netdev - Re: [PATCH v4 5/7] ipv6 addrconf: implement RFC7559 router solicitation backoff

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Message-ID: <cea2e6f6-98f3-50b4-a68e-7af6d9903d91@stressinduktion.org>
Date:   Tue, 27 Sep 2016 12:20:49 +0200
From:   Hannes Frederic Sowa <hannes@...essinduktion.org>
To:     Maciej Żenczykowski <maze@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Linux NetDev <netdev@...r.kernel.org>,
        Erik Kline <ek@...gle.com>,
        Lorenzo Colitti <lorenzo@...gle.com>, vpai@...mai.com
Subject: Re: [PATCH v4 5/7] ipv6 addrconf: implement RFC7559 router
 solicitation backoff

[cc Vishwanath Pai]

On 27.09.2016 11:42, Maciej Żenczykowski wrote:
>> Please just use do_div here and go back to the first version of the
>> patch. Variable names could be more aligned with the RFC maybe?
> 
> So I tried:
> 
> static inline s32 rfc3315_s14_backoff_init(s32 irt)
>  {
>        /* multiply 'initial retransmission time' by 0.9 .. 1.1 */
>        u64 tmp = (900000 + prandom_u32() % 200001) * (u64)irt;
>        do_div(tmp, 1000000);
>        return (s32)tmp;
>  }
> 
> static inline s32 rfc3315_s14_backoff_update(s32 rt, s32 mrt)
>  {
>        /* multiply 'retransmission timeout' by 1.9 .. 2.1 */
>        u64 tmp = (1900000 + prandom_u32() % 200001) * (u64)rt;
>        do_div(tmp, 1000000);
>        if ((s32)tmp > mrt) {
>                /* multiply 'maximum retransmission time' by 0.9 .. 1.1 */
>                tmp = (900000 + prandom_u32() % 200001) * (u64)mrt;
>                do_div(tmp, 1000000);
>         }
>        return (s32)tmp;
> }
> 
> but then building for i386 I get:
> 
> ERROR: "__udivdi3" [net/netfilter/xt_hashlimit.ko] undefined!

Hmm, evidently we have some u64 divisions in xt_hashlimit.c which should
be replaced by do_div?