Re: expected behavior of PF_PACKET on NETIF_F_HW_VLAN_RX device?

[Stephen Hemminger <shemminger@linux-foundation.org>]

Ben Greear wrote:
> Stephen Hemminger wrote:
> > On Wed, 31 Oct 2007 14:43:51 -0400
> > Dave Johnson <djohnson+linux-kernel@sw.starentnetworks.com> wrote:
> >
> >  
> > > Depending on the network driver, I'm seeing different behavior if
> > > a .1q packet is received to an PF_PACKET, SOCK_RAW, ETH_P_ALL socket.
> > >
> > >
> > > On devices what do not use NETIF_F_HW_VLAN_RX, the packet socket gets
> > > the complete packet with vlan tag included as the driver simply calls
> > > netif_receive_skb() or equivilant.  packet_rcv() then gets the whole
> > > thing vlan tag included and sends this through the socket.
> > >
> > > vlan_skb_recv() also gets these all and will drop them because there
> > > are no vlans configured.
> > >
> > >     
> >
> > The VLAN acceleration grabs and hides the tag. It is a design flaw
> > that should be fixed, feel free to post a patch.
> >   
> There may be several ways to 'fix' this.  Perhaps it would be worth 
> discussing what
> we want the end result to be at least?
>
> Should we always pass the vlan header up to raw sockets as part of the
> data payload?
>
> Or, maybe pass it in an auxiliary message such as how timestamps may 
> be passed?
>
> The first option seems cleaner, but maybe there are performance 
> problems with this
> approach?
>
> We should also define what a NIC should do with VLANs it doesn't 
> explicitly know
> about.   I think it should pass them up the stack with VLAN tag 
> intact, but again, perhaps
> there are reasons not to do that?
>
> DaveM did the HW Accel for VLANs if I remember correctly...perhaps he 
> has some input?

The code in AF_PACKET should fix the skb before passing to user space so 
that there is
no difference between accel and non-accel hardware.  Internal choices 
shouldn't
leak to user space.  Ditto, the receive checksum offload should be fixed 
up as well.

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