netdev - Re: [PATCH net] ipv6: use rt6_info members when dst is set in rt6_fill

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Date:   Mon, 10 Sep 2018 10:13:01 -0600
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, davem <davem@...emloft.net>,
        Roopa Prabhu <roopa@...ulusnetworks.com>
Subject: Re: [PATCH net] ipv6: use rt6_info members when dst is set in
 rt6_fill_node

On 9/9/18 12:29 AM, Xin Long wrote:
>>> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
>>> index 18e00ce..e554922 100644
>>> --- a/net/ipv6/route.c
>>> +++ b/net/ipv6/route.c
>>> @@ -4670,20 +4670,33 @@ static int rt6_fill_node(struct net *net, struct sk_buff *skb,
>>>                        int iif, int type, u32 portid, u32 seq,
>>>                        unsigned int flags)
>>>  {
>>> -     struct rtmsg *rtm;
>>> +     struct rt6key *fib6_prefsrc, *fib6_dst, *fib6_src;
>>> +     struct rt6_info *rt6 = (struct rt6_info *)dst;
>>> +     u32 *pmetrics, table, fib6_flags;
>>>       struct nlmsghdr *nlh;
>>> +     struct rtmsg *rtm;
>>>       long expires = 0;
>>> -     u32 *pmetrics;
>>> -     u32 table;
>>>
>>>       nlh = nlmsg_put(skb, portid, seq, type, sizeof(*rtm), flags);
>>>       if (!nlh)
>>>               return -EMSGSIZE;
>>>
>>> +     if (rt6) {
>>> +             fib6_dst = &rt6->rt6i_dst;
>>> +             fib6_src = &rt6->rt6i_src;
>>> +             fib6_flags = rt6->rt6i_flags;
>>> +             fib6_prefsrc = &rt6->rt6i_prefsrc;
>>> +     } else {
>>> +             fib6_dst = &rt->fib6_dst;
>>> +             fib6_src = &rt->fib6_src;
>>> +             fib6_flags = rt->fib6_flags;
>>> +             fib6_prefsrc = &rt->fib6_prefsrc;
>>> +     }
>>
>> Unless I am missing something at the moment, an rt6_info can only have
>> the same dst, src and prefsrc as the fib6_info on which it is based.
>> Thus, only the flags is needed above. That simplifies this patch a lot.
> If dst, src and prefsrc in rt6_info are always the same as these in fib6_info,
> why do we need them in rt6_info? we could just get it by 'from'.
> 

I just sent a patch removing rt6i_prefsrc. It is set with only 1 reader
that can be converted.

rt6i_src is checked against the fib6_info to invalidate a dst if the src
has changed, so a valid rt will always have the same rt6i_src as the
rt->from.

rt6i_dst is set to the dest address / 128 in cases, so it should be used
for rt6_info cases above.