netdev - Re: [PATCH] netfilter: turn NF_HOOK into an inline function

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Date:	Fri, 09 Oct 2015 13:28:23 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Pablo Neira Ayuso <pablo@...filter.org>,
	Patrick McHardy <kaber@...sh.net>,
	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	linux-kernel@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] netfilter: turn NF_HOOK into an inline function

Arnd Bergmann <arnd@...db.de> writes:

> A recent change to the dst_output handling caused a new warning
> when the call to NF_HOOK() is the only used of a local variable
> passed as 'dev', and CONFIG_NETFILTER is disabled:
>
> net/ipv6/ip6_output.c: In function 'ip6_output':
> net/ipv6/ip6_output.c:135:21: warning: unused variable 'dev' [-Wunused-variable]
>
> The reason for this is that the NF_HOOK macro in this case does
> not reference the variable at all. To avoid that warning now
> and in the future, this changes the macro into an equivalent
> inline function, which tells the compiler that the variable is
> passed correctly but still unused.

For clarification the actual change that trigger this is I passed in net
instead of computing net as net = dev_net(dev).  Which was the second
use of the dev variable.

> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Fixes: ede2059dbaf9 ("dst: Pass net into dst->output")
>
> diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
> index edb3dc32f1da..1ff5c3f82820 100644
> --- a/include/linux/netfilter.h
> +++ b/include/linux/netfilter.h
> @@ -347,8 +347,23 @@ nf_nat_decode_session(struct sk_buff *skb, struct flowi *fl, u_int8_t family)
>  }
>  
>  #else /* !CONFIG_NETFILTER */
> -#define NF_HOOK(pf, hook, net, sk, skb, indev, outdev, okfn) (okfn)(net, sk, skb)
> -#define NF_HOOK_COND(pf, hook, net, sk, skb, indev, outdev, okfn, cond) (okfn)(net, sk, skb)
> +static inline int
> +NF_HOOK_COND(uint8_t pf, unsigned int hook, struct net *net, struct sock *sk,
> +	     struct sk_buff *skb, struct net_device *in, struct net_device *out,
> +	     int (*okfn)(struct net *, struct sock *, struct sk_buff *),
> +	     bool cond)
> +{
> +	return okfn(net, sk, skb);
> +}
> +
> +static inline int
> +NF_HOOK(uint8_t pf, unsigned int hook, struct net *net, struct sock *sk, struct sk_buff *skb,
> +	struct net_device *in, struct net_device *out,
> +	int (*okfn)(struct net *, struct sock *, struct sk_buff *))
> +{
> +	return okfn(net, sk, skb);
> +}
> +
>  static inline int nf_hook(u_int8_t pf, unsigned int hook, struct net *net,
>  			  struct sock *sk, struct sk_buff *skb,
>  			  struct net_device *indev, struct net_device *outdev,
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