Re: [dpdk-dev] [PATCH] ethdev: warn only once for badly behaving applications

[David Marchand <david.marchand@redhat.com>]

On Wed, Oct 27, 2021 at 10:16 AM Olivier Matz <olivier.matz@6wind.com> wrote:
> > Do you have the explanation or can you point me at some standard
> > explaining the difference in treatment?
>
> Let me try an explanation, hope it is the correct one.
>
> In the first case, this is an assignment as described in 6.5.16 of
> the standard [1]:
>
>   *fpo = (struct rte_eth_fp_ops) { .rx_pkt_burst = dummy_eth_rx_burst, ... };
>
> The compiler expects the right side to be an expression. The expression
> is a "compound literal", as described in 6.5.2.5:
>
>  1. The type name shall specify a complete object type or an array of
>     unknown size, but not avariable length array type.
>  2. All the constraints for initializer lists in 6.7.9 also apply to
>     compound literals
>
> The second cast { ..., .rxq = (struct rte_ethdev_qdata) { ... } } is
> inside a construction that behaves like an initialization (according to
> the second point above). The compiler already knows the type of the
> struct (and therefore the types of the fields), so the cast is not
> required.
>
> [1] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1548.pdf

I read/understand it like this too.
Thanks a lot, reading standards is always illuminating.


-- 
David Marchand