From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754717AbbKWXTj (ORCPT ); Mon, 23 Nov 2015 18:19:39 -0500 Received: from mail-yk0-f181.google.com ([209.85.160.181]:36116 "EHLO mail-yk0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752489AbbKWXTi (ORCPT ); Mon, 23 Nov 2015 18:19:38 -0500 Date: Mon, 23 Nov 2015 18:19:35 -0500 From: Tejun Heo To: Rasmus Villemoes Cc: Andrew Morton , Maurizio Lombardi , Joe Perches , linux-kernel@vger.kernel.org Subject: Re: [PATCH 04/14] lib/vsprintf.c: expand field_width to 24 bits Message-ID: <20151123231935.GL19072@mtj.duckdns.org> References: <1448314171-25856-1-git-send-email-linux@rasmusvillemoes.dk> <1448314171-25856-5-git-send-email-linux@rasmusvillemoes.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1448314171-25856-5-git-send-email-linux@rasmusvillemoes.dk> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 23, 2015 at 10:29:21PM +0100, Rasmus Villemoes wrote: > Maurizio Lombardi reported a problem [1] with the %pb extension: It > doesn't work for sufficiently large bitmaps, since the size is stashed > in the field_width field of the struct printf_spec, which is currently > an s16. Concretely, this manifested itself in > /sys/bus/pseudo/drivers/scsi_debug/map being empty, since the bitmap > printer got a size of 0, which is the 16 bit truncation of the actual > bitmap size. > > We do want to keep struct printf_spec at 8 bytes so that it can > cheaply be passed by value. The qualifier field is only used for > internal bookkeeping in format_decode, so we might as well use a local > variable for that. This gives us an additional 8 bits, which we can > then use for the field width. > > To stay in 8 bytes, we need to do a little rearranging and make the > type member a bitfield as well. For consistency, change all the > members to bit fields. gcc doesn't generate much worse code with these > changes (in fact, bloat-o-meter says we save 300 bytes - which I think > is a little surprising). > > I didn't find a BUILD_BUG/compiletime_assertion/... which would work > outside function context, so for now I just open-coded it. > > [1] http://thread.gmane.org/gmane.linux.kernel/2034835 > > Reported-by: Maurizio Lombardi > Cc: Tejun Heo > Cc: Joe Perches > Signed-off-by: Rasmus Villemoes FWIW, Acked-by: Tejun Heo Thanks. -- tejun