From: Arnd Bergmann <arnd@arndb.de>
To: Ingo Molnar <mingo@elte.hu>
Subject: Re: I.1 - System calls - ioctl
Date: Mon, 22 Jun 2009 19:41:48 +0200
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Cc: Christoph Hellwig <hch@infradead.org>, eranian@gmail.com,
       LKML <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Thomas Gleixner <tglx@linutronix.de>,
       Robert Richter <robert.richter@amd.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Paul Mackerras <paulus@samba.org>, Andi Kleen <andi@firstfloor.org>,
       Maynard Johnson <mpjohn@us.ibm.com>, Carl Love <cel@us.ibm.com>,
       Corey J Ashford <cjashfor@us.ibm.com>,
       Philip Mucci <mucci@eecs.utk.edu>, Dan Terpstra <terpstra@eecs.utk.edu>,
       "perfmon2-devel" <perfmon2-devel@lists.sourceforge.net>
References: <7c86c4470906161042p7fefdb59y10f8ef4275793f0e@mail.gmail.com> <20090622125837.GA9429@infradead.org> <20090622135611.GA5329@elte.hu>
In-Reply-To: <20090622135611.GA5329@elte.hu>
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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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