netdev - Re: [PATCH net-next] ipv4: use IS_ENABLED() macro to cleanup code

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Message-Id: <20111025.193037.1312584002692004360.davem@davemloft.net>
Date:	Tue, 25 Oct 2011 19:30:37 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] ipv4: use IS_ENABLED() macro to cleanup code

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 25 Oct 2011 09:12:32 +0200

> Remove some ugly #ifdef, using IS_ENABLED(CONFIG_xxx) macro
> 
> IS_ENABLED(CONFIG_xxx) evaluates to 1 if CONFIG_xxx is set to 'y' or 'm'
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>

I can understand the desire to do this, but it is going to run
afoul in cases where the definitions of datastructures in header
files are protected by real CPP ifdef guards rather than these
run-time variants.

So you build tested this with IPV6 disabled, right?

Didn't think so...

net/ipv4/ip_sockglue.c: In function ‘do_ip_setsockopt’:
net/ipv4/ip_sockglue.c:523:29: error: ‘LOOPBACK4_IPV6’ undeclared (first use in this function)
net/ipv4/ip_sockglue.c:523:29: note: each undeclared identifier is reported only once for each function it appears in

This fails because ip_sockglue.c guards the net/transp_v6.h header
inclusion with a real CPP guard.