From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Henrik Rydberg" Subject: Re: [PATCH v3] Input: Add EVIOC mechanism for MT slots Date: Sun, 5 Feb 2012 08:59:06 +0100 Message-ID: <20120205075906.GA7698@polaris.bitmath.org> References: <1328036403-2827-1-git-send-email-rydberg@euromail.se> <4F2B24AC.1020408@gmail.com> <20120203072725.GA6914@polaris.bitmath.org> <4F2D7730.3090704@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from smtprelay-b22.telenor.se ([195.54.99.213]:50457 "EHLO smtprelay-b22.telenor.se" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752765Ab2BEH5w (ORCPT ); Sun, 5 Feb 2012 02:57:52 -0500 Content-Disposition: inline In-Reply-To: <4F2D7730.3090704@gmail.com> Sender: linux-input-owner@vger.kernel.org List-Id: linux-input@vger.kernel.org To: Chase Douglas Cc: Dmitry Torokhov , linux-input@vger.kernel.org, linux-kernel@vger.kernel.org > > This is resolved on the preprocessor level, so C99 or not does not > > enter the problem. Compile-time constant, as you can see in the code > > example in the patch summary. > > You're right, I didn't catch that. It will be compatible with all C > compilers if you use a static number of slots. Yes, but this statement is merely repeating something that has been true since the sixties. > However, it will break if you use a non-C99 C compiler and the code > wants to do dynamic number of slots calculations. Of course, which is why C99 cannot be used for portable code. And it still has nothing to do with this patch. > I imagine most callers would do: > > EVIOCGABS call on ABS_MT_SLOT; > int num_slots = ABS_MT_SLOT.max - ABS_MT_SLOT.min > struct INPUT_MT_REQUEST(num_slots) req; Besides leaving a possible giant stack crash in your code, it assumes memory is somehow magically allocated. Not good practise in low-level programming. You wouldn't use a template this way, would you? > This will break on non-C99 C compilers and other language compilers. Of course, since you use the C99 dynamic stack construct, which, again, is not portable. > It also will lead to head-scratcher bugs when someone compiles it > just fine in their C99 project, copies the code to another project > with a different compiler, and is confronted with the issue. No, since people how know C do not do things like that. > I think this issue should be enough to rethink the interface. No, since your issues with C99 has nothing to do with this patch. Henrik