netdev - Re: [PATCH net-next v3 1/2] ipv6: introduce and uses route look hints for list input

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Date:   Tue, 19 Nov 2019 09:21:07 -0700
From:   David Ahern <dsahern@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Edward Cree <ecree@...arflare.com>
Subject: Re: [PATCH net-next v3 1/2] ipv6: introduce and uses route look hints
 for list input

On 11/19/19 9:00 AM, Paolo Abeni wrote:
> Hi,
> 
> On Tue, 2019-11-19 at 08:39 -0700, David Ahern wrote:
>> +static struct sk_buff *ip6_extract_route_hint(struct net *net,
>>> +					      struct sk_buff *skb)
>>> +{
>>> +	if (IS_ENABLED(IPV6_SUBTREES) || fib6_has_custom_rules(net))
>>
>> ... but basing on SUBTREES being disabled is going to limit its use. If
>> no routes are source based (fib6_src is not set), you should be able to
>> re-use the hint with SUBTREES enabled. e.g., track fib6_src use with a
>> per-namespace counter - similar to fib6_rules_require_fldissect.
> 
> Thank you for the feedback! Would you consider this as an intermediate
> step? e.g. get these patches in, and then I'll implement subtree
> support? 
> I'm asking because I don't have subtree setup handy, it will a little
> time to get there.
> 


IPV6_SUBTREES is just a matter of source based routing, so with iproute2
just add 'from <addr>'

If you delay dealing with it, then this patch needs a change: since
ip6_extract_route_hint will only return NULL, ip6_can_use_hint will only
take NULL as an input so leaving it enabled just adds overhead with no
benefit.