From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753672AbbIJOgg (ORCPT ); Thu, 10 Sep 2015 10:36:36 -0400 Received: from mail-pa0-f42.google.com ([209.85.220.42]:33978 "EHLO mail-pa0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753170AbbIJOge (ORCPT ); Thu, 10 Sep 2015 10:36:34 -0400 Date: Thu, 10 Sep 2015 10:36:29 -0400 From: Tejun Heo To: Joe Perches Cc: Rasmus Villemoes , Maurizio Lombardi , akpm@linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] lib/vsprintf.c: increase the size of the field_width variable Message-ID: <20150910143629.GB8114@mtj.duckdns.org> References: <1441793590-23856-1-git-send-email-mlombard@redhat.com> <1441816432.17219.57.camel@perches.com> <87mvwv4ea2.fsf@rasmusvillemoes.dk> <1441826799.17219.80.camel@perches.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1441826799.17219.80.camel@perches.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, Joe. On Wed, Sep 09, 2015 at 12:26:39PM -0700, Joe Perches wrote: > > > %*pb is meant for smallish bitmaps, not big ones. I'm not so sure about that. It's one thing to truncate printk output cuz the actual formatted result is too long but crippling the entire printf family of functions regardless of the actual output, which might as well be just "7-65540", doesn't seem like a good idea. These are pretty basic library functions and people shouldn't need to worry about niggles like that. > > Yup. And that leads to my other confusion: Given that the expected > > output is given as "0-15", does the bitmap really consist of > S16_MAX > > bits with only the first 16 set? > > No idea. Tejun? The use case isn't from me, but why not? > Perhaps the code in lib/vsprintf.c that sets > spec.field_width and spec.precision from format argument > input should be changed to use a temporary int and > clamped to S16_MIN -> S16_MAX. I think it should be able to handle bitmaps >64k. We don't want to cripple the fundamental string formatter because we can't pass around struct larger than 8 bytes. That just reeks of poor decision making. Why are we even copying the struct on invocations? Only some functions modify the values after all. We might as well pass around pointer to the struct and let the callees wihch modify them copy the fieldsin local vars like normal functions. Thanks. -- tejun