netdev - RE: [PATCH net-2.6] bridge: fix br_multicast_ipv6

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Date:	Fri, 31 Dec 2010 23:16:29 +0200
From:	"Winkler, Tomas" <tomas.winkler@...el.com>
To:	David Miller <davem@...emloft.net>,
	"stephen.hemminger@...tta.com" <stephen.hemminger@...tta.com>
CC:	"shemminger@...tta.com" <shemminger@...tta.com>,
	"johannes@...solutions.net" <johannes@...solutions.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>
Subject: RE: [PATCH net-2.6] bridge: fix br_multicast_ipv6_rcv for paged skbs



> -----Original Message-----
> From: David Miller [mailto:davem@...emloft.net]
> Sent: Friday, December 31, 2010 10:46 PM
> To: stephen.hemminger@...tta.com
> Cc: Winkler, Tomas; shemminger@...tta.com; johannes@...solutions.net;
> netdev@...r.kernel.org; linux-wireless@...r.kernel.org
> Subject: Re: [PATCH net-2.6] bridge: fix br_multicast_ipv6_rcv for paged
> skbs
> 
> From: Stephen Hemminger <stephen.hemminger@...tta.com>
> Date: Thu, 30 Dec 2010 15:06:16 -0800
> 
> > Although copy is slower for large packets, this is a non performance
> > path. The code in question is for bridged multicast Ipv6 ICMP
> > packets. This case is so uncritical it could be done in BASIC and no
> > one could possibly care!
> 
> I still think we should be judicious and keep using skb_clone() here.
> 
> Simply combine the two pskb_may_pull() calls into one on "skb2" after
> the clone and before the blind __skb_pull() call.  Then add a error
> path "out:" called "out_nopush:" for the error path to goto.
> 
> Also, I think the "+ 1" in the ipv6 stack code comes from the fact that
> the parsing loop can "peek" into the next header's byte to see the type.
> And I really don't think it's relevant here.
> 
> Also, all of these "x_header + ... + 1 - skb->data" factors are
> irrelevent and shouldn't be used.  Just pass "offset + sizeof(*icmp6h)"
> to pskb_may_pull().

Sounds reasonable but maybe we shall pass offset + sizeof(struct mld_msg) as *icmp6h is casted to this struct mld_mca is accessed.

struct mld_msg {
        struct icmp6hdr         mld_hdr;
        struct in6_addr         mld_mca;
};

Thanks
Tomas


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