From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753336Ab1KXTAY (ORCPT ); Thu, 24 Nov 2011 14:00:24 -0500 Received: from he.sipsolutions.net ([78.46.109.217]:39321 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751031Ab1KXTAX (ORCPT ); Thu, 24 Nov 2011 14:00:23 -0500 Subject: Re: [PATCH v2] printk: add console output tracing From: Johannes Berg To: Frederic Weisbecker Cc: Steven Rostedt , Christoph Hellwig , LKML , Ingo Molnar In-Reply-To: <20111124154519.GB18579@somewhere.redhat.com> (sfid-20111124_164601_383201_AB72557F) References: <20111117145502.GA18437@somewhere> <1321541877.3997.31.camel@jlt3.sipsolutions.net> <20111117150040.GB18437@somewhere> <1321543268.3997.40.camel@jlt3.sipsolutions.net> <20111118184401.GA24787@somewhere.redhat.com> <1321641975.10266.73.camel@jlt3.sipsolutions.net> <20111118185449.GB24787@somewhere.redhat.com> <1321642752.10266.75.camel@jlt3.sipsolutions.net> <20111123131622.GA10669@somewhere.redhat.com> <1322140919.5366.17.camel@jlt3.sipsolutions.net> <20111124154519.GB18579@somewhere.redhat.com> (sfid-20111124_164601_383201_AB72557F) Content-Type: text/plain; charset="UTF-8" Date: Thu, 24 Nov 2011 20:00:16 +0100 Message-ID: <1322161216.5366.52.camel@jlt3.sipsolutions.net> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2011-11-24 at 16:45 +0100, Frederic Weisbecker wrote: > > I don't really feel comfortable modifying the _call_console_drivers() > > function to not handle start > end (modulo log buf size of course), but > > at the same time I don't feel comfortable putting code into it that > > doesn't handle it. > > So, the: > > BUG_ON(((int)(start - end)) > 0); > > check is there to ensure we haven't wrapped INT_MAX. If we have reached > that point it definetly means we have a bug because log_buf_len is itself > an int and we shouldn't overlap INT_MAX. Ok that makes sense. > The care on the wrapping that is done in _call_console_drivers() is > different and concerns log_buf_len itself. If log_buf_len = 8, start = 7 > and end = 9, then you will enter the "((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK))" > condition that handle the wrap on LOG_BUF_MASK to print the two chars. > But this is totally different from "start > end" which would mean we have > a bug. Oh. So we get end = 9 in that case? That seems confusing ... I would have expected end = 1 then! Which is the whole reason I got confused I guess. > So, in your tracepoint you can safely use "end - start" as a length for your > dynamic array. But the rest of your tracepoint (all the fast assign part) > still needs the masks as you did. Oh, that's all you were trying to say? I can see that, ok. I just didn't see that end would be 9 instead of 1 and tried to handle that. The _call_console_drivers() code is a bit different I guess. I'll send a new version. johannes