifindex;
> >  	__vlan_hwaccel_put_tag(skb, vlan_tci);
> >  	skb->dev = vlan_group_get_device(grp, vlan_tci & VLAN_VID_MASK);
> >  
> > @@ -85,6 +86,7 @@ vlan_gro_common(struct napi_struct *napi, struct vlan_group *grp,
> >  	if (skb_bond_should_drop(skb))
> >  		goto drop;
> >  
> > +	skb->skb_iif = skb->dev->ifindex;
> >  	__vlan_hwaccel_put_tag(skb, vlan_tci);
> >  	skb->dev = vlan_group_get_device(grp, vlan_tci & VLAN_VID_MASK);
> >  
> 
> How about pulling the skb->iif assignment in netif_receive_skb() up
> before the vlan_hwaccel_do_receive() call instead?

I'm not sure how that will help.  My goal with the two changes in
vlan_core.c was to capture the input device index before we lost it --
which is precisely what happens when coming up through a driver like
bnx2 that supports vlan acceleration:

(NAPI poll)
bnx2_poll
  bnx2_poll_work
    bnx2_rx_int
      vlan_hwaccel_receive_skb
        __vlan_hwaccel_rx
          (skb->dev set to vlan device)
          netif_receive_skb

In that case, setting skb_iif in netif_receive_skb would be too late.
The original dev would no longer be known.

> I'd actually call
> this a bug fix since hardware accelerated devices should not differ
> from non-accelerated devices in their iif value.

This dances the line between bugfix and feature since the arp monitoring
component was never really advertised as working, but you are correct
that it could be a bug since skb_iif should be consistent depending the
the devices capabilities.
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