netdev - Re: [RFC PATCH] fix IP_ECN_set

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Date:	Wed, 19 Dec 2012 17:11:59 +0800
From:	RongQing Li <roy.qing.li@...il.com>
To:	Julian Anastasov <ja@....bg>
Cc:	netdev@...r.kernel.org
Subject: Re: [RFC PATCH] fix IP_ECN_set_ce

2012/12/19 Julian Anastasov <ja@....bg>:
>
>         Hello,
>
> On Wed, 19 Dec 2012, RongQing Li wrote:
>
>> >>  static inline int IP_ECN_set_ce(struct iphdr *iph)
>> >>  {
>> >> -     u32 check = (__force u32)iph->check;
>> >> -     u32 ecn = (iph->tos + 1) & INET_ECN_MASK;
>> >> -
>> >> -     /*
>> >> -      * After the last operation we have (in binary):
>> >> -      * INET_ECN_NOT_ECT => 01
>> >> -      * INET_ECN_ECT_1   => 10
>> >> -      * INET_ECN_ECT_0   => 11
>> >> -      * INET_ECN_CE      => 00
>> >> -      */
>> >
>> >         I think, the above comment explains how an
>> > increment (iph->tos + 1) serves the purpose to check
>> > for ECT_1 and ECT_0, there is no such thing as
>> > addressing the next byte from header. It is just an
>> > optimized logic that avoids complex INET_ECN_is_XXX
>> > checks.
>> Thanks for your reply.
>> Do you mean this comment are valuable?
>
>         It looks better to me with the comment and the
> original checks. But I can't comment the correctness of
> the other changes in your patch.

I do not know how they are useful, and how the original check
works, since the value in comments are wrong, the correct is:

enum {
        INET_ECN_NOT_ECT = 0,
        INET_ECN_ECT_1 = 1,
        INET_ECN_ECT_0 = 2,
        INET_ECN_CE = 3,
        INET_ECN_MASK = 3,
};


   00: Non ECN-Capable Transport — Non-ECT
    10: ECN Capable Transport — ECT(0)
    01: ECN Capable Transport — ECT(1)
    11: Congestion Encountered — CE

-Roy


>
>> >> -     if (!(ecn & 2))
>> >> +     u32 ecn = iph->tos & INET_ECN_MASK;
>> >> +
>> >> +     if (INET_ECN_is_ce(ecn) || INET_ECN_is_not_ect(ecn))
>> >>               return !ecn;
>> >
>> >         May be return INET_ECN_is_ce(ecn) ?
>> >
>>
>> I like to set the return value to void, since noone cares about the
>> return value.
>
>         It is used by INET_ECN_set_ce and its users in
> net/sched/
>
>> -Roy
>
> Regards
>
> --
> Julian Anastasov <ja@....bg>
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