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

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Message-ID: <20180228192122.liokziwr7xqwddkh@kafai-mbp.dhcp.thefacebook.com>
Date:   Wed, 28 Feb 2018 11:21:22 -0800
From:   Martin KaFai Lau <kafai@...com>
To:     David Ahern <dsahern@...il.com>
CC:     Wei Wang <weiwan@...gle.com>,
        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>,
        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 03:55:14PM -0700, David Ahern 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.
Agree on at most 1 level.

> 
> 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.
My understanding is, the rt0 first inherits the expires from its rt0->from.

The following dst_set_expires() set a new timeout if the new timeout
is earlier than the existing expires.  I think it is essentially
taking a min.

One question, would avoid taking the min cause the rt0 somehow
have a longer expires than its parent (or f6i after this series)?

> 
> 
> > 
> >>         dst_set_expires(&rt0->dst, timeout);
> >>         rt0->rt6i_flags |= RTF_EXPIRES;
> >>  }
>