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 EC623C433EF for ; Thu, 9 Sep 2021 06:07:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D0B976101A for ; Thu, 9 Sep 2021 06:07:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351206AbhIIGI4 (ORCPT ); Thu, 9 Sep 2021 02:08:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:43994 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231438AbhIIGIz (ORCPT ); Thu, 9 Sep 2021 02:08:55 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id F228360F23; Thu, 9 Sep 2021 06:07:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1631167666; bh=t0iK+sdxllEwEgBTPmQBM+xn0mJiwXrd0TpwzlGAz9k=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=YI7oHCdsfQC7345VYcMaTLHggmFXs9JAVTp/AePcnmRBCe/9+ggUUy4EL8FZGlM4+ GqBD+p+8ziz7JAizYyw6zKDDB4JDhWWzDtebzK8aaAClS0qwOUm611JxqSnXg0OfO2 BFaqjPjrOmm9kH6Mr7N7zb4ohNin3L0uPqGGc56U= Date: Thu, 9 Sep 2021 08:07:44 +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 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? thanks, greg k-h