From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755456Ab1G2I1f (ORCPT ); Fri, 29 Jul 2011 04:27:35 -0400 Received: from mail-gw0-f46.google.com ([74.125.83.46]:41153 "EHLO mail-gw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755233Ab1G2I1c (ORCPT ); Fri, 29 Jul 2011 04:27:32 -0400 Message-ID: <4E326D88.20701@gmail.com> Date: Fri, 29 Jul 2011 10:21:28 +0200 From: Marco Stornelli User-Agent: Mozilla/5.0 (X11; U; Linux i686; it; rv:1.9.2.18) Gecko/20110616 SUSE/3.1.11 Thunderbird/3.1.11 MIME-Version: 1.0 To: Sergiu Iordache CC: Greg KH , Andrew Morton , "Ahmed S. Darwish" , Artem Bityutskiy , Kyungmin Park , linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 3/3] char drivers: ramoops debugfs entry References: <1309994990-4729-1-git-send-email-sergiu@chromium.org> <1309994990-4729-4-git-send-email-sergiu@chromium.org> <20110707130130.8dd02f01.akpm@linux-foundation.org> <20110707155426.fd95445f.akpm@linux-foundation.org> <20110707162727.f361f053.akpm@linux-foundation.org> <20110707233335.GA15120@kroah.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Il 29/07/2011 02:15, Sergiu Iordache ha scritto: > On Mon, Jul 11, 2011 at 11:41 PM, Marco Stornelli > wrote: >> 2011/7/11 Sergiu Iordache: >>> On Thu, Jul 7, 2011 at 11:43 PM, Marco Stornelli >>> wrote: >>>> 2011/7/8 Greg KH: >>>>> On Thu, Jul 07, 2011 at 04:27:27PM -0700, Andrew Morton wrote: >>>>>> On Thu, 7 Jul 2011 16:16:43 -0700 >>>>>> Sergiu Iordache wrote: >>>>>> >>>>>>> Ramoops currently dumps the log of a panic/oops in a memory area which >>>>>>> is known not to be overwritten on restart (for example 1MB starting at >>>>>>> 15MB). The way it works is by dividing the memory area in records of a >>>>>>> set size (fixed at 4K before my patches, configurable after) and by >>>>>>> dumping a record there for each oops/panic. The problem is that right >>>>>>> now you have to access that memory area through other means, such as >>>>>>> /dev/mem, which is not always possible. >>>>>>> >>>>>>> What my patch did was to add a debugfs entry which returns a valid >>>>>>> record each time (a single dump done by ramoops). The first call >>>>>>> returns the first dump. The first call after the last valid dump >>>>>>> returns an empty buffer. . >>>>>> >>>>>> Please fully describe this "record" in the v2 patch changelog. We'll >>>>>> want to review it for endianness, 32/64-bit compat issues, >>>>>> maintainability, extensibility, etc. >>>>>> >>>>>>> After it has returned nothing, the next >>>>>>> calls return records from the start again. >>>>>> >>>>>> That sounds a bit weird. One would expect it to keep returning zero, >>>>>> requiring userspace to lseek or close/open. >>>>>> >>>>>>> The validity of a dump is >>>>>>> checked by looking after the header. Any comments on this approach are >>>>>>> welcome. >>>>>>> >>>>>>> Changing the entry from debugfs to sysfs wouldn't be a problem. If >>>>>>> sysfs is a valid solution I'll come with a patch that updates the >>>>>>> documentation as well along with the sysfs entry. >>>>>> >>>>>> sysfs sounds OK to me. Then again, sysfs is supposed to be >>>>>> one-value-per-file, so using it would be naughty. >>>>>> >>>>>> I dunno, I'd be inclined to abuse the sysfs rule and hope that nobody >>>>>> notices rather than create a fake char device. But there's certainly >>>>>> plenty of precedent for the fake char driver. >>>>> >>>>> No, please don't abuse sysfs that way. >>>>> >>>>> Use debugfs or a char device node. >>>>> >>>>> thanks, >>>>> >>>>> greg k-h >>>>> >>>> >>>> I agree with Greg. I asked to not break the existent way to read data >>>> via /dev/mem because for me it's the right way to do this thing. >>>> However to do an easy *debug* a debugfs entry can be useful. IMHO, a >>>> "production" script/application that use debugfs instead of /dev/mem >>>> in this case is simply broken because the debugfs can't be like a >>>> system call or other kernel interaction mechanism. Debugfs should be >>>> used only for debug. >>>> >>>> Marco >>> >>> Any consensus/decision on how to go on with this patch idea? >>> >>> The options that I see right now are: >>> - keep access through /dev/mem only (but access to /dev/mem is >>> sometimes restricted); >>> - keep the debugfs entry as well(as in the patch); >>> - remove the debugfs entry and add a char driver to access the memory >>> using read and seek operations. >>> >>> + the rejected(?) options from before >>> >>> Sergiu >>> >> >> For me the best option it's to use a sysfs/proc entry to export >> (read-only) the memory address, record size etc. At that point we can >> use a generic script/program to access via /dev/mem. However I let >> Andrew/Greg say the last word. > > Well, since the only method to read the dump data is /dev/mem, > exporting the record size/address/etc is needed in order to parse it > properly. But as far as I can see the data is already exported through > sysfs in /sys/module/ramoops/parameters/. > The current module still needs a patch to write the variables of the > module parameters from the platform data in case that is used, but is > there any reason why we would need other sysfs entries except these? I'd say no. I think it's sufficient. Marco