Date: Wed, 7 Jan 2009 16:00:25 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Casey Dahlin <cdahlin@redhat.com>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>,
       Randy Dunlap <randy.dunlap@oracle.com>,
       Roland McGrath <roland@redhat.com>, Oleg Nesterov <oleg@redhat.com>,
       Davide Libenzi <davidel@xmailserver.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [RESEND][RFC PATCH v2] waitfd
Message-ID: <20090107150025.GC23455@elte.hu>
References: <49639EB8.40204@redhat.com> <4963ABF0.6070400@redhat.com> <20090107123457.GB16268@elte.hu> <4964A888.3070400@redhat.com>
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* Casey Dahlin <cdahlin@redhat.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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