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=-6.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 CE34DC4332F for ; Thu, 9 Sep 2021 07:38:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B3F13610A3 for ; Thu, 9 Sep 2021 07:38:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352694AbhIIHjW (ORCPT ); Thu, 9 Sep 2021 03:39:22 -0400 Received: from mail.kernel.org ([198.145.29.99]:39374 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1352683AbhIIHjO (ORCPT ); Thu, 9 Sep 2021 03:39:14 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 8404861108; Thu, 9 Sep 2021 07:38:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1631173086; bh=vLimwSuXdBEJjY5N4C6UWA9j1b2uBr51BAvYhV2PK+Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=D3xDRPSbld2dt+9IVbS+u/Q2u1CjeDEqbu1ET21O/foyFBzrmS7SUOBHX1Ckm6uhO l7Nt60GWnxHgBrAtlIZl42RsgOWgNuB1QKw8dvtvmuHHf7q5WbldLELpB01IKgndBi J7ZfcOMFGz12rOTn/1ZU3vKRV5V1kNxK6uFVLOGM= Date: Thu, 9 Sep 2021 08:35:35 +0200 From: Greg Kroah-Hartman To: "Yu, Lang" Cc: Joe Perches , "Rafael J . Wysocki" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] sysfs: Remove page boundary align limitation on sysfs_emit and sysfs_emit_at Message-ID: References: <20210908120723.3920701-1-lang.yu@amd.com> <04b52ef5b63abf25e6d50fd5bdfa90727e100a09.camel@perches.com> <685524a360bc910210cbbb7b13a46ead26ed8a22.camel@perches.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 09, 2021 at 06:22:54AM +0000, Yu, Lang wrote: > [Public] > > > > >-----Original Message----- > >From: Greg Kroah-Hartman > >Sent: Thursday, September 9, 2021 2:08 PM > >To: Yu, Lang > >Cc: Joe Perches ; Rafael J . Wysocki ; > >linux-kernel@vger.kernel.org > >Subject: Re: [PATCH] sysfs: Remove page boundary align limitation on sysfs_emit > >and sysfs_emit_at > > > >On Thu, Sep 09, 2021 at 05:52:23AM +0000, Yu, Lang wrote: > >> [Public] > >> > >> > >> > >> >-----Original Message----- > >> >From: Joe Perches > >> >Sent: Thursday, September 9, 2021 1:44 PM > >> >To: Yu, Lang ; Greg Kroah-Hartman > >> >; Rafael J . Wysocki ; > >> >linux- kernel@vger.kernel.org > >> >Subject: Re: [PATCH] sysfs: Remove page boundary align limitation on > >> >sysfs_emit and sysfs_emit_at > >> > > >> >On Thu, 2021-09-09 at 05:27 +0000, Yu, Lang wrote: > >> >> [AMD Official Use Only] > >> > > >> >this is a public list and this marker is not appropriate. > >> > >> Sorry for that. > >> > > >> >> > -----Original Message----- > >> >> > From: Joe Perches On Wed, 2021-09-08 at 20:07 > >> >> > +0800, Lang Yu wrote: > >> >> > > The key purpose of sysfs_emit and sysfs_emit_at is to ensure > >> >> > > that no overrun is done. Make them more equivalent with scnprintf. > >> >> > > >> >> > I can't think of a single reason to do this. > >> >> > sysfs_emit and sysfs_emit_at are specific to sysfs. > >> >> > > >> >> > Use of these functions outside of sysfs is not desired or supported. > >> >> > > >> >> Thanks for your reply. But I'm still curious why you put such a limitation. > >> >> As "Documentation/filesystems/sysfs.rst" described, we can just > >> >> use scnprintf(buf, PAGE_SIZE, "%s\n", dev->name) in show functions > >> >> without such a limitation. > >> > > >> >There's nothing particularly wrong with the use of scnprintf as above. > >> > > >> >The only real reason that sysfs_emit exists is to be able to reduce > >> >the kernel treewide quantity of uses of the sprintf family of > >> >functions that need to be analyzed for possible buffer overruns. > >> > > >> >The issue there is that buf is already known to be both a PAGE_SIZE > >> >buffer and PAGE_SIZE aligned for sysfs show functions so there's no > >> >real reason to use scnprintf. > >> > > >> >sysfs_emit is a shorter/smaller function and using it could avoid > >> >some sprintf defects. > >> > > >> >> Some guys just try to replace scnprintf with sysfs_emit() or > >> >> sysfs_emit_at() per > >> >above documents. > >> > > >> >So don't do that. > >> > > >> >> But sprintf and sysfs_emit/sysfs_emit_at are not totally > >> >> equivalent(e.g., page > >> >boundary align). > >> >> > >> >> In my opinion, we add a new api and try to replace an old api. Does > >> >> we need to make it more compatible with old api? > >> > > >> >IMO: no. > >> > > >> But why you said " - show() should only use sysfs_emit() or > >> sysfs_emit_at() when formatting the value to be returned to user space. " in > >Documentation/filesystems/sysfs.rst ? > >> > >> Obviously, sysfs_emit() and sysfs_emit_at() can't cover all the cases in show > >functions. > > > >Why not, what usage model can it not cover? > > Of course, we can modify driver code to obey sysfs_emit and sysfs_emit_at rules or just use scnprintf in show functions. Great, please do. > Now that you introduced them, why not make them more flexible like scnprintf family functions. Because that is not what they are for. > The page boundary align rule makes life hard and I don't like it : ). Many thanks for your explanations! Then fix your sysfs files to not violate the sysfs rules. Again, which files are having problems and need to be fixed? I will be glad to do this for you. thanks, greg k-h