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

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Date:   Mon, 26 Feb 2018 15:55:14 -0700
From:   David Ahern <dsahern@...il.com>
To:     Wei Wang <weiwan@...gle.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Ido Schimmel <idosch@...sch.org>, 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 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.

After my change 'from' will still point to the FIB entry as a fib6_info
which has its own expires.

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;
>>  }