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Subject: Re: [patch 13/17] Use WARN() in drivers/base/
From: Johannes Berg <johannes@sipsolutions.net>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Arjan van de Ven <arjan@infradead.org>, linux-kernel@vger.kernel.org,
       mingo@elte.hu
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Date: Sat, 12 Jul 2008 01:10:36 +0200
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> I don't suppose there's any way of tricking the preprocessor into
> supporting
>=20
> 	WARN_ON(foo =3D=3D 42);
>=20
> as well as
>=20
> 	WARN_ON(foo =3D=3D 42, "bite me!");

Here's one that abuses variadic macros and limits the number of
arguments to 19.

#include <stdarg.h>
#include <stdio.h>

#define cnt(y...)   _cnt( , ## y)
#define _cnt(y...) __cnt(y,19,18,17,16,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1,=
0)
#define __cnt(x0,x1,x2,x3,x4,x5,x6,x7,x8,x9,x10,x11,x12,x13,x14,x15,x16,x17=
,x18,x19,n,ys...) n

static void warn_on_slowpath(int argcount, ...)
{
        va_list args;
        char *fmt;

	// print beginning of warning

        if (argcount) {
	        va_start(args, count);
        	fmt =3D va_arg(args, char *);
	        vprintf(fmt, args);
	        va_end(args);
	}

	// print rest of warning
}

#define WARN_ON(test, fmt...)           	\
  do {                                  	\
      if (test) {                       	\
          warn_on_slowpath(cnt(fmt) , ## fmt);	\
          printf("WARN\n");             	\
      }                                 	\
  } while (0)

int main(void)
{
        WARN_ON(1);
        WARN_ON(1, "asdf %d\n", 7);

        return 0;
}


johannes

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