Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753628Ab0LGMwp (ORCPT ); Tue, 7 Dec 2010 07:52:45 -0500 Received: from mail-gw0-f42.google.com ([74.125.83.42]:57510 "EHLO mail-gw0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753384Ab0LGMwo convert rfc822-to-8bit (ORCPT ); Tue, 7 Dec 2010 07:52:44 -0500 MIME-Version: 1.0 In-Reply-To: <201012071344.01173.arnd@arndb.de> References: <1291706726-8835-1-git-send-email-rydberg@euromail.se> <20101207105620.GB23729@core.coreip.homeip.net> <201012071344.01173.arnd@arndb.de> From: Kay Sievers Date: Tue, 7 Dec 2010 13:52:28 +0100 Message-ID: Subject: Re: [RFC][PATCH] input: Introduce device information ioctl To: Arnd Bergmann Cc: Dmitry Torokhov , Henrik Rydberg , Jiri Kosina , linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, Ping Cheng , Chris Bagwell Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1470 Lines: 34 On Tue, Dec 7, 2010 at 13:44, Arnd Bergmann wrote: > On Tuesday 07 December 2010, Kay Sievers wrote: >> On Tue, Dec 7, 2010 at 11:56, Dmitry Torokhov wrote: >> > On Tue, Dec 07, 2010 at 11:48:28AM +0100, Kay Sievers wrote: >> >> >> Please don't add new ioctls which are not extensible. The ioctl should >> >> carry the length or the version of the structure it asks for, so it >> >> can be extended in the future. >> > >> > Size of ioctl data is encoded in ioctl, it can be extended easily. For >> > examples take a look at how EVIOCGKEYCODE and EVIOCGSKEYCODE are handled >> > in recent kernels. >> >> Oh, how does that work? With the ioctl call, userspace has to supply >> the size it expects to be returned from the kernel. How does the >> kernel otherwise know how much it is allowed to copy to the user? > > The ioctl command number itself is calculated from the size of the > data that gets passed: > > #define EVIOCGDEVINFO          _IOR('E', 0x09, struct input_devinfo) > > If struct input_devinfo ever changes (which it can, but should not), > the command changes as well. So unlike statet, it's not extensible, and this struct and this ioctl can never change? Kay -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/