From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.8 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_EF,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=unavailable autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 82FF37E2EB for ; Wed, 4 Sep 2019 19:06:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733154AbfIDQRm (ORCPT ); Wed, 4 Sep 2019 12:17:42 -0400 Received: from mail.kernel.org ([198.145.29.99]:53296 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731559AbfIDQRl (ORCPT ); Wed, 4 Sep 2019 12:17:41 -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 9FA5521670; Wed, 4 Sep 2019 16:17:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567613860; bh=PrSi2ibHZgZSkJmHetTy+766/nLwL4tOkYmbPtMEER0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=SZrIovPrfpx5iAPrdV/I8ro1AynIDDflLbO8u64LP+oLzB/40AMLskh4qVlIJ4znx 1HPojvyBGTZ1d6qpI0cxstL6+jso3XM5Jt39eI3tlcte8qiUF656pOhURstZGVBuah yaYJ6YAU3oFzPQ5Ta+1vNW/4aYfx5kTCqcnmgdoU= Date: Wed, 4 Sep 2019 18:17:37 +0200 From: Greg KH To: Mathieu Poirier Cc: Mike Leach , linux-arm-kernel , Coresight ML , "open list:DOCUMENTATION" , "Suzuki K. Poulose" , Jon Corbet Subject: Re: [PATCH v2 09/11] coresight: etm4x: docs: Update ABI doc for sysfs features added. Message-ID: <20190904161737.GA20662@kroah.com> References: <20190829213321.4092-1-mike.leach@linaro.org> <20190829213321.4092-10-mike.leach@linaro.org> <20190903195951.GA25008@kroah.com> <20190904054809.GB4511@kroah.com> 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-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Wed, Sep 04, 2019 at 10:05:51AM -0600, Mathieu Poirier wrote: > On Tue, 3 Sep 2019 at 23:48, Greg KH wrote: > > > > On Tue, Sep 03, 2019 at 04:51:40PM -0600, Mathieu Poirier wrote: > > > On Tue, 3 Sep 2019 at 13:59, Greg KH wrote: > > > > > > > > On Thu, Aug 29, 2019 at 10:33:19PM +0100, Mike Leach wrote: > > > > > Update document to include the new sysfs features added during this > > > > > patchset. > > > > > > > > > > Updated to reflect the new sysfs component nameing schema. > > > > > > > > > > Signed-off-by: Mike Leach > > > > > --- > > > > > .../testing/sysfs-bus-coresight-devices-etm4x | 183 +++++++++++------- > > > > > 1 file changed, 115 insertions(+), 68 deletions(-) > > > > > > > > > > diff --git a/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x b/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x > > > > > index 36258bc1b473..112c50ae9986 100644 > > > > > --- a/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x > > > > > +++ b/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x > > > > > @@ -1,4 +1,4 @@ > > > > > -What: /sys/bus/coresight/devices/.etm/enable_source > > > > > +What: /sys/bus/coresight/devices/etm/enable_source > > > > > > > > You are renaming sysfs directories that have been around since: > > > > > > > > > Date: April 2015 > > > > > > > > ??? > > > > > > > > Really? > > > > > > > > That's brave. > > > > > > > > > When I worked on the coresight sysfs ABI a while back I specifically > > > added it at the "testing" level as I was well aware that things could > > > change in the future. According to the guidelines in the > > > documentation userspace can rely on it which was accurate since the > > > interface didn't change for 4 years. But the guidelines also mention > > > that changes can occur before the interfaces are move to stables, and > > > that programs are encouraged to manifest their interest by adding > > > their name to the "users" field. > > > > > > The interface was changed in 5.2 to support coresight from ACPI and > > > make things easier to understand for users. It is a lot more > > > intuitive to associate an ETM tracer with the CPU it belongs to by > > > referring to the CPU number than the memory mapped address. Given the > > > "testing" status of the interface and the absence of registered users > > > I decided to move forward with the change. If "testing" is too strict > > > for that I suggest to add an "experimental" category where it would be > > > more acceptable to change things as subsystems mature. > > > > "testing" is not really "testing" if you have userspace tools/programs > > assuming the location and contents of specific files in sysfs. > > > > You can change things in sysfs by creating new files, but to do > > wholesale renaming like you did here can be very dangerous as you might > > be breaking things. > > Yes, something I have definitely considered. > > > Usually new files are created, not existing ones > > moved. > > In this case it would have meant a new symbolic link for every > coresight device, so twice a many entries under > $(SYS)/bus/coresight/device/. That would have been a lot of clutter > and an increasing source of problems as the number of CPU and sinks > increases. To me, and given the permissive definition of "testing" > found in the documentation, a clean break was a better option. Well, "testing" doesn't really matter in the end, if a tool/user relies on it, we have to keep it working properly. > > What tools use these today? What is going to break? > > Other than local shell scripts I am not aware of any tools using these > today. I am certainly open to discuss a better alternative but right > now, I just don't see one. Be aware that you might have to change this back if there is any objections. thanks, greg k-h