netdev - Re: [PATCH] ipv4: use IS_ENABLED instead of ifdef

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Date:   Tue, 17 Nov 2020 17:55:54 -0700
From:   David Ahern <dsahern@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>, Florian Klink <flokli@...kli.de>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Kim Phillips <kim.phillips@....com>
Subject: Re: [PATCH] ipv4: use IS_ENABLED instead of ifdef

On 11/17/20 5:01 PM, Jakub Kicinski wrote:
> On Sun, 15 Nov 2020 23:45:09 +0100 Florian Klink wrote:
>> Checking for ifdef CONFIG_x fails if CONFIG_x=m.
>>
>> Use IS_ENABLED instead, which is true for both built-ins and modules.
>>
>> Otherwise, a
>>> ip -4 route add 1.2.3.4/32 via inet6 fe80::2 dev eth1  
>> fails with the message "Error: IPv6 support not enabled in kernel." if
>> CONFIG_IPV6 is `m`.
>>
>> In the spirit of b8127113d01e53adba15b41aefd37b90ed83d631.
>>
>> Cc: Kim Phillips <kim.phillips@....com>
>> Signed-off-by: Florian Klink <flokli@...kli.de>
> 
> LGTM, this is the fixes tag right?
> 
> Fixes: d15662682db2 ("ipv4: Allow ipv6 gateway with ipv4 routes")

yep.

> 
> CCing David to give him a chance to ack.

Reviewed-by: David Ahern <dsahern@...nel.org>

I looked at this yesterday and got distracted diving into the generated
file to see the difference:

#define CONFIG_IPV6 1

vs

#define CONFIG_IPV6_MODULE 1