netdev - Re: [PATCH net-next 3/7] ipv6: improve ipv6_find

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Date:	Tue, 4 Dec 2012 10:15:11 -0800
From:	Jesse Gross <jesse@...ira.com>
To:	Pablo Neira Ayuso <pablo@...filter.org>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	dev@...nvswitch.org, Ansis Atteka <aatteka@...ira.com>
Subject: Re: [PATCH net-next 3/7] ipv6: improve ipv6_find_hdr() to skip empty
 routing headers

On Mon, Dec 3, 2012 at 10:06 AM, Pablo Neira Ayuso <pablo@...filter.org> wrote:
> On Mon, Dec 03, 2012 at 09:28:55AM -0800, Jesse Gross wrote:
>> On Mon, Dec 3, 2012 at 6:04 AM, Pablo Neira Ayuso <pablo@...filter.org> wrote:
>> > On Thu, Nov 29, 2012 at 10:35:45AM -0800, Jesse Gross wrote:
>> >> @@ -159,9 +162,10 @@ int ipv6_find_hdr(const struct sk_buff *skb, unsigned int *offset,
>> >>       }
>> >>       len = skb->len - start;
>> >>
>> >> -     while (nexthdr != target) {
>> >
>> > If the offset is set as parameter via ipv6_find_hdr, we now are always
>> > entering the loop even if we found the target header we're looking
>> > for, before that didn't happen.
>> >
>> > Something seems wrong here to me.
>>
>> If the target header is a routing header then you might still need to
>> continue searching because the first one that you see could be empty.
>
> OK, but if it's not a routing header what we're searching for (which
> seems to be the case of netfilter/IPVS) we waste way more cycles on
> copying the IPv6 header again and with way more things that are
> completely useless.

We could add a check to short circuit this but it seems like a
premature optimization to me.

Ansis, can you comment?
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