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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 98C5DC3A5AB for ; Thu, 5 Sep 2019 12:00:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7363922DBF for ; Thu, 5 Sep 2019 12:00:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567684854; bh=1xeBfYskUOKOC0SaWvO+Y+ILr+BecrmFnTQs8zVFl50=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=eDeSN1jJ3/rkY/7SN6F2ez4j7vPafmLGuyi4F2ukFKyPkrM+CfwdmNuc55F+sn4iV CkxZGnLq15EIJsJBhr9/t1CkdvkQDAhFNj3dl+7U/jPwvuYpdmxUVa4ybtwestHRix stH6+Kbd3kS2rryM2FFB/1TVEDMDx1rf/3caobV0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732114AbfIEMAu (ORCPT ); Thu, 5 Sep 2019 08:00:50 -0400 Received: from mail.kernel.org ([198.145.29.99]:45602 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730767AbfIEMAu (ORCPT ); Thu, 5 Sep 2019 08:00:50 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A5DD121883; Thu, 5 Sep 2019 12:00:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567684849; bh=1xeBfYskUOKOC0SaWvO+Y+ILr+BecrmFnTQs8zVFl50=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=O7ZKkc1lP219Poi6xqKaQgcEbNWBZjpRM+hT8SY5Se9MidWdhWqCTwhjTpGjpN4nD WCMVt5asF1oqgG8825623EO5kDyielgIOW8VGBywGk3lFfl9Jf8Kmivv59G3O4o9QU cNKDVjNSLQ6OC6TBoVcwdmsHfBrC4iHpgxsw7pBA= Date: Thu, 5 Sep 2019 14:00:46 +0200 From: Greg Kroah-Hartman To: Masahiro Yamada Cc: Jessica Yu , Arnd Bergmann , Matthew Dharm , Guenter Roeck , Matthias Maennich , Linux Kernel Mailing List , "Cc: Android Kernel" , "Joel Fernandes (Google)" , Lucas De Marchi , Martijn Coenen , Sandeep Patil , Will Deacon , Linux Kbuild mailing list , linux-modules@vger.kernel.org, linux-usb , USB Mass Storage on Linux , LINUXWATCHDOG Subject: Re: [usb-storage] Re: [PATCH v4 12/12] RFC: watchdog: export core symbols in WATCHDOG_CORE namespace Message-ID: <20190905120046.GA7952@kroah.com> References: <20190903150638.242049-1-maennich@google.com> <20190903150638.242049-13-maennich@google.com> <20190903161045.GA22754@roeck-us.net> <20190905104147.GA27788@linux-8ccs> <20190905111617.GB27788@linux-8ccs> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) Sender: linux-watchdog-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-watchdog@vger.kernel.org On Thu, Sep 05, 2019 at 08:25:32PM +0900, Masahiro Yamada wrote: > On Thu, Sep 5, 2019 at 8:16 PM Jessica Yu wrote: > > > > +++ Arnd Bergmann [05/09/19 12:52 +0200]: > > >On Thu, Sep 5, 2019 at 12:41 PM Jessica Yu wrote: > > >> +++ Matthew Dharm [04/09/19 09:16 -0700]: > > >> >On Wed, Sep 4, 2019 at 5:12 AM Guenter Roeck wrote: > > > > > >> >HOWEVER, I have one question: If these patches are included, and > > >> >someone wants to introduce a bit of code which needs to use two > > >> >symbols from different namespaces but with the same name, can that be > > >> >done? That is, if driver A has symbol 'foo' and driver B has symbol > > >> >'foo' (both in their respective namespaces), and driver C wants to use > > >> >A.foo and B.foo, can that be supported? > > >> > > >> As of now, we currently don't support this - modpost will warn if a > > >> symbol is exported more than once (across modules + vmlinux), and the > > >> module loader currently assumes exported symbol names are unique. Do > > >> you have a concrete use case? If there is a strong need for this, I > > >> don't think it'd be too hard to implement. > > > > > >I think what would prevent this from working in general is that having > > >two modules with the same exported symbol in different namespaces > > >won't link if you try to build both modules into the kernel itself. > > > > > > Arnd > > > > Ah yeah, you are right. I only tried building an identically named > > exported symbol in a module and in the kernel, and there I got away > > with a modpost warning. But this breaks when building the module into > > the kernel, so I guess this is out of the question. > > > > Thanks, > > > > Jessica > > > > > The cover letter starts with > "As of Linux 5.3-rc7, there are 31207 [1] exported symbols in the kernel". > > Whether or not we apply this patch set, > we will have to carefully maintain them > so that 31207 symbols are unique, anyway. > (And, we can do this with allmodconfig + modpost) > > So, what is the point of the namespace, > where it does not loosen the scope of uniqueness? It does not "loosen" anything. The problem is, we have 31207 exported symbols and no one has any idea how they are "clustered" :) Ideally we would have separate namespaces where we could "keep" others from accessing symbols that are required to be global, but we do not want anyone else to use them. But we have C, and we need to live with that. This is the "next best thing". This provides a namespace and a marking by the user of that exported symbol that they really do know what they are doing. The USB storage exports are a concrete example of this in this patchset. Those symbols are to only be used by other USB storage drivers, and they are marked that way here. This also gives us the ability to start to actually understand what our different exported symbols are for. Right now the USB core exports a ton of stuff, but who is expected to use what? Right now any USB driver can use any of those functions and no one notices. After this patchset is merged, I will start to "carve up" the USB exports into different "namespaces". One example will be the functions only for use by USB host controller drivers. Then if someone submits a new driver that says "use the USB host controller driver namespace", and that driver is _not_ a USB host controller driver, it's a huge red flag that something really isn't correct here. Some other USB functions will probably get marked "USB core only" or some such thing, and then to use them you have to say you are importing from the "usb core only" which again, is a huge flag that you are doing something wrong. So on it's own, this patchset doesn't do much. But it gives us the building blocks on which to start to make sense of those 31000+ different exported symbols. As an aside, this is something that I know I and others have been wanting to see happen for 10+ years now, and I'm very happy to see it show up in a workable form as we have known this is a issue for a very long time. Hope this helps explain things better, greg k-h