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 CCE0AC433EF for ; Thu, 9 Sep 2021 08:00:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AC06A61108 for ; Thu, 9 Sep 2021 08:00:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231598AbhIIIBO (ORCPT ); Thu, 9 Sep 2021 04:01:14 -0400 Received: from mail.kernel.org ([198.145.29.99]:44242 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229871AbhIIIBL (ORCPT ); Thu, 9 Sep 2021 04:01:11 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 4059960F11; Thu, 9 Sep 2021 08:00:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1631174401; bh=/t1lB3Y3QLMGalzyaUsgE4tfQzVs2EheXt/DrAAb6/k=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=vyifDwJv4Y0GkZgNLP3l9t+atA/xzu1InF6U4WuDL2WjrcxwllFqyM0uDxSD6dybz kZ9TxQQM9QqRRpCBwqFAsCyksS00yVsNa+dfFGMysg4LSFYSDnqjhivwDXP3UTkcAV dhqsN4LuIRn7nXPPp/boi/i2YnThYHBfoaIuMgXw= Date: Thu, 9 Sep 2021 09:59:58 +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 07:48:38AM +0000, Yu, Lang wrote: > [Public] > > > > >-----Original Message----- > >From: Greg Kroah-Hartman > >Sent: Thursday, September 9, 2021 2:36 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 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. I can do it by myself instead of wasting your time... Many thanks! When doing so, please switch to using DEVICE_ATTR_RO() instead of the "open coded" DEVICE_ATTR() usage in the driver. That way we all "know" that these are read-only attributes. thanks, greg k-h