Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752305AbaFDLAT (ORCPT ); Wed, 4 Jun 2014 07:00:19 -0400 Received: from mail2-relais-roc.national.inria.fr ([192.134.164.83]:6678 "EHLO mail2-relais-roc.national.inria.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751899AbaFDLAQ (ORCPT ); Wed, 4 Jun 2014 07:00:16 -0400 X-IronPort-AV: E=Sophos;i="4.98,972,1392159600"; d="scan'208";a="77997003" Date: Wed, 4 Jun 2014 13:00:07 +0200 (CEST) From: Julia Lawall X-X-Sender: jll@hadrien To: Geert Uytterhoeven cc: Julia Lawall , David Laight , linux-rdma , "kernel-janitors@vger.kernel.org" , Linux Fbdev development list , Linux-sh list , "linux-kernel@vger.kernel.org" , "ath10k@lists.infradead.org" , linux-wireless , "netdev@vger.kernel.org" , driverdevel , "iss_storagedev@hp.com" , scsi , linux-s390 , "adi-buildroot-devel@lists.sourceforge.net" , Arnd Bergmann Subject: Re: [PATCH 0/10] use safer test on the result of find_first_zero_bit In-Reply-To: Message-ID: References: <1401872880-23685-1-git-send-email-Julia.Lawall@lip6.fr> <063D6719AE5E284EB5DD2968C1650D6D1725705F@AcuExch.aculab.com> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 4 Jun 2014, Geert Uytterhoeven wrote: > Hi Julia, > > On Wed, Jun 4, 2014 at 11:52 AM, Julia Lawall wrote: > >> Maybe the documented return code should be changed to allow for the > >> existing behaviour. > > > > Sorry, I'm not sure to understand what you suggest here. > > include/asm-generic/bitops/find.h: > > | /** > | * find_first_zero_bit - find the first cleared bit in a memory region > | * @addr: The address to start the search at > | * @size: The maximum number of bits to search > | * > | * Returns the bit number of the first cleared bit. > | * If no bits are zero, returns @size. > > "If no bits are zero, returns @size or a number larger than @size." OK, thanks. I was only looking at the C code. But the C code contains a loop that is followed by: if (!size) return result; tmp = *p; found_first: tmp |= ~0UL << size; if (tmp == ~0UL) /* Are any bits zero? */ return result + size; /* Nope. */ In the first return, it would seem that result == size. Could the second one be changed to just return size? It should not hurt performance. julia > > | */ > | extern unsigned long find_first_zero_bit(const unsigned long *addr, > | unsigned long size); > > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/