netdev - Re: [PATCH net 1/2] ipv6: add ipv6_dev

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Date:   Thu, 6 Aug 2020 08:03:20 -0600
From:   David Ahern <dsahern@...il.com>
To:     Xin Long <lucien.xin@...il.com>,
        Hideaki Yoshifuji <hideaki.yoshifuji@...aclelinux.com>
Cc:     network dev <netdev@...r.kernel.org>, davem <davem@...emloft.net>,
        Jon Maloy <jon.maloy@...csson.com>,
        Ying Xue <ying.xue@...driver.com>,
        tipc-discussion@...ts.sourceforge.net,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
Subject: Re: [PATCH net 1/2] ipv6: add ipv6_dev_find()

On 8/6/20 2:55 AM, Xin Long wrote:
> On Thu, Aug 6, 2020 at 10:50 AM Hideaki Yoshifuji
> <hideaki.yoshifuji@...aclelinux.com> wrote:
>>
>> Hi,
>>
>> 2020年8月4日(火) 0:35 Xin Long <lucien.xin@...il.com>:
>>>
>>> This is to add an ip_dev_find like function for ipv6, used to find
>>> the dev by saddr.
>>>
>>> It will be used by TIPC protocol. So also export it.
>>>
>>> Signed-off-by: Xin Long <lucien.xin@...il.com>
>>> ---
>>>  include/net/addrconf.h |  2 ++
>>>  net/ipv6/addrconf.c    | 39 +++++++++++++++++++++++++++++++++++++++
>>>  2 files changed, 41 insertions(+)
>>>
>>> diff --git a/include/net/addrconf.h b/include/net/addrconf.h
>>> index 8418b7d..ba3f6c15 100644
>>> --- a/include/net/addrconf.h
>>> +++ b/include/net/addrconf.h
>>> @@ -97,6 +97,8 @@ bool ipv6_chk_custom_prefix(const struct in6_addr *addr,
>>>
>>>  int ipv6_chk_prefix(const struct in6_addr *addr, struct net_device *dev);
>>>
>>> +struct net_device *ipv6_dev_find(struct net *net, const struct in6_addr *addr);
>>> +
>>
>> How do we handle link-local addresses?
> This is what "if (!result)" branch meant to do:
> 
> +       if (!result) {
> +               struct rt6_info *rt;
> +
> +               rt = rt6_lookup(net, addr, NULL, 0, NULL, 0);
> +               if (rt) {
> +                       dev = rt->dst.dev;
> +                       ip6_rt_put(rt);
> +               }
> +       } else {
> +               dev = result->idev->dev;
> +       }
> 

the stated purpose of this function is to find the netdevice to which an
address is attached. A route lookup should not be needed. Walking the
address hash list finds the address and hence the netdev or it does not.