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

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Message-Id: <200907301920.52257.arnd@arndb.de>
Date:	Thu, 30 Jul 2009 19:20:52 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	eranian@...il.com
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Robert Richter <robert.richter@....com>,
	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 Thursday 30 July 2009, stephane eranian wrote:
> But that won't always work in the case of a 32-bit monitoring tool
> running on top of
> a 64-bit OS. Imagine the target id is indeed 64-bit, e.g., inode
> number (as suggested
> by Peter). It's not because you are a 32-bit tool than you cannot name
> a monitoring
> resource in a 64-bit OS.

Right, there are obviously things that you cannot address with 
a 'long', but there are potentially other things that you could
that you cannot address with an 'int', e.g. an opaque user
token (representing a user pointer) that you can get back in
the sample data.

In the worst case, you could still redefine the argument as a
transparent union to a long and pointer in the future if you
use a 'long' now. AFAICT, there are no advantages of using
an 'int' instead of a 'long', but there are disadvantages of
using a 'long long'.

	Arnd <><
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