linux-kernel - Re: [RESEND][RFC PATCH v2] waitfd

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Message-ID: <20090107150025.GC23455@elte.hu>
Date:	Wed, 7 Jan 2009 16:00:25 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Casey Dahlin <cdahlin@...hat.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Roland McGrath <roland@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RESEND][RFC PATCH v2] waitfd


* Casey Dahlin <cdahlin@...hat.com> wrote:

> >> +asmlinkage long sys_waitfd(int which, pid_t upid, int options, int unused)
> >> +{
> >> +	int ufd;
> >> +	struct waitfd_ctx *ctx;
> >> +
> >> +	/* Just to make sure we don't end up with a sys_waitfd4 */
> >> +	(void)unused;
> > 
> > looks a bit silly ...
> 
> 
> Do you mean the principle of having an unused argument around for future 
> use or the cast to void? The cast to void is there to suppress the 
> "Waning: unused argument" messages and make gcc happy.

gcc will not warn about unused function arguments - only about unused 
local variables. The 'unused' argument should either be removed 
altogether, or replaced with a properly named parameter and a check 
returning -ENOSYS if the argument is not zero (or something like that). 

(It's generally better to keep such syscalls extensible via such trivial 
means, if there's a remote chance for ever needing to extend that 
syscall.)

	Ingo
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