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

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Date:	Fri, 27 Aug 2010 03:02:54 +0300
From:	"Yossi Etigin" <yosefe@...taire.com>
To:	"Jason Gunthorpe" <jgunthorpe@...idianresearch.com>,
	"Christoph Lameter" <cl@...ux.com>
Cc:	<rdreier@...co.com>, <linux-rdma@...r.kernel.org>,
	"Or Gerlitz" <ogerlitz@...taire.com>, <netdev@...r.kernel.org>
Subject: RE: [IPoIB] Identify multicast packets and fix IGMP breakage V3

> 
> 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.
> 

Shouldn't struct ib_grh be packed to make this really work?
The code looks a little messy to me anyway... 
How about using a local var which is a ptr to packed struct ib_grh? The
compiler will probably eliminate it anyway.

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