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

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Date:	Thu, 26 Aug 2010 18:26:58 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
cc:	David Miller <davem@...emloft.net>, 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, 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.



Subject: [IPoIB] Identify multicast packets and fix IGMP breakage V3

IGMP processing is broken because the IPOIB does not set the
skb->pkt_type the right way for Multicast traffic. All incoming
packets are set to PACKET_HOST which means that the igmp_recv()
function will ignore the IGMP broadcasts/multicasts.

This in turn means that the IGMP timers are firing and are sending
information about multicast subscriptions unnecessarily. In a large
private network this can cause traffic spikes.

Signed-off-by: Christoph Lameter <cl@...ux.com>

---

Index: linux-2.6/drivers/infiniband/ulp/ipoib/ipoib_ib.c
===================================================================
--- linux-2.6.orig/drivers/infiniband/ulp/ipoib/ipoib_ib.c	2010-08-26 18:24:07.842079559 -0500
+++ linux-2.6/drivers/infiniband/ulp/ipoib/ipoib_ib.c	2010-08-26 18:25:33.859815544 -0500
@@ -271,6 +271,14 @@
 	ipoib_ud_dma_unmap_rx(priv, mapping);
 	ipoib_ud_skb_put_frags(priv, skb, wc->byte_len);

+	/* First byte of dgid signals multicast when 0xff */
+	if ((wc->wc_flags & IB_WC_GRH) &&
+		((struct ib_grh *)skb->data)->dgid.raw[0] == 0xff)
+
+		skb->pkt_type = PACKET_MULTICAST;
+	else
+		skb->pkt_type = PACKET_HOST;
+
 	skb_pull(skb, IB_GRH_BYTES);

 	skb->protocol = ((struct ipoib_header *) skb->data)->proto;
@@ -281,9 +289,6 @@
 	dev->stats.rx_bytes += skb->len;

 	skb->dev = dev;
-	/* XXX get correct PACKET_ type here */
-	skb->pkt_type = PACKET_HOST;
-
 	if (test_bit(IPOIB_FLAG_CSUM, &priv->flags) && likely(wc->csum_ok))
 		skb->ip_summed = CHECKSUM_UNNECESSARY;

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