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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 CFC95C2D0A3 for ; Tue, 3 Nov 2020 16:49:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 715A820E65 for ; Tue, 3 Nov 2020 16:49:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728514AbgKCQto (ORCPT ); Tue, 3 Nov 2020 11:49:44 -0500 Received: from smtprelay0079.hostedemail.com ([216.40.44.79]:58844 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725997AbgKCQto (ORCPT ); Tue, 3 Nov 2020 11:49:44 -0500 Received: from filter.hostedemail.com (clb03-v110.bra.tucows.net [216.40.38.60]) by smtprelay04.hostedemail.com (Postfix) with ESMTP id E3FE4180A9113; Tue, 3 Nov 2020 16:49:42 +0000 (UTC) X-Session-Marker: 6A6F6540706572636865732E636F6D X-HE-Tag: card07_4c0643e272ba X-Filterd-Recvd-Size: 3077 Received: from XPS-9350.home (unknown [47.151.133.149]) (Authenticated sender: joe@perches.com) by omf15.hostedemail.com (Postfix) with ESMTPA; Tue, 3 Nov 2020 16:49:40 +0000 (UTC) Message-ID: Subject: Re: [PATCH v4 1/1] lib/vsprintf: Add support for printing V4L2 and DRM fourccs From: Joe Perches To: Sakari Ailus , Andy Shevchenko Cc: linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, Petr Mladek , Dave Stevenson , dri-devel@lists.freedesktop.org, hverkuil@xs4all.nl, laurent.pinchart@ideasonboard.com, mchehab@kernel.org, Sergey Senozhatsky , Steven Rostedt , Jani Nikula , Rasmus Villemoes Date: Tue, 03 Nov 2020 08:49:36 -0800 In-Reply-To: <20201103145616.GJ26150@paasikivi.fi.intel.com> References: <20201103133400.24805-1-sakari.ailus@linux.intel.com> <20201103144747.GD4077@smile.fi.intel.com> <20201103145616.GJ26150@paasikivi.fi.intel.com> Content-Type: text/plain; charset="ISO-8859-1" User-Agent: Evolution 3.38.1-1 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2020-11-03 at 16:56 +0200, Sakari Ailus wrote: > On Tue, Nov 03, 2020 at 04:47:47PM +0200, Andy Shevchenko wrote: > > On Tue, Nov 03, 2020 at 03:34:00PM +0200, Sakari Ailus wrote: > > > Add a printk modifier %p4cc (for pixel format) for printing V4L2 and DRM > > > pixel formats denoted by fourccs. The fourcc encoding is the same for both > > > so the same implementation can be used. > > > > ... > > > > > +static noinline_for_stack > > > +char *fourcc_string(char *buf, char *end, const u32 *fourcc, > > > + struct printf_spec spec, const char *fmt) > > > +{ > > > + char output[sizeof("(xx)(xx)(xx)(xx) little-endian (0x01234567)")]; > > > > I would add a comment that there is another possibility, i.e. big-endian, but > > it occupies less space. I think it's unnecessary as it's obvious and similarly done in other _string type functions. > > > + p = special_hex_number(p, output + sizeof(output) - 2, *fourcc, > > > + sizeof(u32)); > > > > I would go with one line here. > > It's wrapped since the result would be over 80 otherwise. Perhaps simpler as p = special_hex_number(p, p + 10, *fourcc, sizeof(u32)); > > The (theoretical) problem is here that the case when buffer size is not enough > > to print a value will be like '(0xabc)' but should be rather '(0xabcd' like > > snprintf() does in general. Isn't the stack buffer known to be large enough? > > > + *p++ = ')'; > > > + *p = '\0'; > > > + > > > + return string(buf, end, output, spec); Isn't the actual output buffer used here truncating output? If the general problem is someone using a limited length pointer output like %10p4cc, then all the output is getting truncated no?