From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hutterer Subject: Re: [PATCH 2/4] Input: introduce ABS_MAX2/CNT2 and friends Date: Thu, 19 Dec 2013 10:25:42 +1000 Message-ID: <20131219002542.GB6315@yabbi.redhat.com> References: <1387295334-1744-1-git-send-email-dh.herrmann@gmail.com> <1387295334-1744-3-git-send-email-dh.herrmann@gmail.com> <20131218234009.GA9360@yabbi.redhat.com> <1950536.BXYYX85NB4@dtor-d630.eng.vmware.com> <20131218235504.GA17958@yabbi.redhat.com> <20131219000537.GA838@core.coreip.homeip.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from leo.clearchain.com ([199.73.29.74]:10784 "EHLO mail.clearchain.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753001Ab3LSAW6 (ORCPT ); Wed, 18 Dec 2013 19:22:58 -0500 Content-Disposition: inline In-Reply-To: <20131219000537.GA838@core.coreip.homeip.net> Sender: linux-input-owner@vger.kernel.org List-Id: linux-input@vger.kernel.org To: Dmitry Torokhov Cc: David Herrmann , linux-input@vger.kernel.org, Jiri Kosina , Benjamin Tissoires , Antonio Ospite , linux-kernel@vger.kernel.org, input-tools@lists.freedesktop.org On Wed, Dec 18, 2013 at 04:05:37PM -0800, Dmitry Torokhov wrote: > On Thu, Dec 19, 2013 at 09:55:04AM +1000, Peter Hutterer wrote: > > On Wed, Dec 18, 2013 at 03:48:37PM -0800, Dmitry Torokhov wrote: > > > On Thursday, December 19, 2013 09:40:09 AM Peter Hutterer wrote: > > > > > + memset(&abs, 0, sizeof(abs)); > > > > > + for (i = valid_cnt; i < cnt; ++i) > > > > > + if (copy_to_user(&pinfo->info[i], &abs, sizeof(abs))) > > > > > + return -EFAULT; > > > > > + > > > > > + return 0; > > > > > > > > why don't you return the number of valid copied axes to the user? > > > > that seems better even than forcing the remainder to 0. > > > > > > Well, if your program messed up buffers that it faulted we do not know > > > for sure if data that did not cause fault ended up where it should have > > > or if it smashed something else. This condition I think should be > > > signaled early. > > > > not 100% sure I understand but I wasn't proposing to remove the -EFAULT, i > > was proposing to replace "return 0" with "return valid_cnt". > > I understand what you were saying. Now consider: your program supplied > buffer that is actually smaller than what it said to the kernel. > Depending on the exact placement we may or may not fault when we get > pass the buffer boundary, most likely not. We are likely to fault when > we go way past the buffer boundary and wracked process' memory. If we > return -EFAULT the program will at least notice that something wrong. If > we return count it will try to resubmit the remainder of operation and > not even know that there was something very bad happening. > > IOW we should not treat fault condition as other partial read/write > conditions. I'm still not sure we're talking about the same thing :) let me rephrase: why can't we use the behaviour bits_to_user() provides? it limits the output to maxlen and returns that value (or -EFAULT), it's only a small step from that to limit the output to min(maxbit, ABS_CNT2). Cheers, Peter