linux-kernel - Re: Question on FIELD

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Message-ID: <1539285754.4027.6.camel@sipsolutions.net>
Date:   Thu, 11 Oct 2018 21:22:34 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     John Garry <john.garry@...wei.com>, Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        jakub.kicinski@...ronome.com, yamada.masahiro@...ionext.com,
        Arnd Bergmann <arnd@...db.de>, viro@...iv.linux.org.uk,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     linux-wireless@...r.kernel.org, nbd@....name
Subject: Re: Question on FIELD_PREP() for static array

On Thu, 2018-10-11 at 21:13 +0200, Johannes Berg wrote:
> 
> However, I have another trick:
> 
> #define __NLA_ENSURE(condition) (0 * sizeof(struct { unsigned int x:1 - 2*!(condition);}))
> 
> or, in this context,
> 
> #define BUILD_BUG_ON_RET_ZERO(cond) (0 * sizeof(struct { unsigned int x:1 - 2*!(condition);}))

Oops, I forgot to insert the second !, it must be

#define BUILD_BUG_ON_RET_ZERO(cond) (0 * sizeof(struct { unsigned int x:1 - 2*!!(condition);}))

johannes