wrapping a vararg C function (specifically, log() in the kernel)

[Ian Lepore]

On Thu, 2014-12-18 at 15:21 +0100, Luigi Rizzo wrote:
> Hi,
> in the porting of some kernel code to FreeBSD, i need to remap one
> function with a variable number of arguments to the log() function
> from the freebsd kernel.
> 
> Normally i would do
> 
> 	#define WARN(x, args...)	log(LOG_WARNING, args)
> 
> but this does not work in my case because the function is called in
> (many) blocks where there is already a local variable with the same name
> 
> 	bool log;
> 
> which is used a ton of times.
> 
> I was wondering if there is some C compiler magic i can use to do the
> remapping without going through a macro; I haven't found any direct one,
> though perhaps something like
> 
> 	extern void (*freebsd_log)(int level, const char *fmt, ...);
> 
> 	#define WARN(x, args...)    freebsd_log(LOG_WARNING, args)
> 
> followed somewhere in a safe place by
> 
> 		freebsd_log = log;
> 
> may do the job.
> 
> Any other option ?
> 
> 	cheers
> 	luigi

Normally I'd fix it like:

 #define WARN(x,args...) locallog(LOG_WARNING, args)

 static inline void
 locallog(int lvl, const char *fmt, ...)
 {
   	va_list ap;

	va_start(ap, fmt);
	logv(level, fmt, ap);
	va_end(ap);
 }

But unfortunately we don't have a logv() function.  I think maybe we
should have one.  :)

-- Ian