netdev - Re: [PATCH 17/29] l2tp: avoid precidence issues in L2TP_SKB

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Date:   Tue, 28 Jul 2020 09:21:07 -0700
From:   Joe Perches <joe@...ches.com>
To:     Tom Parkin <tparkin@...alix.com>, netdev@...r.kernel.org
Subject: Re: [PATCH 17/29] l2tp: avoid precidence issues in L2TP_SKB_CB macro

On Tue, 2020-07-21 at 18:32 +0100, Tom Parkin wrote:
> checkpatch warned about the L2TP_SKB_CB macro's use of its argument: add
> braces to avoid the problem.
[]
> diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
[]
> @@ -93,7 +93,7 @@ struct l2tp_skb_cb {
>  	unsigned long		expires;
>  };
>  
> -#define L2TP_SKB_CB(skb)	((struct l2tp_skb_cb *)&skb->cb[sizeof(struct inet_skb_parm)])
> +#define L2TP_SKB_CB(skb)	((struct l2tp_skb_cb *)&(skb)->cb[sizeof(struct inet_skb_parm)])

Likely better to use a static inline.

Something like:

static inline struct l2tp_skb_cb *L2TP_SKB_SB(struct sk_buff *skb)
{
	return &skb->cb[sizeof(struct inet+skb_parm)];
}