[dpdk-dev] [PATCH] lpm6: make IPv6 addresses immutable
Stephen Hemminger
stephen at networkplumber.org
Mon Mar 9 20:13:44 CET 2020
On Mon, 9 Mar 2020 18:02:21 +0000
"Medvedkin, Vladimir" <vladimir.medvedkin at intel.com> wrote:
> On 09/03/2020 15:52, Stephen Hemminger wrote:
> > On Mon, 9 Mar 2020 13:38:53 +0000
> > "Medvedkin, Vladimir" <vladimir.medvedkin at 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 *).
>
Agree, just drop it from the bulk functions.
The array of array semantics is confusing compiler (and users).
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