Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756931AbYH0PVy (ORCPT ); Wed, 27 Aug 2008 11:21:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753914AbYH0PVo (ORCPT ); Wed, 27 Aug 2008 11:21:44 -0400 Received: from cluster-d.mailcontrol.com ([217.69.20.190]:44105 "EHLO cluster-d.mailcontrol.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753594AbYH0PVn (ORCPT ); Wed, 27 Aug 2008 11:21:43 -0400 Message-ID: <48B570D6.7070301@csr.com> Date: Wed, 27 Aug 2008 16:20:54 +0100 From: David Vrabel User-Agent: Thunderbird 2.0.0.16 (X11/20080724) MIME-Version: 1.0 To: Al Viro CC: Roland Dreier , Kernel development list , linux-usb , torvalds@linux-foundation.org Subject: Re: [patch] Add helper macros for little-endian bitfields References: <48AD6AF0.3050504@csr.com> <48AD6B93.7020702@csr.com> <20080825014311.GS28946@ZenIV.linux.org.uk> In-Reply-To: <20080825014311.GS28946@ZenIV.linux.org.uk> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 27 Aug 2008 15:20:54.0402 (UTC) FILETIME=[7F61A620:01C90858] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1501 Lines: 37 Al Viro wrote: > On Sun, Aug 24, 2008 at 06:37:43PM -0700, Roland Dreier wrote: >> > + * NOTE: When using multibyte bitfields, you need to convert the data >> > + * from Little Endian to CPU before you can access the bitfield >> > + * (to make it simpler): > > NOTE: When tempted to use multibyte bitfields on fixed-layout data, you > need to look in the mirror, ask yourself "what will they do to me during > code review for that?", shudder and decide that some temptations are > just not worth the pain. But why is this worthy of a crispy flaming? I've not seen anything definite beyond a somewhat vague 'some compilers don't optimize bitfields very well'. The structure definition and the DECL_BF_LEx() macros might be ugly but the code using the structures is clearer. For example, get_random_bytes(&tiebreaker, sizeof(unsigned)); drp_ie->tiebreaker = tiebreaker & 1; versus get_random_bytes(&tiebreaker, sizeof(unsigned)); drp_ie->drp_control |= (tiebreaker & 1) ? UWB_DRP_IE_DRP_CTRL_TIEBREAKER : 0; David -- David Vrabel, Senior Software Engineer, Drivers CSR, Churchill House, Cambridge Business Park, Tel: +44 (0)1223 692562 Cowley Road, Cambridge, CB4 0WZ http://www.csr.com/ -- 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/