netdev - Re: [IPoIB] Identify multicast packets and fix IGMP breakage V3

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Date:	Thu, 26 Aug 2010 17:43:42 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	rdreier@...co.com, linux-rdma@...r.kernel.org,
	ogerlitz@...taire.com, yosefe@...taire.com, netdev@...r.kernel.org
Subject: Re: [IPoIB] Identify multicast packets and fix IGMP breakage V3

On Thu, Aug 26, 2010 at 06:26:58PM -0500, Christoph Lameter wrote:
> On Thu, 26 Aug 2010, Jason Gunthorpe wrote:
>
> > The 40 bytes at this location are defined by the HW specification to
> > be an IB GRH which has an identical layout to an IPv6 header. Roland
> > is right, it would be clearer to use ib_grh ->dgid
>
> Ok but then we have no nice function that checks for multicast anymore.

Were you going to try it this way?

     /* First byte of dgid signals multicast/broadcast when 0xff */
     if ((wc->wc_flags & IB_WC_GRH) &&
         ((struct ib_grh *)skb->data)->dgid.raw[0] == 0xff) {
	     if (memcmp(((struct ib_grh *)skb->data)->dgid.raw,
                        dev->broadcast + 4, sizeof(union ib_gid)) == 0)
                     skb->pkt_type = PACKET_BROADCAST;
             else
                     skb->pkt_type = PACKET_MULTICAST;
     }
     else
             skb->pkt_type = PACKET_HOST;

I think doing the memcmp only in the multicast path should be
reasonable overhead wise.

Jason
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