netdev - Re: [PATCH RFC net-next 10/20] net/ipv6: move expires into rt6

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Date:   Mon, 26 Feb 2018 16:31:21 -0800
From:   Wei Wang <weiwan@...gle.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Ido Schimmel <idosch@...sch.org>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
Subject: Re: [PATCH RFC net-next 10/20] net/ipv6: move expires into rt6_info

On Mon, Feb 26, 2018 at 2:55 PM, David Ahern <dsahern@...il.com> wrote:
> On 2/26/18 3:28 PM, Wei Wang wrote:
>>> @@ -213,11 +234,6 @@ static inline void rt6_set_expires(struct rt6_info *rt, unsigned long expires)
>>>
>>>  static inline void rt6_update_expires(struct rt6_info *rt0, int timeout)
>>>  {
>>> -       struct rt6_info *rt;
>>> -
>>> -       for (rt = rt0; rt && !(rt->rt6i_flags & RTF_EXPIRES); rt = rt->from);
>>> -       if (rt && rt != rt0)
>>> -               rt0->dst.expires = rt->dst.expires;
>>
>> I was wondering if we need to retain the above logic. It makes sure
>> dst.expires gets synced to its "parent" route. But  it might be hard
>> because after your change, we can no longer use rt->from to refer to
>> the "parent".
>
> As I understand it, the FIB entries are cloned into pcpu, uncached and
> exception routes. We should never have an rt6_info that ever points back
> more than 1 level -- ie., the dst rt6_info points to a from representing
> the original FIB entry.
>
Yes. Agree.

> After my change 'from' will still point to the FIB entry as a fib6_info
> which has its own expires.
>
understood. And fib6_age() is using fib6_check_expired() and
rt6_age_exceptions() is checking rt->dst.expires which I think is
correct.

> When I looked this code I was really confused. At best, the for loop
> above sets rt0->dst.expires to some value based on the 'from' but then
> the very next line calls dst_set_expires with the passed in timeout value.
>
>
>>
>>>         dst_set_expires(&rt0->dst, timeout);
>>>         rt0->rt6i_flags |= RTF_EXPIRES;
>>>  }
>