Re: [dpdk-dev] [PATCH] lpm6: make IPv6 addresses immutable

["Medvedkin, Vladimir" <vladimir.medvedkin@intel.com>]

On 09/03/2020 15:52, Stephen Hemminger wrote:
> On Mon, 9 Mar 2020 13:38:53 +0000
> "Medvedkin, Vladimir" <vladimir.medvedkin@intel.com> wrote:
>
>> Hi Andrze,
>>
>> Adding const qualifier for bulk lookup leads to compilation problems
>> (see http://c-faq.com/ansi/constmismatch.html)
>> Also I don't think it would be good for usability to make users
>> explicitly cast to (const uint8_t **) when passing 'ips' argument. I'd
>> suggest leaving lookup_bulk as is.
>
> Please give a more concrete example. There is no need for explicit cast
> in current C.

Hi Stephen,

In theory, i agree - all modern versions of GCC don't give warnings for 
this code. The problem is, we don't only support modern versions of GCC. 
For a "more concrete example", see the following error in gcc-4.8 on 
CentOS 7:

http://mails.dpdk.org/archives/test-report/2020-March/119455.html

I have reproduced this on my non-CentOS machine with gcc4.8, so it 
appears to be gcc4.8 specific rather than CentOS-specific. That said, 
the same email contains a compile check from RHEL7 with the same 
compiler version, and it didn't trigger the warning, and also it seems 
to be that only meson build has triggered the warning (while i have 
reproduced it with make on my machine).

So, i think it is best to leave lookup_bulk as is, and add const 
qualifiers in other places (for const uint8_t *).

-- 
Regards,
Vladimir