Re: [PATCH 6/6] netfilter: xtables: add const qualifiers

[Alexey Dobriyan <adobriyan@gmail.com>]

On Thu, Feb 11, 2010 at 11:27 AM, Patrick McHardy <kaber@trash.net> wrote:
> Alexey Dobriyan wrote:
>>> -static inline int ebt_basic_match(struct ebt_entry *e, struct ethhdr *h,
>>> -   const struct net_device *in, const struct net_device *out)
>>> +static inline int
>>> +ebt_basic_match(const struct ebt_entry *e, const struct ethhdr *h,
>>> +                const struct net_device *in, const struct net_device *out)
>>
>> These const modifiers are pointless because compilers are smart enough
>> to notice non-modifiability and generate the very same code in both cases.
>>
>> Nowadays, half of functions declarations in generic
>> xtables/iptables/ip6tables/arptables
>> code are littered with const which makes them pretty unpleasant to read.
>
> Well, the benefit is that the compiler can catch accidental modification
> of data that is supposed to be constant.

Did it ever? Realistically?

From what I see, const is used with string functions
(to make string literals go to rodata) and with structures full of hooks
(to make them go to rodata).

>>> -    struct ebt_entry *e = (struct ebt_entry *)chain->data;
>>> +    const struct ebt_entry *e = (struct ebt_entry *)chain->data;
>>
>> And such things are wrong (not second const).
>
> What's wrong about this?

Should it be (const struct ebt_entry *)?
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