netdev - Re: [PATCH v2 net-next 1/5] net_sched: constify qdisc

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Date: Wed, 20 Sep 2023 16:45:19 -0400
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Willem de Bruijn <willemb@...gle.com>, 
	Soheil Hassas Yeganeh <soheil@...gle.com>, Neal Cardwell <ncardwell@...gle.com>, 
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com
Subject: Re: [PATCH v2 net-next 1/5] net_sched: constify qdisc_priv()

On Wed, Sep 20, 2023 at 4:17 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> In order to propagate const qualifiers, we change qdisc_priv()
> to accept a possibly const argument.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
>  include/net/pkt_sched.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
> index 15960564e0c364ef430f1e3fcdd0e835c2f94a77..9fa1d0794dfa5241705f9a39c896ed44519a9f13 100644
> --- a/include/net/pkt_sched.h
> +++ b/include/net/pkt_sched.h
> @@ -20,10 +20,10 @@ struct qdisc_walker {
>         int     (*fn)(struct Qdisc *, unsigned long cl, struct qdisc_walker *);
>  };
>
> -static inline void *qdisc_priv(struct Qdisc *q)
> -{
> -       return &q->privdata;
> -}
> +#define qdisc_priv(q)                                                  \
> +       _Generic(q,                                                     \
> +                const struct Qdisc * : (const void *)&q->privdata,     \
> +                struct Qdisc * : (void *)&q->privdata)

Didnt know you could do this - C11? Would old compilers work here or
do we have some standardization version around compiler versions?

cheers,
jamal