From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=FROM_EXCESS_BASE64, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3AB28C3A59F for ; Thu, 29 Aug 2019 19:43:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 15FA82166E for ; Thu, 29 Aug 2019 19:43:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728213AbfH2TnX convert rfc822-to-8bit (ORCPT ); Thu, 29 Aug 2019 15:43:23 -0400 Received: from mx2.suse.de ([195.135.220.15]:43366 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727958AbfH2TnX (ORCPT ); Thu, 29 Aug 2019 15:43:23 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 1CF54ABE7; Thu, 29 Aug 2019 19:43:21 +0000 (UTC) Date: Thu, 29 Aug 2019 21:43:19 +0200 From: Michal =?UTF-8?B?U3VjaMOhbmVr?= To: Arnd Bergmann Cc: Michael Neuling , Allison Randal , Nicolai Stange , David Hildenbrand , Greg Kroah-Hartman , Christian Brauner , Heiko Carstens , Linux Kernel Mailing List , Nicholas Piggin , Geert Uytterhoeven , David Howells , Paul Mackerras , Joel Stanley , Andrew Donnellan , Breno Leitao , Firoz Khan , Thomas Gleixner , linuxppc-dev , Hari Bathini , "Eric W. Biederman" Subject: Re: [PATCH v4 1/4] powerpc: make llseek 32bit-only. Message-ID: <20190829214319.498c7de2@naga> In-Reply-To: References: <061a0de2042156669303f95526ec13476bf490c7.1567072270.git.msuchanek@suse.de> <20190829143716.6e41b10e@naga> <20190829161923.101ff3eb@kitsune.suse.cz> X-Mailer: Claws Mail 3.17.4 (GTK+ 2.24.32; x86_64-suse-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 29 Aug 2019 16:32:50 +0200 Arnd Bergmann wrote: > On Thu, Aug 29, 2019 at 4:19 PM Michal Suchánek wrote: > > On Thu, 29 Aug 2019 14:57:39 +0200 Arnd Bergmann wrote: > > > On Thu, Aug 29, 2019 at 2:37 PM Michal Suchánek wrote: > > > > On Thu, 29 Aug 2019 14:19:46 +0200 Arnd Bergmann wrote: > > > > > On Thu, Aug 29, 2019 at 12:23 PM Michal Suchanek wrote: > > > > > In particular, I don't see why you single out llseek here, but leave other > > > > > syscalls that are not needed on 64-bit machines such as pread64(). > > > > > > > > Because llseek is not built in fs/ when building 64bit only causing a > > > > link error. > > > > > > > > I initially posted patch to build it always but it was pointed out it > > > > is not needed, and the interface does not make sense on 64bit, and > > > > that platforms that don't have it on 64bit now don't want that useless > > > > code. > > > > > > Ok, please put that into the changeset description then. > > > > > > I looked at uses of __NR__llseek in debian code search and > > > found this one: > > > > > > https://codesearch.debian.net/show?file=umview_0.8.2-1.2%2Fxmview%2Fum_mmap.c&line=328 > > > > > > It looks like this application will try to use llseek instead of lseek > > > when built against kernel headers that define __NR_llseek. > > > > > > > The available documentation says this syscall is for 32bit only so > > using it on 64bit is undefined. The interface is not well-defined in > > that case either. > > That's generally not how it works. If there is an existing application > that relies on the behavior of the system call interface, we should not > change it in a way that breaks the application, regardless of what the > documentation says. Presumably nobody cares about umview on > powerpc64, but there might be other applications doing the same > thing. Actually the umview headers go out of their way to define the llseek syscall as invalid on x86_64 so that the non-llseek path is taken. mview-os/xmview/defs_x86_64_um.h:#define __NR__llseek __NR_doesnotexist It is probably an oversight that this is not done on non-x86. I am not even sure this builds on non-x86 out of the box. > It looks like sparc64 and parisc64 do the same thing as powerpc64, > and provide llseek() calls that may or may not be used by > applications. And if they are supposed to build with !compat it should be removed there as well. > > I think your original approach of always building sys_llseek on > powerpc64 is the safe choice here. That's safe but adds junk to the kernel as pointed out in the reply to that patch. Thanks Michal