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=-0.8 required=3.0 tests=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 6049FC43331 for ; Fri, 3 Apr 2020 11:54:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3A3842078C for ; Fri, 3 Apr 2020 11:54:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390845AbgDCLyi (ORCPT ); Fri, 3 Apr 2020 07:54:38 -0400 Received: from mga04.intel.com ([192.55.52.120]:57346 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390632AbgDCLyi (ORCPT ); Fri, 3 Apr 2020 07:54:38 -0400 IronPort-SDR: dijLxQS/MoWpstj+9ivruchsn7c4Au+be+sfeIrYj8KoKeYRa21Y5EGsHhPIIJCgvqOxFi46qe vn8yiUJFwTZQ== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Apr 2020 04:54:37 -0700 IronPort-SDR: DVwCbmHW9ZMpGxGiBAr9d5FKQY6dyp+OIcOV0vaurqBLKuq7e2cTj8JMX0ejF1Rb4rtW04bqI/ MkemSyY1vAIA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,339,1580803200"; d="scan'208";a="241105550" Received: from smile.fi.intel.com (HELO smile) ([10.237.68.40]) by fmsmga007.fm.intel.com with ESMTP; 03 Apr 2020 04:54:34 -0700 Received: from andy by smile with local (Exim 4.93) (envelope-from ) id 1jKKuC-00FQDf-55; Fri, 03 Apr 2020 14:54:36 +0300 Date: Fri, 3 Apr 2020 14:54:36 +0300 From: Andy Shevchenko To: Mauro Carvalho Chehab Cc: Sakari Ailus , Laurent Pinchart , Petr Mladek , linux-media@vger.kernel.org, Dave Stevenson , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, hverkuil@xs4all.nl, Sergey Senozhatsky , Steven Rostedt , Joe Perches , Jani Nikula Subject: Re: [PATCH v2 1/1] lib/vsprintf: Add support for printing V4L2 and DRM fourccs Message-ID: <20200403115436.GY1922688@smile.fi.intel.com> References: <20200403091156.7814-1-sakari.ailus@linux.intel.com> <20200403102449.GB4882@pendragon.ideasonboard.com> <20200403104701.GC3172@kekkonen.localdomain> <20200403131926.7caf3288@coco.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200403131926.7caf3288@coco.lan> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 03, 2020 at 01:19:26PM +0200, Mauro Carvalho Chehab wrote: > Em Fri, 3 Apr 2020 13:47:02 +0300 > Sakari Ailus escreveu: > > > > > +static noinline_for_stack > > > > +char *fourcc_string(char *buf, char *end, const u32 *fourcc, > > > > + struct printf_spec spec, const char *fmt) > > > > +{ > > > > +#define FOURCC_STRING_BE "-BE" > > > > + char s[sizeof(*fourcc) + sizeof(FOURCC_STRING_BE)] = { 0 }; > > > > + > > > > + if (check_pointer(&buf, end, fourcc, spec)) > > > > + return buf; > > > > + > > > > + if (fmt[1] != 'c' || fmt[2] != 'c') > > > > + return error_string(buf, end, "(%p4?)", spec); > > > > + > > > > + put_unaligned_le32(*fourcc & ~BIT(31), s); > > > > + > > > > + if (*fourcc & BIT(31)) > > > > + strscpy(s + sizeof(*fourcc), FOURCC_STRING_BE, > > > > + sizeof(FOURCC_STRING_BE)); > > > > + > > > > + return string(buf, end, s, spec); > > > > > > Taking V4L2_PIX_FMT_Y16_BE as an example, this will print 'Y16 -BE' > > > (without quotes). There are other 4CCs that contain spaces and would > > > suffer from a similar issue. Even in little-endian format, it would > > > result in additional spaces in the output string. Is this what we want ? > > > Should the caller always enclose the 4CC in quotes or brackets for > > > clarity ? Or should still be done here ? > > > > Good question. Space is indeed a valid character in a 4cc code. > > > > If I omit one or more spaces, it will no longer be a 4cc, but a 3cc or even > > a 2cc. Jokes aside, there are probably fair arguments both ways. > > > > I presume there's no 4cc code where the location of a space would make a > > difference but all of the spaces are trailing spaces. > > Yes. I guess it doesn't make any sense to allow a 4cc code with an > space before or in the middle. > > Btw, on a quick search at the Internet for non-Linux definitions, > a Fourcc code "Y8 " is actually shown at the lists as just "Y8", > e. g. removing the leading spaces: > > https://www.fourcc.org/codecs.php > http://abcavi.kibi.ru/fourcc.php > https://softron.zendesk.com/hc/en-us/articles/207695697-List-of-FourCC-codes-for-video-codecs > https://www.free-codecs.com/guides/guides.php?f=fourcc > > One interesting detail there is that some tables show some codes > like "BGR(15)". While I'm not sure how this is encoded, I suspect > that the fourcc is actually "BGR\x15". > > We don't do that on V4L, nor we have plans to do so. Not sure if > DRM would accept something like that. Of so, then the logic should > have some special handler if the code is below 32. It is easy to achieve I think, with help of string_escape*() functions. > > It's also worth noting that the formats printed are mostly for debugging > > purpose and thus even getting a hypothetical case wrong is not a grave > > issue. This would also support just printing them as-is though. > > > > I'm leaning slightly towards omitting any spaces if the code has them. > > I would just remove trailing spaces, and then use a loop from the end > to remove trailing spaces (and optionally handle codes ending with a > value below 32, if are there any such case with DRM fourcc codes). > > On the other hand, I don't mind if you prefer to use just one for() > loop and just trip any spaces inside it. > > > This is something that couldn't be done by using a macro... > > Well, I suspect that it might be possible to write a macro > for doing that too, for example using preprocessor concatenation > logic that could produce the same results. If you do something > like that, however, I suspect that te macro would face some > portability issues, as, as far as I know, not all C compilers > would handle string concatenation the same way. > > Thanks, > Mauro -- With Best Regards, Andy Shevchenko