linux-kernel - Re: I.1 - System calls

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Message-Id: <200906221941.49470.arnd@arndb.de>
Date:	Mon, 22 Jun 2009 19:41:48 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Christoph Hellwig <hch@...radead.org>, eranian@...il.com,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Robert Richter <robert.richter@....com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Andi Kleen <andi@...stfloor.org>,
	Maynard Johnson <mpjohn@...ibm.com>,
	Carl Love <cel@...ibm.com>,
	Corey J Ashford <cjashfor@...ibm.com>,
	Philip Mucci <mucci@...s.utk.edu>,
	Dan Terpstra <terpstra@...s.utk.edu>,
	"perfmon2-devel" <perfmon2-devel@...ts.sourceforge.net>
Subject: Re: I.1 - System calls - ioctl

On Monday 22 June 2009, Ingo Molnar wrote:
> There is another, more theoretical argument in favor of 
> sys_perf_counter_chattr(): it is quite conceivable that as usage of 
> perfcounters expands we want to change more and more attributes. So 
> even though right now the ioctl just about manages to serve this 
> role, it would be more future-proof to use sys_perf_counter_chattr() 
> and deprecate the ioctl() straight away - to not even leave a 
> chance for some ioctl crap to seep into the API.
> 
> So ... we are on two minds about this, and if people dont mind a 
> second syscall entry, we are glad to add it.

I think adding one or more system calls is definitely worth it
if that means getting rid of the ioctl interface here. While I
don't generally mind adding ioctl calls, I would much prefer to
restrict their use to device files, sockets and to the existing
cases for regular files.

Conceptually, ioctl is a different class of interface from the
'new system call' case, in a number of ways. For new subsystems
I would just never mix them by allowing ioctl on something that
was not returned by open() or socket().

	Arnd <><
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