From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753282AbbD0QOl (ORCPT ); Mon, 27 Apr 2015 12:14:41 -0400 Received: from mail-vn0-f52.google.com ([209.85.216.52]:43775 "EHLO mail-vn0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753016AbbD0QOi (ORCPT ); Mon, 27 Apr 2015 12:14:38 -0400 Date: Mon, 27 Apr 2015 12:14:34 -0400 From: Tejun Heo To: Sudeep Holla Cc: linux-kernel@vger.kernel.org, Pawel Moll , Andrew Morton , "Peter Zijlstra (Intel)" Subject: Re: [PATCH] bitmap: remove explicit newline handling using scnprintf format string Message-ID: <20150427161434.GF1499@htj.duckdns.org> References: <1430128018-14667-1-git-send-email-sudeep.holla@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1430128018-14667-1-git-send-email-sudeep.holla@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Sudeep. On Mon, Apr 27, 2015 at 10:46:58AM +0100, Sudeep Holla wrote: > int bitmap_print_to_pagebuf(bool list, char *buf, const unsigned long *maskp, > int nmaskbits) > { > - ptrdiff_t len = PTR_ALIGN(buf + PAGE_SIZE - 1, PAGE_SIZE) - buf - 2; > + ptrdiff_t len = PTR_ALIGN(buf + PAGE_SIZE - 1, PAGE_SIZE) - buf; > int n = 0; > > - if (len > 1) { > - n = list ? scnprintf(buf, len, "%*pbl", nmaskbits, maskp) : > - scnprintf(buf, len, "%*pb", nmaskbits, maskp); > - buf[n++] = '\n'; > - buf[n] = '\0'; > - } > + if (len > 1) > + n = list ? scnprintf(buf, len, "%*pbl\n", nmaskbits, maskp) : > + scnprintf(buf, len, "%*pb\n", nmaskbits, maskp); > return n; > } > EXPORT_SYMBOL(bitmap_print_to_pagebuf); So, there's one behavior difference stemming from this. When the buffer is too small, the original code would still output '\n' at the end while the new code would just continue to print the formatted string. Given that bitmap outputs can be pretty long, this behavior difference has a minute but still non-zero chance of causing something surprising. There are multiple copies of the above function in arch codes too. We prolly want to audit the usages to verify that the passed in buffer is always big enough at which point the above function and its copies can simply be replaced with direct scnprintf() calls. This function doesn't actually add anything. Thanks. -- tejun