From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1754145AbcICMfv (ORCPT <rfc822;w@1wt.eu>);
        Sat, 3 Sep 2016 08:35:51 -0400
Received: from merlin.infradead.org ([205.233.59.134]:53856 "EHLO
        merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1753168AbcICMft (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Sat, 3 Sep 2016 08:35:49 -0400
Date: Sat, 3 Sep 2016 14:35:44 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Keno Fischer <keno@juliacomputing.com>
Cc: linux-kernel@vger.kernel.org, vincent.weaver@maine.edu,
        mingo@redhat.com
Subject: Re: How does the size field work in IOCTL numbers?
Message-ID: <20160903123544.GE2794@worktop>
References: <CABV8kRyzR1-0XYjY2i-imU51NF3hkg-HQmvRMVTgggyOyHV2FQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CABV8kRyzR1-0XYjY2i-imU51NF3hkg-HQmvRMVTgggyOyHV2FQ@mail.gmail.com>
User-Agent: Mutt/1.5.22.1 (2013-10-16)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, Sep 02, 2016 at 07:27:27PM -0400, Keno Fischer wrote:
> I don't understand what the rule is for what to put in that third
> argument, or is it ioctl specific? Please let me know if I missed
> something.

You can do whatever you like, but everything that is different between
ILP32 and LP64 requires COMPAT fixups.