From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753032AbbIJIRq (ORCPT ); Thu, 10 Sep 2015 04:17:46 -0400 Received: from smtprelay0103.hostedemail.com ([216.40.44.103]:42610 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750843AbbIJIRm (ORCPT ); Thu, 10 Sep 2015 04:17:42 -0400 X-Session-Marker: 6A6F6540706572636865732E636F6D X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,joe@perches.com,:::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1373:1437:1515:1516:1518:1534:1542:1593:1594:1711:1730:1747:1777:1792:2393:2553:2559:2562:2689:2693:2828:3138:3139:3140:3141:3142:3354:3622:3865:3866:3867:3868:3870:3871:3872:3873:3874:4321:4470:5007:6119:6261:7903:7904:8603:10004:10400:10450:10455:10848:11232:11658:11914:12296:12517:12519:12555:12663:12740:13095:14096:14097:19904:19999:21080,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0 X-HE-Tag: straw98_8aded8d7004f X-Filterd-Recvd-Size: 3223 Message-ID: <1441873056.17219.139.camel@perches.com> Subject: Re: [PATCH] lib/vsprintf.c: increase the size of the field_width variable From: Joe Perches To: Rasmus Villemoes Cc: Maurizio Lombardi , akpm@linux-foundation.org, tj@kernel.org, linux-kernel@vger.kernel.org Date: Thu, 10 Sep 2015 01:17:36 -0700 In-Reply-To: <87613ik8r9.fsf@rasmusvillemoes.dk> References: <1441793590-23856-1-git-send-email-mlombard@redhat.com> <1441816432.17219.57.camel@perches.com> <87mvwv4ea2.fsf@rasmusvillemoes.dk> <55F12B94.30503@redhat.com> <1441870684.17219.132.camel@perches.com> <87613ik8r9.fsf@rasmusvillemoes.dk> Content-Type: text/plain; charset="ISO-8859-1" X-Mailer: Evolution 3.12.11-0ubuntu3 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2015-09-10 at 09:56 +0200, Rasmus Villemoes wrote: > On Thu, Sep 10 2015, Joe Perches wrote: > > On Thu, 2015-09-10 at 09:04 +0200, Maurizio Lombardi wrote: > >> On 09/09/2015 08:51 PM, Rasmus Villemoes wrote: > >> > I'm also a little confused; I don't see what printk has to do with the > >> > reported problem (I'd expect the /sys/... file to be generated by > >> > something like seq_printf). > >> > >> In the scsi-debug case scnprintf is used, but it doesn't really matter > >> because the change I made would influence printk and all its friends as > >> well... everything that will parse "%*pb[l]". > >> > >> > > >> >> %*pb is meant for smallish bitmaps, not big ones. > >> > > >> > 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? > >> > > >> > >> Yes. To be precise, in the example I mentioned in the commit message, a > >> bitmap of size = 524288 bits is created. > >> If you assign this number to a s16 variable the result will be zero and > >> nothing will be printed. > > > > Maurizio, did you try the patch I posted? > > I think it'll work, but it doesn't fix the > > fundamental issue of %*pbl with large bitmaps. > > It also won't work for the case at hand if/when the actual bitmap ever > gets a bit set beyond S16_MAX. But at least it should work for the bitmap sized <= S16_MAX which should be the majority of uses. > A (somewhat ugly?) solution might be to teach %pb another flag, say h (for > huge), meaning that the pointer is actually (struct printf_bitmap*), > with > > struct printf_bitmap { unsigned long *bits; unsigned long nbits; } > > Then callers with potentially huge bitmaps would do > > struct printf_bitmap tmp = { my_bitmap, my_size }; > snprintf("%pbhl", &tmp) Yes, but it still couldn't work without the ability to have large output buffers and printk doesn't support that. seq_printf might have some performance issue with it too as it would repetitively try to emit, fail, and grow the buffer.